Experimental study of fracture response in granite specimens subjected to hydrothermal conditions relevant for enhanced geothermal systems

Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Permeability Evolution in a CO2-Circulated Geothermal Reservoir

“…Enhanced geothermal systems (EGS) have a significant potential to efficiently extract geothermal energy with CO2based EGS systems exhibiting several advantages: the density difference between the cold and hot CO 2 in the injection and production wells provides a large buoyant drive; CO 2 has a large ratio of fluid density to viscosity, which results in high mobility; CO 2 can be continuously sequestered as a result of fluid losses from the reservoir to the surrounding formation [2][3][4][5]. Despite its potential, the likelihood of steep production decline [6][7][8][9] has hindered the deployment of EGS at fully commercial scales.…”

“…For a better understanding of anticipated changes in fracture permeability, numerous flow-through experiments have been conducted to examine the impacts of coupled THMC processes. These have demonstrated the impact of pressure solution in impacting permeability change [9][10][11][12] and the propensity for pressure solution effects at lower temperatures to be overcome by dissolution and precipitation at high temperatures [7]. The decreases in fracture permeability can reach 1-2 orders of magnitude [8] mainly due to mineral precipitation processes [6] and potentially the presence of clay particles released by the dissolution of carbonate cement, which have then been transported in the fluid flow path and accumulated at pore throats [13,14].…”

Application of Water Fracturing in Geothermal Energy Mining: Insights from Experimental Investigations

“…The experimental results of Chen et al [7] indicated that average fracture conductivities of about 10 mDm can be expected for water fracturing in granite at confining pressures greater than 40 MPa. Experimental investigations by Caulk and Kamali-Asl et al [8,9] found that chemical and physical effects lead to reduced permeability of the self-propping fracture, and thus reduced EGS system longevity. However, compared to the conventional gel fracturing, water fracturing is undoubtedly the most effective method to minimize self-propping fracture damage.…”

Thermally driven fracture aperture variation in naturally fractured granites

“…The effect of temperature on fracture permeability, under constant normal stress, has been recognized both in laboratory experiments (Morrow et al 2001;Yasuhara et al 2006;Luo et al 2018) and during field tests (Hardin et al 1982;Yow and Wilder 1993;Barton 2007;Rutqvist et al 2008), even at moderate temperatures of 100-120 °C (Yasuhara et al 2011;Faoro et al 2016;Kamali-Asl et al 2018). Fracture permeability has been reported to decrease monotonically with increasing temperature.…”

“…For example, Polak et al (2003) have observed reductions of ∼ 80% in hydraulic aperture widths in naturally fractured novaculite specimens, caused by thermal-chemical processes, during a 900-h flow-through experiment at 25-150 °C. Such temperature-driven fracture closure may result from reversible elastic compaction or irreversible mechanical fracturing of the propping asperities (Yasuhara et al 2011;Faoro et al 2016), chemical dissolution of the contacting asperities (Yasuhara et al 2006;Faoro et al 2016;Kamali-Asl et al 2018), and/or clogging of the fracture void spaces by mineral precipitation (Morrow et al 2001;Dobson et al 2003;Caulk et al 2016). While it is challenging to decouple the thermal-mechanical and chemically induced responses, it is generally accepted that chemical processes occur on an extended timescale, while mechanical processes may occur over a relatively short timescale (Yasuhara et al 2011).…”