Objective This study addresses limited modern recharge, low reinjection capacity, and the lack of a reinjection-constrained production basis for sandstone geothermal fields in the inland Hexi Corridor. The KC1-ZK3 production-reinjection well pair in the Zhangye-Minle Basin was used to evaluate resource potential and a production-by-reinjection development mode.

Methods Drilling, well logging, multi-step pumping tests, same-reservoir reinjection of native geothermal water, pressurized injection of external clean water, hydrochemistry, and isotope data were integrated. Reinjection performance was jointly evaluated using specific injectivity, clogging ratio, backflow recovery ratio, and the reservoir damage coefficient. The volumetric heat-in-place method and a 100-year thermal-breakthrough constraint were used to distinguish static heat storage from dynamic circulation potential.

Results The principal reservoir is the Neogene Baiyanghe Formation sandstone, with an effective thickness of approximately 154 m and a total heat-in-place of 2.76 × 10¹⁷ J. The specific injectivity of native-water gravity reinjection was approximately 0.40 m³/(h·m), and K_r/K_e was 0.96, indicating low natural injectivity but only a small short-term change in integrated permeability. The engineering-controlled production rate of the current well field is 1408.32 m³/d, corresponding to 3.86 MW, whereas the idealized regional circulation potential under the 100-year thermal-breakthrough constraint is 9023.93 m³/d.

Conclusions Under the short-term test conditions, same-reservoir reinjection of native geothermal water showed good hydrochemical compatibility. Moderate pressurization and periodic backflow may compensate for insufficient gravity injectivity. Long-term operation should nevertheless be verified through continuous monitoring of water level, temperature, water chemistry, and injectivity.