Archive

2024, Volume 31 Issue 6
25 November 2024 Previous Issue    Next Issue

---

For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Select

The thermal status of China’s land areas and heat-control factors WANG Guiling, LIN Wenjing 2024, 31(6): 1-18.  DOI: 10.13745/j.esf.sf.2024.10.13 Abstract ( 489 )   HTML ( 29 )   PDF (10722KB) ( 338 )   The thermal state of a region is crucial for understanding the main source of geothermal heat flow in the region, which help to solve the basic problem of regional heat source, and provide a basis for the study of the regional geothermal resources. Based on the regional geothermal measurements and deep borehole temperature logging carried out in China in recent years, this paper analyzes the crust-to-mantle heat flow ratio in China’s land area and divides the land area into four geothermal zonal types, namely high-temperature geothermal zone with a crustal heat source, medium- and low-temperature geothermal zone with a mantle heat source, low-temperature geothermal equilibrium zone with a crust-mantle heat source, and medium- and high-temperature geothermal equilibrium zone with a crust-mantle heat source. On this basis, typical geothermal zones—such as the northeastern Tibetan Plateau, the Tengchong area, the southeastern coastal area, and the North China Basin—are selected to systematically analyze the basin-scale regional thermal state and its main controlling factors, such as the characteristics of the regional geothermal field, the distribution of heat flow, and the crustal-mantle thermal structure. The paper summarizes the deep and shallow geologic factors affecting the regional thermal state—including crust-mantle architecture, tectono-thermal events, stratigraphic lithology, fracture structure, etc.—and establishes multilevel controlling factors of regional thermal states, providing a scientific basis for the geothermal resource exploration and heat source condition analysis in different regions. Figures and Tables | References | Related Articles | Metrics

Select

Recent advances in heat flow measurement and new understanding of terrestrial heat flow distribution in terrestrial areas of China LIU Feng, WANG Guiling, JIANG Guangzheng, HU Shengbiao, ZHANG Wei, LIN Wenjing, LIU Jinhui, ZHANG Xinyong, QU Zewei, LIAO Chuanzhi 2024, 31(6): 19-30.  DOI: 10.13745/j.esf.sf.2024.7.8 Abstract ( 375 )   HTML ( 17 )   PDF (6577KB) ( 167 )   Terrestrial heat flow is a key parameter in geothermal researches. Building upon the analyses of previously compiled terrestrial heat flow data, this paper examines the newly measured (260 sets), collected and screened (112 sets) data by authors since 2016. The added heat flow data effectively filled large data gaps in the southwest, northwest and northeast and improved the data density in the eastern region of China mainland. The proportion of high-quality data was improved to 86.3%. Using the latest data the calculated average terrestrial heat flow in China was 63.8 mW/m2, higher than the national average value in the fourth compilation, with higher average values found for most of the primary and secondary tectonic units of China and lower values for the Qinghai-Tibet Plateau. The statistics of heat-flow data of typical geothermal systems showed that high average heat flow conditions could significantly improve the distribution range of conductive geothermal resources and the output temperature of hot springs, but were not a controlling factor for the formation of the two types of geothermal resources. Based on the latest terrestrial heat flow data and contour map of China related phenomena and problems were discussed, such as the increase of low heat flow area in the Qinghai-Tibet Plateau, the “overestimation” of early heat flow data in the North China Plain, and the existence of heat flow indicator magma sacs in the Changbai Mountain. It was noted that heat flow monitoring stations in China were still relatively few, and, with the continuous updating and standardization of the measurement methods, plus further improvements in data quantity/quality and sampling locations, the previously assessed regional heat flow characteristics might need to be re-examined. This study deepens the understanding of the status of terrestrial heat flow in China, and can provide better support for regional geothermal basic research and resource exploration. Figures and Tables | References | Related Articles | Metrics

Select

Formation of high-temperature geothermal reservoirs in central and eastern North China KANG Fengxin, ZHANG Baojian, CUI Yang, YAO Song, SHI Meng, QIN Peng, SUI Haibo, ZHENG Tingting, LI Jialong, YANG Haitao, LI Chuanlei, LIU Chunwei 2024, 31(6): 31-51.  DOI: 10.13745/j.esf.sf.2024.7.9 Abstract ( 391 )   HTML ( 9 )   PDF (13899KB) ( 229 )   High-temperature geothermal reservoirs with temperature above 150 ℃ have been successively discovered in China—mainly in southern Tibet, Yunnan and Sichuan in the Mediterranean-Himalayan geothermal belt, and Taiwan in the Pacific Rim geothermal belt. In recent years breakthroughs in high-temperature geothermal prospecting have also been made in cental and eastern North China. For example, in 2019 in Hebei, granite dry hot rock mass with a temperature of 151 ℃ was drilled at a depth of 4000 m in Matouying. In 2020, a geothermal fluid of 167 ℃ in high temperature gneiss fissure reservoir was drilled at 1586 m depth in Tianzhen County, Shanxi Province. And in 2023 in Shandong, a high-temperature Ordovician limestone karst reservoir with a temperature of 167.5 ℃ was drilled at 4283 m depth in Zhuanxi area, Dongying City. It is therefore an urgent task to systematically study the formation of high-temperature geothermal reservoirs in this region as well as related exploration technologies. Taking the above three high-temperature geothermal fields as examples, this paper analyzes the dynamic process underlying the effect of regional crust-mantle structure, deep geological processes—such as crust-mantle upwelling and Moho uplift-on the shallow high-temperature thermal anomalies in the Earth’s crust. Combined with geophysical and geochemical studies and exploration results, this paper explains how deep geodynamic processes shape the Earth’s shallow geothermal field and constrain high-temperature thermal anomalies, and discusses technologies to identify deep heat sources, upwelling channels and thermal energy gathering structures. The paper also explores the formation mechanism of high-temperature geothermal reservoirs in typical locations and its significance for high-temperature geothermal exploration in central and eastern North China. Briefly, (1) under the far field effect of the India-Eurasia plate collision and subduction retreat of the Western Pacific plate, the destruction of the North China Craton (NCC) leads to deep geodynamic processes—such as lithospheric thinning, asthenospheric upwelling and thermal erosion, extensional rift basin and deep strike-slip fault development—which are the main driving forces behind the upwelling of mantle-derived molten material to the shallow crust. (2) There is a good corresponding relationship between a high conductivity-low velocity-low resistivity body, geochemical evidence and high-temperature geothermal resource distribution. Therefore, it is believed that the upward infiltration of molten materials causes shallow thermal anomalies, and the molten/semi-molten magma sac in the crust provides a stable heat source to form high-temperature geothermal reservoirs. The weak lithospheric structures-such as plate margin zones and deep strike-slip faults—cut into the lithosphere, constituting the main channels for the upward infiltration of the molten material. (3) The concave-convex tectonic pattern and groundwater flow field mainly control the heat distribution in the shallow crust. Under the “thermal refraction” effect driven by the difference in thermal conductivity of shallow rocks, heat flow accumulates from the sag to the uplift, forming high-temperature thermal anomalies in ancient buried hills. Figures and Tables | References | Related Articles | Metrics

