山川地域における3次元弾性波探査実証試験
Demonstration Field Experiment of ThreeDimensional Seismic Survey in the Yamagawa
Geothermal Field
独立行政法人 石油天然ガス・金属鉱物資源機構
地熱部 地熱技術課 福田真人
株式会社 地球科学総合研究所 研究開発部
物性解析グループ長 青木直史
JOGMEC Masato Fukuda
JGI Inc., Naoshi Aoki

Geothermal Reservoirs Exploration Techniques
2013 FY – 2017 FY
High-Accuracy Geothermal Reservoir Imaging➢ 2013FYSurvey of Existing Conditions of Seismic method in Geothermal Exploration➢ 2014-15 FY Phase Ⅰ⇒ 3D seismic data acquisition in Kagoshima pref., South Western Japan.
➢ 2016-17 FY Phase Ⅱ⇒ Integrated analysis and interpretation with other geophysical survey data

Increasing Drilling Success Rate

Reduce Geological Risk

Getting a Greater Understanding of Geothermal Reservoir Structure2

Geothermal Reservoirs Exploration Techniques
Achievements in 2013FY・Literature Research・Hearing Investigation

・Reprocess of the seismic data

Current Challenges✓Optimizing a survey design✓Applying an appropriate staticcorrection✓Reinforcing a seismic
interpretation skill ofgeothermal explorationist✓Reducing a survey cost Clarification of current
challenges in applying seismic
method in geothermal
exploration.
 Confirmation of the efficacy ofcurrent seismic processing
techniques.
Acquired (1995)

Reprocessed (2013)

Seismic Sections from Ogiri geothermal field3

Geothermal Reservoirs Exploration Techniquesin 2014-15FY
Application and Verification by Field Experimentin Yamagawa Geothermal Field

Current Challenges✓Optimizing a survey design✓Applying an appropriate static correction✓Reinforcing a seismic interpretation skill of geothermal
explorationist✓Reducing a survey cost

Yamagawa

4Outline• Overview of the Experiment• Visualization of Geological Features in theYamagawa Geothermal Field• A Mismatch between Seismic and GravityInterpretations. Why?

5Overview of the Experiment

6

Demonstration Site: the Yamagawa Geothermal Field
Geothermal Plant
NameLocation
Permitted output
Operator
Start of operation
Type of plant

Location

Yamagawa Geothermal
Power Plant
Ibusuki, Kagoshima
25.96 MW(modified on 2014/12/29）
Kyushu Electric Power Co., Inc.
1995/ 3/ 1
Single Flash

Yamagawa
Okada et al., 2000

View of Geothermal plant, withTakeyama peak, a volcanic neck.

7

Geological Structure and Characteristics
Yamagawa geothermal field has the following characteristics (Okada et al.,2000):• Located in a depression, surrounded by normal faults.
• High reservoir temperature (>350℃).
• The main reservoir occurs in a fractured zone developed around a daciteintrusion.
• High permeability zones associated with fault zones.
Structural Map

Geological Cross Sections

Original figure:
Sakuma, 19998

Three-Dimensional Seismic Survey in the Yamagawa Geothermal Field
Wireline Telemetry
SystemVibrator

Autonomous
SystemReflection Wave
Refraction Wave

Seismic Reflection and Refraction Data Acquisition
Yamagawa Geothermal Power Plant

Sources (VPs) 3262
Receivers (RPs) 4989

Field Experiment Period:
8/20/2015～10/14/2015（56 Days）
3-D Seismic Survey Layout

Vibrators
Width ………… 2.4 m
Length ……… 8.4 m
Height ……… 3.2 m
Weight ……… 18.9 ton

Cable-based Seismic Recording System

Cable-less Seismic Recording System

9Visualization of Geological Features in theYamagawa Geothermal Field

10

3D Seismic Sections along Wells
SKG
TD-3 OYM

TD-1

NRKW-2
NRKW-1
0.2
YMGW Top

Sonic log
Welded Tuff
Middle Nansatsu
LowerNansatsu

Upper Nansatsu
Dacite-3[km]11Geological Features: Dacite Intrusion
SKG
TD-3 OYM

TD-1NRKW-2
NRKW-1
0.2

Dacite Top Surface-3[km]

12

Geological Features: Depression

Upper Nansatsu Top13

Geological Features: Depression

Upper Nansatsu Top14

Geological Features: Depression

Upper Nansatsu Top

15

Geological Features: Depression

Upper Nansatsu Top16

Fracture Visualization• Coherence analysis• Faults and fracture zones can be visualized bymeasurement of incoherence between seismic traces.
• Semblance, a coherence function, will have lower value
around a discontinuity.
Continuous
10.85
Discontinuous
Semblance Section

