Japan’s Methane Hydrate
R&D Program

Phase 1
Comprehensive Report of
Research Results

August 2008 Edition

Research
Consortium for
総括成果報告書
Methane Hydrate Resources in Japan

メタンハイドレート資源開発研究コンソーシアム

平成20年7月

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Contents

1.

Highlights of Phase I Accomplishments ................................................................................................... 1

2.

Methane Hydrate ....................................................................................................................................... 3

3.

Japan’s Methane Hydrate R&D Program and Implementation Structure of Phase 1 ........................ 6
3.1 Japan’s Methane Hydrate R&D Program .................................................................................................... 6
3.2 Implementation Structure of Phase 1........................................................................................................... 94.

Principal Events in Phase 1 ..................................................................................................................... 11

5.

Status of Achievement of R&D Program Goals ..................................................................................... 12
5.1 Objective 1: Clarification of MH occurrences and characteristics offshore Japan .................................... 12
5.2 Objective 2: Assessment of methane gas amounts in promising methane hydrate bearing offshore areas 18
5.3 Objective 3: Selection of methane hydrate resource fields from promising methane hydrate bearing
offshore areas and deliberation of economic potential .............................................................................. 20
1) Selection of the Methane Hydrate Resource Fields .......................................................... 202) Deliberation of Economic Potential .................................................................................... 21
5.4 Objective 6: Establishment of a development system complying with environment ................................ 24
1) Analyses of the Core Samples from the METI/MITI Exploratory Test Wells andDevelopments of Prediction Techniques of the Sediment Deformation ........................... 24
2) Acquisition of the Baseline Data in the Offshore Environments and Development of thePrediction Technique for Biological Influences ................................................................. 27
3) The Relationship between Methane Hydrates and the Global Environmental Risk ..... 30

6.

Achievements of the Onshore Gas Hydrate Production Test ............................................................... 33
6.1 Results of the first Onshore Gas Hydrate Production Test ........................................................................ 33
6.2 Result of the Second Onshore Gas Hydrate Production Test .................................................................... 33
1) Purpose of the Second Onshore Gas Hydrate Production Test ........................................ 33
2) Preparatory Work ................................................................................................................ 34
3) Production Test .................................................................................................................... 34
4) Implication of the Onshore Gas Hydrate Production Test ............................................... 35

7.

The Production Simulator ....................................................................................................................... 38
7.1 Functions, Features and Achievements of the Production Simulator ........................................................ 38
7.2 Evaluation of the Production Method by MH21-HYDRES ...................................................................... 42iResearch Consortium on Developing Methane Hydrate Resources

8.

Phase 1 Comprehensive Report of Research Results

Predominant Results of Items Above...................................................................................................... 46
8.1 Clarification of the Methane Hydrate Accumulation Mechanism and the Origin of Methane Gas (1.
Exploration Section) .................................................................................................................................. 46
8.2 Physical Property Measurements of Methane hydrate-bearing layers (2. Modeling Section) ................... 48
1) Establishment of the Core Test Technology Basis at In-Situ Condition .......................... 48
2) Development of the Consolidation and Deformation Analysis Simulator of Methane
hydrate-bearing layers ........................................................................................................ 48
3) Establishment of the Imaging Analysis Technology of Physical Property andDissociation Characteristics ............................................................................................... 49
8.3 Technology of Well Drilling and Completion (4. Development Section) ................................................. 51
8.4 Development of Technologies to Monitor Seafloor Environment and The HSE Inquiry (5. Environment
Section) ..................................................................................................................................................... 52
1) Development of Technologies to Monitor Seafloor Environment ..................................... 52
2) HSE Inquiry ......................................................................................................................... 54

9.

Perspective for the Future from Phase 1 Achievements ........................................................................ 55
9.1 The issues of Developing Technologies of Phase 2 ................................................................................... 55
9.2 Preparation for the Offshore Production Test ............................................................................................ 57

10.

Predominant Research and Test Facilities ............................................................................................. 59

10.1 Improved PTCS ......................................................................................................................................... 59
10.2 Laboratory Facilities of Core Testing ........................................................................................................ 59
10.3 Research Facilities Related to the Offshore Environment Survey ............................................................. 61
11.

Others ........................................................................................................................................................ 62

11.1 Cooperation and Collaborations with Foreign Countries .......................................................................... 62
11.2 Conference Presentations and Publications ............................................................................................... 63
11.3 Patents ....................................................................................................................................................... 63
11.4 Public Offering Research Proposals .......................................................................................................... 65
11.5 Reinforcement of Internal Cooperation, Dissemination of Research Results, and Publicity .................... 65
1) Reinforcement of Internal Cooperation ............................................................................. 652) Dissemination of Research Results and Publicity............................................................. 66
12.

English Abbreviations Cited .................................................................................................................... 69

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Research Consortium on Developing Methane Hydrate Resources

1.

Phase 1 Comprehensive Report of Research Results

Highlights of Phase I Accomplishments
Continuous efforts have been made to elucidate the characteristics of pore filling type methane
hydrate bearing sediments in marine environments and to execute our responsibility as one of thefront runners in methane hydrate research.
(1) Success of continuously methane gas production from subsurface methane hydrate-bearingzones.


Methane hydrate-bearing zones have been recognized in subsurface layers of the Arctic
region for approximately 40 years.

As the world’s first attempt, we succeeded in producing methane gas continuously by
dissociating methane hydrates that saturate the sandstone layers at depths of approximately
1,000m below the surface in Canada.

Both the hot water circulation method (2002) and the depressurization method (2007 and2008) were successfully conducted to produce methane gas, and the depressurization
method was proven to be effective as a production method that could be utilized in future.
See article 6. Achievements of the Onshore Gas Hydrate Production Test.

(2) For the first time in the world, turbidite sand and mud alternation layers were discovered in theeastern Nankai Trough area, which were considered viable and prosperous for developing
methane hydrates resources.


The occurrence of methane hydrate filling pore spaces of sand layers offshore was revealed
for the first time through the drilling of the MITI Exploratory Test Well “Nankai Trough” in
FY 1999. Those sand layers were also confirmed to be turbidite sand and mud alternation
layers through the drilling of METI Exploratory Test Wells “Tokai-oki to Kumano-nada” in
FY 2003.



The technique of picking out the methane hydrate concentrated zones which were thealternations of sand and shale composed of sand layers with high methane hydrate saturation
has been established.
See article of 5.1. Objective 1: .

(3) Experimental testing methods of core samples obtained from methane hydrate-bearing layers andassociated layers at the in-situ conditions were established.
The occurrence and properties at the in-situ conditions of turbidite sand and mud alternation
layers were elucidated.

Improvements of the PTCS (Pressure-Temperature Core Sampler) system originally developedin Japan contributed somewhat to the retrieval of layer samples while maintaining the in-situ
pressures and temperatures.

1Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

See article of 8.2. Physical Property Measurements of Methane hydrate-bearing layers (2.
Modeling Section) and 10.2. Laboratory Facilities of Core Testing.
(4) In a world first, the probabilistic method based on the well data and seismic data calculating thevolume of resource of methane gas contained in methane hydrate-bearing layers was established,
and the amount of gas trapped in the eastern Nankai Trough area was estimated with this method.
See article of 5.2. Objective 2: Assessment of methane gas amounts in promising methane
hydrate bearing offshore areas.
(5) The Japan's own simulator dedicated to evaluating the production behaviors of methane gas frommethane hydrate-bearing layers was developed.
See article of 7. The Production Simulator.

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Research Consortium on Developing Methane Hydrate Resources

Methane Hydrate
Methane hydrate is one of a number of unconventional natural gas resources. It is an ice-like whitesolid form that is composed of water and methane gas, and is sometimes called fiery ice. Methane
hydrate is stable in a limited range of pressures and temperatures (stability field), as indicated in
Figure 2-1.

M

Ice

Pressure (MPa)2.

Phase 1 Comprehensive Report of Research Results

MITI Exploratory Test Well
“Nankai Trough”
Second Onshore
Gas Production TestFirst Onshore Gas Hydrate
Production Test
Stability
field

Methane gas+ waterTemperature (℃)

Figure 2-1 Stability field of methane hydrate

Methane hydrate crystals are usually comprised of two kinds of polyhedral structures, of which thesmaller one is shown in Figure 2-2. Each methane molecule is contained in a cage of water molecules.
Methane hydrate consists of numerous cages that do not always contain all methane molecules. In
occasional cases, some cages are empty. The ratio of methane molecule occupied cages is indicated as
the methane cage occupancy. According to recent studies, cage occupancy of natural methane hydrate
ranges from 0.9 to 0.95.
One m3 of methane hydrate would dissociate to 0.8m3 of water and methane. The volume of methane
becomes to 172m3 (0°C, 1atm) when the cage occupancy is 100%. It usually ranges from 155 to
165m3 depending on the cage occupancy, and may be 165m3 on average.

3Research Consortium on Developing Methane Hydrate Resources

Figure 2-2

Phase 1 Comprehensive Report of Research Results

A small cage composed of the crystalline structure of methane hydrate
Green: methane molecule Red: water molecule

Methane hydrate offshore exists in a variety of shapes and occurrences.
Figure 2-3 shows the sandy core obtained from the formation at the depth of 164.3m below seafloor in
METI Exploratory Test Wells “Tokai-oki to Kumano-nada” of which water depth is 720m. Methane
hydrate fills the intergranular pore spaces among sand grains. Gas is trapped in pore spaces of theconventional natural gas layers, but the pore spaces of methane hydrate-bearing layers are occupied
by methane hydrate instead of gas. When methane hydrate dissociates, gas and water may fill the porespaces in a way similar to that of conventional natural gas layers. Those methane hydrate-bearing
sandy layers are the target of the exploitation of methane hydrate.

Figure 2-3

A core from the sandy methane hydrate-bearing layer

Figure 2-4 shows a sample of massive methane hydrate contained in a muddy sediment obtained froma depth of 126m below the seafloor at the Kumano-nada offshore in METI Exploratory Test Wells“Tokai-oki to Kumano-nada” where water depth is 1,862m. Such an occurrence is recognized in4Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

marine environments worldwide, and is considered low in the order of priority for exploitationcompared to methane hydrate existing in sandy sediments.

Figure 2-4

A massive sample of methane hydrate in muddy sediment

Figure 2-5 shows an example of massive methane hydrates exposed on the seafloor, which was
discovered at a water depth of 545m in the Gulf of Mexico, in the United States. This is not white incolor due to it containing impurities, and it has been discovered on seafloors around the world. It wasalso discovered in the southwest offshore of the Sado Island in Japan, and is considered low in theorder of priority for exploitation compared to methane hydrate existing in sandy sediments.

Figure 2-5

A methane hydrate exposure on the seafloor(Fire in the Ice, Winter 2004)

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Research Consortium on Developing Methane Hydrate Resources

3.

Phase 1 Comprehensive Report of Research Results

Japan’s Methane Hydrate R&D Program and Implementation Structure of Phase 1

3.1 Japan’s Methane Hydrate R&D Program
According to the accomplishments of the MITI Geophysical Exploration “Nankai Trough” in FY
1996 conducted by METI and the MITI Exploratory Test Well “Nankai Trough” in FY 1999 that wasundertaken based on the results of "drilling of a methane hydrate research well in Mackenzie delta,
Canada" in FY 1998, the result confirming the existence of methane hydrate layers in marine sandy
sediments was obtained for the first time in the world. Therefore, there is a possibility that methane
hydrate deposits may be able to be used as an energy resource.
Japan’s Methane Hydrate R&D Program (hereafter called "the R&D Program") (July, 2001) was
organized from a medium- to long-term viewpoint of aspiring to find solutions to various issues
regarding the economical extraction and utilization of methane gas from methane hydrate-bearing
layers.
The relevant articles in the R&D Program are quoted below.
“Japan’s Methane Hydrate R&D Program”
I.

II.

III.

Objectives
Methane hydrate, of which there is expected to be substantial amounts
offshore Japan, is positioned as a future energy resource, and impelling
technological developments into drilling and production of methane hydrate on
an economical basis for future utilization will contribute to the acquisition of along-term steady supply of energy.
Goals of the Methane Hydrate R&D Program
In order to improve technologies for the commercial production of methane
hydrate distributed offshore Japan, the following goals have been configured.
To help turn the plan into reality, efficient technological developments will bepromoted in conjunction with ideas from international collaborations. This
scheme and associated achievement will be reflected in government energy
policy.
1. Clarification of MH occurrences and characteristics offshore Japan
2. Assessment of methane gas amounts trapped in promising methane
hydrate bearing offshore areas
3. Selection of methane hydrate resource fields from promising methane
hydrate bearing offshore areas and deliberation of economic potential
4. Implementation of production test in the selected methane hydrate
resource fields (until FY 2011)
5. Improvement of technologies for the commercial production (until FY
2016)
6. Establishment of a development system complying with environment
Road map for achievement of goals
The road map and prioritized technological issues to accomplishment theabove goals are described below. In addition, the scheme will be advanced byinvestigating specific technology development items and implementation
structure.

6

Research Consortium on Developing Methane Hydrate Resources

1

Phase 1 Comprehensive Report of Research Results

Targets for developing methane hydrate resources(1) Occurrences expected
1) Occurrences in sandy sediments (unconsolidated sandsediments and sandstone sediments)
a. Methane hydrate-bearing layers
b. Methane hydrate-bearing layers and associatedfree gas layers beneathGas phase is network-saturated and has effective
permeability2) Occurrences in sedimentary formations other than sandy
sediments(2) Targets for development
In this plan, occurrences of methane hydrate in sandy
sediments should be near-term targets for exploitation.
Methane gas contained in hydrate is expected to be mainly
biogenic, however, the presence of thermogenic gas should be
noted.
(the rest is omitted)

We have targeted methane hydrate contained in sandy sediments for research and development for
Phase 1. Each of the items in the goals in the R&D Program is allocated to Phases 1 to 3 as follows.
1. Clarification of MH occurrences and characteristics offshore Japan
According to the findings obtained from the eastern Nankai Trough area till FY 2006, we will
investigate the existing seismic data offshore Japan. In Phase 1 we have principally targeted thewestern Nankai Trough and southwest offshore of the Sado Island in addition to the eastern
Nankai Trough area. We re-examined the BSR distributions in offshore Japan, and identified areasthat were potentially methane hydrate concentrated zone.
2. Assessment of methane gas amounts trapped in promising methane hydrate bearing offshore areas
We developed a probabilistic method to calculate the volume of resource of methane gas trapped
in methane hydrate contained in sandy sediments especially in the eastern Nankai Trough area.
Future tasks remain to be carried out for other areas.
3. Selection of methane hydrate resource fields from promising methane hydrate bearing offshore
areas and deliberation of economic potential
We developed a method to select methane hydrate resource fields in the eastern Nankai Trougharea, and implemented it. We also evaluated the economic potential in a section of those areas.
4. Implementation of production test in the selected methane hydrate resource fields (until FY 2011)
Although this item was supposed to have been implemented in Phase 2, necessary technologies
for the offshore production test in the methane hydrate-bearing layers were partially researchedand developed in Phase 1.

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Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

5. Improvement of technologies for the commercial production (until FY 2016)
This item is expected to be implemented in Phase 3.
6. Establishment of a development system complying with environment
Fundamental data about the natural environment in the eastern Nankai Trough area where theoffshore production test is expected to be carried out are examined in Phase 1. We began toresearch and develop technologies to establish a development system complying withenvironment in Phase 1, which will be continued to the end of the R&D Program.
FY limits of time specified in the items 4 and 5 are the future tasks that remain to be carried out.
Phase 1 was initially planned for six years from FY 2001 to FY 2006. However, a two-year extension
was demanded by the following reasons; (1) It became clear through METI Exploratory Test Wells“Tokai-oki to Kumano-nada” (FY 2003) that methane hydrate of the eastern Nankai Trough existed insandy sediments of alternating beds of sand and mud, (2) Depressurization method was suggested as
an efficient production method at the methane hydrate-bearing layers and, (3) Optimal design torealize the depressurization method in the production test was required. Evaluations andadmonishments from the Advisory Committee for Promotion and Evaluation of National Methane
Hydrate R&D Program, the Evaluation Subcommittee of Industrial Technology Sectional Committee
of Industrial Structure Council and the Council for Science and Technology Policy Expert Panel on
Evaluation conducted in FY 2005 allowed Phase 1 to be extended by two years. Therefore, Phase 1
was amended for eight years from FY 2001 to FY 2008 (refer to Figure 3-1).

(1)Extraction of technical issues through offshore production tests(2)Recommendation of economical and efficient recovery methods(3)Evaluation of methane hydrate distribution off the coast of Japan(4)Recommendation of EIA methods through offshore production tests

Figure 3-1

Phase 3

Final evaluation for Phase 2

Offshore Methane
Hydrate Production
Test

Onshore Methane Hydrate
Production Test

Offshore Methane
Hydrate Production
Test

Phase 2

Preparation for Offshore
Methane Hydrate Production Test

Interim appraisal

Baseline Researches (Exploration Techniques, Decomposition & Formation Techniques, Production
Techniques, Environmental Impact Assessment Techniques)Preparations forCommercial Productions
Comprehensive Evaluations(Economic Potential,
Environmental Impact
Assessment)

Final evaluation

Phase 1
FY2001/2002
2D and 3D Seismic Surveys
in the Eastern Nankai Trough Area

FY2007/2008
Second Onshore Methane
Hydrate Production Test
in CanadaInterim appraisal

FY2003MITI Exploratory Test
Wells in the Eastern
Nankai Trough Area

FY2001First Onshore Methane
Hydrate Production Test
in Canada

Final evaluation for Phase 1

Japan's Methane Hydrate R&D ProgramThis schedule was revised at
the end of Phase 1.

