| Abstract |
Fluid injection-induced fault reactivation triggering seismicity has emerged as a prominent geological safety challenge in deep geothermal resource exploitation, where the in-situ stress regime serves as fundamental data for seismic risk assessment in hot dry rock (HDR) development. This study elucidates the characteristics of the regional stress field in the Gonghe Basin through an integrative analysis of tectonic evolution, focal mechanism inversion, and in-situ stress measurements. A three-dimensional geomechanical model was developed, incorporating the structural framework and lithological properties of the GR2 geothermal reservoir. Utilizing an orthotropic elastic constitutive relationship, the three-dimensional stress distribution surrounding the GR2 well was determined through numerical simulations, enabling a systematic investigation of HDR stimulation and fault stability. Key findings include: (1) The simulated stress distribution demonstrates congruence with theoretical predictions, satisfying initial displacement constraints and effectively characterizing the wellbore stress architecture; (2) Within the 500-4500 m depth interval, principal stress magnitudes follow σv (vertical stress) > σH (maximum horizontal stress) > σh (minimum horizontal stress), indicative of a normal faulting tectonic regime; (3) Continuous 30-year injection at 183 m³/h induces maximum excess pore pressure below 11 MPa, with spatial propagation confined within 15 km from the injection well; (4) Prolonged fluid injection significantly compromises the stability of blind faults within 2 km, exhibiting slip instability probabilities exceeding 42% and elevated reactivation potential that may trigger moderate-magnitude seismic events. These findings provide critical insights for risk mitigation strategies in HDR geothermal development. |