17

Geological Features: Fractures

Amplitude
18Geological Features: Fractures

Semblance
19

Geological Features: Fractures

Semblance
20

Multi-Scale Fracture Visualization:
Input Seismic Sections
Amplitude (original)

IL246
Amplitude (low pass 8 Hz)

IL246

21

Multi-Scale Fracture Visualization:
Semblance Sections
Amplitude (original) + Semblance (original)

IL246
Amplitude (low pass 8 Hz) + Semblance (low pass 8 Hz)

IL246

22

Multi-Scale Fracture Visualization:
Images of the Geothermal Reservoir Zone
Amplitude (original) + Semblance (both)

Indication offracture zones
in the reservoir

IL246
Amplitude (low pass 8 Hz) + Semblance (both)

IL246

23

Multi-Scale Fracture Visualization:
Images of the Geothermal Reservoir Zone
EN

Upper Nansatsu top

Dacite top

Indication offracture zones

IL146

XL540

24

Multi-Scale Fracture Visualization:
Images of the Geothermal Reservoir Zone
W

N

Indication of
fracture zones

IL146

XL540

25

Multi-scale Fracture Visualization:
Surface slice and Transparent View on the Upper Nansatsu Top
Semblance fromthe original
volumeSemblancefrom the low
pass volume

Corendered multi-scaleImages

Structural Map-220

Elevation[m] -1470

26

Multi-scale Fracture Visualization:
Surface slice and Transparent View on the Upper Nansatsu Top
Semblance fromthe original
volumeSemblancefrom the low
pass volume

Corendered multi-scaleImages

Transparent view

Dacite topstructure27

Multi-scale Fracture Visualization:
Surface slice and Transparent View on the Upper Nansatsu Top

Dacite topstructure
The major
loss zone28A Mismatch between Seismic and Gravity
Interpretations. Why?

29

A Mismatch between Seismic and Gravity
Interpretations. Why?

Seismic Interpretation

Velocity [m/s]

Why?

Existing Model

Upper Nansatsu Top

Original figure:
Sakuma, 1999

Seismic interpretation was consistent with the former geological model except in the west
rim of the depression. Since no well existed in the area, the fault in the model was estimatedfrom gravity data.
30

Fault in the West Rim of the Depression
Residual gravity

Unit：mgal
Data source
Yoshimura et al., 1988

Former Structural Interpretation

Original figure:
Sakuma, 1999

Estimated faults

31

A New Fact: High Velocity Anomalies in the Shallow
3D Refraction Tomography
80mbmslAA

A’
02

4 [km]

B’0A’

B

1[km]

B 02

46B’

8 [km]

01[km]

Velocity

32High Velocity Zone at an elevation of -40 m

Velocity [m/s]A massive high velocity geologic body exists in the shallow
from Tsujinodake to the coast.

33

High Velocity Zone at an elevation of -40 m

Structural map:
Original figure:
Sakuma, 1999

Velocity [m/s]

The former interpretation of the west rim of the depression
coincides with the east edge of the high velocity zone.

34

Residual Gravity and Seismic Velocity Comparison
Residual gravity

Unit：mgal
Data source
Yoshimura et al., 1988

Refraction tomography

The residual gravity
anomaly coincides withthe shallow velocity
anomaly.

Velocity [m/s]

Estimatedfaults

35

A Mismatch between Seismic and Gravity
Interpretations
The anomaly seen
at -40 m elevation.

Horst or high density deposits?

Why?

Upper Nansatsu Top

Velocity [m/s]Higher velocities are always observed inthis zone .

Original figure:
Sakuma, 1999

36

A Mismatch between Seismic and Gravity
Interpretations
Fault or facies change?

Velocity [m/s]

An integrated multi-geophysical study should answer
these questions.
37

Summary
Demonstration field experiment has beensuccessfully made.
Geological features in the Yamagawa geothermal
field, such as a depression, a dacite intrusion, andfractures, were clearly visualized.
The seismic interpretation of the west rim of thedepression different from existing model based ongravity. An Integrated multi-geophysical study
should be made in the next phase.

38Demonstration Field Experiment of Three-Dimensional Seismic
Survey in the Yamagawa Geothermal Field

Section:Attributes:
Amplitude(2D)Vint (IL230)

Surface: Upper Nansatsu Top
Attribute: Semblance
Surface: Dacite top
Attribute: Elevation
Depth slice: -1,900 m
Attribute: Amplitude
Semblance

We wish to thank for everyone who involved with this experiment.

39

Appendix

Seismic Characterization of Sedimentary Fill of the Depression
Depth slice: -40~-1360m
Velocity (Rainbow)
Semblance (Gray)

Velocity[km/s]
24
Semblance

0.85

1

Surface slice:
Upper Nansatsu top
Attribute:
Semblance40