Yanguang Liu

A typical high-temperature metamorphic rock geothermal reservoir was newly discovered in the Tianzhen geothermal field in Datong City, China. However, due to the complex geological structure and thermal properties, the seepage heat transfer mechanism of metamorphic rock reservoirs is still unclear, seriously impeding the efficient development and sustainable utilization of geothermal resources. This study established a percolation-heat transfer model through tracer testing and numerical simulation to reveal the percolation mode and heat transfer mechanism of high-temperature metamorphic rock reservoirs during the reinjection process. We also predicted the distribution characteristics of various physical fields in the geothermal reservoir after the geothermal system has been in operation for 100 a, analyzed the influence of different reinjection schemes on seepage heat transfer in the geothermal reservoir, and proposed an optimization strategy for the reinjection scheme. The results show that: (1) The connectivity between production and injection wells is poor, and there are water-conducting fractures connecting the shallow and bottom layers; (2) The seepage channels through fractures guide the migration of the reinjected fluid and form a cold front surface with a protruding shape towards the mining well in the temperature field, resulting in temperature changes in the production well; (3) Seepage heat transfer in thermal reservoirs is greatly affected by the reinjection flow rate and the distance between production and reinjection wells, but less by the reinjection temperature. As the reinjection temperature drops, the flow rate increases, the well spacing decreases, and the temperature variation range of the production well becomes greater; (4) Under the current reinjection test conditions, the temperature of the mining well decreased by approximately 4°C after 100 a of geothermal reinjection operation, and a thermal breakthrough occurred at 78 a. Under the condition of maintaining a reinjection flow rate of 60 m3/h and a reinjection temperature of 80°C unchanged, the well spacing should be no less than 470 m to ensure that the well temperature does not cause a thermal breakthrough during the reinjection operation for 100 a. This research provides a theoretical basis and optimization methods for the efficient development of high-temperature metamorphic rock thermal reservoirs.

Mid-deep geothermal reinjection technology is crucial for the sustainable development of geothermal resources, which has garnered significant attention and rapid growth in recent years. Currently, various geothermal reinjection technologies lag behind, lacking effective integration to address issues like low reinjection rates and thermal breakthrough. This paper reviews the basic principles and development history of mid-deep geothermal reinjection technology, focusing on various technical methods used in the process and analyzing their applicability, advantages, and disadvantages under different geological conditions. It highlights the unique challenges posed by deep geothermal resources, including high temperature, high pressure, high stress, chemical corrosion, and complex geological structures. Additionally, it addresses challenges in equipment selection and durability, system stability and operation safety, environmental impact, and sustainable development. Finally, the paper explores future directions for mid-deep geothermal reinjection technology, highlighting key areas for further research and potential pathways for technological innovation. This comprehensive analysis aims to accelerate the advancement of geothermal reinjection technology, offering essential guidance for the efficient reinjection and sustainable development of geothermal resources.

This paper focuses on the study of the evolutionary mechanism governing the temperature field of geothermal reservoir under low-temperature tailwater reinjection conditions, which is crucial for the sustainable geothermal energy management. With advancing exploitation of geothermal resources deepens, precise understanding of this mechanism becomes paramount for devising effective reinjection strategies, optimizing reservoir utilization, and bolstering the economic viability of geothermal energy development. The article presents a comprehensive review of temperature field evolution across diverse heterogeneous thermal reservoirs under low-temperature tailwater reinjection conditions, and analyzes key factors influencing this evolution. It evaluates existing research methods, highlighting their strengths and limitations. The study identifies gaps in the application of rock seepage and heat transfer theories on a large scale, alongside the need for enhanced accuracy in field test results, particularly regarding computational efficiency of fractured thermal reservoir models under multi-well reinjection conditions. To address these shortcomings, the study proposes conducting large-scale rock seepage and heat transfer experiments, coupled with multi-tracer techniques for field testing, aimed at optimizing fractured thermal reservoir models' computational efficiency under multi-well reinjection conditions. Additionally, it suggests integrating deep learning methods into research endeavors. These initiatives are of significance in deepening the understanding of the evolution process of the temperature field in deep thermal reservoirs and enhancing the sustainability of deep geothermal resource development.

Underground Thermal Energy Storage (UTES) store unstable and non-continuous energy underground, releasing stable heat energy on demand. This effectively improve energy utilization and optimize energy allocation. As UTES technology advances, accommodating greater depth, higher temperature and multi-energy complementarity, new research challenges emerge. This paper comprehensively provides a systematic summary of the current research status of UTES. It categorized different types of UTES systems, analyzes the applicability of key technologies of UTES, and evaluate their economic and environmental benefits. Moreover, this paper identifies existing issues with UTES, such as injection blockage, wellbore scaling and corrosion, seepage and heat transfer in cracks, etc. It suggests deepening the research on blockage formation mechanism and plugging prevention technology, improving the study of anticorrosive materials and water treatment technology, and enhancing the investigation of reservoir fracture network characterization technology and seepage heat transfer. These recommendations serve as valuable references for promoting the high-quality development of UTES.