Select

Dominant heat transfer mechanism in buried-hill reservoirs in North China: A case study in Xiong’an new area WANG Guiling, MA Feng, ZHANG Wei, ZHU Xi, YU Mingxiao, ZHANG Hanxiong, LUO Cheng 2024, 31(6): 52-66.  DOI: 10.13745/j.esf.sf.2024.7.10 Abstract ( 515 )   HTML ( 8 )   PDF (6525KB) ( 133 )   Buried-hill reservoirs are the primary geothermal reservoirs widely developed in northern China. They are characterized by significant heat storage capacity, shallow depth, and easy re-injection. The reservoirs, constrained by their physical properties, spatial distribution, and geological structures, have diverse heat control mechanisms and complex heat transfer processes, and recent research is focused on the heat transfer and accumulation mechanisms. In this paper, based on the analysis of geothermal exploration wells constructed in Xiong’an, we propose a theory of dominant heat transfer in the buried-hill geothermal field of North China. According to this theory, the heat source of the buried-hill reservoirs originates mainly from the deep mantle, while the crustal heat flow is less than 30 mW/m. The enhanced mantle convection from the destruction of the North China Craton (NCC) leads to dominant heat flow from the deep mantle to shallower depths, and with the tensile thinning of the lithosphere in the NCC the surface heat flow increases significantly. The high thermal conductivity buried-hill reservoirs creates conductive dominant heat flow, vertically and horizontally, towards the carbonate reservoirs, while fluid circulation in the highly porous carbonate reservoirs creates convective dominant heat flow. Faulting exacerbates the conduction and convection heat gathering effect along the fault direction. The temperature profiles of boreholes at various sites in the buried hill exhibit five types: conduction, conduction-convection-conduction, conduction-convection-weak convection, conduction-strong convection, and conduction-weak convection. The percentage of thermal convection in groundwater in the Rongcheng Fault was calculated to be 29.2%. Through comprehensive analysis of the influencing factors of the dominant heat flow and heat accumulation in the buried-hill geothermal field, this research provides new insights into the heat transfer mechanism in North China. Figures and Tables | References | Related Articles | Metrics

Select

Occurrence rules and enrichment mechanism of geothermal resources in Shandong Province KANG Fengxin, ZHENG Tingting, SHI Meng, SUI Haibo, XU Meng, JIANG Haiyang, ZHONG Zhennan, QIN Peng, ZHANG Baojian, ZHAO Jichu, MA Zhemin, CUI Yang, LI Jialong, DUAN Xiaofei, BAI Tong, ZHANG Pingping, YAO Song, LIU Xiao, SHI Qipeng, WANG Xuepeng, YANG Haitao, CHEN Jingpeng, LIU Beibei 2024, 31(6): 67-94.  DOI: 10.13745/j.esf.sf.2024.10.25 Abstract ( 583 )   HTML ( 7 )   PDF (18362KB) ( 192 )   Shandong Province possesses abundant geothermal resources with widespread distribution of geothermal reserviors of different types. However, the occurrence rules and accumulation mechanism of geothermal resources are not well understood. In this paper, based on previous geothermal well temperature logging, geothermal exploration, well drilling, pumping test and long-term dynamic monitoring data, we explain the distribution characteristics of geothermal resources in Shandong, and delineate the geological structure that controls the geothermal flow and water conduction. The heat and water sources and accumulation mechanisms and the occurrence of thermal reservoirs were explored. Four geothermal resource areas were delineated: eastern Shandong, Yishu fault zone, western Shandong uplift and northwestern Shandong depression. Combining the characteristics of major ore-controlling factors such as geothermal water source, heat source and occurrence of thermal reservoir, the geothermal systems were divided into three models: open-convection-cavity tubular; weakly open-convection/conduction-banded stratified; and closed-convection/conduction-banded stratified. Insights on the heat/water sources and accumulation mechanisms under different types of geothermal systems and the occurrence law of hydrothermal accumulated reservoirs provide a basis for targeted geothermal exploration and well drilling. Figures and Tables | References | Related Articles | Metrics

Select

Carbonates of the Wumishan Formation, Jixian System in the North China Plain: Mechanical properties under in-situ geothermal conditions ZHOU Wei, MA Xiao, CHEN Wenyi, GAO Rui, WANG Yan, HU Dawei 2024, 31(6): 95-103.  DOI: 10.13745/j.esf.sf.2024.7.11 Abstract ( 188 )   HTML ( 2 )   PDF (5420KB) ( 110 )   The uncertainties in the mechanical properties of carbonate rocks under high-temperature, high-pressure in-situ geothermal conditions lead to a lack of accurate data and mechanistic understanding for assessing wellbore stability. In this study, carbonates of the Wumishan Formation of the Jixian System are investigated, and suitable outcrops are identified along the stratum extension direction for sampling purposes. The mechanical properties of the reservoir rocks under the combined effect of high temperature and high pressure are studied, and the mechanism of the effect of temperature on the rock’s mechanical properties is analyzed. The increase in temperature led to a slower growth rate of the strength threshold of carbonate rocks with increasing confining pressure. When the confining pressure increased from 40 to 60 MPa, the peak strength increased by 15.9% at room temperature and only by 7.9% at 150 ℃. Above 110 ℃, the friction angle decreased while cohesiveness increased with increasing temperature. Within the temperature and confining pressure ranges in this study, the observed temperature effect was the result of the temperature-induced enhancement and weakening of rock mechanical properties. Within the studied temperature range, temperature had no effect on the chemical composition of minerals in carbonate rocks, but temperature variation could lead to uneven thermal expansion among different mineral particles, resulting in increased intercrystalline thermal stress and causing micro-fracture compaction between mineral particles. Results from this study provide accurate data and a research basis for wellbore stability analysis in the carbonate thermal reservoirs of the North China Plain. Figures and Tables | References | Related Articles | Metrics

