EGU21-10538, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-10538
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Characteristics and mechanism of CO2-based fracturing of granite in conventional and superhot geothermal environments

Eko Pramudyo, Noriaki Watanabe, Ryota Goto, Kiyotoshi Sakaguchi, Kengo Nakamura, and Takeshi Komai
Eko Pramudyo et al.
  • Graduate School of Environmental Studies, Tohoku University, Sendai, Japan (eko.pramudyo.q2@dc.tohoku.ac.jp)

Creation of fractured reservoir for enhanced geothermal system (EGS) in granitic rock at unconventional superhot geothermal environments (>400°C) has been found possible by injection of low viscosity supercritical water (Watanabe et al., 2017, Geoph. Res. Lett.; Watanabe et al., 2019, Sci. Rep.). Accordingly, the complex cloud-fracture network is formed through stimulation of pre-existing microfractures by the low viscosity (<50 μPa∙s) water. Nonetheless, water reactivity to rock forming minerals (Brown, 2000, Proc. 25th wksh. Resv. Engr.) and its high water footprint (Wilkins et al., 2016, Environ. Sci. Technol.) hinder water application. Therefore, CO2 is proposed to replace water, since it less reactive to rock forming minerals (Brown, 2000), and can reduce water footprint (Wilkins et al., 2016). CO2 has also low viscosity at conventional (c.a. 150 – 300°C) and superhot geothermal temperatures (based on Heidaryan et al., 2011, J. Supercrit. Fluid), which motivates to create similarly complex fracture pattern in those geothermal environments. A set of traditional-triaxial stress fracturing experiments was performed on cylindrical granite samples subjected to 200 – 450-°C temperature and varying differential stress to determine characteristics and mechanism of CO2-based fracturing in conventional and superhot geothermal environments. The experiments demonstrated that complex fracture pattern was formed at low pressure in all experimental-stress state and temperature. Breakdown pressure was also found to decrease with increasing differential stress. Hence, it was hypothesized that fracturing mechanism by injection of CO2 is governed by Griffith fracture theory. To unveil the fracturing process in detail, a CO2-based fracturing experiment was conducted on cubical granite sample with a realistic true-triaxial stress state and 300-°C temperature. The later experiment confirmed the above-mentioned hypothesis and showed that the fracturing occurs gradually.

How to cite: Pramudyo, E., Watanabe, N., Goto, R., Sakaguchi, K., Nakamura, K., and Komai, T.: Characteristics and mechanism of CO2-based fracturing of granite in conventional and superhot geothermal environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10538, https://doi.org/10.5194/egusphere-egu21-10538, 2021.

Corresponding formerly uploaded have been withdrawn.