Migration and Evolution of Geothermal Fluids in Karst Reservoirs and Geothermal Energy Development Model: A Case Study

Against the backdrop of the energy transition and to support the sustainable development of karst geothermal resources in the Laiyuan area, this study addresses the insufficient understanding of its formation mechanisms and thermal accumulation patterns. By innovatively integrating hydrogeochemical analysis, hydrogen–oxygen isotope tracing, and coupled water-heat numerical modeling, we systematically reveal the origin, evolution, and thermal controlling factors of geothermal fluids in this region. The results indicate that the geothermal water in Laiyuan is of the HCO3–Ca–Mg type with low mineralization, which is controlled by carbonate rock weathering. The average temperature of the thermal reservoir estimated by the quartz geothermometer is 48.5 °C with a circulation depth of approximately 1363 m. Hydrogen and oxygen isotope data indicate that geothermal water originates from atmospheric precipitation, which undergoes deep circulation after vertical infiltration through karst fissures. Upon heating at depth, it ascends along compressional-torsional fault zones, thereby forming a regional thermal anomaly. Hydrothermal coupling modeling further confirms that groundwater flow in karst aquifers significantly controls the distribution of the geothermal field, while conductive faults serve as the main thermal pathways and demarcate the temperature field boundaries. The thermal reservoir volume method estimates the geothermal resources in the study area to be approximately 5.50 × 1015 kJ, indicating considerable exploitation potential. However, extraction schemes must be optimized based on geological conditions to delay thermal breakthrough. This study elucidates the genetic mechanism and heat accumulation model of the Laiyuan karst geothermal system, providing a scientific basis for the exploration and sustainable development of geothermal resources.