Select

Numerical simulation of hydrothermal cycling process and lithium isotope fractionation in a typical high-temperature geothermal system SHI Honglei, WANG Wanli, WANG Guiling, XING Linxiao, LU Chuan, ZHAO Jiayi, LIU Lu, SONG Jiajia 2024, 31(6): 104-119.  DOI: 10.13745/j.esf.sf.2024.7.12 Abstract ( 396 )   HTML ( 3 )   PDF (11154KB) ( 99 )   Multifield coupling interactions have significant effects on hydrothermal cycles and geothermal fluid chemistry in hydrothermal systems. In this paper, a hydraulic-thermal-chemical (isotope) multifield numerical simulation model is developed using COMSOL-Multiphysics, and the simulation method for lithium isotope fractionation is validated by a simplified profile model. On this basis, a multifield coupling model of the hydrothermal cycle in a typical profile of Yangbajing is established based on the understanding of the hydrothermal cycling process in the Yangbajing geothermal field. Futher, the hydrothermal cycling of the Yangbajing geothermal system and lithium isotope fractionation under water-rock reactions are reproduced, and the influence of the main model parameters on the effect of thermal energy convergence is discussed. The results indicated that high fracture-zone permeability accelerated temperature decline in wall rock near the deep fracture zone, while low permeability limited near-surface hydrothermal activity. After constraining the fracture-zone permeability by surface drainage, it was found that long-lived (nearly 150 ka) high-temperature geothermal features could form near the surface, but only when the fracture zone made direct contact with the deep melt. Provided that such contact occurred and the temperature of the melt heat source remained constant, the depth of the melt had little effect on hydrothermal activity. Prolonged water-rock interactions could lead to significant lithium depletion in the fracture zone, and only when the deep melts provided a continuous source of material for the fracture system could it guarrantee sustained high lithium concentration in geothermal fluids. Based on the lithium isotope fractionation process, the estimated mass fraction of lithium in the involved rocks was ~25—35 mg/kg, and the value of δ7Lirock was ~-2.0‰—0.5‰. The research results contribute to the further understanding of the formation of typical high-temperature geothermal systems. Figures and Tables | References | Related Articles | Metrics

Select

New technologies, methodology and application in directional high-temperature hard rock drilling—a critical review WENG Wei, WU Shuo, HE Yunchao, LIN Wenjing, FENG Meigui, GAN Haonan, LI Xiaodong 2024, 31(6): 120-129.  DOI: 10.13745/j.esf.sf.2024.7.13 Abstract ( 468 )   HTML ( 5 )   PDF (3227KB) ( 143 )   The depth of well drilling has been continuously rising in recent years with the increasing demands for energy resources development and earth systems research. Problems encountered in deep drilling include high formation temperature, high rock hardness, low drilling efficiency, high cost and frequent accidents. Key drilling technologies such as downhole motors, efficient drill bits, measurement-while-drilling tools and mud cooling systems have been researched abroad to address the above problems; the research results have been applied in the fields of oil and gas drilling, high-temperature geothermal exploration, etc. Relevant researches have also been conducted in China, but gap exists compared to the level of research abroad. This paper analyzes the technical difficulties in drilling high-temperature hard rock well in China and summarizes the technical requirements. A new drilling method, along with its technical characteristics and application results, are also introduced. The new method, in principle, seeks to utilize the existing equipments to achieve directional drilling of deep wells. It uses a bottom hole assembly (BHA) consisting of high-speed, strong diameter-retaining tri-con drill bits, high-temperature resistance positive displacement motor (PDM) and measurement-while-drilling (MWD) technique, and combines with high-temperature resistance drilling fluid, mud cooling system and segmented circulating cooling technology. However, future researches are needed in the areas of durable drill bits (e.g., polycrystalline diamond compact (PDC) and impregnated diamond drill bits), all metal downhole motors, impact drilling tools and high-temperature resistance MWD. Figures and Tables | References | Related Articles | Metrics

Select

In-situ stress measurements in hot dry rock, Qinghai Gonghe Basin and simulation analysis of reservoir fracture modification XU Jiading, ZHANG Chongyuan, ZHANG Hao, BAI Jinpeng, ZHANG Shi’an, ZHANG Shengsheng, QIN Xianghui, SUN Dongsheng, HE Manchao, WU Manlu 2024, 31(6): 130-144.  DOI: 10.13745/j.esf.sf.2024.7.14 Abstract ( 382 )   HTML ( 3 )   PDF (11784KB) ( 99 )   China has made some progress in recent years in the exploration and development of hot dry rock (HDR) resources and drilling technology, but is relatively lacking in basic research on high-temperature HDR fracturing technology. For enhanced geothermal systems, hydraulic fracturing is generally used to inject high-pressure fluid into the reservoir to expand and extend natural fractures, in order to increase the reservoir permeability and heat exchange area. Thus, reliable in-situ stress data are important for guiding the stimulation of reservoir reconstruction. Taking the Qinghai Gonghe HDR pilot project as an example, this paper first obtains the in-situ stress state by combining the anelastic strain recovery (ASR), diametrical core deformation analysis (DCDA), core cake, and image logging methods. Next, the influence of the in-situ stress state on the development of HDR reservoirs is discussed. Finally, to evaluate the effectiveness of reservoir fracturing under the current in-situ stress state, a three-dimensional fracture geological model of the hydraulic fracturing zone is established using the discrete fracture network (DFN) method. The sliding tendency (Ts) and dilation tendency (Td) of each fracture are calculated through numerical simulation, and fracturing activities under different injection pressures are analyzed. According to the results, (1) the main type of in-situ stress state was the thrust faulting regime developed within the granite reservoir range (3500—4000 m) in the Gonghe HDR reservoir, with the horizontal compressive stress being the dominant stress. (2) The average direction of the maximum principal stress at 3500—4000 m depth was 39.35°±14.23°, predominantly oriented in the NE direction, consistent with the notion that the compressive stress was associated with the NE-trending compression movement on the northeastern rim of the Qinghai-Tibet Plateau. (3) The suitable fracturing pressure for the Gonghe HDR field area was 46—55 MPa, and most fractures tend to open after shear activation (high-dilation tendency), which was conducive to increasing the area of heat exchange and improving extraction efficiency. (4) Results of in-situ stress measurement and microseismic monitoring showed that natural fractures expanded horizontally and vertically under hydraulic fracturing, ultimately forming a horizontal-vertical fracture network. The research results provide a reference for future in-situ stress measurement and its application in the assessment of hot dry rock development in China. Figures and Tables | References | Related Articles | Metrics