"Japan’s Methane Hydrate R&D program": Schedule(the Phase 1 after amendment of a two-year enlargement)

8

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

3.2 Implementation Structure of Phase 1“Research Consortium for Methane Hydrate Resources in Japan” (abbreviated name: MH21 ResearchConsortium) was set up to attain the goals of Phase 1. Three organizations comprising Japan Oil, Gas
and Metals National Corporation (JOGMEC), the National Institute of Advanced Industrial Scienceand Technology (AIST), and the Engineering Advancement Association of Japan (ENAA) wereselected to make up of the Research Consortium for Methane Hydrate Resources in Japan. These
three organizations consigned and subcontracted work to approximately 30 industries, universities andresearch institutes, which conducted research and development work by collating knowledge fromalmost 300 researchers.
The R&D Program was carried out by three groups, and the Secretariat for Research Consortium for
Methane Hydrate Resources in Japan was set up to assist those groups in carrying out their activities.
Each group took charge as follows.
(1) The Research Group for Resources Assessment (JOGMEC in charge)-

Researches for exploration techniques of methane hydrate-bearing layers-

Developments and evaluations of technologies for resource assessment-

Researches for technologies of well drilling / completions / production.

(2) The Research Group for Production Method and Modeling (AIST in charge)-

Investigation of fundamental properties of methane hydrate-bearing layers-

Developments of production simulator and various recovery technologies.

(3) The Research Group for Environment Impact (ENAA in charge)-

Investigation of offshore environment-

Environment impact assessment(4) The Secretariat for Research Consortium for Methane Hydrate Resources in Japan (JOGMEC incharge)-Administering, budgeting and contracting projects of the Research Consortium for Methane
Hydrate Resources in Japan-

Management of public affairs, promotion of achievements, and other activities

Working groups and taskforces were set up as sites for information sharing and collaborative work
among researchers of these groups in order to promote the research and facilitate operations (refer toFigure 3-2).

9

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Research
Consortium for Methane Hydrate Resources in Japan
メタンハイドレート資源開発研究コンソーシアム
Secretariat for Research Consortium for
Methane Hydrate推進グループ
Resources in JapanJOGMECJOGMEC
Research Group for
資源量評価グループ
Resource
Assessment
JOGMECJOGMEC

Figure 3-2

Research Group for Production
生産手法開発グループ
Method & Modeling
AIST
AIST

Research Group for

環境影響評価グループ
Environment Impact
ENAA
ENAA

Implementation structure of the Research Consortium for Methane Hydrate
Resources in Japan10

Research Consortium on Developing Methane Hydrate Resources

4.

Phase 1 Comprehensive Report of Research Results

Principal Events in Phase 1July 19, 2001: “Japan’s Methane Hydrate R&D Program” was announced.



December 2001 to March 2002: The First Onshore Methane Hydrate Production Test was carriedoutMarch 20, 2002: The Research Consortium for Methane Hydrate Resources in Japan was
founded.



April 3, 2002: The first Advisory Committee for National Methane Hydrate R&D Program

FY 2001: METI "Tokai-oki to Kumano-nada" (2D) seismic surveys

(Reference) FY 2001: METI "Sado-oki Nansei" (2D) seismic surveys



FY 2002: METI "Tokai-oki to Kumano-nada" (3D) seismic surveys



December 2003: Mallik International Symposium in Makuhari

January to May 2004: METI Exploratory Test Wells “Tokai-oki to Kumano-nada”

April to May 2005: The Advisory Committee for Promotion and Evaluation of National Methane
Hydrate R&D Program (the first and the second meetings)

July 2005: The Evaluation Subcommittee of Industrial Technology Sectional Committee ofIndustrial Structure Council

January to March 2006: Council for Science and Technology Policy Expert Panel on Evaluation

July 2006: The Advisory Committee for Promotion and Evaluation of National Methane Hydrate
R&D Program (the third meeting)

December 2006 to April 2007: The first winter test for the Second Onshore Methane Hydrate
Production Test

January to April 2008: The second winter test for the Second Onshore Methane Hydrate
Production Test

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Research Consortium on Developing Methane Hydrate Resources

5.

Phase 1 Comprehensive Report of Research Results

Status of Achievement of R&D Program Goals
The implementation plan of Phase 1, which was instituted in line with the R&D Program., wasdeliberated and investigated in the first Advisory Committee for National Methane Hydrate R&D
Program, and the plan has almost been accomplished except for the delay related to the Onshore
Production Test. The status of the achievements of the goals of the objectives 1, 2, 3, and 6 in R&D
Program chapter II are summarized below, which may comprehensively indicate the accomplishmentsof Phase 1.
Regarding the achievements of the Onshore Production Test and the advances of simulators, they areof such importance that we describe them in detail in the articles of “6. Achievements of the Onshore
Gas Hydrate Production Test,” and “7. The Production Simulator,” respectively.
Emphatic points of the achievements of the other items are summed up in the article of “8.
Predominant Results of Items Above.”

5.1 Objective 1: Clarification of MH occurrences and characteristics offshore JapanAs the investigation of BSR (Bottom Simulating Reflector) distributions around Japan (Figure 5-1)
predominantly conducted by the former JNOC (Japan National Oil Corporation) has been taken over,geophysical explorations in southwest offshore of the Sado Island as well as geophysical explorations
and MITI exploratory test well in the eastern Nankai Trough area have been carried out after the R&D
Program commenced. Thirty two (32) wells were drilled in the METI Exploratory Test Wells“Tokai-oki to Kumano-nada,” and various new analysis techniques have been established bycomparing the data of LWD (Logging While Drilling), wireline logging and core recovery with the
2D/ 3D seismic data. We are now able to interpret existing seismic survey data to a high level ofaccuracy.

12Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Southwest offshoreof the Sado Island

Eastern Nankai
Trough Area

Figure 5-1 BSR distributions in the surrounding offshore areas around Japan
While the BSR has usually been used as an indicator of the existence of methane hydrate, the newtechnique was obtained to clarify what the BSR indicates and to quantitatively recognize the methane
hydrate-bearing layers according to comprehensive examinations of the geophysical explorations andthe MITI exploratory test well in the eastern Nankai Trough area.
(1) Since the BSR occurs at the interface between the base of the methane hydrate stability zone andthe free gas-bearing water layers beneath, the BSR is not observed when methane hydrates exist
only in shallower depths away from the BSR.
(2) The BSR is sometimes recognized simply due to the seismic phase change and so on instead of
the identification of distinct seismic reflector.
(3) The BSR denotes the existence of methane hydrate qualitatively, and as an indicator is insufficientfor showing the amount of resources.
(4) The methodology was established to delineate methane hydrate concentrated zones and theamount of gas trapped was evaluated.
The existence of methane hydrate became clear in the METI Exploratory Test Wells “Tokai-oki to
Kumano-nada” and was found to be distributed in sand sediments of turbidite sand and mudalternation layers (refer to the picture in Figure 2-3). Figure 5-2 shows an example of logging data13

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

denoting methane hydrate concentrated zones in turbidite sand and mud alternation layers. Thosemethane hydrate concentrated zones are recognized as being high-resistivity and high-velocity zones
on the logging data.

Distribution of borehole resistivity

Downhole well log records

MH concentrated zone
Depth from 815 to 920m
Layer thickness 105m

Figure 5-2 Example of the downhole well log data denoting turbidite sand and mudalteration layers
The geological characteristics of turbidite sand and mud alternation layers in the eastern Nankai
Trough area are summarized in Figure5-3.

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Research Consortium on Developing Methane Hydrate Resources

Mud layer
Parallel laminations

Phase 1 Comprehensive Report of Research Results

Silty to
muddy

Cross
laminations
Parallellaminations

Graded layer

Grains ofsand size● Sand and mud transported bydebris flow are re-deposited on theseafloor.
● After coarse sand is deposited,
more finer-grained sands form
parallel laminations and crosslaminations.
●Silty sediments are deposited on
top.
●Mud is deposited on them that are
not associated with turbidites.

Figure5-3 Geological characteristics of turbidite sand and mud alternation layers

When coarse sediments deposited at shallow depths are mixed with circumjacent fluids, fluidized andtransported into the deep sea by earthquakes, storm winds and tsunami once every few decades or
hundred years, these sediments form into so-called submarine fans. They form alternating beds ofsand and mud offshore where only fine-grained mud can be deposited, and are called turbidite layers.
These are recognized as the shapes of a channel and a lobe in seismic data. In these layers, methane
hydrate is understood to concentrate in the methane hydrate stability zone indicated by BSRs (Figure
5-4).
Since sedimentary formations where methane hydrate is concentrated continuously on a broad scale
are considered to be promising, they are defined as methane hydrate concentrated zones and evaluateddifferently from other methane hydrate-bearing layers.
We then examined all the data obtained from the METI Exploratory Test Wells “Tokai-oki to
Kumano-nada,” and fixed criteria of the high resistivity layer to be greater than 3Ω•m in wells andthicker than 10m in net thickness as a threshold level to distinguish the methane hydrate concentrated
zones from other zones. Based on this criterion, we checked several properties shown on the seismic
data at the locations with well controls, and confirmed the method to be used by picking themethane hydrate concentrated zones out from the reflection seismic data by using the following four
indices:15

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

A) Existence of BSRs
B) Distributions of turbidite sand and mud alternation layers such as channels and lobes above BSRs
C) High amplitude reflector
D) High velocity anomaly
In addition, 16 methane hydrate concentrated zones have been identified in the eastern Nankai Trougharea using this method. The normal characteristics of methane hydrate concentrated zones are
estimated, and values of net/ gross ratio 0.37, porosity 0.44 and methane hydrate saturation 0.51 are
obtained.

MH-bearingzone

Upper channel
High-amplitudereflectorMH
concentratedzone

MHstabilityzone

MH
concentrated
zone
reflector

reflector

Base of channel

Figure 5-4 Example of methane hydrate concentrated zones(the methane hydrate concentrated zone β)

Since the concept of “Methane Hydrate Concentrated Zone” and the method for its evaluation wereconfirmed, the following have become feasible.
(1) Probabilistic calculations of original gas in places became feasible (refer to the article 5.2).
(2) Abstractions of the potential areas with methane hydrate concentrated zones became feasible byapplying the newly established analytical technique of geophysical exploration to other areas.
The physical properties of turbidite sand and mud alternation layers as reservoirs recognized in the
METI Exploratory Test Wells “Tokai-oki to Kumano-nada” have been pursued by the analyses ofrecovered core samples and the project standard samples simulating methane hydrate-bearing layers.
For this purpose, the technique of making the artificial methane hydrate sediment core that simulate
the core samples recovered from the METI/MITI Exploratory Test Wells has been developed, and the16Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

basic technique of measuring the physical properties of sediments at the in-situ conditions has been
improved (refer to the article 8.2).
The physical properties of those turbidite sand and mud alternation layers as reservoirs may serve as abasis of data input to the production simulators for evaluating the production volumes and figuring
out the economic potential. Prevailing values of the physical properties are shown below.
A) Thermal property
Thermal conductivity;
Sandy cores: 1.56W/m•K, Muddy cores: 1.15W/m•K
Cores in the vicinity of the interface between alternating beds of sand and mud:
1.7 - 2.3W/m•K
Specific heat (15˚C);
Sand grain of sandy cores: 0.82J/g•K
Muddy parts: 0.77J/g•K
Methane hydrate-bearing layers (porosity 40%, methane hydrate saturation 60%): 1.26J/g•K
Massive methane hydrates: 1.91J/g•KB) Permeability characteristics
Absolute permeability of sandy cores after methane hydrate dissociated: a few millidarcies - a
couple of 100 millidarcies (anisotropic nature possibly)
Absolute permeability of muddy sediments: a few μ darcies - a couple of 100μ darcies
C) Characteristics of Elastic Wave
Core samples recovered from the METI/MITI Exploratory Test Wells with 30% of methane
hydrate saturation: P wave 2,000m/s, S wave 800m/s
Increasing rate per 10% of methane hydrate saturation: P wave 140m/s, S wave 110m/s
D) Resistivity characteristics
At around 3Ω•m for core samples with a few percent of methane hydrate saturationE) Grain size (sandy sediments cores)
Relatively large sand grains with 100μm - 300μm in grain diameter, 200μm on average grain sizeat the base of sandy sediments, smaller than 100μm on average grain size at the top of sandy
sediments. Alternations may contain silts more than 10% near the boundary with muddy
sediments.
F)

Bulk density
Sandy cores: 1.6 - 1.9, Muddy cores: 1.9 - 2.0

G) Porosity
Sandy cores: 40% - 45%, Muddy cores: 36% - 40%
H) Methane hydrate saturation17

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Cores of sandy sediments: 40% - 50% (those values are considered much larger at the in-situ
conditions due to hydrate dissociation processes at the time of measurements)
Muddy cores: those scarcely contain methane hydrate.
Cores in the vicinity of the interface between alternating beds of sand and mud: 1% - 3%
I)

Dissociation gas
Sandy cores: methane, ethane is detected to 600ppm - 2,800ppm in the cores from some areas
Muddy cores: around 1ml/g of CO2 has been detected.

J)

Strength of methane hydrate-bearing layers
Strength of the alternating beds of sand and mud with 60% of methane hydrate saturation aroundthe depth of 100m below the seafloor, which is estimated from the measured values of sandy
cores: 7MPa - 8MPa. Studies on strength of the interface between alternating beds of sand andmud are also in progress.

K) Influence of methane hydrate dissociation
Strength of alternations decreases to about half the primary strength due to dissociation of
methane hydrate accompanied by the advancement of consolidation and a decrease in absolutepermeability.
L) Capillary pressure measurement
Muddy cores: Pressure at the beginning of injection is 0.14MPa. Pressure at 20% of injection is
1MPa. They have sufficient seal capacity of gas.

5.2 Objective 2: Assessment of methane gas amounts in promising methane hydrate bearing offshore
areas

Under the study of the preceding section 5.1 (the Objective 1), we selected the eastern Nankai Trougharea (refer to Figure 5-1) as being a promising methane hydrate bearing area, and calculated theoriginal methane gas in place in methane hydrate-bearing layers in sea areas. The calculation method
is based on the volumetric method taking the range of uncertainty of each parameter into account, andevaluations by the stochastic method were adopted. We abstracted the methane hydrate concentrated
zones and the spatial distributions of methane hydrate-bearing layers at the same offshore area shownin Figure 5-4, and calculated the amount of original gas in existence. An equation was introduced thatwas modified and was applicable to methane hydrate from the equation of volumetric method adapted
to the conventional resources.
The methane hydrate concentrated zones:
The original methane gas in place = GRV × N/G × φ × SMH × VR × CO

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Methane hydrate-bearing layers (other than the methane hydrate concentrated zones):
The original methane gas in place = Area × Net × φ × SMH × VR × COParameters used above are listed in Table 5-1.

Table 5-1 Parameters used in calculating resource volume of methane hydrate
Parameters
GRV (gross rock volume)
N/G (net/gross ratio, ratio of sandy layer
in alternating beds of sand and mud)φ (porosity)
SMH (methane hydrate saturation)
VR (volume ratio)

unit
million m3
fraction

Assumed probability distribution
Log normal distribution
Log normal distribution

fraction
fraction
fixed number

CO (cage occupancy)

fraction

Area (area of distribution)
Net (net thickness of sandy sediment)

km3
m

Normal distribution
Normal distribution
Uniform distribution(172@0˚C•atmospheric pressure)
Triangular distribution (0.95 on averageobtained from natural samples)
Log normal distribution
Log normal distribution

The original methane gas in place in the methane hydrate-bearing layers in the eastern Nankai Trougharea is calculated using the above methods, and their results are summarized in Table 5-2.
Calculations are carried out in each field containing a distribution of methane hydrate, and the total
amounts are simply a sum. The original methane gas in place is a volume of methane at standard
conditions (0˚C, atmospheric pressure), which are assumed to derive from the dissociation of methane
hydrates into water and methane in subsurface formations. Some of these gases are produced to thesurface, and the rest remains in the subsurface formations. The ratio of gas produced at the surface has
not yet been determined, however it should become clear from an analysis of the results of the
production test and a study of the production simulation.

Table 5-2 Calculation results of the original methane gas in placein the methane hydrate-bearing layers in the eastern Nankai Trough area

Grouping
Methane hydrate concentrated zones
Methane hydrate-bearing layers
Total

Total volume of methane initially considered toexist (100million m3)
P90
Pmean
P10
1,769
5,739
11,148
1,067
5,676
12,2082,836
11,41523,356

P90:
Estimated occupied volume greater than this value, the probability of which exceeds 90%
Pmean: The mean value
P10:
Estimated occupied volume larger than this value of which probability exceeds 10%

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5.3 Objective 3: Selection of methane hydrate resource fields from promising methane hydrate
bearing offshore areas and deliberation of economic potential
This objective is divided into two aims such as selecting the methane hydrate resource fields anddeliberating economic potential. Evaluations of the achievements of both of the above are conductedwith scrupulous coordination, and are described separately for practical convenience.

1)

Selection of the Methane Hydrate Resource Fields
The locations with well data of the METI/MITI Exploratory Test Wells extracted from methane
hydrate concentrated zones at the 16 zones defined in section 5.1 were targeted for investigation of 41
items, and three methane hydrate concentrated zones (α, β, and γ) were adopted as the candidate areas
for offshore production tests. Detailed geological models were constructed at the two concentrated
zones of α and β. Based on these models, reservoir models were built in a 1km2 vicinity around thewell, and production simulations were carried out. (Regarding the production simulation, refer tosection “7. The Production Simulator”)
The 41 items used for the adoption are listed below.


