Performance of Fault-Controlled Hydrothermal System: Insights from Multi-Field Coupled Rock Mechanics Analysis

As is typical of deep rock engineering, fault-controlled hydrothermal systems (FHS) have emerged as a highly promising solution for geothermal energy exploitation. The stability and thermal recovery performance of such systems are critical to their long-term efficiency and viability. In this study, we establish a coupled Thermo-Hydro-Mechanical (THM) model to investigate the mechanical response and thermal output of an FHS. The stability of the system is evaluated based on the evolution of the failure zone within the fault. Key findings include the following: (1) The pore pressure distribution between injection and production wells leads to an elliptical failure pattern in the fault, caused by the constraint exerted by the negative pore pressure zone around the production well on the positive pressure zone around the injection well along the well connectivity direction; (2) Reducing the injection flow rate by 50% can result in a 76% decrease in the thermal recovery efficiency. Meanwhile, reducing the number of reinjection sub-wells from seven to three can lead to a 95% reduction in the failure volume; and (3) Larger fault thickness diminishes both failure volume and thermal performance; specifically, increasing the fault thickness from 5 m to 30 m can result in an 89% reduction in the failure volume. The fault damage zone volume exhibits a sharp decrease as permeability rises from 2 × 10−12 m2 to 8 × 10−12 m2. This study provides scientific insights and practical guidelines for the design and stability assessment of FHS-based geothermal systems.