Select

The applicability of traditional chemical geothermometers LI Jiexiang, XU Yadong, LIN Wenjing 2024, 31(6): 145-157.  DOI: 10.13745/j.esf.sf.2024.7.15 Abstract ( 409 )   HTML ( 6 )   PDF (2307KB) ( 109 )   Geothermometers are used to estimate the reservoir temperatures in hydrothermal systems. To clarify the limitations and validity of traditional chemical geothermometers we conduct a comprehensive review in this study. We found that certain chemical geothermometer types (Na-Li, Li-Mg, Ca-Mg, SO4-F) were not widely usable, as hydrochemical equilibrium systems in some areas were influenced by the regional geological conditions. Meanwhile, the use of Na-K-Ca type(β=1/3) was constrained by a variety of hydrochemical factors, thus it should be used with caution in low-medium-temperature geothermal systems. The types more suitable for estimating the reservoir temperatures were Na-K, K-Mg, and SiO2. The Na-K type gave relatively accurate estimates for the high-temperature reservoirs (>200 ℃) where extensive water-rock reactions occurred; while the K-Mg and SiO2 types were more suitable for the low-medium-temperature reservoirs. In sedimentary geothermal systems, chemical geothermometers were not recommended for estimating the equilibrium temperature of geothermal waters directly. Besides, determining the occurrence state and the hydrothermal equilibrium status of a geothermal reservoir was prerequisite for selecting chemical geothermometers; yet, even within a suitable application range, the measurement results should be compared and validated against the calculation results. In high-temperature geothermal systems the accuracy of chemical geothermometers could be verified by the mixing processes; in low-medium-temperature systems the measurement uncertainty increased due to lack of extensive water-rock reactions, thus validation by various methods became even more important. Results from this study can be used to guide the selection of chemical geothermometers. Figures and Tables | References | Related Articles | Metrics

Select

Control factors and guidelines for urban-scale shallow geothermal energy development based on control units: An example from Xiong’an WANG Wanli, DUAN Yajuan, ZHANG Wei, ZHU Xi, MA Feng, WANG Guiling 2024, 31(6): 158-172.  DOI: 10.13745/j.esf.sf.2024.7.16 Abstract ( 372 )   HTML ( 2 )   PDF (7677KB) ( 76 )   The rational utilization of shallow geothermal energy (SGE) has great potential in promoting urban energy conservation, greenhouse emission reduction and green development. In addition to the effects of geological conditions, urban-scale SGE utilization and development is also affected by urban planning. Based on the regulatory planning of the starting area of Xiong’an, this paper summarizes the main controlling factors—geological, resource and socio-ecological factors—and formulates a workflow of spatial suitability evaluation and guidance rules. First, fully considering the constrains from the main controlling factors, combined with the indoor and field test data from geothermal measurement, thermophysical property test, field thermal response test, etc., the single element analysis of 30 control units planned in the starting area was carried out. Then, the comprehensive evaluation of SGE development was performed, and the development guidelines were formulated. Factors including geothermal field conditions, hydrogeological conditions, heat conductivity, heat capacity, heating/cooling areas, urban planning and land subsidence directly affect the SGE utilization in Xiong’an. Within the study area, 43% of the control units demonstrated good suitability for SGE development. Such areas were designated as “utilizable area”, which were mainly distributed in the north in units A, B, C, and D, mainly in the developed urban areas with high comprehensive thermal conductivity, large heating/cooling load per unit area, and higher likelihood of SGE occurrences. Units with medium suitability, i.e., 33% of the control units, were designated as “limited utilization area”; they mainly included sporadic areas of unit E and other units, with medium comprehensive thermal conductivity, small heating/cooling load per unit area, and heat capacity. The rest 23%, designated as “restricted utilization area”, were poor suitability units, mainly included areas in the south in F unit, with rich water systems and restricted spatial planning. The research results provide support for the SGE utilization and development in the starting area of Xiong’an, and also provide a reference for standardized urban-scale SGE valuation. Figures and Tables | References | Related Articles | Metrics

Select

Distribution and hydrogeochemical characteristics of hot springs in northeastern Tibetan Plateau LIU Lingxia, LU Rui, XIE Wenping, LIU Bo, WANG Yaru, YAO Haihui, LIN Wenjing 2024, 31(6): 173-195.  DOI: 10.13745/j.esf.sf.2024.7.17 Abstract ( 395 )   HTML ( 6 )   PDF (6068KB) ( 116 )   The Tibetan Plateau is the most active geothermal area in China, and its northeastern region is traditionally considered to be on a relatively stable landmass with average geothermal endowment conditions. Within this region, Qinghai Province possesses a complete range of geothermal resources. Previous studies have been mainly focused on the areas with high levels of exploration or with high-temperature hot springs, yet the overall distribution characteristics of geothermal resources and the heat sources are poorly understood. In this paper, the hot springs are divided into 11 districts from NE to SW according to the main heat-control activity fractures and hot springs areas, and the distribution characteristics and formation of hot springs are comprehensively studied by means of hydrogeochemistry and isotope analysis. The results showed that atmospheric precipitation and snow/ice melt were the source of hot springs recharge. The chemical characteristics of hot spring water were related to the stratigraphy of the hot springs. In granite, chert and sandstone hot springs the dominant cation/anions were Na+/ {\mathrm{SO}}_4^{2-}-Cl-, Ca2+-Mg2+/ {\mathrm{HCO}}_3^{-} and Ca2+-Na+-Mg2+/Cl-- {\mathrm{SO}}_4^{2-}- {\mathrm{HCO}}_3^{-}, respectively. Hot springs were mainly distributed along the fracture lines-resembling a string of beads, and concentrated at intersections of different tectonic units, or at bends of tectonic units. Areas between the primary and secondary fractures had the largest thermal-storage depth, the longest runoff path, and more adequate water-rock reactions; whilst the opposites were found along the ternary fractures. From NE to SW, the temperatures of geothermal reservoirs were high in the central areas and SW, and low in the S and NE, and the medium- and high-temperature reservoirs mainly distributed in Gonghe, Guide, Wulan and Tanggula Mountain areas, with the reservoir temperatures ranging from 89.0 ℃ to 139.0 ℃, averaging 117.7 ℃. The heat sources of hot springs included heat gain by conduction of Earth heat flow; heat from the decay of radioactive elements; residual heat from magma; frictional heat from fault ruptures; and heat from low-velocity-high-conductivity melts and mantle channel flow. With focuses on the distribution pattern of hydrothermal resources and heat source of hot springs, this study can provide a reference basis for the later development and utilization of geothermal resources in Qinghai. Figures and Tables | References | Related Articles | Metrics

