Geothermal reservoir characteristics, genesis, and potential in the Sanjiaochenggou area, Jinchang Depression
Abstract
Medium- to low-temperature geothermal resources hosted in sedimentary basins are important for regional heating and direct utilization. This study investigates the geothermal reservoir characteristics, fluid origin, genesis, and development potential of the Sanjiaochenggou area in the Jinchang Depression, a poorly explored inland sedimentary basin in the eastern Hexi Corridor. An integrated investigation was conducted using hydrogeological surveys, wide-field electromagnetic and controlled-source audio-frequency magnetotelluric surveys, geothermal drilling, comprehensive well logging, borehole temperature measurements, pumping tests, hydrochemical analyses, and environmental isotope techniques. The results indicate a confined sedimentary-basin geothermal system, with the principal reservoirs hosted in sandstone and sandy conglomerate of the Lower Neogene and Cretaceous strata beneath a relatively impermeable Neogene mudstone caprock. The temperature reaches 61.7 °C at 1,992 m, with an average geothermal gradient of approximately 1.77 °C/100 m. Pumping-test analyses yielded a representative transmissivity of 21.69 m 2 /day. The geothermal fluid is Cl–Na-type brine with an average total dissolved solids concentration of 40.99 g/L. Isotopic evidence indicates meteoric recharge followed by deep circulation, prolonged water–rock interaction, and long residence within a relatively closed hydrogeological system. For the 47.02 km 2 assessment area, the reference heat-in-place estimate is 2.27 × 10 18 J, while deterministic scenarios yield 8.84 × 10 17 –2.86 × 10 18 J. By cross-validating geophysical interpretations against the JCDR-1 borehole and separating borehole-controlled from inferred resources, this study establishes a site-specific conceptual model and deterministic uncertainty framework for evaluating comparable inland sedimentary-basin geothermal systems with limited deep-borehole control.