On the utilisation of Super-critical
Carbon Dioxide (ScCO2) in thegeothermal power generation
Japan Oil, Gas and Metals National Corporation (JOGMEC),Geothermal Unit

Toshiyuki TOSHA

10/Dec/2021 Joint Seminar between GNS and JOGMECContents
1. Background of the technology

6th electric power supply plan in 2030, Concept of HDR, CCS
project in the geothermal field

2. Geothermal system using CO2

Conceptual image of the geothermal system, Characteristics ofScCO2

3. The outline of the new project using CO2

Ⅰ．Overall system design, Ⅱ．Fracture creation using ScCO2
Ⅲ．Geochemical properties of ScCO2 in a geothermal reservoir

4. Closed circulation system
Another EGS project in JOGMEC

2Background for the technology

3Problems for the geothermal development
in JapanGeothermal energy demand
The 6th energy supply plan in2030 by the Japanese
government
Carbon freeH2 andNH3 (1%)

1. Agreement for the development byOnsen (Spring) owners
Understanding of the geothermal fluidin the hot spring and geothermall
reservoirs is necessary

2. Development in the national park
Environmental friendly development
Geothermalsuch as height restrictions on power
1%(=1.5GW)
plants is required
NuclearRenewable

ThermalThermal2019(result)

5th Plan

Thermal

3. Long time for the development
Financial support such as subsidy is
supported by JOGMEC

6th Plan

Basic figure https://www.asahi.com/articles/ASP7P4V2QP7NULFA01D.html

Concelt of Hot Dry Rock (HDR)

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Geothermal power generation by the idea of HDR (Hot Dry Rock) has beentechnologically developed since the 1970s. This technology creates ahydrothermal system by artificial cracks where the natural hydrothermal system
is underdeveloped, injects water from the injection well, and takes it out fromthe production well. For this reason, geothermal power generation is possible byexcavating deep wells in any region of the world. It is, currently, developing as
an EGS (Enhanced Geothermal System) technology.

Injection
wellProduction
well It is impossible to control 100%of artificial cracks (dominatedcracks, induced seismicity).
 Recovery rate is less than half(the whereabouts of leakedwater is unknown).

Artificial reservoir
Impermeable
layer

Inject water or CO2 into the reservoir

 The concept of crack-free rock
body has change to various
types of fracture structures.

CCS project in Iceland using geothermal heat5

【Orca Project】（https://edition.cnn.com/2021/1
0/20/world/carbon-capturestorage-climate-iceland-intlcmd/index.html）

CO2 capture by DAC using heat from the geothermal power plant
CO2 injection to a depth of about 2,000 m
CO2 reacts with basalt and is converted to the carbonate over
several years
Geological storage of about 4,000 tons of CO2 in every year
Audi press release（2020）

Conceptual image of the geothermal system using CO2
CO2 Turbine

CO2 SourceInjection（CO2）• Factory• CO2 Capture• DAC(Direct Air Capture)6

GeneratorProduction（CO2）
Leakage = Capture?
Caprock

CO2 reservoir

Characteristics of Supercritical Carbon Dioxide(ScCO2)• Density is close toliquid• Viscosity /diffusion
coefficient is closeto gasMagma•••

Injection of ScCO2 into a geothermal reservoir and production of heated ScCO2 generate
electricity by a CO2 turbine which would be smaller than that of using vapour.
Siphon effect by the high compressivity of ScCO2 causes the circulation without power.
Mineral trapping would be happened by the escaped CO2.

Characteristics of ScCO2

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Critical point of carbon dioxide
Temperature 31.1 ℃ & Pressure 7.38MPa
Physical property of ScCO2Pressure(MPa)
SubｃｒｉｔｉｃａｌSolid

Superｃｒｉｔｉｃａｌ
Criticalpoint

LiquidGas

Viscocity of water via temp.

10-4～10-3 (Pa/s)

H2O
CO2Temperature(℃)
Phase Diagram of CO2（https://shinko-airtech.com/supercritical/critical.html）

Subjects for the technology development
Ⅰ. Overall System Design Basic design for the system including the CO2 turbine
 Pumping system to inject the CO2 into the reservoir
 Selection for the suitable field and the estimation of the potentialfor this CO2 geothermal system

Ⅱ. Reservoir creation using ScCO2 as fracturing fluid Fracture experiments in the laboratory
 Comparison of water and CO2 in the fracture creation
 Modelling of the experiments by a simulation
 Prediction of the reservoir creation in a field

Ⅲ．CO2 flow and geochemical reaction in a geothermal reservior
 Interaction between rocks and CO2 in a laboratory scale Simulation to explain the geochemical reactions in the laboratory.
 Simulation to explain the flow and geochemical reaction in the field scale Monitoring methods to detect the flow in the reservoir and trapped minerals.

8Ⅰ. Overall System Design Design for the CO2 turbine in
the geothermal system
Comparison of the same output
Steam Turbine
CO2 Turbine
10 times the volumeat the turbine inletbut

9 Map of the geothermal energy
for EGS technology (nonhydrothermal system)

1/60 volume atturbine output

The size of the turbine is expected tobe smaller
CO2
SteamEGS Map

https://www.americangeosciences.org/criticalissues/maps/geothermal-energy-resource-US

1. Geomagnetic survey data by aircraft
2. Curie temperature profile
3. Estimation of the heat source
4. Estimation of the electricity output

Ⅱ．Reservoir creation using ScCO2 as fracturing fluid

10⇒ What kind of cracks will occur by the injection of ScCO2?
How is the risk of an earthquake?

water

CO2

 Creates cracks with a pressure smaller than that of water.
 Cracks develop more three-dimensionally than those caused by water.
 The cracks created by ScCO2 have a largeｒsurface area and form flow paths that is moresuitable for the heat exchange in HDR than those created by water.（Ishida et al., 2015）

Ⅲ．CO2 flow and geochemical reaction in a geothermal reservior

11⇒ How does ScCO2 behave at the geothermal reservoir with thehigh temperature and pressure?
Where does the mineral trapping of CO2 happen?

ScCO2Mineralisation?

Shield?

Degassing?
Reservoir(CO2 +water) When CO2 is injected into theground, CO2 dissolves in waterand reacts with rocks, causing Caand Mg to leached from the rocks.
 Eluted metal ions react with CO2
dissolved in water to precipitate
calcite and other carbonate
minerals.
Ueda（2009）

Degassing?

CaAl2Si2O8 + H+ + HCO3- + H2O⇒ CaCO3 + Al2Si2O5(OH)4
Plagioclase

CalciteKaolinite

Another EGS project in JOGMEC

Closed circuit heat exchange technology
HDR technique problems• Reservoir creation by fracturing(controlled by the existing cracks)• Control of water flow in cracks (shortcircuit and regression)• Induced seismicity
One of ｔhe closed circuit heat exchanges
is developed by Eavor Technology Inc.
in Canada and has also been created inCanada and Germany.
Technology to be developed

Eavor Technologies Inc. https://eavor.com/• Drilling technology (horizontal drilling anddirectional drilling)• How to join a well
• Heat flow control (heat imbalance betweenwells and improvement of heat recovery rate)

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Acknowledgememts

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Any Questions or Comments?

For the better global environments

Toshiyuki Tosha (Ph.D)
tosha-toshiyuki@jogmec.go.jp