Original gas in place

Geological items: volume, area, thickness of layer, stratigraphy, reservoir type, sedimentation
pattern

Site situations: water depth, distance from the shore

Reservoir characteristics: reservoir thickness, sand/mud ratio, reservoir continuity, verticalpermeability in reservoirs, degree of consolidation of sands and mud, depth of reservoirs,
reservoir temperature, dip and strike of the reservoirs, existence of water layers in thereservoirs, permeability of the layer above the reservoir, existence of methane hydrate in thelayer above the reservoir, existence of fault and fracture, permeability of the layer beneath thereservoir



Production relevance: predictions of productivities, predictions of production damages



Seafloor environments: inclinations of the seafloor, properties of sediments on the seafloor,
existence of drilling troubles, circumjacent seafloor topographyOffshore environments: meteorological phenomena, hydrographic phenomena, ocean currents
and tidal currents, background concentrations of dissolved methane in sea water, methane
fluxes from the sediments, methane fluxes presumed by SMI depths, marine mammals, marine
reptilians, ocean ranging fishes, benthonic living organisms



Others: fishing activities, submarine cables, sham battle fields(Remarks: SMI=Sulfate Methane Interface, which is a sulfate-methane boundary and one of the markers indicating
methane fluxes adjacent to the sea floor.)

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Characteristics of the ten out of the 41 items investigated in the three selected zones of the methane
hydrate resource field are summarized in Table 5-3.

Table 5-3 Three candidates of the methane hydrate concentrated zones
in the methane hydrate resource fields
Items
Original gas in place: Pmean(100million m3)
Area (km2)
Total average thickness (m)Water depth (m)Distance from shore (km)Reservoir types
Depth of reservoirs (m)Formation temperature (˚C)
Inclination of seafloor

Circumjacent seafloor
topography

2)

Methane Hydrate
Concentrated Zone α

Methane Hydrate
Concentrated Zone β

Methane Hydrate
Concentrated Zone γ

591

87

111

35.5
62.3
675 - 878
40 - 50
turbidite sand and mudalternation layers
α-1 Well: 815 - 919
α-2 Well: 922 - 953
α-1Well Site
8.6 - 10.3
Less than 2 degrees aroundthe α-1 and α-2 wells.

12.3
39.6
857 - 1405
70 - 80
turbidite sand and mudalternation layers

23.7
37.8
855 - 1,035
40 - 50
turbidite sand and mudalternation layers

β-1 Well: 1,295 - 1,339

γ-1 Well: 1,167 - 1,193

β-1 Well Site
12.7 - 14.3
Sometimes exceeds 10
degrees at some sites as thecircumjacentseafloor
topography is convolutedaround the β-1 well. The
generalinclinationisapproximately 3 degrees on
average. Some areas of theseafloors are virtually flat.
The seafloor topography isconvoluted around the β-1
well and has a rise in thesouth.
The
trace
ofsubmarine landslide isrecognized at the site 4km
northwest of the well.

γ-1 Well Site
12.5 - 13.2
Less than 2 degrees
around the γ-1 well.

The topography is a gentle
slope around the α-1 andα-2wells.
A
steep
escarpment begins at thesite 5km east of the well,and continues to thedepression.

The topography is a gentle
slope around the γ-1 well.
A steep escarpment begins
at the site 4km from thewell continuing to thesubmarine canyon.

Deliberation of Economic Potential
The aims of the economic potential deliberations are to develop an economic evaluation program thatis suitable for the exploitation of methane hydrate, to create a vision for the feasibility of methane
hydrate exploitation, to compare the estimated production costs expected from the present stage of
research to those of conventional resources, to discover issues related to developing technologies, andso on.
We deliberated on economic potential based on the production behaviors simulated for the methane
hydrate concentrated zone α that were selected in the preceding section. We used the
MH-ECONOMICS Basic Model economic evaluation program that has been developed and foundsuitable for the exploitation of methane hydrate.
The R&D Program was configured with business operations to commence in 2016, production tocommence in 2021, a production period of 15 years, and a production leadtime of each well for eight21

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

years. Also, according to inquiries about fluctuating gas prices and other factors, the price of gas in2004 was configured to be 23.8JPY/m3, the rate of inflation was 2.56% as an annual percentage rate,
and the rate of increase in gas prices was 3.88% as an annual percentage rate.
Regarding the development system, production facilities will be put into place on the seafloor. Gases
produced will be collected on the offshore platform and transported via pipeline to the destination for
consumption. More specifically, a number of wells will be connected to the manifold set up on theseafloor, and the gases produced and water on the manifold will be separated by the separator. Afterbeing separated, the produced waters will be injected into the subsurface formations. After the gases
produced are pressurized to a few MPa and collected on the offshore platform, they will be
re-pressurized and delivered via pipeline to the destination for consumption.
Prevailing assumptions used for the deliberation of economic potential at this time are as follows.
(1) The geology is assumed to be uniform horizontally. The data of one of the wells drilled in thisregion have been adopted.
(2) Long-term production damage is estimated to be within the scope of the assumption. It isnecessary for this to be substantiated by production and other tests.
(3) It is assumed that the volume of production will be fulfilled. The calculation by the production
simulator has been applied.
(4) It is assumed that the equipment, technologies and other factors will be implemented. A study of
unproved instruments and technologies will be necessary.
Since economic evaluation has been carried out for the six developing methods to the methane
hydrate concentrated zone α, the flow chart and the evaluation results of the fundamental development
method α-1, which is used as a case to exploit the circumference of the well α-1, are summarized in
Figure 5-5.

22

Research Consortium on Developing Methane Hydrate Resources[Resource field data]
Distance from shore: 50km
Water depth: 722m
Exploitation area: 9.6km2
Depth of MH layer (below sea
level): 814-920m
Total methane initially in place: 244(100million m3)[Exploitation concept, production facilities related data]【開発コンセプト・生産設備関連データ】
Production duration:
15 years (production commencement:
2021, production
生産期間：
年(生産開始：2021 年、1坑井生産期間：8年)
leadtimeof15each
well: 8 years)
経済環境因子
2004年ガス価：23.8円/?
Economical
坑井数：49 environment factors
Gas price in 2004: 23.8JPY/ m3
ガス価上昇率：
3.88%/年
坑井深度：920m
Rate of gas
price
インフレ率：
2.56%/年 increase: 3.88%/year
坑井間隔：
m 49
Numberof443
wells:Inflationrate:
2.56%/year
為替レート：
11011円/$
洋上プラットフォーム：
SPAR
Well depth: 920m
Currency exchange rates: 110JPY/US$
Well spacing: 443m
Offshore platform: SPAR
Gathering numbers of flowline by subsea manifold
Produced water is injected into the layer by the injection well after separated by thesubsea separator[Production method data]
Production method: depressurization
method, vertical well
Production condition: bottom holepressure 3MPa
[Formation data]
Formation sequence: sand, silt,
muddy layer
Formation thickness: 106m
Porosity of sandy layer: 42%
MH saturation of sandy layer: 50%
Permeability: α-1 NMR logging +core analyses
Formation temperature(BSR):
10.2˚C
Geothermal gradient: 3˚C/100m

Phase 1 Comprehensive Report of Research Results

Production simulator
MH21HYDRES

Economic evaluation program
MH Economics BM[Results of production volume, etc. Analyses]
Average gas production rate per well: 55,600
m3/dCumulative gas production volume per well:
162million m3
Average water production rate per well:
640 m3/d
Cumulative water production volume per well:
1.87million m3
Recovery factor: 32%
Others, production profiles, recoverable
reserves, etc.

[Results of economic potential
evaluation]
Average production costs
in production period: 46JPY/ m3(Average gas price in production
period: 56JPY/ m3)
IRR: 6%
NPV (0%): 826 (100million JPY)
Payout time: 8 years

Figure 5-5 Flow chart of deliberating economic potential and evaluation results for themethane hydrate concentrated zone α-1
A trial calculation has been carried out for the production costs withdrawn from the methane
hydrate-bearing layers assuming the following three patterns.
(1) A case postulating present construction costs:

92JPY/m3(the base price was set at that of 2004, and is assumed to have temporarily tripled)(2) All the assumed conditions come into effect:

46JPY/m3(the base price of 2004)(3) Production volume lower (by a quarter) than expected:

174JPY/m3

Technology development issues have been investigated with sensitivity analysis of the economic
potential. The approaches to an increase in the gas production rate, an improvement in the recovery
factor, a reduction in the water production rate, a reduction in the sanding rate and so on from theviewpoint of technology development, a cost reduction analysis of the subsea system, and a cost
reduction analysis of the building of facilities from viewpoint of development system were analyzed
as being highly effective with regard to advancing the economic potential.

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5.4 Objective 6: Establishment of a development system complying with environment
The basic concepts for objective 6 are described in the section “V. Contents of Technology
Developments, 5. Environment” of the R&D Program as follows.
“Regarding the exploitation of methane hydrate, it is necessary to take the influence to the margin ofsafety of the exploitation operation itself, the impact to marine ecosystems, and the effects of leaked
methane gas into account.
The causes of the above are considered to be the effluence of development-related low-temperature
fluid coming to the sea surface, the critical damage of cement and the casing in itself due toconsolidation of the formations around the well associated with the production, the decreased
functional status of the formation seal capacity above the methane hydrate-bearing layer due to thedeformation, subsidence and other reasons related to the seafloor, the collapse of the methane
hydrate-bearing layer itself, and so on.
As these phenomena are closely related to the in-situ characteristics of the formations as well as the
exploitation and production methods, it should be necessary to gain a thorough understanding of theproperties of the methane hydrate-bearing layers and the nature of circumference formations and tocarry out an analysis after due consideration of their characteristics is made. Furthermore, it is crucial
to investigate the interannual environmental change of the topography and ecological systems of theseafloor, and so on in the model fields.”
In Phase 1, surveys of offshore environment centered around the eastern Nankai Trough have been
carried out on two occasions - before and after the METI Exploratory Test Wells “Tokai-oki to
Kumano-nada,” and interannual observations have been conducted for some items. In the METI
Exploratory Wells mentioned above, entire interval core recoveries were attempted in two sites toretrieve all the geological core samples from the seafloor to the layer below the methane
hydrate-bearing layer. The core recovery ratio was low due to water depths ranging from 700 to
1,000m, most of which were clayey samples at shallower depths.
The research status relating to the developments of prediction techniques of the sediment deformation,
the offshore environment surveillances and “the macro risk assessments of environmental impacts”
directed by the Council for Science and Technology Policy Expert Panel on Evaluation (March 2006)
are summarized in this section.

1)

Analyses of the Core Samples from the METI/MITI Exploratory Test Wells and Developments of
Prediction Techniques of the Sediment Deformation
The corings were carried out to recover the geological core samples from the seafloor to a depth ofapproximately 250m below the BSR in the two wells of the METI Exploratory Test Wells “Tokai-oki
to Kumano-nada.” The water depth was approximately 1,000m, and the core recovery ratio of sandy

24Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

samples was low. The physical and mechanical properties of the seafloor were estimated by index
tests, consolidation tests and triaxial compression tests using those core samples recovered from the
METI Exploratory Test Well.
Measurements of density, consistency, grain size distribution and clay minerals were taken by index
tests, and subsequently, the fundamental physical properties were understood. Those samples should
be classified as low liquidity clays from an engineering viewpoint.
The consolidation yielding stress was obtained under one-dimensional compression to theconsolidation pressure up to 5MPa. It was confirmed that those sediments were in a state ofoverconsolidation near the seafloor, but that they were in a normally consolidation state below a depthof approximately 100m.
In the triaxial compression tests, the undrained shear tests with controlling strain rate were carried out
after reproducing in-situ stress history by K0 consolidation to the consolidation yielding stressobtained from the consolidation tests and K0 unloading to the in-situ overburden pressure so as tominimize the influences of sample disturbance on the test results.
The constitutive equation of the ground was built to express to an adequate level of accuracy themechanical properties of the seabed ground on the basis of the test results noted above.
The simulations and the three dimensional analyses by the finite element method were undertaken for
the results of triaxial compression tests, and the microscopical behaviors in the specimens such as thenon-uniformities in deformations and strains as well as the macroscopic behaviors of the specimens
were also investigated.

Figure 5-6 shows an example of the distribution of volumetric strain on thesurface of specimen. It can be seen that the volumetric strain in the compression direction in the upperand bottom ends of the specimen as the volumetric strain in the expansion direction graduallyconcentrates at the center of the specimen with the axial strain increasing. As the analytical results andexperimental results show identical tendencies, it is confirmed that the analytical results express wellthe experimental results.

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Axial strain(1) Analytical results(2) Experimental results (by digital image analysis)

Figure 5-6 A result of the numerical analyses for the tri-axial compression tests of the core
Figure 5-6 A result of the numerical analyses for the triaxial compression tests of the core samples
samples obtained from the METI/MITI Exploratory Test Wells (the distribution of volumetric strain)obtained from the METI/MITI Exploratory Test Wells (the distribution of volumetric strain)

From the results investigated above, it is confirmed that the constructed constitutive equation can
express well the experimental results.
The prediction program for stratum deformation was developed by taking in account the constructed
constitutive equation of the seabed ground. After the modules of the core system which controls thewhole program, stratum subsystem, analysis subsystem and load subsystemwere created, thevalidation between subsystems and whole system including including core system were carried out.
It became possible to predict the deformation of the whole seabed ground with the development
program noted above by taking in the displacement data of production stratum calculated by thesimulator developed in the Research Group for Production Method and Modeling. By indirect
combination, the preliminary analyses for the offshore production test was carried out, and thefundamental data contributing to the seafloor displacement monitoring and measuring plan at the timeof offshore production tests were documented based on the above analytical results.

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Research Consortium on Developing Methane Hydrate Resources

2)

Phase 1 Comprehensive Report of Research Results

Acquisition of the Baseline Data in the Offshore Environments and Development of the Prediction
Technique for Biological Influences
Offshore environment surveys have been conducted in the Tokai-oki to Kumano-nada to evaluate theoverall offshore environment where drillings of METI Exploratory Wells is being prepared. Offshore
environment surveillance in a broad area of the Nankai Trough was carried out from FY 2003 to FY
2005, and the interannual characteristics of the water mass structure, the environmental water andsediment quality and the biological environment were obtained in the three areas of Tokai-oki, theDaini-Atsumi Knoll offshore, and Kumano-nada. In addition, offshore environment surveillance wasalso conducted in various seasons in FY 2006 and FY 2007 at the same location around the area
where the METI/MITI Exploratory Test Wells were drilled, and the seasonal differences of the above
items were obtained. According to this baseline data, the characteristics of offshore environments inthe surrounding area of the eastern Nankai Trough and that where the METI/MITI Exploratory Test
Wells were drilled were analyzed, and the following points were clarified.
The relevant area is affected by the movements of the Kuroshio axis, and offshore structure iscomposed of the four masses of water such as coastal water, the water of the Kuroshio region, thewater of subtropical zones and Pacific deep water.
The current pattern has a fifteen-day cycle near the seafloor in the Tokai-oki region. The current
field from the intermediate to the bottom layers near the Daini-Atsumi Knoll is complex, because it
may possibly be influenced by the complex topography of the seafloor. The current pattern in the
Kumano-nada region has a 31-day cycle near the seafloor, which is different in flow patterns from thatin the Tokai-oki region. Results also indicate the possibility it has been affected by the meandering
state of Kuroshio
The maximum concentrations of dissolved methane reache approximately 10nmol/kg. This methane isassumed to be supplied from the seafloor anywhere in this offshore area.
The vertical distribution profile of dissolved methane in the water column has a trend toincrease the concentration such as 3 - 4nmol/kg near the seafloor and the intermediate layer inthese three areas. In particular, it exceeds 7nmol/kg near the seafloor in the Kumano-nada. The
cause of increasing dissolved methane near the seafloor and the intermediate layer of watercolumn is considered to arise from the existence of cold seep zones in the Tokai-oki and near
the Daini-Atsumi Knoll regions, and from mud volcanoes in the Kumano-nada region.

The leaching rate of methane from the seafloor was 3.1 - 64.6 (average 27.7) nmol/m2/h in the
Tokai-oki, 6.1 - 31.9 (average 19.4) nmol/m2/h near the Daini-Atsumi Knoll, and 6.5 - 173.6(average 64.9) nmol/m2/h in the Kumano-nada regions. A higher leaching rate of methane wasobserved in the Kumano-nada region. It is confirmed that the leaching rate is higher in casethat the volume of organic matter in sea bottom sediments in the offshore area is a lot.

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Research Consortium on Developing Methane Hydrate Resources



Phase 1 Comprehensive Report of Research Results

The grain size distribution of surfical sediment is significantly different among the three
offshore areas. In the Tokai-oki region, sand and sand/mud are the main components, and the
median of grain size is 94 - 200μm. Near the Daini-Atsumi Knoll region, sand and mud are
the main components, and the median of grain size is 13 - 94μm, which is a little finer
sediment compared to that of the Tokai-oki region. Meanwhile, in the Kumano-nada region,
silt and clayey silt are the main components, and the median of grain size is 11μm, which are
the finest sediments among these three ocean regions.



The major plankton groups living near the seafloor were the copepoda and amphipoda. In
addition, large differences in species and biomass are not observed between in the Tokai-oki
and the Daini-Atsumi Knoll regions.