Select

Insights into the root causes of difficulties in reinjection in sandstone geothermal reservoir and countermeasures ZHAO Kan, SHEN Jian, CAI Yun, ZHAO Sumin 2024, 31(6): 196-203.  DOI: 10.13745/j.esf.sf.2024.7.18 Abstract ( 287 )   HTML ( 7 )   PDF (1963KB) ( 82 )   Abundant sandstone geothermal reservoirs with large reservoir thickness are widely distributed in China, and they are the main geothermal resource for heating in the country’s northern and western regions. However, sandstone reserviors are difficult to recharge due to the small rechargeable volume, high recharge decay, and difficulty to develop on a large scale. Previous researches mainly focused on the common causes, such as drilling fluid contamination and physical/chemical clogging. Based on comprehensive review of oilfield water injection technology and results from sandstone core experiments and field reinjection tests, combined with analysis and summary of production reinjection data as well as results from sandstone reservoirs in Tianjin, Shandong and Shaanxi, we considered that the root causes of small recharge volume and recharge decay were small pore diameter, highly tortuous pore channel, and high frictional resistance (pressure dissipation) along the seepage channel of reinjection fluids. The countermeasures identified included accurate characterization of sandstone reservoirs, enlargement of reinjection wells, reduction of reinjection flow rate in the near-well area, and inhibition of speed-sensitive hydrological interactions. Figures and Tables | References | Related Articles | Metrics

Select

Single-well in-situ heat extraction technology—a review and perspectives DAI Chuanshan, LIU Dongxi, LI Jiashu, LEI Haiyan, CHEN Shuhuan, CHEN Qianhan, WANG Qilong 2024, 31(6): 204-214.  DOI: 10.13745/j.esf.sf.2024.7.19 Abstract ( 210 )   HTML ( 1 )   PDF (5137KB) ( 90 )   Geothermal energy is a widely distributed, stable, sustainable, clean, and low-carbon renewable energy resource, and the only renewable energy that exists in the form of thermal energy. Efficient development and utilization of geothermal energy can not only meet the needs of building heating in northern China but also alleviate the country’s power shortages. This is of significant importance for achieving China’s dual carbon (carbon peak and carbon neutrality) goals. Used best for heating, geothermal energy poses a natural advantage over other renewable energies in building heating. Currently, however, geothermal energy utilization in China only accounts for ~1.5% of the country’s total energy consumption, far below the one-third share of energy consumption by buildings. For many years China has maintained a worldwide leader in geothermal direct use, but ~60% of which comes from shallow ground-source heat pumps. The traditional use of geothermal energy is relatively low, mainly because the conventional geothermal production and reinjection modes largely rely on the local hydrogeological conditions, and reinjection is difficult or uneconomical in some sandstone formations. As a result, government have tightened control on geothermal resources to prevent the rapid decline of water levels. In recent years, the “no-water-withdrawal-heat-only” single-well geothermal system has gained widespread attention. This technology eliminates reinjection issues and adapts well to the current energy development and utilization situation in China, offering excellent application prospects. This paper provides a brief overview of the research and application status of single-well heat extraction technology, focusing on the status of interactional and domestic researches on the no-water-withdrawal-heat-only technology. The basic principles and shortcomings of different single-well technologies are analyzed, emphasizing the importance of implementing site-specific in-situ technologies. The paper proposes that deep single-well heat extraction technology is an environmentally friendly, sustainable, and stable heating model that can effectively address the issue of building heating in winter in northern China. This technology has gained a certain level of market competitiveness with the advancement of drilling technology. It is recommended that relevent management policies should be formulated, which are crucial for promoting geothermal energy utilization in China and achieving the “dual carbon” goals. Figures and Tables | References | Related Articles | Metrics

Select

System design and performance analysis of a modular thermoelectric generator for low- and medium-temperature geothermal resource LONG Xiting, LI Shuheng, XIE Heping, SUN Licheng, GAO Tianyi, XIA Entong, LI Biao, WANG Jun, LI Cunbao, MO Zhengyu, DU Min 2024, 31(6): 215-223.  DOI: 10.13745/j.esf.sf.2024.7.20 Abstract ( 102 )   HTML ( 2 )   PDF (3606KB) ( 58 )   Geothermal energy, widely recognized as a green, clean, stable and reliable resource, exhibits significant potential to replace traditional fossil energy. Geothermal resources are abundant and widely distributed in China, but geothermal power generation technology in China remains far behind global advancements. Thermovoltaic power generation technology shows great application potential in the low- and medium-temperature range, however, its large-scale application remains challenging. Modulization is a promising method to scale up the installed capacity of a thermovoltaic generator (TEG). This paper proposes a modular TEG with symmetrical arrangement of the heat sinks, which can be installed with different number of thermoelectric modules depending on the heat source types. The heat sinks employe a compact design to increase the volumetric power density of the system. A modular TEG was developed and tested at Shenzhen University on the test platform for low- and medium-temperature geothermal thermovoltaic power generation system. The TEG yielded a maximum output power of 136.5 W and volumetric power density of 26.9 kW/m3, under the conditions of cooling water flow rate of 3.3 m3/h, temperature of 20 ℃ and heat input power of 9 kW. The relative thermoelectric conversion efficiency reached 82.5% of the maximum theoretical value, which was achieved with a figure of merit (ZT) of 0.5 for the current module. If the equivalent ZT value can be improved to 1—2, under the same operating conditions the maximum output power of the TEG can be as high as 1.69—2.63 kW, and the volumetric power density can reach 338.3—518.8 kW/m3. Accordingly, the thermoelectric conversion efficiency would increase to 10.5%, or 92.8% of the theoretical maximum value. Under this scenario, the modular design of the thermovoltaic generator proposed in this paper can achieve higher application value. Figures and Tables | References | Related Articles | Metrics

