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Objective In order to accomplish the objective of sustainable development and utilization of geothermal energy, it is imperative to elucidate the optimal production-reinjection well spacing considering varying quantities and temperatures of reinjection. Methods The thermal reservoir of the Guantao Formation in northern Shandong Province is selected as the research subject, and a conceptual model and mathematical model for layered thermal reservoir development are established. COMSOL Multiphysics multifield coupling simulation software is employed to develop a geothermal production-reinjection well spacing calculator. The accuracy of the model is validated through parameter fitting and simulation results. Results Based on the software APP development function, which is guided by the input of ordinary users, the relevant parameter input was simplified for ease of use, leading to the establishment of an application for calculating geothermal production-reinjection well spacing. In contrast to previous studies that solely focused on production-reinjection well spacing, this study calculates optimal spacings under various conditions to meet real-world operational needs. The results indicate that the optimal production-reinjection well spacings, without experiencing thermal breakthrough are 290, 330, 360 m and 390 m at flow rates of 40, 60, 80 and 100 m3/h respectively. Conclusion In the layered conductive sandstone thermal reservoir area of northern Shandong, a reliable geothermal production-reinjection well-spacing calculator was developed through simplification of the conceptual model and credible numerical simulation results. Hydrothermal numerical simulation serves as a robust approach to determine rational production-reinjection well spacings, which are crucial parameters for geothermal development and utilization projects including exploitation quantity, recharge quantity, injection temperature, and production-reinjection well spacing. These determinations contribute to the sustainable development and utilization of geothermal resources.

Objective To establish a series of hydrogeological parameter for karst areas in North China, an on-site experimental study on water balance has been carried out since the 1980s in a closed spring-drainage karst water system in Yangzhuang, Shandong Province. Methods Based on long-term field observations of water balance elements spanning more than 40 years, the formulas for calculating precipitation infiltration recharge coefficients in bare, semi-covered and covered karst areas were derived. The correlation equations of the precipitation infiltration recharge coefficient α with precipitation P and water table depth D, as well as the series of adjustable maximum precipitation infiltration recharge coefficients in karst areas, were also established. The processes of precipitation infiltration and recharge and the mechanism of α change were explored. Results The results showed that α varied with D. Each rainfall segment P corresponded to a maximum precipitation infiltration recharge coefficient αmax and a maximum precipitation infiltration recharge volume, namely, the recharge limit Gmax, while the corresponding depth of water table was the optimal depth of water table Dcritical. When D was greater than Dcritical, the interception of the vadose zone increased with increasing water table depth and α was less than αmax.When D was less than Dcritical, the surface runoff increased with decreasing water table depth and α was less than αmax. Different rainfall segments corresponded to different Dcritical, and the corresponding αmax and Dcritical increased with increasing precipitation. At any water table depth, Gmax was constant and equal to the difference between the critical rainfall of saturation excess runoff and the maximum interception volume of vadose zone. Conclusion This study addressed the key scientific issues related to precipitation infiltration recharge in karst areas and improved the research level of karst water resources in North China.

Abstract To study the evolution rules and behaviors of heat transport in a sandstone geothermal reservoir caused by cooled water reinjection, this research focuses on the quantitative relationship among reinjection parameters and the thermal breakthrough time of production wells. The permeation, tracer, and reinjection tests were conducted in a simulation model using a large sand tank in conjunction with the numerical simulation method based on COMSOL Multiphysics. Subsequently, sensitivity analysis and nonlinear fitting were performed to investigate the effects of fluid viscosity and density on the reinjection process, and to analyze the impact of reinjection parameters on the thermal breakthrough time of production wells, along with their underlying mechanisms and law. The results indicate that the migration velocity of reinjection water is greater in coarse sand layer compared to that in medium sand layer, and the thermal breakthrough time t is linearly correlated with reinjection rate (Q) raised to the power of − 0.85, temperature difference (ΔT) raised to the power of − 0.21, and spacing between the production and reinjection wells (R) raised to the power of 1.4. The correlation equation and analysis show that when the temperature difference between production and reinjection ΔT is more than 30 ℃, the influence of ΔT on the thermal breakthrough time of production well becomes weak, because ΔT exerts an effect on the thermal breakthrough time of production well t by influencing the relative position of the 18.5 ℃ isotherm in the temperature transition region. The error in reinjecting high-temperature fluid into low-temperature fluid may be corrected by introducing a viscosity correction coefficient α μ.

From 2019 to 2021, we constructed two high-productivity geothermal wells with wellhead temperatures of 109.2 and 123.4°C in the Gaoyang geothermal field. Based on the two wells, it was proved that Gaoyang is a medium-temperature carbonate geothermal field with great development potential. The article reported the latest exploration achievements of deep buried hill geothermal resources in the geothermal field. The productivity of D34 and D35 geothermal wells were evaluated by James end-pressure method: the total flow of steam–water mixture was 234.59–331.92 (t/h), the dryness was 1.36–2.03%, and the single-well power generation potential was 2.10–2.55 MW. Combined with those results, the heat control factors and heat accumulation mechanism of the deep carbonatite geothermal field were confirmed. The westward subduction of the Pacific plate caused obvious damage to the eastern North China Craton and greatly reduced the thickness of the lithosphere and crust. This process facilitated the conduction of mantle-derived heat to shallow crust. Deep strike-slip faults (e.g., Maxi fault) cut through the lithosphere, leading the deep mantle-derived heat and magma to migrate into the crust. The heat accumulated from the depression with low thermal conductivity to the uplift with high thermal conductivity. Groundwater was heated up by deep cycle and convection along faults. The catchment of regional karst groundwater also had a certain effect on the heat accumulation. The Gaoyang geothermal field was formed by these factors.