Deep geothermal reservoirs have great potential for exploitation and are characterized by high temperatures, high stress, and strong heterogeneity. However, these reservoirs contain widely and continuously distributed dominant flow channels with high permeability, predisposing these reservoirs to the formation of dominant flow, which notably decreases the efficiency of heat extraction. Focusing on the dominant flow in fractures, this study provides a definite concept, systematically reviews current studies, and puts forward suggestions for future research. It is expected that this study will serve as a reference for the sustainable, high-quality development of deep geothermal resources.

The conglomeratic reservoirs of the Permian Wutonggou Formation in the Yingyeer area of the Turpan–Hami Basin are key petroliferous horizons, with enormous potential for hydrocarbon exploration. Existing studies on the conglomeratic reservoirs in this area mainly focus on the sedimentary environment and sand body distribution, while few of them concern the diagenesis and evolution of the conglomeratic reservoirs, leading to deficient knowledge about relevant mechanisms. By comprehensively utilizing the data from ordinary and casting thin section identification, the x-ray diffraction analysis of whole rock and clay, scanning electron microscopy, and other analyses and assays, this study analyzed and investigated the petrological characteristics, diagenetic types, and characteristics, and diagenetic evolutionary stages and mechanisms of the conglomeratic reservoirs of the Permian Wutonggou Formation in the Yingyeer area. The study results are as follows. Under the influence of sedimentary provenances, tectonic evolution, and paleogeomorphology, the conglomeratic reservoirs of the Permian Wutonggou formation have low clastic grain maturity and low structural maturity, suggesting proximal provenances. The reservoirs are subjected to various diagenesis, including carbonate cementation, which fills pores and throats; compaction as a major factor leading to poor reservoir quality, and dissolution, which significantly improves the reservoir properties. The conglomeratic reservoirs in the Wutonggou formation are generally in substage A of the middle diagenetic stage. The diagenetic evolution of the reservoirs generally underwent early mechanical compaction, calcite precipitation, secondary quartz overgrowth, the injection of organic fluids, the dissolution of feldspars and lithic grains, the transformation of clay minerals, and calcite cementation in sequence. Hydrocarbon charging mainly occurred during the late Middle Jurassic and was greatly influenced by early compaction and dissolution.

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。

The precise exploration of the characteristics of geothermal fields in sedimentary basins, such as the temperature and burial depth of their deep geothermal reservoirs, is of great significance for improving the probability of penetration and reducing exploration risks and development costs. This study proposed a joint exploration method combining magnetotelluric (MT) sounding and geothermometers. Using this method, this study estimated the geothermal reservoirs’ temperature and the circulation depth of geothermal water in the Xianxian geothermal field, a typical geothermal field in a large sedimentary basin in northern China, and prepared the temperature and depth maps of the geothermal reservoirs. The main results are as follows. First, the bedrock’s geothermal reservoirs with karst fissures in the Xianxian geothermal field have great potential for development. Among them, geothermal reservoirs in the Jixianian Wumishan formation have a top depth of 1100–1500 m and a thickness of 700–1700 m, and the geothermal reservoirs in the Jixianian Gaoyuzhuang formation have a top depth of 3700–4000 m and a maximum drilled thickness of 400 m. The geothermal reservoirs of the Xianxian geothermal field mainly have medium and low temperatures of 138–160 °C and the circulation depth of the geothermal water is 5873 m.

The hydrogeochemical characteristics and isotopic analyses of geothermal water are effective in the genetic study of a geothermal system. This study systematically investigated the geochemical and isotopic compositions of the geothermal water in the Qutan and Reshuizhou geothermal fields. The geothermal water in these two fields is of HCO₃ (·F)-Ca·Na type and has undergone protracted water runoff and deep thermal cycle. Based on the mineral-water solubility equilibrium, the reservoir in the Qutan geothermal field has a temperature of 60–74°C and a depth range of 770–1003 m. The geothermal water in the Reshuizhou geothermal field has been mixed with cold water, which accounts for 58% in weight. The reservoir in the Reshuizhou geothermal field has a temperature range of 131-150°C and a depth range of 1953–2287 m. The geothermal water in the Qutan and Reshuizhou geothermal fields have ¹⁴C ages of 8251–7961 BC and 3514–2254 BC, respectively, which are consistent with the result of the ³H isotopic analyses. When recharging and transiting to geothermal water, the meteoric water underwent changes in geochemical compositions, which were dominantly controlled by water-rock interactions, including the precipitation of chalcedony and muscovite and the dissolution of calcite, fluorite, K-feldspar, and albite. In the Reshuizhou geothermal field, the hydrogeochemical compositions of the geothermal water are affected by cold water mixing.