Regarding the biomass of the benthic organisms that have habitats in surfical sediment, themacrobenthos is the largest and lives in an area from the sediment surface to 5cm below thesurface in the Tokai-oki region. The bacteria is the largest and lives in an area from thesediment surface to 25cm below the surface near the Daini-Atsumi Knoll region. This depth isdeeper than that observed in the Tokai-oki region. The biomass in the Kumano-nada region is
the highest in the three offshore regions, more than 90% of which is occupied by the bacteria.

On the basis of the results noted above, we considered the kind of index we should use to assess theenvironmental variation during the offshore production test in the relevant offshore areas in the future.
As the prediction technique for biological influences, we have created a new model that added thefunction of reproducing the behavior of frothy methane seeped from seafloor to sea water into the
diffusion model of oil and natural gas in water columns called CDOG (Comprehensive Deepwater Oiland Gas Blowout Model). Its behaivor is that the change of bubble size against temperature andpressure change, the formation of hydrate film coating bubble surfaces and so on. We have also
developed a prediction model for the diffusive areas of water from dissociation of methane hydrate insea water.
We considered the advisability of the direct effect and the extent of the impact for aquatic organisms
incorporated the results for diffusions of methane and discharged dissociated water using our models
into the acute toxicity value, that is median lethal concentration and median effective concentration,of methane for aquatic organisms and the resistant data of aquatic organisms for the discriminative
low salinity of discharged dissociated waters.
Figure 5-7 (left hand figure) showed an example of calculation for the continuous leakage of methanegas from the seafloor for six hours with the rate of 0.1Nm3/sec under the condition of watertemperature, salinity and current velocity in October near the Daini-Atsumi Knoll. The methane gas
came up rapidly, diluted and diffused with having dissolved in sea water. The hydrate formed methanegas did not reach the sea surface since it dissolved in sea water after disaggregating to gas up to the28Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

depth 100 - 200m below the sea surface. As a result of investigating the extent of methane impact onliving organisms from the median lethal concentration for fish and the median effective concentration
for shellfish, the organism group living tens of meters from the center of the methane plume isestimated to be directly affected.
We estimated the diffusion of water from dissociation of methane hydrate in the case of having
discharged from the sea surface, the intermediate layer and the seafloor. In the case of discharge fromthe intermediate layer, it was found that the water from dissociation of methane hydrate rises to thesea surface and spreads due to the lower density there than in surrounding sea water, and that it
diffuses horizontally by the flow of each layer. This is because the water from dissociation of methane
hydrate is supposed to be fresh water.
In discharging from the seafloor (Figure 5-7 (right hand figure)), the water from dissociation of
methane hydrate is not considered to have much of a direct effect on the benthic living organisms as
the discharged water will never emanate from the seafloor. In discharging from the sea surface, theinfluence on the planktons and so on in the surrounding areas is estimated to be small as the verticalextensity is around a few meters and the horizontal extensity is also around 10m. In other results ofcalculation with changing the volume of discharge, the discharged water diffuses relatively for a shorttime because of the effect of the surrounding ocean currents, and the domain of low salinity area islimited in the vicinity of discharge vents. It is presumable that the extent of impact of water from
dissociation of methane hydrate on organisms living in the surrounding sea water is possibly within
narrow limits near the discharge vents.

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Methane Concentration in XY Plane due to Gas and Hydrate at Depth (Z) = 200 m
-5
x 10
200

Y Distance (m)

9

20

8

100

7
6

0

5
4

2

18

1

-200
0
200
Methane-100
Concentrationin100
XY Planedue to 300
Gas and400
Hydrate500
at Depth600(Z) = 400-5 m
X Distance (m)
x 10
200
9

Y Distance (m)(XY)  11 Feb 2008 

0.1 m/s

3-100

Palette

8

100

7
6

0

16

5
4
3

-100

2
1

-200
0
200
Methane-100
Concentrationin100
XY Planedue to300
Gas and400
Hydrate500
at Depth600(Z) = 600-5 m
X Distance (m)
x 10
200

0

-300

6
5
4

12

3

-100

2
1

-200
0
200
Methane-100
Concentrationin100
XY Planedue to 300
Gas and400
Hydrate500
at Depth600(Z) = 750 m-5
X Distance (m)
x 10
200

-400

9

-500

Y Distance (m)Depth Z (m)870(meter)Y Distance (m)

-200

-600
-700

8

100

10

7
6

0

5
4
3

-100

2
1

-800

-200
-100
0
100
200
300
400
500
600
X Distance(m)and Hydrate at Depth (Z) = 850 m
Methane Concentration in XY Plane
due to Gas
-5
x 10
200

-900

8

Y Distance (m)

9

-1000
-1100
-1200
-500

8

100

7
6

0

6

5
4
3

-100

2

0
500
Distance X (m)
水平距離（ｍ）

Horizontal distance (m)

1000

1

-200
-100

0

100

200

300

400

500

600

X Distance(m)and Hydrate at Depth (Z) = 950 m
Methane Concentration in XY Plane
due to Gas
-5
x 10
200
9

Y Distance (m)(m)
Water depth
水深(m)

14

9

-100

100

Above 33.50
33.25 - 33.50
33.00 - 33.25
32.75 - 33.00
32.50 - 32.75
32.25 - 32.50
32.00 - 32.25
31.75 - 32.00
31.50 - 31.75
Below 31.50

μ M/kg

8

100

7

4

6

6

0

5
4

5

3

-100

2

2
1

-200
0
100Plane200
300 and Hydrate
400
500
Methane -100
Concentrationin XY
due to Gas
at
Depth 600
(Z) = 1125m
-5
X Distance (m)
x 10
200

0

4
3

0
0

7
6

0

5

2

4
3

-100

2

1

2

4

6

400

500

600

400

500

600

200
300
X Distance (m)

300

100

200

0

100

1

-200
-100

-100

-200

8

100

0

-100

9

Y Distance (m)

200
100

8

10
12
(meter)

14

16

18

0

水平距離（ｍ）
Horizontal
distance (m)Figure 5-7 An example of calculation results for the prediction model(left hand figure) An example of the calculation result for the prediction model of the behaviorof leaked methane. The result of diffusion calculations in the case of methane that has
leaked at 0.1Nm3/s from the seafloor (after six hours)(right hand figure) An example of the calculation result for the prediction model of the effectsof water from dissociation of methane hydrate. The salinity distribution in the case of
releasing discharged dissociated water from the seafloor at the rate of 0.001m3/s (two hours
after the release)

3)

The Relationship between Methane Hydrates and the Global Environmental Risk
Based on the understanding in this report that “the macro risk assessments of environmental impacts”
means the assessment of global environmental risks (such as global warming), we have carried out
research on environmental risks which naturally occurs on a global scale, and human-induced
environmental risks derived from exploitating methane hydrate.

(a)Environmental risks naturally occurring on a global scale
There is a hypothesis that methane could be discharged naturally from the subsurface methane
hydrate-bearing layers into sea water and moreover into the air after the collapse of the subsurface
methane hydrate-bearing layers sometimes arise spontaneously. Literature review has been carried out
to investigate the hypothesis of the three conceivable effects (risks) on the global environment andthose effects are summarized as follows.
(1) The collapse of methane hydrate-bearing layers due to global warming, which further accelerates
warming.

30

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results(2) As the earth moves toward glacial stage, sea level would decrease and it would cause decrease of
seafloor pressure and increase of sea water temperature. This may result in collapse of themethane hydrate-bearing layers and may cause large-scale landslides(3) A significant amount of methane discharged from the collapsed methane hydrate-bearing layers
will consume oxygen in ocean water, which may result in the death of the significant number ofliving marine organisms due to the ocean anoxic event.
Many researchers are now undertaking research into the three risks mentioned above. Althoughseveral theories have been proposed to ascertain whether these were caused by the collapse of
methane hydrate-bearing layers or other causes, there are still no commonly-accepted notions atpresent.
According to the theory that proposes that these phenomena were caused by the collapse of methane
hydrate-bearing layers, the collapse of methane hydrate-bearing layers itself is considered to be
ascribed to climate change of the geological time-scale ranging from a few thousands to hundreds ofthousand years. More specifically, those theory claims that the collapse of the methane
hydrate-bearing layers would occur as a result of climate change such as increase of seafloor
temperature or significant decrease of the sea level over a significantly long period of time.
As stated above, the current discussion over the risk of global warming on methane hydrate aremainly based on hypothesis that global-scale collapse of the methane hydrate-bearing layer occurs due
to global climate change over the geological time-scale that is longer than a few thousands of years.
(b)

The human-induced environmental risks derived from exploitating methane hydrate
The exploitation of methane hydrate assumed in the R&D program is to use depressurization method
to dissociate and extract methane hydrate from the methane hydrate-bearing layers distributed below
the seafloor in the eastern Nankai Trough area.
The pressure and temperature conditions of the methane hydrate-saturated sandy sediments, whichwere discovered by the MITI Exploratory Test Well “Nankai Trough” drilled in the eastern Nankai
Trough area, is depicted as an example in Figure 2-1.

As just described, offshore methane hydrates

are distributed as solid substances in conditions in which temperature is approximately ten Degree
Celsius and pressure is higher than 10MPa at 200m below the seafloor locating approximately 1,000m
below the sea level.

The exploitation of methane hydrate targets hydrate that is stably occupied as asolid state filling the pore spaces of sandy sediments. The exploitation of this type of methane hydrate
requires human operation such as depressurization or increase of temperature through extraction well.
If operations are terminated, the pressure and temperature may spontaneously return to their former
state. Once pressure and temperature enter into the stable state, the dissociated methane gas will goback to the solid methane hydrate. This process will be deemed to be a safety mechanism during the
exploitation and production process.

31Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

For this reason, the risks of methane gas leaking continuously out of the production system areconsidered to be rather low in the case some problems occur with production facilities and it has evenbeen estimated that production of methane gas may stop during methane gas exploitating activities.
In addition, methane gas that is dissociated in the methane hydrate-bearing layers is transported fromthe subsurface formation to the offshore facilities through the well for production, and this process issimilar to the exploitation of conventional natural gas. Therefore, for this process, the risk assessmentof conventional natural gas exploitation could be applied.
(c)

Further responses
As mentioned above, the anxiety over global warming accompanied by the collapse of methane
hydrate-bearing layers as a natural phenomenon should be evaluated in terms of the geological timescale. In terms of human- induced environmental risks related to the production of methane gas frommethane hydrate-bearing layers, we may be able to investigate those risks by looking at case examples
involving the production of conventional natural gas. At the same time, as a number of researches onboth issues are expected to be carried out, it would be necessary to collect information on researchand developments etc. from academic meetings and other sources.
Although naturally-occurring global-scale environmental risks are not an issue directly associatedwith the R&D program, it is crucial to continuously collect and analyze information and to introduce
beneficial information to the exploitation of methane hydrate, and to provide adequate information to
the public.

32

Research Consortium on Developing Methane Hydrate Resources

6.

Phase 1 Comprehensive Report of Research Results

Achievements of the Onshore Gas Hydrate Production Test

6.1 Results of the first Onshore Gas Hydrate Production Test
The first Onshore Gas Hydrate Production Test was carried out at the Mallik site in the Mackenzie
Delta area, Northwest Territories, Canada, in 2002 as a collaborative research project among fivecountries (Japan, Canada, USA, India, and Germany) and seven research institutes (the former Japan
National Oil Corporation- JOGMEC, Geological Survey of Canada, US Department of Energy, US
Geological Survey, German GFZ, Indian Ministry of Petroleum and Natural Gas-India Oil and Gas
Corporation, and Project of BP-ChevronTexaco Mackenzie Delta Joint Venture). At this site JNOC
(Japan National Oil Corporation), the former JOGMEC, and the GSC (Geological Survey of Canada)conducted a survey in 1998, and discovered four or five pore filling type hydrate bearing sediments insand layers at depths ranging from 890m to 1,100m below the permafrost zone continuing to a depthof 650m. From the production test carried out in 2002 in the Mallik 5L-38 well, we succeeded in
producing about 470m3 of gas within a five-day production period using the hot water circulation
method, which is one of the thermal stimulation methods. In addition, the process of depressurization
was monitored by the MDT (Modular Formation Dynamics Tester: registered mark of Schlumberger),and the emergence of gas was confirmed. Besides, data related to the formation permeability has beenobtained through the pressure analyses and other information.
The JNOC took part in the production test, and analyses and studies of the acquired data have been
conducted by the MH21.

6.2 Result of the Second Onshore Gas Hydrate Production Test
1)

Purpose of the Second Onshore Gas Hydrate Production Test
The First Onshore Gas Hydrate Production Test carried out in 2002 was the first trial that had been
carried out in the world up to that time that attempted to produce methane gas by dissociating the
subsurface hydrate. However, future tasks remained to be carried out in terms of the issues of small
production volumes and continuity. On the other hand, as the depressurization method became
increasingly likely to be applied to the layers noted in the previous section, verification of thedepressurization method in a field scale was desired with the intention of carrying out offshore
production tests in future, and, moreover, the commercial viability of methane hydrate resources.
The purpose of the Second Onshore Gas Hydrate Production Test were to confirm that methane
hydrates dissociate continuously over a long period of time in sediment using the depressurization
method and to improve the accuracy of the production simulator by using obtained data there.

33

Research Consortium on Developing Methane Hydrate Resources

2)

Phase 1 Comprehensive Report of Research Results

Preparatory WorkThe Second Onshore Gas Hydrate Production Test was carried out twice in the winters of 2007 and2008 by the JOGMEC and the Natural Resources Canada (NRCan) with the designated operator of
the Aurora College, which is an educational institute in the Northwest Territories, Canada.
Since the area noted above is only accessible in the period when the rivers and the seas are frozen and
ice roads can be constructed, all of the operations were limited to the winter season. Additionally,
because this area is part of a vulnerable ecological system in the Arctic in which rare creatures arefound, we took great care with regard to environmental conservation. Drilling wastes were broughtback to the southern Canada for disposition, and the producted waters were injected into the aquifers
below the hydrate-bearing layers. The Mallik 2L-38 well drilled in 1998 was utilized as the
production well after having deepened, reamed, cased and cemented.
During the period from January through April 2007, the Mallik 2L-38 well was intervened after theice road and the drill site were constructed, and physical property data of the hydrate-bearing layers
was obtained from state of art physical logging tools at the same time. The delay of drilling as
operations and other tasks due to the unusually cold winter made us abandon the plan of drillingobservation well, but the Distributed Temperature Sensor (DTS, only down to the depth of 1,050m)
and the electrodes for the streaming potential measurements were installed outside of the casing in the
production well.

3)

Production Test
Perforations were shot for the completion of the target layer from a depth of 1,081 to 1,093m that was
the deepest layer in the hydrate-occurence zone of this area. Following that, the production test was
carried out using the lower aquifer as the injection layer at a depth of approximately 1,300m in thesame well.
During the limited operational period in the first winter of 2007, we put the electrical submersible
pump below the perforation interval and carried out depressurizing by lowering the downhole waterlevel by injecting the production water into the injection layer below. As a result, generation of gas
was confirmed at a bottom-hole pressure of approximately 8MPa, which was higher than expected(the initial formation pressure was approximately 11.4MPa), and then production of 830m3 of gas wasobserved during the depressurizing period for approximately 12.5 hours after being depressurized to
7.2MPa. However, as a large volume of sand flowed into the downhole much earlier than expected
and the pump malfunctioned, we had no other choice but to stop the test 60 hours after
commencement.
The well was abandoned temporarily in April 2007, and was spudded in again in January 2008.
According to the lesson learned the previous year, we placed a sand control device in the same

34

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Resultsinterval as we did in the first winter, and the production water that was drawn to the surface wasinjected into the subsurface aquifer through another well after being measured. The bottom-holepressure was finally depressurized to 4MPa, and we succeeded in producing a total of 13,000m3 ofgas at a production rate of 2,000 - 4,000m3 per day for six days.
The temperatures and pressures were measured at the bottom-hole, the pump depth and the surface,
and the samples of gas and water were obtained after measuring their production volumes on thesurface.
The obtained samples and data are listed in Table 6-1.
We withdrew from the site after abandoning the well in April 2008.