AbstractThere are 1,000 geothermal wells with depths of 1500–2000 m drilled into the upper Tertiary sandstone geothermal reservoir in the Guantao Formation in the North Shandong Plain, which support about 61 million square meters of domestic space heating. Concerning the large-scale exploitation of the Guantao Formation geothermal reservoir and its important role in clean space heating, it is essential to fully understand the characteristics of the geotemperature, geothermal water flow, and hydrochemical features, especially the heat accumulation and geothermal water enrichment mechanism. Based on the data from pumping tests, temperature logging, water level measurements, and hydrochemistry and isotope sampling and analysis, in this study, the heat sources and accumulation, water sources, and enrichment mechanism of the sandstone geothermal reservoir in the Guantao Formation were explored. The geothermal gradient of the cap rocks and the reservoir’s temperature revealed that the geothermal temperature fields are controlled by fault structures, and the relative high temperature zones are distributed in the area where the uplifts and deep heat-controlled faults converge. The geothermal water-rich area is located in the ancient river channel zone. The closer the water-rich area is to the ancient river channel belt, the deeper and coarser the buried conglomerate aquifer is, and the better the water-rich condition is. The best water-rich areas are found in the alluvial fan of the ancient channel belt.

Previous studies have shown that on the surface, Jiaobei uplift and Weihai uplift have higher heat flow values than Jiaolai depression. However, the mechanism by which the deep heat flow migrates and the exposure of geothermal resources are still unclear. In this study, the geothermal field distribution, thermal conductivity, temperature logging data, and chemical composition of the geothermal fluid in the Jiaodong Peninsula were analyzed. Regarding the thermal field’s characteristics and their controlling factors, a conceptual model of heat flow diversion-accumulation between the uplift and basin areas in the Jiaodong Peninsula is proposed. The lithology of the uplift area is mainly composed of intrusive rocks and metamorphic rocks with high thermal conductivities. The lithology of the basin mainly consists of sandstone with a low thermal conductivity. The bottom of the basin, which has a low thermal conductivity and low permeability, serves as a heat insulation and water insulation roof, which causes the heat flow and the heat-carrying fluids and gases from the deep crust to be refracted and redistributed at the bottom of the basin area. As a result, the bottom of the uplift areas has a higher heat flow. In particular, the axial position in the uplift area has the highest heat flow. In addition, the geothermal resources in the Jiaodong Peninsula are mainly distributed in the V-shaped area where the upper block of the NE- and NW-trending faults intersect, and the scope of the exposure of the geothermal resources is very limited.

Studying the flow path of geothermal water in geothermal fields is an important basis for the scientific development and management of geothermal resources. However, due to the influence of engineering volume, economic benefits and demand, it is very difficult to fully grasp the flow path of deep geothermal water in large areas. The use of hydrogeochemical tracers to determine the flow path of geothermal water is a scientific and effective research method. In order to accurately describe the flow path of carbonate geothermal water in the Xiong’an New Area and its surrounding areas, this study systematically analyzed the 14C, 18O, and 2H data of carbonate and Cenozoic sandstone geothermal water, Quaternary groundwater, as well as mountain spring water of the study area. Based on these results, we can conclude that 1) The 14C, d, and 18O values are favourable clues for indicating the circulating runoff conditions and runoff paths of geothermal water. 2) The salinity of the Xushui-Wenan and Lilan transfer zone are 3 g/l, the 14C values are higher than 40,000 years, the d value is lower, and the phenomenon of “18O drift” is obvious, all these indicating that the tectonic sites are the convergence areas of regional karst geothermal water, featured by relative high temperature. 4) The hydrochemical indicators combined with previous carbonate groundwater flow field indicate that the recharge of carbonate geothermal water in the Xiong’an New Area may not only drive from the western Taihang Mountains, but also along the Xushui-Wenan transfer zone and the Lilan fault, with the recharge of carbonate groundwater from the Cangxian uplift from east to west. By further identifying and defining the dominant flow path and supply direction of carbonate geothermal water in the Xiong’an New Area and surrounding areas, it provides strong support for the scientific development of regional carbonate geothermal water.

The Chazi geothermal field area is located in the large region of Shigatse in southern Tibet. The geothermal resources in this area are abundant, but their exploitation and utilization are low. By studying the water chemistry and isotope characteristics of geochemical fluids in the study area, information on water chemistry, heat storage temperature, recharge source, recharge elevation, and circulation depth was obtained. These results provide a scientific theoretical basis for improving the genetic mechanism of high-temperature geothermal systems in the study area. The type of geothermal fluid hydrochemicals in this area is mainly HCO3–Na. The isotopic geochemical method was used to determine that the recharge source of geothermal fluids was atmospheric precipitation, and the recharge elevation was 5200–6000 m. The geochemical thermometer, Na–K–Mg equilibrium diagram, and silica-enthalpy mixed model indicated the shallow and deep thermal storage temperatures of approximately 150 and 200°C, respectively, and the average circulation depth of 1163.38 m in the study area. Combined with the fracture structure and magmatic activity characteristics of the southwest Qinghai-Tibet Plateau, the source, storage, cover, and general situation of the area were preliminarily summarised, and the conceptual model of geothermal origin was established. The results can provide a scientific theoretical basis for the mechanism of high-temperature geothermal systems and subsequent drilling and resource development.

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