TY - JOUR
T1 - CO2 injection-induced complex cloud-fracture networks in granite at conventional and superhot geothermal conditions
AU - Pramudyo, Eko
AU - Goto, Ryota
AU - Watanabe, Noriaki
AU - Sakaguchi, Kiyotoshi
AU - Nakamura, Kengo
AU - Komai, Takeshi
N1 - Funding Information:
The present study was supported in part by the Japan Society for the Promotion of Science (JSPS) through Grants-in-Aid for Scientific Research (B) (No. 17H03504), Challenging Research (Exploratory) (No. 18K19039), Challenging Research (Pioneering) (No. 21K18200), and JSPS Fellows (No. 20J2020108). The present study was also supported by JSPS and DFG under the Joint Research Program (JRPs-LEAD with DFG) (No. JPJSJRP20181605). The data that supports the findings of the present study are available from the corresponding author upon reasonable request. The authors would like to thank Toei Scientific Industrial Co. Ltd. for manufacturing the experimental system.
Funding Information:
The present study was supported in part by the Japan Society for the Promotion of Science (JSPS) through Grants-in-Aid for Scientific Research (B) (No. 17H03504), Challenging Research (Exploratory) (No. 18K19039), Challenging Research (Pioneering) (No. 21K18200), and JSPS Fellows (No. 20J2020108). The present study was also supported by JSPS and DFG under the Joint Research Program (JRPs-LEAD with DFG) (No. JPJSJRP20181605).
Publisher Copyright:
© 2021 The Authors
PY - 2021/12
Y1 - 2021/12
N2 - Complex cloud-fracture networks, favorable for enhanced geothermal system reservoir development, were shown to be able to be achieved in granite under superhot geothermal conditions, with temperatures of approximately 400–500 °C, by injecting low-viscosity water at these temperatures. Nonetheless, water utilization has several drawbacks, such as its reactivity with rock-forming minerals. Carbon dioxide (CO2), which has a low viscosity similar to that of the low-viscosity water under both superhot and lower-temperature conventional geothermal conditions, is a proposed replacement to overcome these challenges. This low viscosity of CO2 motivates its application to create cloud-fracture networks under various geothermal conditions. The present study, for the first time, demonstrated the formation of cloud-fracture networks in granite under both geothermal conditions through a set of CO2 fracturing experiments conducted from 200 to 450 °C under conventional and true triaxial stress states. The Griffith failure criterion was shown to be applicable for the formation of a cloud-fracture network in both geothermal conditions because it indicated that the fracture network was formed by the stimulation of pre-existing microfractures. The formation of cloud-fracture networks has potential advantages, such as additional fracturing in the presence of sizable natural fractures and a lower risk of induced seismicity; however, CO2 fracturing has the challenge of narrower fracture apertures under conventional geothermal conditions, which should be addressed in future research.
AB - Complex cloud-fracture networks, favorable for enhanced geothermal system reservoir development, were shown to be able to be achieved in granite under superhot geothermal conditions, with temperatures of approximately 400–500 °C, by injecting low-viscosity water at these temperatures. Nonetheless, water utilization has several drawbacks, such as its reactivity with rock-forming minerals. Carbon dioxide (CO2), which has a low viscosity similar to that of the low-viscosity water under both superhot and lower-temperature conventional geothermal conditions, is a proposed replacement to overcome these challenges. This low viscosity of CO2 motivates its application to create cloud-fracture networks under various geothermal conditions. The present study, for the first time, demonstrated the formation of cloud-fracture networks in granite under both geothermal conditions through a set of CO2 fracturing experiments conducted from 200 to 450 °C under conventional and true triaxial stress states. The Griffith failure criterion was shown to be applicable for the formation of a cloud-fracture network in both geothermal conditions because it indicated that the fracture network was formed by the stimulation of pre-existing microfractures. The formation of cloud-fracture networks has potential advantages, such as additional fracturing in the presence of sizable natural fractures and a lower risk of induced seismicity; however, CO2 fracturing has the challenge of narrower fracture apertures under conventional geothermal conditions, which should be addressed in future research.
KW - Carbon dioxide fracturing
KW - Complex fracture pattern
KW - Enhanced geothermal system
KW - Fracturing characteristics
KW - Griffith failure criterion
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U2 - 10.1016/j.geothermics.2021.102265
DO - 10.1016/j.geothermics.2021.102265
M3 - Article
AN - SCOPUS:85116557221
VL - 97
JO - Geothermics
JF - Geothermics
SN - 0375-6505
M1 - 102265
ER -