4)

Implication of the Onshore Gas Hydrate Production Test
This is an important step toward achieving the goal of utilizing methane hydrate as a resource since it
was verified the gas can be produced continuously from the methane hydrate using thedepressurization method. Based on this, the theoretical basis, simulator, and moreover thefundamental techniques for the depressurization were also considered to be verified, but future issues
verifying the longer-term test and technologies able to be used in a offshore environment still remain
to be carried out. As a matter of course, future progress in the research and developments isanticipated.
Water

Methane Gas

Lowering Water by
Pumping Out

Pump

Hydrate Dissociation
by Depressurization
Methane HydrateBearing Layers

Figure 6-1 Schematic diagram of the depressurization method35

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Figure 6-2 Measured production volumesof cumulative waters (blue line) and gases (red line)

Figure 6-3 Continuously burning gas(left: the night of March 10, right: the morning of March 16)36Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 6-1 Samples and data obtained from the Second Onshore
Gas Hydrate Production Test
Source of Information
Data
First Winter Test (2007)
Open-holelogging Resistivity
before the test
Natural gamma ray
Neutron scattering cross section
Density log (gamma ray attenuation)
Seismic velocity (Vp, Vs)
Neutroncapturegamma-rayspectroscopy (ECS)
Nuclear magnetic resonance log(NMR)
Micro-resistivity borehole image
Cement-bond logging
Cased-hole logging
before and after the
test

Impedance ratio of casing and its
behind by ultrasonic log
Sonic attenuation by sonic log
Neutron scattering cross section
Neutron capture cross section

Seismic velocity (Vp, Vs)
Pressure and temperature of the pumpsuction port
Pressure and temperature of the pumpdischarge port
Casing pressure
Samples
Sand sample at retrieving thecompletion assembly
Monitoringoutside Optical fiber thermometerthe casing
Fluid flow potential
Second Winter Test (2008)
Variablesof Pressure and temperature above thedownhole conditions perforation (memory gauge)
during the test
Pressure and temperature of the pumpsuction port
Pressure and temperature of the pumpdischarge port
State variables of Pressure and temperature of the
produced fluids
produced water
Pressure and temperature of gas
Fluid production rate
Water production volume by therotating flow meter and the tankmeasurement
Gas production volume by the orificeflow meter
Samples
Sand samples in the produced fluid
Samples of produced water
Variablesofdownhole conditions
during the test

Monitoring
the casing

Gas samples
outside Optical fiber thermometer
Fluid flow potential

37

Information
Hydrate saturation
Content of clay minerals, lithology
Porosity (φ)
Density (b) -> porosity, hydrate
saturation
Formation strength, hydrate saturation
Mineral composition -> permeability
NMR relaxation time -> permeability,
porosity, hydrate saturation
Hydrate distribution, crack, borehole
wall fracture
Condition of cementation
Condition of cementation
Porosity (φ)
Formation
element
composition,
porosity (φ)
Formation structure, hydrate saturation
Dissociation behaviour of hydrate
Calculation of fluid flow
Calculation of produced gas volume
State of sand trouble
Borehole temperature
Fluid movement in the formation
Dissociation behaviour of hydrate
Data for the pump operation
Data for the pump operation
Correction for produced water volume
Correction for produced gas volume
Produced water volume
Produced gas volume
State of sand trouble
Salinity concentration, origin
produced water
Origin of produced gas
Borehole temperature
Fluid movement in the formationofResearch Consortium on Developing Methane Hydrate Resources

7.

Phase 1 Comprehensive Report of Research Results

The Production Simulator
The Research Consortium for Methane Hydrate Resources in Japan has been developing Japan’s own
production simulator (MH21-HYDRES) especially designed for predicting behaviors of methane
hydrate-bearing layers. This simulator was improved to the 2-dimensional cylindrical coordinate
system model in FY 2000 through the project carried out in the former JNOC based on the
1-dimensional Cartesian coordinate system developed by the University of Tokyo in FY 1999. Since
FY 2001, this simulator has been further expanded to the 3-dimensional Cartesian coordinate systemmodel and its functions have been strengthened in the Research Consortium for Methane Hydrate
Resources in Japan. As discussed in greater detail below, the five production simulators for methane
hydrate-bearing layers are now publicly available worldwide, and the simulator noted above iscompetitive with others.
The production behaviors of gas and water were predicted in the Second Onshore Gas Hydrate
Production Test using this simulator which contributed to the success of the production test bysuggesting the basis of the design of the borehole and surface facilities, and preparing task guidelines.
It was also utilized in the prediction of the gas production performances, which are the basis for thesection “5.3. Objective 3: Selection of methane hydrate resource fields from promising methane
hydrate bearing offshore areas and deliberation of economic potential.”

7.1 Functions, Features and Achievements of the Production Simulator
The MH21-HYDRES is composed of a variety of calculation routines including the routine to define
initial reservoir properties defining the characteristics, properties and conditions of reservoirs, theroutine to calculate changes in reservoir properties describing the reservoir properties that change
during production, the routine to calculate phase behavior calculating the equilibrium conditions forformations and dissociations of methane hydrate and the formation/dissociation rates, and the routine
to calculate phase properties acquiring the state quantity and the enthalpy etc. of each phase. This
simulator also utilizes the dynamic local grid refinement method that makes it possible to speed up
without losing computation accuracy, the hybrid grid system that makes it possible to calculate theproduction behaviors of a group of multiple wells group at high speed, the functions of the parallel
computation, the calculation functions of the fluid flow in wellbore and the fluid flow in completioninterval, and so forth. Additionally, the computation modules were developed for the properties offormation compaction and deformation, the properties of formation and dissociation and thecharacteristics of permeability, all of which are important factors for expressing the production
behaviors of methane hydrate resources. These modules were subsequently incorporated into theMH21-HYDRES as calculation routines. Regarding the characteristics of permeability that is
especially crucial for the evaluation of productivity, the vertical and horizontal absolute permeabilitiesof alternating beds of sand and mud were formulated, and moreover the dependence property of38

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

irreducible water saturations and residual gas saturations on sand grain sizes, the effective
permeability variations of the methane hydrate occurrences in pore spaces, the relationship between
methane hydrate saturations and relative permeabilities and the change in porosity due to compaction
and its effect on permeabilities were formulated and built onto the MH21-HYDRES.
The MH21-HYDRES is featured for its development in stand-alone mode especially for the use in thedevelopment of methane hydrate resources. Its major difference from a reservoir simulator used for
exploitation of conventional oil and gas is that this simulator has the following functions (Figure 7-1).
Possible manipulation of the five phases such as gas, water, methane hydrate, water ice, and saltAble to handle the five components such as methane, nitrogen, water, methanol, and saltIntroducing the equation of kinetics for methane hydrate formation and dissociationAble to handle the exothermic and endothermic behaviors associated with methane hydrate
formations and dissociations

Introducing the equation of kinetics for water ice formations and decompositionsAble to handle salt precipitation from the salty water phase, salt dissolution to the water phase andassociated exothermic and endothermic reactions

Possible transitions of the three phase equilibration curve of methane hydrate- methane- water(water ice) matched to the calculations of methanol or salinity concentration and theconcentrations of methanol or salt

Possible calculations of the solubility of methane into water phase taking the salinity
concentration into accountPossible manipulations of the configuration of multiple production wells and injection wells
including vertical, directional and horizontal wells in methane hydrate-bearing layer

Possible calculations of the fluid flow in the wellbore taking the exterior formation temperature
profile into accountPossible upgrading for the calculation accuracy and the calculation speed by applying the
dynamic local grid refinement method and the hybrid grid systemAble to handle the boundary conditions of constant pressure, constant flow rate, constantpressure-constant temperature surface and so forthAble to handle the lowering permeability due to compaction

Introducing the effective permeability and relative permeability as a function of methane hydrate
saturationAble to handle the analyses of the productivity and the production behavior in various basic
production methods and their combinations such as the depressurization method, the thermal
stimulation method, the thermal flooding, the inhibitor injection method, the nitrogen injection

39

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

methodDepressurizing
production

Core experiments

MethaneHydrateGas

Full field operation

Closed boundary of
constant temperature

Closedboundaryof constanttemperature

Horizontal well

The constant pressure boundary

Single Well Test

Hydrate-bearing layer

Heat

Gas production well

Overburden

Compaction
Heat

Hydrate-bearing
layer
Aquifer

Hot water, steam, inhibitor

Figure 7-1 Outline of the MH21-HYDRESIn the calculation module noted above, the independent simulator for the dynamic property analyses
was created separately concerning the module of the compaction and deformation property evaluation,and the evaluation of the deformation behaviors accompanied by the production corresponding to thereservoir characteristics and forms became possible (refer to article 8.2. Physical Property
Measurements of Methane hydrate-bearing layers (2. Modeling Section)).
MH21 participated in an international project on the comparison of methane hydrate simulators
sponsored by the research institute of the US Department of Energy (NETL: National Energy
Technology Laboratory) and the US Geological Survey of the Department of the Interior (USGS). A
total of five simulators of the MH21-HYDRES as well as the following four participated.


The TOUGH-Fx/Hydrate: developed by the Lawrence Berkeley National Laboratory (LBNL)
based on the TOUGH2 that is famous in the world as a geothermal reservoir simulator.



The HydrateResSim: opened the TOUGH-Fx/Hydrate v1.0 to the public by the NETL.

The STOMP-HYD: modified for possible manipulations of gas hydrate from the multi phasefluid flow simulator (STOMP) jointly created by the Pacific Northwest National Laboratory(PNNL) and the Petroleum Engineering Department of the University of Alaska Fairbanks

The STARS: a commercial oil and gas reservoir simulator especially for predicting reservoir
behaviors by thermal methods created by the Computer Modelling Group Ltd. (CMG) in
Canada.

This project was began with the coupled problem of one-dimensional heat and fluid flow without
methane hydrate, and the seven problems including the reservoir behavior prediction for the40

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

depressurization method representing the actual field were investigated with gradually increasinglevels of difficulty. The MH21-HYDRES presented the rational calculated results either equaling or
surpassing those of the other simulators in all the problems. It also confirmed the possibly adequate
calculations of the physical and chemical phenomena necessary for methane hydrate simulators interms of the methane hydrate formations and dissociations, the water ice formations anddecompositions and so on, and the possibly adequate expressions of the two-phase fluid flow
phenomena after methane hydrate was dissociated. In addition, the calculations converge adequately
in the problem of behavior prediction of the field scale production, and also present the excellent
results in perspective of computational stability. At present, it has prerogatives to the other simulators.
The (MH21-HYDRES) simulator was used to carry out intermediate interpretation and the posterioriinterpretation for the results of the Second Onshore Gas Hydrate Production Test, and the production
behaviors were analyzed and evaluated. Regarding the First Winter Test, the result of the production
test has been approximately reproduced by adjusting the reservoir parameters and assuming thepermeability increase due to sand production in the adjacent formations around the well and thenonsteady wellbore fluid flow in the matching simulation (Figure 7-2), although the details offunctions of the simulator have not been sufficiently verified due to the short production period of
approximately 12.5 hours. Regarding the Second Winter Test, the gas production rate changes during
the test period of approximately six days and the gas and water production rates under the constantbottom hole pressure were reproduced, and moreover the formation temperature in the methane
hydrate dissociation zone estimated by the simulation was consistent with the measured bottomholetemperature. Furthermore, the relative permeabilities to gas and to water in the field were evaluatedby using the matching simulation of the production test, and the improvement of overall accuracy ofthe production simulator was accomplished.

10000

1000

Gas production rate (measured)

6000

Cumulative gas production rate (simulated;corrected [cum. @4/3 15:00=0])
Cumulative gas production rate (simulated;berfore correction)

3

600

4000

400

2000

200

0
2007/4/2 2007/4/2
12:00 PM 3:00 PM

2007/4/2
6:00 PM

2007/4/2 2007/4/3 2007/4/3
9:00 PM 12:00 AM 3:00 AM

2007/4/3
6:00 AM

2007/4/3 2007/4/3 2007/4/3
9:00 AM 12:00 PM 3:00 PM

Pressure

Cumulative gas production (m )800

Cumulative gas production (measured)3

Gas production rate (m /day)Gas production rate (simulated)
8000

Temperature0
2007/4/3
6:00 PMTime(a) Matching of the gas production volume(b) Matching of the borehole temperatureand pressure

Figure 7-2 Matching results of the First Winter Testof the Second Onshore Gas Hydrate Production Test

41

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

7.2 Evaluation of the Production Method by MH21-HYDRES
By utilizing the reservoir model surrounding the well made at selecting the methane hydrate resource
field in the eastern Nankai Trough (refer to article of 5.3. Objective 3: Selection of methane hydrate
resource fields from promising methane hydrate bearing offshore areas and deliberation of economic
potential), the production behaviours and energy efficiency by various production methods were
evaluated.


Thermal methods such as the thermal stimulation method and the thermal flooding etc. on theirown were assessed to have low levels of energy efficiency and only able to be used in the
distant future. In addition, many future issues remain to be dealt with from the viewpoint of thegas sealing capacity of the formation by means of core test results and the dynamic property.

Generally the depressurization method should be applicable (Figure 7-3 (a), (b)) when thepermeability and the reservoir temperature are high, and the reservoir characteristics in theeastern Nankai Trough area are satisfied.

The recovery factor drops away as the heat transfer from the surrounding areas cannot keep up
with the compensation of heat absorptions due to methane hydrate dissociation in the case of
the thick concentrated zones.



The combination of the thermal stimulation methods and the depressurization method is more
adequate when the methane hydrate-bearing layers are thick or the increasing the recovery
factor is aimed in the low temperature reservoirs.

The lowering of the energy efficiency is inevitable by combining these thermal stimulation
methods, and at that point, development of more effective combinable methods will beconsidered necessary in the future.
1000

Average gas rate (m3/day/m)Average gas rate (m3 /day/m)

10000

1000

100

10

k abs = 10mD
k abs = 100mD

1

k abs = 1000mD
0.1
0.000001 0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

100

10

285.15K
283.15K
281.15K
279.15K1

0.1
0.00001

0.0001

0.001

0.01

0.1

1

10

100

Initial effective permeability (mD)

Initial effective permeability (mD)(a) Relationship between the initial effective
permeability and the productivity(b) Relationship between the reservoir
temperature and the productivity

Figure 7-3 Relationships between the productivity using the depressurization method andthe initial effective permeability and the reservoir temperature

42

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Based on the analysis results, after the energy efficiency and the simple provisional calculation of theeconomic potential were done, the economical potential seems promising because the high energy
efficiency in the depressurization method (horizontal well), the depressurization method (verticalwell) and the combined method of the depressurization method and the wellbore heating method is
expected and the payout time is early (Figure 7-4).
400

Rate (Vertical well)3)Rate (Horizontal well)Rate(水平井)
Rate(垂直井（坑井加熱）)

6

Rate (Vertical well) (with wellbore heating)Cum(垂直井)120

300

Cum (Vertical well)Cum(水平井)Cum (Horizontal well) Cum(垂直井（坑井加熱）)
Cum (Vertical well) (with wellbore heating)

80

200

40

100

0
0

365

730

1095

1460

1825

2190

2555

2920

3285

0
3650

Time (day)Energy production/consumption

Rate(垂直井)

Cumulative gas production (10 m )Gas production rate (103 m3/day)160

Depressurization
method vertical wellDepressurization
method horizontal well(a) Example of the prediction results of gas
production behavior by the depressurization
methodPartial hot water
injection method
Huff&Puff
methodCombined method ofdepressurization andwellbore heating(b) Example of the calculation of theenergy efficiency

Figure 7-4 Example of the prediction results of gas production behavior in the single wellusing the simple Nankai Trough model
The “Depressurization method” is carried out to depressurize the pore pressure of methane
hydrate-bearing layers through perforations with reduction of the bottomhole pressure by lading waterin the well using pumping. For this reason, the energy directly expended for production is motiveenergy of the pump, and subsequently, a high level of energy efficiency is theoretically able to be
expected. Methane hydrates are dissociated into gas and water by depressurizing the pore pressureof the methane hydrate-bearing layers that are less than the equilibrium curve, and gases and water are
produced by flow from the subsurface layers into the production well in which pressure is low. As thedissociation in the methane hydrate-bearing layers is accelerated when subjected to heat, thedissociation progresses at the point where heat is supplied (Figure 7-5). It is difficult to continue theprocess of dissociation near the center of the methane hydrate-bearing layers where there is aninsufficient supply of heat. The effective permeability increases due to the lowering of methane
hydrate saturation in pores where dissociation progresses, and dissociation will be accelerated
furthermore by making depressurization occur more effectively. As noted above, the dissociation in
the methane hydrate-bearing layers advances heterogeneously, and the parts contacting the methane
hydrate-free layers above and below the methane hydrate-bearing layers may preferentially contribute43Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

to production.
Well (depressurized)
Heat

Well (depressurized)
Heat

Gas rate

Gas/Water

Heat

Gas/Water

Gas/Water

Gas/Water

Gas/Water

Heat

Time (Days)
Well (depressurized)
Heat
Heat

Gas/Water

Heat

Heat

Well (depressurized)
Heat
Heat

Heat

Gas/Water

Gas/Water

Well (depressurized)
Heat
Heat

Heat

Heat

Gas/Water

Pressure propagation
reaches the boundary→ Increase of thedepressurization speed

Heat

Heat

Gas/Water

Rapid pressure lowering→Acceleration of the hydrate
Gas/Water dissociation→Rapid temperature lowering→Acceleration of external heat flow
→Further hydrate dissociation

Dissociation of methane hydrate only with thermal
Gas/Water conduction from overburden and underburden→Almost stable rate of dissociation
Gas/Water

Gas/Water

Gas/Water

Heat

Hydrate dissociation→Increase of permeability→Further pressure propagation→Enlargement of the dissociation zone
→Increase of gas production rate

Heat

Heat

Heat

Heat

Heat

Heat

Heat

Heat

Heat

Heat

Figure 7-5 Behavior of gas production by the depressurization method accompaniedwith the heat supply from the adjacent formations and the change of the methane
hydrate dissociation zone
In the eastern Nankai Trough area, the potential heat in alternating beds of sand and mud willcontribute to a certain amount of the production and recovery factor without any artificial heat
supplies, however the heating etc. may be considered necessary for increasing the recovery factors
and productivity in low temperature reservoirs. The depressurization method may play a pivotal role
regardless of what we adopted, including the human-induced heat supplies shown in Figure 7-6.
First Onshore Gas Hydrate Production Test

Second Onshore Gas Hydrate Production Test

Wellbore heating method

New methods
Other methods

Combined method ofdepressurization andwellbore heating
Depressurization method
Huff & Puff method
Inhibitor injection method

Huff & Puff method
Hot water injection method

Figure 7-6 Relationship among the various production methods

44Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

The depressurization method can essentially maintain productivity over the long term unless theeffective permeability and absolute permeability of the reservoirs decreases. However, decreasing thepermeability can be predicted from the influences of the skin formation caused by the accumulation ofsilt constituents around the wellbore in the process of production and the compaction accompanied by
the depressurization. In addition, increasing of the water production volume can be predicted to
disturb effective propagation of depressurization to the reservoirs due to the water coning when thepermeable water-bearing layers overlie and underlie the reservoirs. It is necessary to quantitatively
understand these factors of production damage.

