Efficient reinjection is critical for maintaining reservoir pressure and ensuring the sustainable development of sandstone geothermal systems. However, complex thermal–hydraulic–chemical (THC) interactions often lead to progressive permeability reduction, significantly impairing injection performance. This study systematically investigates the coupled effects of injection flow rate, temperature, and suspended particle size on permeability evolution during geothermal reinjection. Laboratory-scale core flow-through experiments were conducted using sandstone samples from the Guantao Formation in the Huanghua Depression, Bohai Bay Basin. The experimental schemes included graded flow rate tests, temperature-stepped injections, particle size control, long-term seepage, and reverse-flow backflushing operations. The results reveal that permeability is highly sensitive to injection parameters. Flow rates exceeding 6 mL/min induce irreversible clogging and pore structure damage, while lower rates yield more stable injection behavior. Injection at approximately 35 °C resulted in a permeability increase of 15.7%, attributed to reduced fluid viscosity and moderate clay swelling and secondary precipitation. Particles larger than 3 μm were prone to bridging and persistent clogging, whereas smaller particles exhibited more reversible behavior. During long-term seepage, reverse injection implemented upon permeability decline restored up to 98% of the initial permeability, confirming its effectiveness in alleviating pore throat blockage. Based on these findings, a combined reinjection strategy is recommended, featuring low flow rate (≤5 mL/min), moderate injection temperature (~35 °C), and fine filtration (≤3 μm). In addition, periodic backflushing should be considered when permeability loss exceeds 30% or a sustained injection pressure rise is observed. This study provides robust experimental evidence and practical guidance for optimizing geothermal reinjection operations.

Geothermal resources are abundant in China and are distributed mainly in the eastern region where energy demand is high, especially in Tianjin. However, a significant disparity remains between the actual heating area and the potential heatable area of geothermal resources in Tianjin, which indicates the vast untapped potential for development and utilization in the region. In this study, we reviewed the history and current status of geothermal development in Tianjin. We further analyzed the factors affecting the development and utilization of geothermal heat in Tianjin. Subsequently, we constructed a system dynamics (SD) model of geothermal development and utilization in Tianjin. We developed four scenarios, including baseline, policy incentives, technological progress, and economic inputs. The results of the multiscenario forecasts and sensitivity analyses of the SD model showed the following: Tianjin will go through four stages of geothermal development and utilization in the future. Policy support and economic investment were the two main factors influencing the development of geothermal energy, and the influence of technological progress was comparatively smaller. Based on the above results, we proposed recommendations to promote sustainable development of geothermal energy in Tianjin according to three aspects: policy mechanism, economic investment, and technological progress.

This study investigated the formation mechanism of the Kahui Geothermal Field in Western Sichuan, China, using geophysical and geochemical approaches to elucidate its geological structure and geothermal origins. This study employed a combination of 2D and 3D inversion techniques involved in natural electromagnetic methods (magnetotelluric, MT, and audio magnetotelluric, AMT) along with the analysis of hydrogeochemical samples to achieve a comprehensive understanding of the geothermal system. Geophysical inversion revealed a three-layer resistivity structure within the upper 2.5 km of the study area. A geological interpretation was conducted on the resistivity structure model, identifying two faults, the Litang Fault and the Kahui Fault. The analysis suggested that the shallow part of the Kahui Geothermal Field is controlled by the Kahui Fault. Hydrochemical analysis showed that the water chemistry of the Kahui Geothermal Field is of the HCO₃−Na type, primarily sourced from atmospheric precipitation. The deep heat source of the Kahui Geothermal Field was attributed to the partial melting of the middle crust, driven by the upwelling of mantle fluids. This process provides the necessary thermal energy for the geothermal system. Atmospheric precipitation infiltrates through tectonic fractures, undergoes deep circulation and heating, and interacts with the host rocks. The heated fluids then rise along faults and mix with shallow cold water, ultimately emerging as hot springs.

The magnetotelluric sounding (MT) method is used to detect and study the deep stratigraphic structure and hidden faults in the Shangqiu Uplift. A total of 4 MT profiles are arranged, and 97 stations are collected. The nonlinear conjugate gradient (NLCG) two-dimensional inversion method is used to jointly invert data from both the TE and TM modes after a dimensionality analysis and impedance tensor decomposition; reliable two-dimensional resistivity models are produced since the data quality is excellent. Three-dimensional inversion is carried out to full impedance tensor as well to produce a three-dimensional resistivity model of the study area, which shows good consistency with the two-dimensional models. The results show that the electrical structure of the Shangqiu Uplift has typical layered characteristics, which can be divided into three layers from top to bottom, namely low-, medium-to-high-, and high-resistivity layers. According to the resistivity models and in combination with the gravity, aeromagnetic, seismic, and regional geological data of the study area, a geological map of the basement rock of the Shangqiu Uplift is produced. Two prospective geothermal anomaly areas are proposed according to the distribution of the high-resistivity anomaly formed by the basement uplift, which has a good corresponding relationship with the high-value area of the regional geothermal field. A geothermal exploration well (SR-1) is constructed in one of the inferred prospective geothermal anomaly areas. The well is 1702 m deep, with a water output of 1500 m³/day and a wellhead water temperature of 51.5 °C. This is the geothermal well with the largest water yield in the Shangqiu area at present, which provides a new basis for future geothermal exploration, development, and utilization.

Geothermal resources are abundant in the Southern North China Basin, which is one of the prospective areas hosting low–medium-temperature geothermal resources in sedimentary basins in China. The purpose of this work is to reveal the formation and storage conditions of the geothermal resources in the western margin of the Taikang Uplift and delineate the range of potential geothermal reservoirs. This paper uses five magnetotelluric sounding profiles for data processing and analysis, including the calculation of 2D skewness and electric strike. Data processing, analysis, and NLCG 2D inversion were performed on MT data, which consisted of 111 measurement points, and reliable two-dimensional resistivity models and resistivity planes were obtained. In combination with drilling verification and the analysis of geophysical logging data, the stratigraphic lithology and the range of potential geothermal reservoirs were largely clarified. The results show that using the magnetotelluric sounding method can well delineate the range of deep geothermal reservoirs in sedimentary basins and that the MT method is suitable for exploring buried geothermal resources in deep plains. The analytical results showed that the XZR-1 well yielded 1480 cubic meters of water per day, with the water temperature of the wellhead being approximately 78 °C, and combined with the results of this electromagnetic and drilling exploration, a geothermal geological model and genesis process of the west of the Taikang Uplift area was constructed. The water yield and temperature were higher than those of previous exploration results, which has important guiding significance for the future development and utilization of karst fissure heat reservoirs in the western Taikang Uplift.