Depressurization-based reinjection method for low-permeability sandstone geothermal reservoirs

The development of low-permeability sandstone geothermal reservoirs is constrained by high reinjection pressures associated with conventional direct reinjection. To address the lack of consideration of reservoir pressure field evolution in existing studies, this paper proposes a depressurization-based reinjection method for low-permeability sandstone geothermal reservoirs. The method adopts staged fluid production to form a pressure drawdown cone, thereby enabling low-pressure reinjection. Taking the H block of the Jilin Oilfield as a case study, a three-dimensional heterogeneous geological model was constructed to simulate reservoir pressure distributions under different depressurization flow rates, and to optimize the depressurization flow rate and well spacing. The results show that, compared with direct reinjection, when the depressurization rate is 600 m³/d and the well spacing is 250–300 m, the reinjection pressure can be reduced by more than 80%, effectively alleviating the high-pressure reinjection challenge in low-permeability sandstone reservoirs. This study provides practical design guidance for the sustainable development of geothermal resources.