Select

Fracture propagation mechanism in artificial reservoir of deep hot dry rock, Matouying and its applications QI Xiaofei, XIAO Yong, SHANGGUAN Shuantong, SU Ye, WANG Hongke, LI Yingying, HU Zhixing 2024, 31(6): 224-234.  DOI: 10.13745/j.esf.sf.2024.7.21 Abstract ( 178 )   HTML ( 2 )   PDF (8409KB) ( 88 )   Hot dry rock (HDR) has the advantages of clean, stable, renewable and power generation potential. The construction of fracture network and artificial thermal reservoir through hydraulic fracturing are the key technology to the efficient development of HDR energy. Traditional oil & gas fracturing mechanics are almost unable to induce tensile failure in deep HDR, therefore fracture network initiation and propagation are the key to the construction of artificial reservoirs. The reservoir construction mainly includes tensile fracture initiation near the wellbore, artificial fracture propagation and rock matrix destablization, and natural fracture displacement and dilatation. In this paper, taking the hydraulic fracturing of deep HDR in Matouying as an example, considering the geological characteristics and fracture network expansion mechanism, the temperature resistance, shear resistance and gel breaking performance of the artificial reservoir are evaluated. Low-viscosity slick water with a resistance reduction rate of 74% was selected as the main fracturing fluid, and variable-viscosity slick water with a viscosity of 40 mPa·s after shear stabilization was selected as the sand-slurry fluid for temporary plugging and diverting. Optimized into five pumping stages and 15 units, alternating between three stimulation methods including acid injection, hydraulic-shearing and sand slurry, the total of 15000 m3 fracturing fluids were pumped into reservoir to expand fracture network. Degradable plugging agents with different particle sizes, 200 mesh, 2 mm and 5 mm, were selected to promote uniform expansion of fractures, and 40/70 medium-density, high-strength proppant was optimized to strengthen the support of high conductivity. Post-fracturing evaluation and microseismic monitoring confirmed that a 1004.03×104 m3 artificial heat reservoir was constructed between underground well groups, which contained 18 typical interconnected fractures and the fracture model was “tension-shear”. The plugging agent carried by the high viscosity slick water with low pumping rate promoted the continuous opening of new fractures at the far end, increasing the area of fracture network without inducing earthquakes. The success of this hydraulic fracturing practice validated the use of multifluid mini fracturing testing, multistage step-by-step main fracturing, and multiplan plugging fracturing in the construction of artificial reservoirs. This engineering approach provides a valuable reference for HDR hydraulic fracturing. Figures and Tables | References | Related Articles | Metrics

Select

Heat transfer in geothermal reservoir of CO2-based enhanced geothermal systems—current research status and prospects JIANG Zheng, SHU Biao, TAN Jingqiang 2024, 31(6): 235-251.  DOI: 10.13745/j.esf.sf.2024.7.22 Abstract ( 277 )   HTML ( 3 )   PDF (2182KB) ( 83 )   Hot dry rock (HDR) resources with large reserves are widely distributed. HDR is considered one of the sources of green energy with a broad development prospect, and the enhanced geothermal systems (EGS) is the main technology to mine HDR resources. In CO2-EGS, supercritical CO2 (ScCO2) used as a working fluid for heat extraction can reduce water and energy consumption in pumping. ScCO2 is a better (higher efficiency) heat transfer fluid than H2O and can be used for geological storage of partial CO2, which has a large development prospect. This paper summarizes recent research progres on heat transfer techniques used in CO2-EGS from three aspects: reservoir fracture models for EGS, physical properties of CO2, and flow and heat transfer properties of CO2 in reservoir fractures. Suggestions on practical application at typical geothermal sites in China are presented. The fracture model based on fractured, porous medium is more practical and efficient, and the local thermal non-equilibrium model is more accurate. CO2 has a high mass flow rate and low mineral dissolution capability, and CO2 mineralization and storage in EGS can reduce seismic risk. However, it will decrease the permeability of the reservoir, and it is recommended to adjust the non-contact area of the main fracture or the CO2 injection parameter to minimize the permeability decrease. In the future, the non-Darcy flow properties of CO2 should be further investigated. When exploring the practical application of CO2-EGS in the Gonghe and Songliao Basins, the loss of CO2 in the reservoirs should be considered, and the sealing performance of the tuff caprock in Zhangzhou, Fujian Province should be evaluated. Figures and Tables | References | Related Articles | Metrics

Select

Fault slip tendency and induced-earthquake risks in hot dry rock development: A case study in the Tangshan Matouying HDR site SHANGGUAN Shuantong, TIAN Lanlan, PAN Miaomiao, YANG Fengliang, YUE Gaofan, SU Ye, QI Xiaofei 2024, 31(6): 252-260.  DOI: 10.13745/j.esf.sf.2024.7.23 Abstract ( 316 )   HTML ( 4 )   PDF (3377KB) ( 85 )   Induced earthquakes are one of the major problems in hot dry rock (HDR) development. Fault slip and fluid overpressure are the two main causes of large induced earthquakes, whilst local geological conditions affect the characteristics of the earthquakes. This study selects the Matouying HDR site was selected as the study area. The seismology, tectonics, and geothermal characteristics of the HDR site were analyzed in great detail. A THM multifield coupling numerical model was established, taking into account the impact of geostresses and multiple faults. The fault stability during the HDR development was evaluated based on the calculated slip tendency of the faults, and the maximum magnitude of injection-induced slip was estimated based on the calculated volume of disturbed rocks. According to the results, during the 10-year HDR development, pore pressure on the faults changed by no more than 0.8 MPa, causing no significant changes in the effective stress on faults. The slip tendency of the faults during exploration was far lower than the slip warning threshold, and the injection process was safe. Two models for calculating seismic moment were optimized, and the calculated maximum magnitude of induced earthquakes by a 10-year loop was between 2.0—2.1. Results from this study can not only support safe development of HDR at the Matouying HDR site, but also help to gain deeper understanding of the geodynamic processes affected by engineering activities. Figures and Tables | References | Related Articles | Metrics

