The Wasabizawa - Akinomiya Geothermal Field:
Reservoir Characterization, Sustainable
Development Plan, Monitoring andStakeholder Engagement

Shigetaka Nakanishi*Electric Power Development Co. Ltd. (J-Power),
Tokyo, Japan[*)Ex-President of Yuzawa Geothermal Power Corporation (YGP),
Yuzawa City, Akita Prefecture, Japan]
JOGMEC-GNS Science Workshop, Rotorua
November 20, 20171

Outline

1. The Wasabizawa - Akinomiya Geothermal System
2. Numerical Reservoir Simulation
3. Monitoring (Hot spring etc.)
4. Stakeholder Engagement (Local community, Hot spring owners)2

Background of the Wasabizawa Geothermal Projectl NEDO supported geothermal development
promotion surveys for the Wasabizawa
area and the Akinomiya area in 1993-1997
and 1998-2002, respectively.
l After the NEDO’s survey, these areas weretransferred to J-Power and MMC(Mitsubishi Material Co.).
l We started exploration cooperatively since2008. Two exploratory wells were drilled.
GW-1:1998m / GW-2:1488m
l Hot spring monitoring program initiated in2009 before the exploratory wells spud in.
l A numerical reservoir simulation study wasperformed.
l Yuzawa Geothermal Power Corporation(YGP) was established in 2010 by J-Power,
MMC and MGC (Mitsubishi Gas andChemical Co.)l Environmental Impact Assessment wasperformed in 2011 - 2014.

>> This project progressed toconstruction phase in 2015.

Yuzawa city
Akita prefecture

Wasabizawa

Uenotai GPSAkinomiya

Onikobe GPSOsaki City
Miyagai prefecture
Wasabizawa
Akinomiya
05310kmExploratory Well Location Map4

Temperature Profile of Wells
Temperature (℃)
050100150200

250

300

1000
800
600
400
GW-2
N9-AY-3

Elevation (mASL)

200

N8-WZ-9N7-WZ-7

0-200

N6-WZ-3
N7-WZ-8GW-1-400-600-800-1000-1200

5Feed Zone Elevation vs Reservoir Pressure
Wells around the Wasabizawa
Akinomiya Spa

Wells around the Akinomiya
Reservoir

Wells around the Akinomiya
Hot spring aquifer

800600Elevation (mASL)

400

Akin om iya Spa

Pressuredifference

Different
reservoir

2000-200-400

The pressure gradientcorresponds to saturated waterof 262 degree C.

AY-5-600
0.00899MPa/m-800

0.00765MPa/m-1000
YO-8-1200
0.0

5.0

10.0

Reservoir pressure (MPaG)

15.06

Inferred temperature distribution at -500 m ASL

7Conceptual Model (SW-NE cross section)
Kawarage Fumarole Area
(Volcanic gas & Acidic
Cl-SO4 type hot spring)

Akinomiya HotSpring Area
(NaCl type)

Doroyu Hot Sp.
Area(Acidic SO4 typehot spring)

Basement rock8

Outline

1. The Wasabizawa - Akinomiya Geothermal System
2. Numerical Reservoir Simulation
3. Monitoring (Hot spring etc.)
4. Stakeholder Engagement (Local community, Hot spring owners)

9

Location of the computational grid•••In x-direction (8.0 km): 24 blocks
In y-direction (7.0 km): 22 blocks
In z-direction(z ≥ –2.5 km RSL): ≤ 23 blockl Total grid blocks：(24×22×23 =) 12,144
n Case 86:
l “void” grid blocks(above surface):2,946
l Active grid blocks:
9,198
10

Computational grid viewed in x-z plane at j =12

For Case 86, the total number of “void” grid blocks was 2,946,
leaving 9,198 blocks that were actually involved in the simulation.

Yellow: drilling data availability••

This means that only the uppermost 36% of the computational grid volume
has been adequately explored by drilling.
The deepest 45% of the grid volume has never been reached at all.

11

Rock Properties (1)•Rock properties other than permeability (grain density, porosity, heat
capacity and thermal conductivity) were fixed in the simulation
calculation, and based on measured data for each rock type.

