Current status of the recharge experiment at

the Okuaizu geothermal field

November 20, 2019

T. Okabe, M. Kato, H. Nakata(GERD),Y. Abe(OAG), H. Asanuma(AIST),

M. Tsuzuki, K. Yoshimatsu(JOGMEC) andH. Kamenosono(JOGMEC, now KEPCO)

1

Presentation

1. Project Overview1.1 Purpose and the schedule1.2 Project structure1.3 Okuaizu geothermal field

2. Present achievements2.1 Recharge Test in 2015 and its results2.2 Workover and recharge test in 2018

3. Summary

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1. Project Overview

• The purpose is to develop a guideline for an artificial water recharge technology and to develop a technical manual through a verification test and numerical simulation clarifying the impact of artificial water recharge on the geothermal reservoir and/or hot spring aquifer.

Research & Development FY2013 FY2014 FY2015 FY2016 FY2017 FY2018 FY2019

Project Planning, Design & Management

Geological/Geophysical Survey and Modeling

Design and Construction of Test Facilities (including wells)

Well Test and Logging

Operation of water injection

Numerical Reservoir Simulation

Monitoring

Preparation of Technical Operation Manual

If necessary

Modelling & Forecast Field data analysis & model upgrade

Background Operation

Injection was stopped due to interference with the nearest production well

Workover

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1.1 Purpose and the schedule

1.2 Project Structure

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JOGMEC

GERD OAG AIST

Tohoku Electric Power Co., Inc. (Yanaizu-Nishiyama Power Plant)

GERD

- Project Planning, Design & Management

- Survey and Modeling (MT)- Well Test and Logging- Numerical Reservoir Simulation- Monitoring (Downhole PT, Tracer test,

etc.)- Preparation of Technical Operation

Manual

- Project Planning, Design- Survey and Modeling (AMT ,

Gravity)- Monitoring (Seismic, Resistivity)- Preparation of Technical

Operation Manual

- Design and Construction of Test Facilities

- Operation of Recharge Test- Monitoring (Hot-spring

sampling )- Preparation of Technical

Manual - Local Coordination

Contract

Cooperation

JOGMEC : Japan Oil, Gas and Metals National Co.GERD : Geothermal Energy Research & Development Co., Ltd.OAG : Okuaizu Geothermal Co., Ltd. AIST : The National Institute of Advanced Industrial Science and Technology

Project leader

1.3 Okuaizu geothermal field

Tokyo

Fukushima

YanaizunishiyamaGeothermal Plant

Aizuwakamatsu

Turbine size was changed to 30MW on 28th August, 2017.

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24 years of operation in 2019

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Okuaizu geothermal field (Plan view)

Seki(1991)

Acidification region

Superheated region

Well-2

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Actual

7" Slotted liner7" Slotted liner

9-5/8"CSGLiner hanger

8-1/2"2,225.00m

17-1/2" 1,005.00m

26" 155.00m

12-1/4" 1,880.00m

8-1/2"2,225.00m

17-1/2" 1,005.00m

26" 155.00m

12-1/4" 1,880.00m

Plan

20" CSG150.00m

20" CSG154.39m

13-3/8"CSG1,000.00m

ECP743m

13-3/8"CSG997.32m

5-1/2"TBG1,814m

9-5/8"CSG1,880.54m

1,840.48～2,100.26m

1,875.00m

2,225.00m

Casing program and a picture of the wellhead

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2. Present achievements

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【Term】1st : Jun. 4, 2015 ~ Aug. 31, 2015 (88 days)2nd : Nov. 27, 2015 ~ Dec. 26, 2015 (29 days)

【Recharge rate】

【Amount of recharge water】1st: approx.120,000 ton, 2nd : approx. 50,000 ton

1st 2ndMS Monitoring

Rech

arge

Rat

e

Steam increase, NCG decrease and easing of acidification were observed. Decrease of the steam rate and cyclic effect of the steam with the brine production was observed in late December at Well-8. The recharge operation was stopped on Dec. 26. This is because of thermal breakthrough from shallow LC zones caused by cementing problem of 9-5/8” casing.

2.1 Recharge test in 2015 and its results

Remove injection pipe

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1

2

3

4

5

6

7

8

9

10

11

12

13

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01/4 02/4 03/4 04/4 05/4 06/4 07/4 08/4 09/4 10/4 11/4 12/4 13/4 14/4 15/4 16/4 17/4

Well-8

(涵養)

12/2

5/25

6/24

7/24

8/21

11/30

1/26

12/25

3/22

4/22

14JN-R1掘削

Well-8 production history

Well-8 NCG change

Recharge effect

Dilution by steam increase

30% steam increase

NCG decrease

NCG(wt%)

Stea

m ra

te(t

/h)

19t/h

14t/h

Recharge

Although effect by reservoir pressure increase while the maintenance increases the steam rate, recharge operation is conducive very much to increase Well-8 steam based on the tracer and NCG results.

Before the recharge : 8.9 wt%After the recharge : 5.0 wt%

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AE/Micro seismic array

NanometricsF: 20s～108HzVelocity＠YAE1-5

アームロック機構

キー

ケーシング側

キー溝

IESE(NZ)Passive F: 15HzVelocity

Recharge point

YAE-7

YAE-8

YAE-9

2km

Existing station 5（OMS# ：OAG）F: 4.5Hz，Fs=100Hz

＋Surface station 5Borehole station 4

Total 14

OYO（ESG）F: 20～1kHz，Accelerometer

Nanometrics dataloggerRealtime observation by Fs=1000Hz

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0 500 m

Back ground

70 t/h

0 500 m

Recharge point

AE/Micro seismicity monitoring result

Back ground Step rate 50t/h 70t/h After injection(May) (Jun.) (Jun.-Jul.) (Jul.) (Aug.-Nov.)