Select

Petrogenesis of Late Cretaceous magmatic rocks in the Zhongcang area of northern Tibet and their implications for early uplift of the plateau WU Hao, YANG Chen, WU Yanwang, LI Cai, LIU Fei, LIN Zhaoxu 2024, 31(6): 261-281.  DOI: 10.13745/j.esf.sf.2023.11.61 Abstract ( 583 )   HTML ( 6 )   PDF (6740KB) ( 67 )   During the late Cretaceous, extensive magmatic activity erupted in the central Tibetan Plateau, accompanied by rapid surface uplift. However, the deep dynamical mechanisms behind this phenomenon have been a subject of considerable debate. This study conducts U-Pb zircon dating, as well as analyses of whole-rock major and trace elements and Sr-Nd-Hf isotopes on the diorite and rhyolite developed in the Zhongcang area of northern Tibet, aiming to provide new constraints on regional tectonic-magmatic evolution. The U-Pb zircon dating results indicate that both the diorite and rhyolite formed in the Late Cretaceous (90—85 Ma). The geochemical characteristics of the diorite show high Sr, low Y content, and high Sr/Y ratios, indicating an affinity to adakite. Combined with its high Mg#, it is proposed to be a product of the mixing of underplated eclogite-facies lower crustal melts with mantle materials. The geochemical and isotopic characteristics of the rhyolite are similar to those of the diorite, reflecting a common magmatic source. However, its significant depletion in Rb, Ba, Sr, and other easily altered elements suggests it underwent intense alteration during the late diagenesis. Coupled with the contemporaneous eruption of high-Mg adakitic magma and large-scale molasse deposition in the region, this study posits that the tectonic-magmatic activity in the central Tibetan Plateau during the Late Cretaceous was a result of the thickening and detachment of the lower crust following the collision of the Bangong Lake—Nujiang suture zone. This deep detachment simultaneously triggered rapid surface uplift, forming a Cretaceous paleo-plateau and laying the foundation for the modern plateau’s formation. Figures and Tables | References | Related Articles | Metrics

Select

Formation of graphite in ultrahigh-pressure pelitic schists from the southwestern Tianshan: Implications for carbon migration and sequestration in subduction zones HU Han, ZHANG Lifei, PENG Weigang, LAN Chunyuan, LIU Zhicheng 2024, 31(6): 282-303.  DOI: 10.13745/j.esf.sf.2024.6.80 Abstract ( 397 )   HTML ( 5 )   PDF (22063KB) ( 79 )   Oceanic sediments, as one of the main contributors of carbon input in subduction zones, provide a large amount of organic and inorganic carbon to the subduction factory. Exploring the fate of these carbon types in subduction zones is critical for a better understanding of Earth’s deep carbon cycle. While the role of subducted organic carbon in this cycle is underscored by evidence from ultra-deep diamonds and arc carbon emissions, petrological evidence for the subduction of organic carbon to subarc depths remains scarce. Additionally, the fate of abiogenic CH4 fluids formed under ultrahigh-pressure (UHP) conditions in subduction zones remains underexplored. The Chinese southwestern Tianshan oceanic-type HP-UHP metamorphic belt, characterized by cold subduction with a low geothermal gradient, is rich in carbon-bearing rocks (e.g., carbonate, graphite, CH4, CO2) and serves as an ideal natural laboratory for studying the carbon cycle in subduction zones. This study conducts detailed petrological observations, Raman spectroscopic, and stable carbon isotopic analyses of different graphite types in the UHP pelitic schists of the southwestern Tianshan orogenic belt in Xinjiang, China. Two types of graphite were identified: Type-1 graphite, occurring as minute inclusions in garnet with low δ13CTOC values (-24.3‰ to -23.2‰), suggesting a biogenic origin; and Type-2 graphite, occurring as foliation-parallel bands with higher δ13CTOC values (-14.8‰ to -12.5‰), indicative of an abiogenic precursor. Both types exhibit similar morphological characteristics and crystallinity, as revealed by BSE images and Raman spectroscopy. Thermodynamic modeling, zirconium-in-rutile thermometry, and Raman Spectroscopy on Carbonaceous Material (RSCM) were used to constrain the formation conditions of these two graphite types. Type-1 graphite formed from the graphitization of organic carbon in subducting slabs during prograde metamorphism, reaching temperatures of 530—555 ℃. Type-2 graphite crystallized from COH fluid at approximately 2.7 GPa and 530 ℃ during eclogite-facies peak metamorphism. CH4-bearing fluid inclusions associated with Type-2 graphite, alongside thermodynamic modeling, suggest the oxidative precipitation of carbon from CH4 fluid. Petrological characteristics of Type-1 graphite coexisting with coesite in garnet, and p—T calculations, suggest that organic graphite was subducted to subarc depths exceeding 90 km. This discovery provides petrological evidence for the deep subduction of organic carbon to mantle depths and may offer insights into the origin of diamonds with light δ13C values. Type-2 graphite highlights the limitations of carbon mobility in subduction zones, affecting carbon retention times, and modulating carbon emissions from arc volcanoes. Furthermore, our findings emphasize the significance of environmental redox states, particularly at lithological interfaces with variable oxygen fugacity, in controlling the fate of COH fluids and carbon transport in subduction zones, pointing to the need for further research on CH4 fluid migration under varying redox conditions. Figures and Tables | References | Related Articles | Metrics

