Formation mechanisms and resource potential of typical carbonate geothermal reservoirs in the Fen Wei Graben System, China

The Fen Wei Graben System, a Cenozoic intracontinental rift basin dominated by far-field tectonic stress in China, hosts abundant geothermal resources, with carbonate formations serving as important geothermal reservoirs for exploration and development. This study aims to clarify the formation mechanisms and to quantify the resource potential of typical geothermal fields within the graben to inform exploration and sustainable utilization. By compiling drilling and production data, temperature–depth profiles, synthesized hydrochemistry and stable-isotope datasets, this study identifies that convective and conductive heat transfer coexist as two dominant modes in different basins, and establishes three end-member conceptual models: 1) conduction-dominated model with lateral recharge, 2) convection-dominated model with vertical heating, and 3) conduction-dominated model with confined paleo-water. Quantitatively, the combined geothermal resources of the three fields reach 14.3 × 10 9 GJ, equivalent to 486 × 10 6 t of standard coal; under balanced extraction–reinjection conditions, the annual allowable fluid production totals 134 × 10 6 m 3 and the corresponding producible heat is 22.9 × 10 6 GJ/a. Extrapolated to basin scale, the carbonate reservoirs of the Jinzhong, Linfen-Yuncheng, and northern Weihe basins could meet ∼118 × 10 6 m 2 of heating demand, demonstrating significant development potential. These findings provide a process-based framework and quantitative benchmarks for prioritizing high-potential targets in the Fen Wei Graben System and analogous intracontinental rifts. • Carbonate geothermal reservoirs in the Fen-Wei Graben System investigated. • Conductive and convective heat transfer modes in geothermal systems identified. • Three conceptual models for karst geothermal reservoirs proposed. • Geothermal potential assessed using volumetric method and well data.