Geothermal resource development and reservoir dynamics in Tianjin, China

Geothermal reservoir dynamic monitoring and research serve as the key scientific foundation for optimizing resource development, ensuring sustainable utilization, and mitigating exploitation risks. This paper systematically compiles nearly 50 years of geothermal utilization demand and management policies in Tianjin, along with data on application scenarios, extraction/injection volumes, thermal reservoir water levels, hydrochemical components, wellhead temperatures, and thermal reservoir temperatures for both porous (e.g., Guantao Formation) and fractured (e.g., Wumishan Formation) reservoirs. It analyzes the relationships among market demand, policy regulation, and the dynamic characteristics of reservoir resources. The findings indicate: (1) Reduced consumption is the direct cause of the shift from declining to recovering water levels. Although porous and fractured reservoirs respond synchronously, their patterns differ. In porous reservoirs, abrupt shutdowns of unlicensed wells led to a sharp decline in non-reinjected extraction, causing water levels to transition from rapid decline to rapid and then slow recovery (a "V"-shaped response). In contrast, fractured reservoirs exhibited gradual consumption reduction due to sustained reinjection increases, resulting in a shift from slow decline to slow and then rapid recovery (a "U"-shaped response). (2) Hydrochemical components in both reservoirs remained stable, with no significant alteration to the subsurface chemical environment, though calcium carbonate scaling in some wells impaired reinjection efficiency. (3) Overly low reinjection temperatures in porous reservoirs risked cold front migration from injection wells, posing thermal breakthrough threats, whereas fractured reservoirs maintained stable temperatures—especially near deep conductive faults, demonstrating high exploitation potential due to deep heat sources. Tianjin’s large-scale reinjection practices hold significant implications for reestablishing thermal reservoir equilibrium, offering valuable insights for sustainable geothermal development in similar regions.