45

Research Consortium on Developing Methane Hydrate Resources

8.

Phase 1 Comprehensive Report of Research Results

Predominant Results of Items Above
In the R&D program “V. Contents of Technology Developments,” the contents of technologicaldevelopment are described in the five sections. The status of the achievements in each section of thetechnological development contents will be submitted as a self-evaluation in the final assessment ofPhase 1 that will be carried out in FY 2008 by METI. The predominant results of them arecomprehensively described in the articles of “5. Status of Achievement of R&D Program Goals,” “6.
Achievements of the Onshore Gas Hydrate Production Test,” and “7. The Production Simulator.” Asmany more achievements have been obtained from the development of recent research other than the
results described in these three articles, the selected achievements in those will be summarized in theorder prescribed in the R&D program.

8.1 Clarification of the Methane Hydrate Accumulation Mechanism and the Origin of Methane Gas(1. Exploration Section)
The objective of this study is to contribute to the improvement of accuracy of the methane hydrate
resource assessment (the presumption of the concentrated zones) around Japan by targeting themethane hydrate distributed below the seafloor in the Nankai Trough by means of elucidating theprocess of how the present appearance of methane hydrate distribution has been made and what thecontrolling factors are.
(a)

Methane Generation and Origin
According to the results of the geochemical analyses for the core samples obtained from the METI
Exploratory Test Wells “Tokai-oki to Kumano-nada,” all of the gases contained in methane hydrates
recovered from the eastern Nankai Trough area have been confirmed to be mainly composed ofbiogenic methane. The total organic carbons (TOC) at the depth of methane hydrate existence in theeastern Nankai Trough are approximately 0.5%, which is not sufficient for forming the concentrated
zones in terms of the mass balance. Although the biogenic gas composing methane hydrates are
estimated to have been generated in the relatively shallow depths after deposited, it is nearly apparent
that they have not been generated only in the present contained formations based on the occurrencesof methane hydrates and the mass balance of carbon, and that the migrations and accumulations ofmethane from the deeper formations have occurred. Regarding the mechanism behind the above, after
biogenic methanes generated at the time of deposition of the accretionary sediments were buried withthe sediments by the accretionary movement, the dissolved methanes become gases when theirdissolved contents exceed the saturated dissolved concentration. It should be estimated that they havemigrated and accumulated through faults, high-permeable sandy layers, unconformities and so on to
the high-permeable sandy layers, and that they have formed the methane hydrate-bearing layers.

46

Research Consortium on Developing Methane Hydrate Resources(b)Phase 1 Comprehensive Report of Research Results

Methane Hydrate Formations
By the analyses of the MH formation experiments, the methane hydrate saturations were found to
relate to the specific surface area and the pore diameter distributions of the sediments. As thesaturations of the sediments predominantly with smaller pore diameters (clay to fine-grained silt) are
low and those of the well-sorted sediments predominantly with larger pore diameters (coarser thanfine-grained sand) are high, it is estimated that the free water volume containing in sediments may
affect the methane hydrate saturations.

(c)Methane Hydrate Reservoir Characteristics and Occurrence
According to the analyses of the core samples obtained from the METI Exploratory Test Wells“Tokai-oki to Kumano-nada,” it has been understood that the methane hydrate concentrated sandlayers are composed of fine- to very fine-grained sands, and that the porosities and permeabilities ofthem are high. It is assumed that these sandy layers have not significantly suffered from the burial
diagenesis. Moreover, the analyses of the sequence stratigraphic studies by means of the seismic data
and the downhole well log data were carried out, and the shapes of the submarine fans of eachdepositional sequence were rebuilt. Subsequently, the methane hydrate-bearing layers in the eastern
Nankai Trough are found to distribute in the sandy layer parts of the turbidite sand and mudalternation layers forming the submarine fans.

(d)Geological and Geochemical Environments of the Shallow Formations and Phenomena on Seafloor
Surface
When the distribution of the SMI depths indicating the methane flux near the seafloor were comparedto the BSR distributions, the significant relationships between them have not been recognized. The
reason for this is considered that fluid containing methane are not controlled by the simple upward
diffusion, but are considered to have migrated to the seafloor by selecting the high permeable
migration paths through the local faults and the high permeable sandy layers with horizontal
continuation.

(e)

Investigations by the Numerical Simulation
A case study was attempted based on data from the eastern Nankai Trough using the newly developed
one-dimensional methane hydrate formation simulator. As a result, it was indicated that the advective
flows of methane from the deeper formations are an especially crucial factor for controlling theformation of the concentrated zones, and that the sediment properties, the volume of methane supply
and the tectonic movements are important as factors controlling the methane hydrate concentration
change in the methane hydrate-bearing layers.
Meanwhile, the two- and three-dimensional methane hydrate accumulation simulator (SIGMA-MH)
was created based on the simulator for integration of generation, migration, and accumulation of oil
and gas owned by the JOGMEC, and the case study was done for the Nankai Trough area (the47Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

two-dimensional profiles of the Tokai-oki and the Daini-Atsumi Knoll). According to the result of thesensitive analyses, it was realized again that the sea level changes in the past have made the methane
hydrate stability zone changed significantly, and that they strongly influence the distribution of
methane hydrate accumulations.

8.2 Physical Property Measurements of Methane hydrate-bearing layers (2. Modeling Section)
1)

Establishment of the Core Test Technology Basis at In-Situ Condition
The methane hydrate-bearing layers are contained in the pore spaces of sandy layers in alternating
beds of sand and mud below the seafloor in very deep waters, which is an environment in which
temperatures are approximately 10 degrees C and pressure is greater than 10MPa (refer to Figure 2-1).
The methane hydrate-bearing layers are overburdened from the sea surface to the formation, and thefluids in the pores are under the formation pressure close to the hydrostatic pressure from the sea
surface to their depth. The technology basis for the core tests at the in-situ conditions replicating theseenvironmental conditions was established. The high-pressure test apparatus of the core holder used foranalyzing and evaluating various basic physical properties, mechanical properties, dissociation
properties of core samples (cylindrical geological samples) is developed, and is available for the
installation of a thermometer and a pressure gauge etc. outside and inside of the samples depending on
the purposes of the tests. In addition, it is specified for explosion protections compliant with thehigh-pressure gas safety law. The evaluation tests on the core samples obtained from the METI/MITI
Exploratory Test Wells and the artificial methane hydrate sediment core were undertaken at the in-situ
conditions to the most extent. A part of these core test results are summarized in the section 5.1.

2)

Development of the Consolidation and Deformation Analysis Simulator of Methane hydrate-bearing
layers
While the methane hydrate is solid, it dissociates into methane gas and water. Therefore, an analytical
tool was developed for the consolidation and deformation behaviours of the methane hydrate-bearing
layers accompanied by methane hydrate exploitation. As the mechanical properties of the methane
hydrate-bearing layers have until now been unclarified, it has been difficult for the analyses by theexisting finite element method to predict the consolidations and deformations of the methane
hydrate-bearing layers to a sufficient level of accuracy.
As part of the development of the production simulator, the module for the consolidation behavior
evaluations was created, of which data were built into the production simulator, MH21-HYDRES. As
a self-sustained type of the module for the consolidation behavior evaluations, the “consolidation anddeformation analyses simulator for methane hydrate-bearing layers” COTHMA (Coupled
thermo-hydro-mechanical analysis with dissociation and formation of methane hydrate in deformation48

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Resultsof multiphase porous media) was developed.
By utilizing COTHMA, the time-dependent changes for the formation consolidations and stress states
associated with the production in the surrounding areas around the well were investigated based on
the representative geologic sections, stratigraphies, formation thicknesses and dips etc. These results
provide the necessary information for drilling and completing the wells.

3)

Establishment of the Imaging Analysis Technology of Physical Property and Dissociation
Characteristics
In order to determine the porosities and methane hydrate saturations of core samples, the method
determining these physical properties by the image analyses was developed using the micro focus
X-ray CT instrument with a high special resolution (finer than 10μm). With combining the coolingmethod to blow the gas gasified from liquid nitrogen, the method identifying the sand grains
composing the sandy sedimentary formations and analyzing the porosities in a high accuracy at theatmospheric pressure and lower than -100 degree C was developed. The brightness value distributionsof the CT images was decomposed into four components such as “sand grain,” “methane hydrate,”“water,” and “free gas,” and the saturation of methane hydrate was calculated from the area ratio of
methane hydrate to pore space (Figure 8-1). Those methane hydrate saturations estimated from thisCT image are highly consistent with the direct values obtained from the dissociation experiments.

Figure 8-1 Four-component discrete image of the sandy coreobtained from the METI Exploratory Test Wells “Tokai-oki to
Kumano-nada,” sand, methane hydrate, water, and methane gas
To clarify the occurrence of methane hydrate contained in the pores, the direct observation method
using an electron microscope was developed. By taking into account the character of methane hydratethat is difficult to observe in high vacuum conditions due to its high saturated vapor pressure, thismethod uses the field emission scanning electron microscope combined with the differential pumping

49Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

equipment-attached low-vacuum specimen room and the low-temperature stage, and subsequently,
steady observations are expected. By using the Energy Dispersive X-ray Spectrometer (EDS), themethane hydrate is discriminated from the frozen pore water. As a result of the analysis, it iselucidated that most of the methane hydrate particles come in contact with sand grains.
In order to construct the model clarifying the methane hydrate dissociation process in core samples bythermal stimulations or depressurizations, the method visually observing the expansion process of themethane hydrate dissociation area and the fluid flow process of gas and water derived from thedissociations at the in-situ conditions was developed. This is the core testing method using the X-ray
CT instrument characterized by high speed scanning and imaging system using the cone-beam methodwith the rotatable X-ray source and flat panel detector around the tri-axial core holder, a maximum
tube voltage of 130kV, a maximum tube current of 20mA of the X-ray source, and a visualization
sectional area of 100x100mm. This is also available for the repeatable observations with a slice pitchof 0.25mm, a single scan time of 40 seconds, and two-minute intervals. By installing the heatexchange bath circulating hot brine in the fixed end plug of the core holder, the end face heating andthe hot water injection experiments are available with a good response of the core temperature.
Figure 8-2 shows the high-speed X-ray CT images indicating the dissociation processes of thedepressurization method, the wellbore thermal stimulation method, and the hot water injection methodfrom the left. The following is assumed: In the depressurization method, the undissociated area has acannonball shape that reveals that dissociation proceeds with a lowering of the specimen temperature
due to hydrate dissociation accompanied by the external heating. In the wellbore thermal stimulation
method, the dissociation front moves only in one direction with dissociation occurring from theheating end. In the hot water injection method, the gas pool occurs adjacent to the channel of hot
water, and the breakthrough of the injection water makes the gas production speed accelerate.
Depending on the dissociation conditions, it is necessary to increase the injection pressure more as aresult of the lowering the permeability due to the regeneration of methane hydrates.

Figure 8-2 High speed X-ray CT visualized images indicating the dissociation processes ofvarious decomposition methods

50Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results(the sample: artificial MH core, the depressurization method, the wellbore thermal stimulation
method, the hot water injection method from the left, 30-40 minutes after dissociation began,
the depressurizing face and the wellbore heating face are the upper end, the hot water
injected from the bottom, the outlets of production fluid are at the upper end)
8.3 Technology of Well Drilling and Completion (4. Development Section)
Most of the methane hydrate-bearing sediments exist at depths ranging from 200 to 500m with water
depths ranging from 800 to 2,000m in the eastern Nankai Trough area. While the water depths ofsome overseas fields targeted for conventional oil and natural gas exceed these water depths, suchshallower depths below the seafloor are rare. When the methane hydrate-bearing sediments aretargeted for development, it is necessary to assure sealing capacity to prevent gas and water fromflowing through the apertures between the casing and the formations in drilled and completed wells in
unconsolidated sediments from more recent geologic ages. There are some issues that differ fromthose related to the development of conventional oil and natural gas. In the METI Exploratory Test
Wells “Tokai-oki to Kumano-nada,” demonstration experiments were carried out focusing on thefollowing five points.


Drilling fluid technology (the fluid types and the borehole wall stability)

Cementing technologyTechnologies of formation pressure and formation fracture pressure measurements

Downhole measurement (measurements of borehole size, borehole pressure and boreholetemperature)Horizontal hole drilling technology

These demonstration experiments were conducted at a water depth of approximately 1,000m in theDaini-Atsumi Knoll area, and two wells were drilled (Figure 8-3). The experimental well 1 is avertical well that was drilled to a depth of 404m below the seafloor. The cementing technology andthe technologies of formation pressure and formation fracture pressure measurements were primarily
experimentally demonstrated in this well.

The experimental well 2 was demonstrated to drill ahorizontal section for a distance of 100m in the methane hydrate-bearing layers at a depth of 340m
below the seafloor. Moreover, the technologies of drilling fluid and wellbore monitoring wereexperimentally demonstrated in both wells.

51Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Pilot
well 1１
実験坑井

Pilot well ２2
実験坑井ScientificJOIDES
drill ship
JOIDES Resolution
科学調査船
Resolution

ライザーレス掘削
Riserless drilling

ライザーレス掘削
Riserlessdrilling

Cementingtechnology
セメンチング技術

水平坑井掘削技術
Fluid
types and the borehole well stability
泥水タイプと坑壁安定性
Horizontal hole
Wellboremonitoring
technology
Technologies
of formation pressure
地層圧・地層破壊圧計測技術
drilling technology
坑内モニタリング技術(measurementsof borehole size, borehole
and formation fracture pressurepressure and borehole temperature)measurements（坑径・坑内圧力・温度測定）
Water depth
991m
水深991m

水深1002m

13-3/8”Casing@1054mBSL

17-1/2”Hole@1055mBSL
BSR

17-1/2”Hole@1045mBSL
BSR

12-1/4”Hole@1406mBSL

9-5/8”Casing@1166mBSL
12-1/4”Hole@1173mBSL
8-1/2”
水平掘削区間8-1/2”
Horizontal
section= 1463m ~ 1563mBSL (100m)=1463m～1563mBSL(100m)

9-5/8”Casing@1403mBSL

Figure 8-3 Schematic diagrams of the experimental well 1 and 2(BSL=below sea level)
From these demonstration experiments, the applicability of well drilling and completion technologies
for offshore methane hydrate production was confirmed.
Regarding the drilling fluid, borehole wall stability has been maintained by using the two types of the
KCl-polymer mud and the sepiolite drilling mud of which there are no significant differences, but theborehole enlargements were recognized in the layers other than the methane hydrate-bearing zone.
Regarding downhole measurement technologies, borehole sizes, borehole pressures and temperatures
were rmonitored during the drillings, and the results were effectively for the used operations.
Furthermore, the drilling of horizontal wells, even in shallow unconsolidated sediment wasdemonstrated to be viable. Although formation pressures and formation fracture pressures were
measured, attention was required to be paid to interpreting the data due to the possible effects ofmethane hydrate dissociation. Remaining future issues involved cementing technology, and it waslearned that it will be necessary to develop technologies both in the cement materials and cementing
operations.

8.4 Development of Technologies to Monitor Seafloor Environment and The HSE Inquiry (5.
Environment Section)
1)

Development of Technologies to Monitor Seafloor Environment
In order to evaluate seafloor environmental impacts associated with the exploitation of methane
hydrate, it is necessary to monitor the environmental impacts of the gas leakages and the sediment
deformations, etc. broadly over the long term. In Phase 1, the development of elemental technologiesof the measurements such as the technique for detecting the ground displacement and the technique52

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Resultsfor detecting the gas leakage, etc., the development of the monitoring network construction
technology to integrate them, and the development of the environmental index mapping technique by
the deep-towing sensors and the ROV will be carried out.
In order to monitor environmental impacts during the offshore production test, the basic design ofthe integrated monitoring system with various sensors (the prototype system) was completed.

The existing dissolved methane sensor (the METS sensor) was improved by reducing the responsetime by more than 50%, and stability was improved. We have developed the prototype sensor, andthen, confirmed by laboratory experiments that the sensor can be used under hydrostatic pressure
equivalent to the pressure at the water depth of 2,000m, that the lower measurement limit ofconcentration is similar compared to that of the conventional METS sensor, and that response andthe stability are improved. Based on these data, we clarified its performance and specifications.



As for developing the new dissolved methane sensor (the IR Absorption based Dissolved Methane
Sensor (IRAMES)), we have developed basic technology capable of detecting the trace-dissolved
methane that cannot be detected by the conventional METS sensor. The basic system (theexperimental system) was composed of the separation membrane and the infrared absorption
technology and so on. We had designed and manufactured the experimental system, and verified
its performance. As a result, the lower measurement limit of concentration became 3.4nmol/L (at4˚C) and less and this value was a half of the conventional METS sensor.

In order to detect the methane leakages on the seafloor early, an experimental system for the
totally integrated and automated system for in-situ gene analysis of microbes (IISA-gene system)
utilizing the biomarkers was developed. Regarding the biomarkers, genes that characteristicallyexist in methane oxidizing bacteria and that occur in abundance in the methane seep area wereselected, and an adequate detection method utilizing the experimental system was established.