•The spatial distributions of absolute permeability were treated as
unconstrained parameters in the modeling study, and were varied
freely from case to case to try to improve the quality of the datamatch.

12

Rock Properties (2) - Fractured Reservoir Formulation•Available data from drilling in the field clearly
indicates that, where formations are permeable,
the permeability arises from the presence of
fractures that penetrate the otherwise
impermeable country rock and provide discrete
conduits for fluid flow.

•

Representative “conductive MINC” assemblyused to represent non-equilibrium heat transfer
between impermeable country rock matrix andpermeable fracture zone for all computational
grid blocks.

•Matrix region (yellow) subdivided into 31
concentric spherical “shells”, each of equalvolume, and with zero porosity and zero
permeability. Fracture zone (red) represented
by single permeable outer shell with 50%
porosity. Volume fraction of “fracture zone”
varies between 4% and 28% of the volume ofthe entire spherical assembly (depending on
the overall porosity of the rock formation).

•

Diameter of spherical assembly (50 meters) isthe “average fracture separation” (λ).

13Calculated heat content changes in computational volume
over 200,000-year history

Change in total thermal energy(× 1018 joules)

Time derivative of upper curve
(MW)

14

Comparison between measured and computed pressure

Comparison between measured feedpoint
pressure (yellow) and computed naturalstate pressure at feedpoint locations (blue)

15

Comparison of measured temperatures with computed results (1)Comparison of stabilized downhole temperatures measured in well AY-3, AY-4
and AY-7 (yellow) with computed natural-state temperatures along well path (red)16Comparison of measured temperatures with computed results (2)Comparison of stabilized downhole temperatures measured in well WZ-7, WZ-9
and KN-2 (yellow) with computed natural-state temperatures along well path(red)17Pressure Interference Calculation••

Although the relatively coarse spatial discretization (minimum block size is 0.3km × 0.3 km × 0.1 km) may not be ideal for simulating the field pressureinterference experiments, the model was employed in several pressureinterference tests calculations to confirm the model responses to the actual
long term flow tests.
Pressure interference data at well AY-2 (Left) and AY-8 (Right) due to
production of well AY-3 and injection to wells AY-1 & 6. Black: measured
pressure. Red: calculated pressure.
AY- 2

9.50

AY- 8
AY-8 production:20t/h

AY-8 injection

7.70

Pressure (MPa)AY-3 production:160t/h

AY-3 shut inAY-6 injection:10 -18t/h
AY-1 injection:80t/h

9.40

7.60
T-501 shut in & open

9.30
Apr.01

Jun.01

Aug.01

Date

Oct.017.50
Dec.01 Oct.06

Oct.21

Nov.05

Nov.20

Date18Base case geometry for future forecast calculation

19

Study on generation capacity and plant design concepts
Ø Base Case: 30MWe Single-flash plant, flash-tank, wet cooling towerØ Single-flash plant design variants. (pressurized injection, hybrid coolingetc.)
Ø Plant capacity: 22.5 MWe, 30 MWe (base case), 35 MWe and 45MWe
22.5MW
Two-phase binarySingle-flash plant•30MW•

Double flush plant

35MW45MW••••Ø Finally planed: 42 MW double-flash plant

20

Drilling requirements to maintainsteam supply for plants

No. of make-up wells

2015105001020304050
Elapsed time after operation start (yr)Produced fluid enthalpy (kJ/kg)

Forecasts of production well drilling requirements, production welldischarge enthalpy histories and pressure changes
1350

Mass-averaged discharge enthalpy
from operating production wells

1300

1250

1200

01020304050
Elapsed time after operation start (yr)01020304050
Elapsed time after operation start (yr)Time-history of pressure at -1 km ASL
in hypothetical Wasabizawa monitor well.

Pressure (bar)140130120110
100021

Evolution of temperature distribution at -0.5 km ASL elevation
for the final double-flash 42 MWe case forecast•

It appears that cold reinjected water from the Akinomiya wellfield will not
influence the production enthalpies even after many years operation.

