The assessment of geothermal extraction efficiency for unstable alternation operation through thermal-hydro mechanical coupling simulations

Mitigating channeling flow is crucial for enhancing the sustainability of geothermal production. To address this, the unstable alternation operation (UAO) methods, involving creating unstable water flooding by alternating water flooding between multiple wells, are introduce. Thermo-Hydro-Mechanical (THM) coupling simulations are conducted to compare the effects of continuous operation and various UAO methods on heat extraction within a fractured geothermal reservoir model featuring a single heterogeneous fracture. Additionally, the impact of aperture distribution, correlation length, normal stiffness, and reservoir temperature on thermal performance using UAO methods are evaluated. The results show that continuous heat extraction results in the increase of directional aperture, exacerbating channeling and reducing production temperature. Conversely, the UAO methods, involving dynamic changes in flow rate and direction, effectively promote fluid migration across the whole fracture, mitigating channeling and resulting in a larger heat transfer area. Consequently, the production temperature and heat achieved through UAO methods are generally higher than those by continuous operation. Furthermore, the heterogeneous aperture distribution was identified as critical in affecting production temperature and heat, while the correlation length, fracture stiffness, and reservoir temperature had minimal influence. The findings indicate that the UAO method is helpful to achieve favorable thermal performance in geothermal energy extraction.