In order to detect methane bubbles in seawater, we inquired regarding the specifications and pastrecords of performances of existing sensors that utilize ultrasonic waves. The method of thewide-area monitoring system using ultrasonic wave and the utilizing sensor were decided, and thebasic design of the verification system was created.

In order to detect the methane gas in an atmosphere, the basic design of the monitoring systemusing light absorption characteristics of methane gas was created.

In order to detect the ground deformation of the seafloor, the sediment deformation monitoring
system using an accelerometer was developed, and experimental demonstration tests were carriedout in the laboratory and the terrestrial landslide areas. Prototype system that reflected theobtained results was created. Methods to supply power and transfer data in order to build onto theintegrated monitoring system were investigated, and power supply and data transfer across thepressure vessel were confirmed to be practicable.

53

Research Consortium on Developing Methane Hydrate Resources

2)

Phase 1 Comprehensive Report of Research Results

HSE Inquiry
The HSE management system is an administration system aimed at health, safety and environmental
conservation. Considering the fact that the commercial production of methane hydrate is producing
hydrocarbons in waters over 1,000m deep, this will be an unprecedented project. Knowledge about
ensuring safety is insufficient both in relevant and supervisory organizations and it should benecessary for it to be compensated for as far as is possible.
Regarding the investigation of safety aspects, articles about safety management issues inpublications and from interviews based on experiences in developing deep water oil in the Gulf of
Mexico and in drilling the METI/MITI Exploratory Test Wells targeting methane hydrates in thesurrounding ocean areas of Japan were summarized.



Requirements for safety management issues adopted in various countries that have many cases
conformable to the methane hydrate exploitation were inquired about and summarized.



The various theories concerning environmental impacts caused by methane hydrates were boxed
up, and these results were stored in the database (HYDREAMS) for public use in order to respondto inquiries from individuals and organizations.

Management methods for environmental impacts chiefly from environmental impact assessment
systems in Norway, U.K., Australia and Canada were inquired about through publications andinterviews. Based on these results, environmental impact assessments envisaged in offshore
production tests were speculated from the viewpoint of global trends.



Case examples of environmental impact assessments in similar operations such as those related tothe exploitation of oil and natural gas at home and abroad, methane hydrate exploitation of the US
Department of Energy, risk assessments involved in large-scale developments, and the methane
hydrate-related publications were inquired about for the purpose of learning about global
environmental risk assessment methods. The selection of risks that should be evaluated in thedevelopment of methane hydrates and risk assessment methods were arranged, the achievementsof which are reflected in article 5.4 3).

54

Research Consortium on Developing Methane Hydrate Resources

9.

Phase 1 Comprehensive Report of Research Results

Perspective for the Future from Phase 1 Achievements
The following items are proposed as the goals of Phase 1 to achieve in the section of the R&D
program “IV Program Schedule for the Goals Achievement.”

Implementations of basic research (exploration techniques, basic physical properties,
dissociation and formation techniques, and so on)Achievements of the optimization of the methane hydrate exploration technology

Understandings of the resource-bearing offshore areas and volume of resources

Selections of the methane hydrate resource fields that can become targets of the offshore
production test in Phase 2Investigations into gas recovery techniques for methane that rises to the surface continuously
from the dissociation of methane hydrates, based on experiences from onshore production tests

The achievement statuses of these research issues have already been briefly described in each section
above, all of which have been accomplished except for the production period finishing in 6 days in theonshore production test. As described in section 6, the second winter test of the Second Onshore Gas
Hydrate Production Test in March 2008 was continued to the originally planned time limit that was set
up by taking the inherent constraints of the operation period in the Arctic region without any budgets
or infrastructure into account, and was finished. Inasmuch as this situation, the goals of Phase 1 havealmost been achieved. It should be considered that the preparations for transition to Phase 2 are now
complete.

9.1 The issues of Developing Technologies of Phase 2
The issues of developing technologies in Phase 2 derived from the evaluations of the results in Phase
1 are summarized in Table 9-1.

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Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 9-1 Issues of developing technologies of the Phase 2
1.

Enlargement of
Resource
Assessment
Targets

2.

Establishment of
the Base
Technology for
Methane Hydrate
Production

3.

Establishment of
the Environmental
Impact Assessment
Method

1.1 Enlargement of the targeted ocean areas(2D•3D seismic surveys, test wells, implementation of the seafloor survey)
1.2 Evaluation technology for the methane hydrate resource fields(sandy layers, non-sandy layers with pore filling methane hydrate)
1.3 Elucidation of the methane hydrate system(research for the accumulation mechanism of methane)
2.1 Long-term production test (onshore desired)
2.2 Offshore production test (refer to the article of 9.2)
2.3 Reservoir evaluation technology(detail geological model, reservoir characterization, monitoring of physical property etc.)
2.4 Development of the offshore production technology(subsea and downhole equipments, well completion technology etc.)
2.5 Optimization technology of the production plan
(improvement of simulator in a higher accuracy, technique of the economic potential
evaluations etc.)
2.6 Improvement of the economic potentials(optimazation of the production system, method of the productivity enhancements etc.)
2.7 Comprehensive evaluation accompanied with the long-term production(change in the methane hydrate-bearing layers, environmental impacts etc.)
3.1 Implementation of the environmental impact assessment for the Offshore Production Test
3.2 Upgrading of the environmental impact prediction model(biological influence, sediment deformation)
3.3 Development of the monitoring technology(sensor, integrated monitoring system)
3.4 Investigation of applicability of the safety management and environment administration
system corresponding to the Offshore Production Test
3.5 Evaluation and investigation of the global environmental risk assessment

The long-term production test will be conducted on land, and it is desired that any issues should be
solved in order to ensure successful implementation of the offshore production test, and that testing
technologies can be improved. It is envisaged that this onshore production test will be carried out aspart of international collaborative research similar to that utilized in previous production tests. Either
on land or offshore, please note the following items that are to be taken into consideration whenplanning the long-term production test:(1)

The period appropriate to the characteristics of the targeted methane hydrate-bearing layers
should be selected. In the depressurization method, the gas production rate is predicted by the
production simulator to increase as time elapses. According to the observations of the
production test, it is necessary to enhance the precision of the simulator quantitatively bycomprehending characteristic production behaviors. Quantitative measuring of production
volumes of gas and water to a high degree of accuracy and the maintaining of bottom-holepressure at the planned value and so forth are important items that are to be investigated.

(2)

Checks to determine whether borehole maintainability is able to meet the requirements of thelong-term production tests should be investigated and designed. In the Onshore Gas Hydrate
Production Test in March 2008, the installation of a sand screen to prevent sand trouble that
affected methane hydrate-bearing layers in the previous year was confirmed to be effective.
Achievements leading up to the solution of unknown issues such as the deformations of the56Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

methane hydrate-bearing layers caused by long-term production, stress changes in thesurrounding formations around the well, changes in retention capability of seal capacities of thecement behind the casing, and so on, is anticipated.

9.2 Preparation for the Offshore Production Test
The achievements of Phase 1 positioned to prepare for the implementation of the offshore production
test that is the main task in Phase 2, and future issues to investigate in Phase 2 are summarized inTable 9-2.
The previous record of the production tests in the conventional oil and natural gas exploration in thesurrounding offshore areas around Japan is the test in the gas-bearing layer at the depth greater than
3,000m (below sea level) with the water depth of 857m carried out in the MITI Exploratory Test Well
“Sanriku-oki” in 1999. It is anticipated that production tests in methane hydrate-bearing layers are to
be undertaken under arduous conditions such as in water depths of approximately 1,000m andformation depths of approximately 1,200m (below sea level), which have never been carried out
before in or around Japan. The implementation of offshore production tests targeting the methane
hydrate-bearing layers has a presupposition that we should take full advantage of the conventional oil
and natural gas exploitation technologies in offshore environments. However, there is an aspect in the
production tests of the methane hydrate-bearing layers that differs from those of the conventional oil
and natural gas layers, and the appropriate design is ascertained to be necessary from past experiencesof onshore production tests. The offshore production tests in the methane hydrate-bearing layers
envisaged in Phase 2 is considered to be the first trial of its kind in the world. In addition to thetechnologies used in the conventional oil and natural gas layers, our unique technological issues thatare adequate to methane hydrate-bearing layers should be steadily solved, and approximately 3 years
will be necessary for research and preparation in order to carry out the offshore production tests safely,
depending on the technical issues involved.
Regarding expedients to resolve various issues, the real equipment-size study matching the actual
field site will be necessary besides other kinds of laboratory research. The following facilities andopportunities are considered to become research settings.
(1) Real equipment-size tests in drilling the onshore METI Exploratory Test Wells, etc.
(2) Real equipment-size tests as the demonstration experiment tests in the METI Exploratory Test
Wells(3) Field tests in the onshore production tests
The achievements in Phase 1 and the technical issues in Phase 2 regarding the unique technologicalissues of the offshore production tests in the methane hydrate-bearing layers are summarized in Table
9-2.

57

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 9-2 Current situation and issues related to preparation for the offshore production test
1

Approach to the results of Onshore
Production Tests
1.1 Provision of sand troubles
1.2

Monitoring system in wellbore

1.3
1.4

Provision for prevention of hydrate
formation in borehole andproduction riser
Method of kill well

1.5

Method of well abandonment

2

Prediction of bottom-hole pressure,water and gas production volume, andproduction behavior by simulation
3 Test evaluation of seal capacity
between well and borehole wall, andwell completion
3.1 Casing program
3.2

Cementing material and injection
technique3.3

Calculation of MH layer
consolidation accompanied withproduction
3.4 Calculation of relative displacement
between formation and boreholeaccompanied with production fromthe bottom of MH layer to theseafloor
4
Solution of issues related to adoptionof ESP dropping into the borehole
4.1
4.2
4.3

Inquiry of adoption examples in the
production tests in the offshore
wells
Issues when used in the production
tests in the offshore wells
Provisions at the time of an
emergency in the production tests

Results in Phase 1

Issues in Phase 2

Effective in the Second Onshore Gas
Hydrate Production Test
Effective in the Second Onshore Gas
Hydrate Production Test
Borehole provision confirmed in theSecond Onshore Gas Hydrate
Production Test
Implemented in the Second Onshore
Gas Hydrate Production Test
Implemented in the Second Onshore
Gas Hydrate Production Test
Succeeded in 6-day simulation
prediction in the Second Onshore Gas
Hydrate Production Test

Applicability to the offshore MH
layersApplicability to the offshore MH
wells
Applicability to the offshore MH
wells

Analysis of the demonstration
experiment results in the METI/MITI
Exploratory Test Wells
Analysis of the demonstration
experiment results in the METI/MITI
Exploratory Test Wells
Investigating by the laboratory coreexperiments and simulations

Investigation of the offshore MH
layers characteristic program

Investigating the deformations fromthe upper MH layer to the seafloor bycores retrieved from the METI/MITI
Exploratory Test Wells
ESP applicability confirmed in theSecond Onshore Gas Hydrate
Production Test
Under investigation
Under investigation of problems of
ESP use from floater
Investigating the results of theSecond Onshore Gas Hydrate
Production Test

4.4

Issues at the time of a
Investigating the results of therecommencement of the production
Second Onshore Gas Hydrate
tests
Production Test
4.5 Issues of the deep water production
Under investigation
tests targeting the conventional oil
and gas reservoirs
5 Relevance environment on theseafloor
5.1 Surveillance systems of gas leakage Partly implemented in thearound subsea wellhead in the
METI/MITI Exploratory Test Wells
production test
5.2 Broader area inquiry systems ofUnder researchingenvironment
Remarks MH: methane hydrate, ESP: electrical submersible pump

58

Investigation of the specificprocedures in offshore wells
Investigation of the specificprocedures in offshore wells
Long-term simulation,
Application to the multiple
alternating beds of sand and mud

Investigation of the offshore MH
layers characteristic issues
Investigation by experiments andsimulations for the offshore MH
layersComprehensive investigation
combining to cementing

Investigation of specific ESP in
offshore wells
Investigation and provision of
specific issues in offshore wells
Investigation of specificprovisions in offshore wells,
investigation and provision of theequipments
Investigation of specific issues inoffshore wells
Investigation and provision of
specific issues in offshore wells

Investigation of the specificequipments and implementation
structure in offshore wells
Investigation of the specificimplementation structure

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

10. Predominant Research and Test Facilities
10.1 Improved PTCS
The PTCS (pressure temperature core sampler) utilized in retrieving the core samples is the sampling
device developed in the special research “Methane Hydrate Development Technology” (FY 1995 2000), which is technology unique to our country and that enables core recovery while maintaining
formation pressures and temperatures. The MITI Exploratory Test Wells “Nankai Trough” contributed
to the discovery of pore-filling methane hydrate-bearing layers. After some improvements were made,it realized a core recovery factor of 80% and a success rate of pressure retention of 90% in the METI
Exploratory Test Wells “Tokai-oki to Kumano-nada.”

Table 10-1 Recovery factors of the PTCS
Number ofCorings

Core Recovery

Pressure-holded

Temperature-holded

METI Exploratory Test
Wells “Tokai-oki to
Kumano-nada”

82 (6 wells)

79% (161.3m/203.5m)

90%

93%

MITI Exploratory Test Wells“Nankai Trough”

12

47% (16.9m/36.0m)

50%

92%

インナーバレル
Changeof the
スイベルの変更
inner-barrel
swivelAdditionof the temperature
温度圧力レコーダーを追加
andpressure recorder

Improvement of the
フィックスドピン・ボー
Removal of the TEC
fixed pin ball valve
ルバルブの改良
cooling equipment,
Change of the pressureTEC冷却装置
圧力補間システム
adoption only of the Creation of theの変更
interpolation system の取り外し、二センタービットアッセンブリ
double tube
重管のみ採用の開発 center bit assembly

Improvedversion
改良型

Figure 10-1 Improved version of PTCS
10.2 Laboratory Facilities of Core Testing
The predominant testing equipment created for various core tests in the Research Group for
Production Method and Modeling are listed in Table 10-2.

59Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 10-2 List of laboratory facilities of core testing
FiscalYear

Facility Name

Intended Purposes and Characteristics of the Facility

Analyses of the Basic Physical Property of MH Sedimentary Layers
coresamplemimicking MH

Equipment of making the MH sediment samples of which pores are filledwith methane hydrate at aimed saturation by high-pressure methane
penetrating through the water content-controlled sand samples. The
sample size is larger than φ50/65mm x 150mm.

2002

Equipmentofpreparations for
sediments

2002

Equipment of decomposition heatand specific heat measurements for
MH cores

Equipment of specific heat and decomposition heat measurements underhigh pressure for methane hydrate-bearing sandy cores and muddy cores.

2004

Equipment of thermal conductivity
measurement for MH cores

Equipment of thermal conductivity measurements for mimic MH samples
and natural core samples

2002

Equipment of compressive strength
measurement for MH cores

Equipment of tri-axial compressive strength measurements for MH
sediments at the in-situ conditions

2002

Equipmentof
3-dimensional
analyses for framework structure of
MH sediments (Microfocus X-ray
CT instrument)

Equipment of 3-dimensionally identifying and visualizing pores, sands,
hydrates and waters in MH core samples, and analyzing theirdistributions. It is also used for nondestructive measurements of porosities
and saturations.

2003

Equipment of gas permeability andhydraulic conductivity measurements

Equipment of measuring permeabilities at the in-situ conditions, andanalyzing the influences of MH saturations etc.

2004

Equipmentofpermeability
measurements for muddy sediments

Equipment of water permeability measurements at the in-situ conditions
by the steady method for MH muddy sediments. It is also capable ofmeasurements of shrinkage changes to the head pressure for sediments.

2005

Equipment of capillary pressure
measurements for sediments

Loading equipment of re-enacting the in-situ stress of sediments.
Equipment of sediments transmembrane pressure measurements fitting up
the pressure cell etc. It is capable of gas seal capacity etc. evaluations of
sedimentary layers.

2005

Equipment of pore diameter/water
permeability measurements at thesame time for MH sediments

Equipment of analyzing the relations between pore diameter andpermeability of MH sandy sediments. It analyzes permeabilities bywater-saturated pore size distributions. It is also used for comparative
investigations to well log data.

Analyses of the production behaviors and the production properties

2002

Facility of explosion protected highpressure experiments

The laboratory for making the mimic MH sediments using high pressure
methane and the core decomposition experiments fitting up the enforced
ventilation and the air-conditioning equipment (5˚C -10˚C). Compliant to
the high pressure gas safety law.

2002

Equipment of dissociation behavior
analyses for MH cores

Experimental equipment of dissociation analyses for the depressurization
method, the borehole thermal stimulation method and the hot water
injection method at the in-situ conditions. Withstand pressure 25MPa,
sample size 50mm x 300mm.

2003

Equipment of dissociation behavior
observations for MH cores (highspeed X-ray CT)

Equipment of real-time visualizing and analyzing the growth and theshifting of the dissociation front at the in-situ conditions in MH sediments.
The shifting phenomena can be modeled by recording the 3-dimensional
CT images of sediments in high speed.

60Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

2003

Equipment of consolidation andpermeability measurements forcores from the METI/MITI
Exploratory Test Wells

Equipment of permeability change measurements due to consolidation at
the in-situ conditions.

2005

Experimental equipment of flushingand sanding phenomena evaluations

Equipment of experimentally observing sanding phenomena causing the
production damages at the in-situ conditions. It observes both of flushingand sanding in time sequence.