ü A numerical model has been constructed for the Wasabizawa-Akinomiya
geothermal field which is conservative in character and in good agreementwith available measurements from the field.
ü Calculation based upon the model indicate that the field can sustain morethan 42 MW of electrical output using a double-flash steam plant for morethan fifty years.

22Outline

1. The Wasabizawa - Akinomiya Geothermal System
2. Numerical Reservoir Simulation
3. Monitoring (Hot spring etc.)
4. Stakeholder Engagement (Local community, Hot spring owners)

23

Hot springs monitoringØ 13 hot springs and 1 water springü Objective: To confirm changes in discharge conditions (discharge rate,temperature etc.).
ü Monitoring program initiated in June 2009, and continued nowü 10 years background information will be available before commencement ofoperation of the plant.
ü We share the data with hot spring owners and local government; Yuzawa city.

GW-1 Drilling (2009)
Photos: from YGP

24

Outline

1. The Wasabizawa - Akinomiya Geothermal System
2. Numerical Reservoir Simulation
3. Monitoring (Hot spring etc.)
4. Stakeholder Engagement (Local community, Hot spring owners)

25

Stakeholder engagement
ü The Environment Impact Assessment report meeting to localcommunity.
ü Detailed and timely explanation to hot spring owners about
exploration results and the relationship between hot springs and thegeothermal reservoir to be exploited.
ü Report monitoring data to hot spring owner individually, and to local
government; Yuzawa city.
ü Local community meetings for each district. (Exploration results andnext year’s plan, P/S plan and construction schedule, etc. )ü Site visiting tours for local community.
These activities made possible to build trust in a relationshipwith local residents.
26

Local community meetings
Meeting to explain to local residents
about project progress and futureplanØ We started to hold such meetingssince exploration phase.
Ø The meetings were held timely andtwice a day (daytime and night) for
their convenience.

Photos: from YGP

27

Site visiting tour for local residents

YGP’s “Yuzawa Geothermal PowerStation” constructing site

Photos: from YGP

We expect that local people feel close
to the power station by such a tour.

28Local government’s support
ü The Yuzawa Japanese Geopark activity led by Yuzawa city involves“geothermal manifestations and geothermal energy utilization”, and it
makes more people familiar with “geothermal development”.
ü All-party parliamentary group to promote geothermal development wasestablished in the Yuzawa municipal council, and supported our project inthe back.
ü Yuzawa city set up an advisory panel of local community including hot sprig
owners to provide us an opportunity to keep a channel of communication open.

Yuzawa JapaneseGeopark
Geo-site; Dai-funtou:
Steam discharging
from fractured rock)[View from bridge]
Advisory panel of local community
Photo: from YGP

Yuzawa Japanese Geopark
Geo-site; Dai-funtou: Steam discharging
from fractured rock)
Photo: from Yuzawa Geopark web site29Concluding Remarks: What have we learned?
Ø Correct understanding of subsurface geothermal system (; correctcharacterization of reservoir) is required for both of sustainable
development and stakeholder engagement.
Ø Extensive and continuous stakeholder engagement is required forbuilding trust in a relationship with local community, and for successful
implementation of project.
Ø Monitoring is essential:
ü Continued hot spring monitoringü Various monitoring for reservoir performance are also planed in orderto observe changes in reservoir conditions:••••

Reservoir pressure monitoring at the observation wells.
Micro seismic monitoring
Surface micro-gravity monitoring
Geochemical monitoring of production fluid etc.

Ø Local government’s role is important in establishing a symbiotic
relationship between a developer and local residents including
hot spring owners.

30

YGP’s new “Wasabizawa Geothermal Power Station” (42MWe)(under construction)

Production test of
new well WB-1
(May 19, 2017)
Photos: from YGP

Production test of well WC-1
after workover(Oct. 24, 2017)31

Thank you for your kind attention!!

ü Commercial operation of the plant will begin in May 2019.

Photo: from YGP

Drilling of new well WC-2 and land preparation of the plant (May 19, 2017)32