Number of eventsper day 2.8 1.8 4.0 7.5 4.5

Local magnitude -0.53 -0.58 -0.38 -0.37 -0.59

Recharge stage

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Initial geothermal model was updated considering MS events.We reviewed:• Cap rock shape (② is not a cap rock) • Migration area and boundary of recharged water

(④&⑤ are very low permeability zone)

①

②

④⑤

⑥ ⑧

⑩

⑦⑨

Updated ModelA A’Initial Model

Cap rock

Heat Source

Model improvement

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New faults evaluated

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Temperature (deg.C)

ActualSimulation

Temperature profile

Temperature (deg.C)

Dept

h (m

)De

pth

(m)

A’

A

A A’

A A’Before

After

TOUGH2 simulation (Challenging)Natural state⇒History matching⇒Injection for superheated area

14The accuracy of the temperature simulation was improved.

26"坑 20"CSG 20"CSG 159.00m 150.00m 154.39m

ECP743m

17-1/2"坑 13-3/8"CSG 13-3/8"CSG 1002.00m 1,000.00m 997.32m

12-1/4"坑1560.00m ～1,610m

9-5/8"CSG12-1/4"坑 1880.54m

7"孔明管2100.26m

8-1/2"坑2100.26m

1890.00m

26"坑 20"CSG 20"CSG 159.00m 150.00m 154.39m

ECP743m

17-1/2"坑 13-3/8"CSG 13-3/8"CSG 1002.00m 1,000.00m 997.32m

12-1/4"坑1560.00m ～1,610m

9-5/8"CSG12-1/4"坑 1880.54m

7"孔明管2100.26m

8-1/2"坑2100.26m

1890.00m

26"坑 20"CSG 20"CSG 159.00m 150.00m 154.39m

ECP743m

17-1/2"坑 13-3/8"CSG 13-3/8"CSG 1002.00m 1,000.00m 997.32m

12-1/4"坑1560.00m ～1,610m

9-5/8"CSG12-1/4"坑 1880.54m

7"孔明管2100.26m

8-1/2"坑2100.26m

1890.00m

(1)Present (2)Side track (3)Metal packer+casing cement

Injection water L/C behind the casing

Side track

Plug back

Metal packer

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Slotted linerSlotted liner Slotted liner

2. 2 Workover and recharge test in 2018

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GoodA bit good

A bit goodMetal Packer

【Bonding】

Enlarged view

Metal Packer

Metal Packer deployment during cement curing

Result of the recharge test

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Existing Fault

Recharge Well

Well06

Steam increase (1.7t/h)

Steam increase (1.4t/h)

Production was suspended in advance to prevent interference caused by water injection : H30/11/22~12/18

Estimated Fault Target

During the workover, recharge test to check the present recharge situation for long term recharge operation in future was conducted for a month. Injection rate was 5t/h.

①In 2015 recharge tests, 170,000t water was successfully injected and a response to recharge (increase in steam flow) at Well-8 is observed and is estimated by approx. 30%.

Although further study is required about the recharge effect, production rate at wells close to the recharge well increased. In addition, non condensable gas(NCG) decreased at those wells as another benefit of the recharge operation.

Thermal break through at Well-8 was observed at the end of December 2015. From the observed Well- 8 steam stable behavior between Dec 5 and Dec 23, the slow decline of the steam at Well-6 and the decrease of the superheated amount together with the slow decline of the steam at Well-5, it is possible to maintain and/or increase of steam production by proper control of the recharge operation.

②In 2018 recharge tests, a response to recharge (increase in steam flow) at Well-3 and Well-6 isobserved and is estimated by 1.7t/h and 1.4t/h respectively.

③New geothermal model was created with new information from the latest technologies such as MT 3 dimensional analysis, PTS + sampler logging, high temperature PT monitoring, etc.

④The accuracy of the simulation was improved based on the geothermal model, and details such as (1)permeability of the formation , the range and boundary of fluid migration, (2) new faults, and (3) the relationship between the fracture and the fault were revealed.

3. Summary

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⑤A metal packer and cementing procedure was used to shut off the leakage at 7 ” casing shoe completely and it was deployed successfully . The metal packer was used for the first time in Japan.

⑥In 5-7/8 “ drilling, the main injection zone at about 2030m in the original well was captured at 2023m of the side track well as expected.

⑦Recharge test was started from July 2019 and is currently ongoing. An artificial recharge technology manual applicable to geothermal areas in Japan will be created with analyzing long-term recharge test data and establishing appropriate recharge injection design and management technology considering economic aspects.

Introduced cutting edge technologya. 3D MT analysisb. Recharge simulation for superheated reservoir (add supercritical option)c. New technology(combination of the focal mechanism analysis, scattering analysis,

migration method and accurate hypocenter determination) for flow path identification of injected water based on microseismic monitoring data

d. High temperature borehole PTS+fluid samplere. High temperature (300deg.C) downhole pressure/temperature measurementf. Installed high temperature downhole seismic toolsg. Installed a metal packer for the first time in Japan

3. Summary(Cont.)

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Thank you for your attention.