2006

Equipmentofanalyzingfine-grained
sand
flow
and
accumulation in pores

Equipment of experimentally analyzing the flow and accumulation
behaviors of silty sands accompanied with production under the in-situ
condition, and evaluating the production damages caused by skinformations.

2004

Test equipment of the hot water
injection method evaluation

Dissociation experimental equipment of evaluating the productivity of the
hot water injection method at the in-situ condition.

2004

Equipment of inhibitor injection anddissociation experiments

Dissociation experimental equipment of evaluating the productivity of theinhibitor injection method at the in-situ conditions.

2005

Equipment of steam injection anddissociation experiments

Dissociation experimental equipment of evaluating the productivity of thesteam injection method at the in-situ conditions.

2002

Equipment of fluid flow property
simulator

Basic equipment of water and gas permeability measurements undervarious flow conditions. Equipment of fluid flow observations fordeveloping the permeability property calculation module.

2002

Equipmentofconsolidation
property simulator tests

Equipment of analyzing the consolidation property of MH sandy sediments
and alternating beds of sand and mud. Equipment of mechanical tests forcreating the consolidation property calculation module.

Remarks) MH: methane hydrate

10.3 Research Facilities Related to the Offshore Environment Survey
The main facilities used in the research of the Research Group for Environment Impact are listed inTable 10-3.

Table 10-3 Primary facilities used in Research Group for Environment Impact researchFiscalYear

Facility Name

Intended Purposes and Characteristics of the Facility

2003

Database hardware (Web/Apl server/
GIS server/DB server/peripheraldevices/device installation)

The response system to the inquiries from the unspecified number ofindividuals and organizations with having stored the achievements of
the Research Group for Environment Impact.

2003

Acoustic Doppler velocimeter Current
Profiler

2003

Sediment trap

2003

Mooring system (releaser system
attached)

2006

Benthic chamber

Used in measurements of current direction and velocity in the marine
environmental surveillance.
Used in measurements of flux of sedimented particles in the marine
environmental surveillance.
Used in installation and recovery of the measurement devices suchas the current profiler, the sediment trap etc. in the marine
environmental surveillance.
Used in measurements of methane flux etc. in the marine
environmental surveillance.

2003

High pressure triaxial compression test
apparatus for low-temperature
condition

Soil test apparatus of taking in the seafloor ground physicalproperties.

61

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

11. Others
11.1 Cooperation and Collaborations with Foreign Countries
Relevant cooperation and collaborations with foreign countries are as follows.
(1)

The First Onshore Methane Hydrate Production Test (2002) The First Onshore Methane
Hydrate Production Test executed in the Mackenzie Delta, Canada in cooperation andcollaboration with Canada, USA, Germany and India.

(2)

The Second Onshore Methane Hydrate Production Test (2007 and 2008) The Second Onshore
Methane Hydrate Production Test was executed in the Mackenzie Delta, Canada in cooperationand collaboration with Canada.

(3)

Joint Industry Program “Characterizing Natural Gas Hydrates in the Deep Water Gulf of
Mexico: Application for Safe Exploration and Production Activity” (2001 - )The purpose of this program is to characterize the natural gas hydrate-bearing sediments indeep water areas off the Gulf of Mexico. In particular, the basic physical properties of methane
hydrate-bearing layers that will become necessary for the safe exploitation and operations inconventional oil and gas fields should be obtained, and furthermore, necessary studies forconstructing the reservoir model will be carried out. Participating organizations and industries
are listedin Table 11-1.

Table 11-1 Organizations and Industries participating in the Joint Industry Program
Japan Oil, Gas and Metals National Corporation
Schlumberger Technology Corporation
ConocoPhillips Inc.
Halliburton Company
Minerals Management Service (MMS)

Reliance Industries Limited, Oil and Gas Division(private company in India)
Korean National Oil Company (KNOC)(participated from October in 2007)
STATOILHYDRO(participated from March in 2008)

TOTAL E&P USA, INC(4)

Chevron Energy Technology Company

International project on the comparison of production simulators
This international project was sponsored by the research institute of the US Department ofEnergy and the US Geological Survey of the Department of the Interior, where Japan, Canada
and the US have participated. At present, the simulator in Japan has prerogatives to the othersimulators (refer to the section 7. The Production Simulator).

(5)

Collaboration between Japan and India
The JOGMEC contracted the MOU with the Indian Ministry of Petroleum and Natural Gas-

62

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Directorate General of Hydrocarbons (DGH) in February 2007. The exchange of informationon the researches of methane hydrate has been undertaken between both countries.
(6)

The collaborative researches between Japan and the US
The US Department of Energy and the METI agreed the collaborative researches in June 2008.
An onshore production test is planned in Alaska as a joint implementation.

11.2 Conference Presentations and Publications
Conference presentations and publications in Phase 1 are listed in Table 11-2.

Table 11-2 Conference presentations and publications in Phase 1(as at the end of July 2008)

Number of cases
160

150
140

143

130
127

120

122

110

120

100
99

90
80

83

70
60
50

48

40
30

31

20
10

20

33
22

8

15

14

FY2002

FY2003

FY2004

FY2005

FY2006

FY2007

FY2008Paperspublications

8

15

14

48

31

33

22

Conference
presentations

20

83

99

143

127

122

120

0

*Number as at the end of July in FY 2008

11.3 Patents
Table 11-3 is available only in Japanese.

63

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 11-3 フェーズ１の研究で取得した特許一覧
出願番号・公開番号

出願日・公開日

出願人

発明者

発明の名称

特許出願 2003-289857
特許公開 2005-60957<生産手法開発＞

2003 年 8 月 8 日
2005 年 3 月 10 日

秋田大学長 外１名

佐々木 久郎外３名

メタンハイドレート堆積層からの
主にメタンガスの生産方法、及び模擬ハイドレート堆積層モデ
ルを用いる主にメタンガスの生産特性を測定する方法

特許出願 2003-379600
特許公開 2005-139825<資源量評価＞

2003 年 11 月 10 日
2005 年 6 月 2 日

鹿島建設株式会社

三浦 悟
外４名

ガスハイドレートの生産方法及びシステム

特許出願 2004-20524
特許公開 2005-213824<生産手法開発＞

2004 年 1 月 28 日
2005 年 8 月 11 日

秋田大学長 外１名

佐々木 久郎外５名

メタンハイドレート堆積層からの天然ガス生産設備と発電設備を具備する統合設備

2004 年 6 月 23 日
2006 年 1 月 12 日

三菱重工業株式会
社

橋本 秀昭
外１名

加圧試験装置2004 年 7 月 27 日
2006 年 2 月 9 日

三菱重工業株式会
社

有川 究
外２名

ガスハイドレードの採集方法、ガスハイドレード採集システム

2004 年 8 月 5 日
2006 年 2 月 16 日

独立行政法人産業
技術総合研究所

羽田 博憲
外６名

メタンハイドレートの分解方法及び分解装置

2004 年 9 月 28 日
2006 年 4 月 13 日

独立行政法人産業
技術総合研究所

羽田 博憲
外６名

窒素によるメタンハイドレートの分解方法及び分解装置

2004 年 11 月 11 日
2006 年 6 月 1 日

三井造船株式会社

星島 一輝
外３名

ハイドレート層の層厚推定方法

2005 年 1 月 17 日
2006 年 7 月 27 日

応用地質株式会社

内山 成和
外２名

加速度センサを用いる地盤等の変位モニタリング方法

特願 2005-100353
特開 2006-284184＜環境影響評価＞2005 年 3 月 31 日
2006 年 10 月 19 日

石川島検査計測株
式会社
国立大学法人山口
大学

森田 幹
外３名

溶存可燃性ガス濃度の測定方
法及び装置

特許出願 2005-166253
特許公開 2006-336435<生産手法開発＞

2005 年 6 月 6 日
2006 年 12 月 14 日

独立行政法人産業
技術総合研究所

川村 太郎
外７名

温度勾配付加型コアホルダー
装置及びこれを用いた成分産
出挙動時間変化測定方法

特許出願 2005-317536
特許公開 2007-120257<生産手法開発＞

2005 年 10 月 31 日
2007 年 5 月 17 日

独立行政法人産業
技術総合研究所

坂本 靖英
外７名

熱水と窒素の同時圧入によるメ
タンハイドレート貯留層の浸透性改善および分解促進技術

2006 年 2 月 27 日
2006 年 10 月 5 日

シュルンベルジュ ホ－ルディン グス リミ
テッド

福原 政文
外２名

ダウンホール内の熱特性を測定するシステム及び方法

2006 年 5 月 16 日
2007 年 11 月 29 日

独立行政法人産業
技術総合研究所

皆川 秀紀
外４名

メタン採取方法2007 年 7 月 27 日
（出願中・未公開）

日本海洋掘削株式
会社

中村 雅洋
外3名

メタンハイドレートの分解促進およびメタンガス採取システム

特許出願 2004-185103
特許公開 2006-10400<生産手法開発＞
特許出願 2004-219219
特許公開 2006-37518<生産手法開発＞
特許出願 2004-229000
特許公開 2006-45128<生産手法開発＞
特許出願 2004-280861
特許公開 2006-96779<生産手法開発＞
特許出願 2004-327728
特許公開 2006-138706＜資源量評価＞
特願 2005-8938
特開 2006-194822＜環境影響評価＞

特許出願 2006-51099
特許公開 2006-267096＜資源量評価＞
特許出願 2006-136601
特許公開 2007-308891<生産手法開発＞
特許出願 2007-196650
特許公開--＜資源量評価＞

64Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

11.4 Public Offering Research Proposals
Business projects from the public offering research proposals were carried out from FY 2002 to 2005
for the purpose of applying these achievements to present research by broadly soliciting and realizing
the proposals of the inventive and innovative technical issues regarding the technical issues related toeach research field of the Resources Assessment, the Production Method and Modeling, and theEnvironment Impact in the Research Consortium for Methane Hydrate Resources in Japan fromapplicants other than the Research Consortium for Methane Hydrate Resources. The numbers ofapplications was 6 in 2002, 5 in 2003, 4 in 2004, and 4 in 2005.

11.5 Reinforcement of Internal Cooperation, Dissemination of Research Results, and Publicity
1)

Reinforcement of Internal Cooperation(a)

The Steering Committee Meeting
The project leader, group and subgroup leaders of the Research Group for Resources Assessment, theResearch Group for Production Method and Modeling, and the Research Group for Environment
Impact, and the group leader of the Secretariat for Research Consortium for Methane Hydrate
Resources in Japan convene the steering committee meeting, which has confirmed the current
research status of the Research Consortium for Methane Hydrate Resources in Japan and investigatedthe direction it should take. Steering committee meetings have been held a total of 46 times (as at theend of July 2008).

(b)

Workshops
During the initial phase of the Research Consortium for Methane Hydrate Resources in Japan in
2002-2004, cross-sectional workshops have been held 8 times inside the Research Consortium for
Methane Hydrate Resources in Japan in order to deepen exchanges and share fundamental knowledge.

(c)Working groups and the task force
12 workings (WG) and one task force (TF) were founded (Table 11-4), and cross-sectional research
themes have been scrutinized beyond the groups.

65

Research Consortium on Developing Methane Hydrate Resources

Table 11-4

Phase 1 Comprehensive Report of Research Results

Already launched working groups (WG) and task forces (TF)
WG Name(d)Installation Period

The Marine Survey WG

June 2002 - May 2007

The Core Test Investigation WG

April 2004 - May 2007

The Second Onshore Methane Hydrate Production Test WG

October 2003 - May 2004

The Production Test Analysis WG

June 2002 - September 2003

The Offshore Production Test Preparation WG (First)

September 2003 - May 2004

The Artificial Methane Hydrate Sediment Core WG

March 2003 - May 2007

The MH Resource Field Selection WG

May 2007 -The Economic Potential Deliberation WG

May 2007 -The Phase 2 Plan Preparation WG

May 2007 -The Offshore Production Test Preparation WG (Second)

May 2007 -The Environmental Impact Macro Risk Evaluation WG

May 2007 -The Onshore Production Test Analysis WG

May 2008 - March 2009 (plan)

The TF of Production Test Planning

May 2004 -Interim meeting of accomplishment reporting
In order to share the achievements derived from each research group among the members of the
Research Consortium for Methane Hydrate Resources in Japan, interim meetings to reportaccomplishments of the previous fiscal year have been held 7 times from FY 2002 to FY 2008.

(e)

Information sharing
The group wares and mail lists were created for the exclusive use of members of the ResearchConsortium for Methane Hydrate Resources in Japan, and they shared information inside the
Research Consortium for Methane Hydrate Resources in Japan.

2)

Dissemination of Research Results and Publicity(a)

The data and samples provided to the mass media and education-related organizations
Data and samples such as photos, figures and so on have been provided in 252 cases to the mass
media and education-related organizations (as at the end of July in FY 2008).

66

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 11-5 Data and samples provided to the mass media andeducation-related organizations
Fiscal Year

Mass Media

Education-Related

Others*Total

FY 2002

10

3

9

22

FY 2003

18

7

13

38

FY 2004

16

10

13

39

FY 2005

9

1

17

27

FY 2006

20

6

25

51

FY 2007

10

10

28

48

FY 2008 (as of end of July)

16

4

7

27

Total

99

41

112

252

*Remarks)

Data and samples provided to home pages of companies and organizations,company newsletters, and advertisements(b)Public meeting to report accomplishments
In order to open the achievements of the Research Consortium for Methane Hydrate Resources inJapan to the public, public meetings reporting the accomplishments of the previous fiscal year havebeen held 7 times from FY 2002 to FY 2008.

(c)Creation of a brochure of the Research Consortium for Methane Hydrate Resources in Japan
A brochure concerning the Research Consortium for Methane Hydrate Resources in Japan was created
and distributed.

(d)Creations of the documentary films and the explanatory films
In addition, the following records and explanatory films were created and posted on the home page.
They were also delivered as DVD or in VHS format to education-related institutes.
Documentary: “Mallik 2002 Gas Hydrate Research Well Program” (Japanese and English)

Explanatory film: “Methane Hydrate, Growing Prospective Resources for the Next Generation”

Explanatory film: “MH21, the Research Consortium for Methane Hydrate Resources in Japan”

Explanatory film: “MH21, the research achievements of Phase 1 (tentative)” (scheduled forcompletion in fall 2008)(e)Home pageAs part of the publicity for the Research Consortium for Methane Hydrate Resources in Japan, a home
page titled, “The Research Consortium for Methane Hydrate Resources in Japan” was created(Japanese and English) and opened to the public in January 2003. A total of 466,063 hits have beenrecorded since January 2003 (as at the end of July 2008). In addition, an “Inquiry Corner” was built
into the home page, which by the end of July FY2008, had responded to 205 inquiries.

67

Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

Table 11-6 Year-on-year numbers of accesses and inquiries to the MH21 home page
(Number of accesses to HP)(Number of inquiries)

120,000

60

110,063

52

94,767100,000
80,00060,00020,00025
30Number ofaccesses to HP
Number ofinquiries

38

71,72940,00050

75,131

68,68940

4442,129

30
20

24

19

3,555

10
0

FY2002

FY2003

FY2004

FY2005

FY2006

FY2007

FY20083,555

71,72968,689110,063

75,131

94,76742,129

3

52

25

24

38

44

19

*Number as at the end of July in FY 2008

http://www.mh21japan.gr.jp/

Figure 11-1 Home page of the Research Consortium for Methane Hydrate Resources
in Japan

68Research Consortium on Developing Methane Hydrate Resources

Phase 1 Comprehensive Report of Research Results

12. English Abbreviations Cited


JOGMEC: Japan Oil, Gas and Metals National Corporation ⇒ (独)石油天然ガス・金属鉱物資源機構

AIST: National Institute of Advanced Industrial Science and Technology ⇒ (独)産業技術総合研究所



ENAA: Engineering Advancement Association of Japan ⇒ (財)エンジニアリング振興協会



BSR: Bottom Simulating Reflector ⇒ 海底擬似反射面



LWD: Logging While Drilling ⇒ 掘削同時検層SMI: Sulfate Methane Interface ⇒ 硫酸塩-メタン境界

IRR: Internal Rate of Return ⇒ 内部利益率

SPAR ⇒ 浮遊式生産システムのひとつ



NPV: Net Present Value ⇒ 正味現在価値CDOG: Comprehensive Deepwater Oil and Gas Blowout Model

GSC: Geological Survey of Canada ⇒ カナダ地質調査所

MDT: Modular Formation Dynamics Tester ⇒ Schlumberger社登録商標



NRCan: Natural Resources Canada ⇒ カナダ天然資源省

DTS: Distributed Temperature Sensor



NETL: National Energy Technology Laboratory ⇒ 米国エネルギー省研究機関

USGS: United States Geological Survey ⇒ 米国内務省地質調査所

TOC: Total Organic Carbon ⇒ 全有機炭素量



COTHMA: Coupled thermo-hydro-mechanical analysis with dissociation and formation of
methane hydrate in deformation of multiphase porous media ⇒ メタンハイドレート層圧密・変形解析シミュレータ



EDS: Energy Dispersive X-ray Spectrometer ⇒ エネルギー分散型X線分析装置



ROV: Remotely Operated Vehicle ⇒ 有索無人潜水機



METSセンサー: 溶存メタンセンサー（Franatech社登録商標）

HSE: Health, Safety & Environment ⇒ 労働安全衛生及び環境PTCS: Pressure Temperature Core Sampler ⇒ 圧力・温度保持コアサンプラー



DGH: Directorate General of Hydrocarbons ⇒ インド石油天然ガス省石油ガス総局

MOU: Memorandum of Understanding ⇒ 研究交流の覚書

69