Select

Outgassing processes of carbon in deep Earth: A review LI Zhuoqi, XU Cheng, WEI Chunwan 2024, 31(6): 304-319.  DOI: 10.13745/j.esf.sf.2024.10.10 Abstract ( 218 )   HTML ( 6 )   PDF (3969KB) ( 70 )   The Earth’s deep interior is a massive carbon reservoir, containing more than 98% of the Earth’s carbon. In the uppermost mantle, carbon primarily exists as carbonates and CO2. Under certain temperature and pressure conditions, they can lower the solidus of mantle rocks, participating in mantle melting processes and forming carbon-bearing silicate or carbonate melts. Carbon-bearing melts are an important form of carbon migration in the lithospheric mantle and are the direct carrier of deep-sourced carbon release to the surface. During the migration and upwelling of carbonate melts and carbonated silicate melts in the mantle, they may react with olivine, causing melt decomposition and releasing CO2. In the crustal stage, in addition to degassing caused by volcanic activity, during the upwelling of carbon-bearing melts, pressure reduction leads to a decrease in the solubility of CO2 in the melt, or decarbonation reactions between the melt and crustal rocks are also important pathways for CO2 release. Surface carbon can enter the Earth’s deep interior through plate subduction and other processes. This process, together with the release of deep-sourced carbon, constitutes a deep carbon cycle that significantly influences the carbon content in the Earth’s historical atmosphere and climate change. In modern cold plate subduction, the main form of carbon release is the dissolution and migration of carbon in the slab by fluids released from the subducting slab, and most of the subducted carbon can enter the deep Earth. The complexity of deep decarbonation processes makes the pathways and corresponding fluxes of deep carbon release during geological history still controversial. Comprehensive research on different decarbonation processes is an important basis for further clarifying carbon release during geological history. Therefore, this paper systematically summarizes the different decarbonation processes and their identification markers in the deep carbon cycle, and takes the Mesozoic decarbonation process in the eastern margin of the North China Craton as an example to discuss the significance of deep-sourced carbon release for paleoenvironmental changes. Figures and Tables | References | Related Articles | Metrics

Select

Taihu crater: New evidence of impact metamorphism in sedimentary rocks, Taihu Lake, Jiangsu, China WANG Henian, CHEN Yang, SHENG Xuefeng, QIAN Handong 2024, 31(6): 320-330.  DOI: 10.13745/j.esf.sf.2024.8.30 Abstract ( 602 )   HTML ( 19 )   PDF (14441KB) ( 62 )   This paper summarizes the results of fifteen years of research on the area surrounding Taihu Lake and its inner islands. Taihu Lake exhibits diagnostic features of an impact crater, including shatter cones, impact-metamorphosed breccias, and evidence of impact metamorphism in quartzite (PDFs and PFs) and impact melting. The ideal profile of an impact crater, comprising a vaporized melt zone, an impact metamorphic zone, impact-metamorphosed breccias, and a fracture zone, is fully present, confirming the existence of the Taihu impact crater. A schematic map of the distribution of impact metamorphism in Taihu has been compile based on these diagnostic features. For the first time, the Taihu impact crater, previously speculated from satellite images, has been confirmed in the Taihu Lake area, laying a solid foundation for further research. The distribution of impact metamorphism in Taihu can be divided into two concentrated zones and one ejecta distribution zone. These zones are located in the interior and edges of the lake area, primarily concentrated in the central and southern parts of Taihu Lake, indicating a relationship between the impact crater and the formation, evolution, and development of Taihu Lake. The Taihu impact crater, located in a fold belt at the margin of a continental platform with target rocks of sedimentary limestone and porous quartz sandstone, represents a new type of impact crater with many novel impact metamorphic phenomena and characteristics. The paper introduces the diversity, new features, and new types of shatter cones; reveals new characteristics of impact metamorphic PDFs in porous quartz sandstone; and describes new phenomena such as silica glass formed by intergranular shear friction-local melting and solidified melt inclusions. These findings enrich and advance the understanding of new characteristics and theories related to impact metamorphism in sedimentary rocks. Figures and Tables | References | Related Articles | Metrics

Select

Strategic mineral resources in coal: A case study on gallium and germanium ZENG Zhaoyang, NING Shuzheng, WANG Ziguo 2024, 31(6): 331-349.  DOI: 10.13745/j.esf.sf.2024.10.18 Abstract ( 475 )   HTML ( 3 )   PDF (4537KB) ( 90 )   Strategic coal-associated mineral resources hold significant importance for national economic development and security. These minerals, often referred to as coal-type minerals, include not only coal seams enriched with critical metals but also partings, coal seam roofs and floors, other enriched layers within coal measures that do not contain coal seams, and even acid mine waters from coal mines enriched with metals. Based on a systematic review of domestic and international literature on coal-type minerals, this paper organizes and analyzes strategic coal-type mineral resources throughout China’s geological history, listing the main periods during which coal-type strategic minerals were formed. It compiles maps showing the spatial distribution of coal mining resources and strategic key minerals during major geological periods nationwide. Using gallium and germanium as examples, the study dissects typical deposits, delving into the geological background and ore-forming mechanisms of coal-type deposits represented by gallium and germanium, and summarizes key prospecting information such as the enrichment sites of gallium and germanium within these deposits. The results show that during various geological periods, strategic critical metal resources, represented by gallium, germanium, and other “four scarcities” and bulk minerals, are the main products. Since the Phanerozoic Eon, “four scarcities” minerals and bulk minerals have been produced. Gallium and germanium deposits in China are mainly concentrated in coal-bearing basins of the North China Platform and Yangtze Platform during the Carboniferous-Permian, Triassic-Jurassic, Early Cretaceous, and Neogene periods. The formation of coal-type germanium deposits is closely related to magmatic activity and associated hydrothermal processes. The enrichment of elements such as gallium and germanium has specific locations within coal-bearing strata: gallium is typically found at the top of coal-forming cycles, such as in the Ga-enriched No.6 coal seam of the Shanxi Formation in the Carboniferous-Permian coal-bearing basin of North China, exemplified by the Heidaigou deposit. The Benxi Formation at the base of the coal cycle also contributes to some extent. Germanium, on the other hand, is usually enriched at the beginning or base of coal cycles, as seen in the Bangmai germanium deposit in Lincang. The gallium and germanium resources in China’s coal have great potential. Figures and Tables | References | Related Articles | Metrics

Select

Experimental research on big data-based intelligent exploration models and advance ZHOU Qi, WU Chonglong 2024, 31(6): 350-367.  DOI: 10.13745/j.esf.sf.2024.9.10 Abstract ( 417 )   HTML ( 3 )   PDF (12873KB) ( 116 )   This paper presents a comprehensive summary of exploratory experimental research conducted by the ‘Industry-college-institute Cooperation’ technology innovation talent team in Guizhou Province, focusing on a novel intelligent exploration model leveraging big data. Utilizing a collaborative innovation system integrating industry-college-institute cooperation, the team undertook a retrospective analysis of mineral exploration processes employing big data for the famous ‘Datangpo’ manganese ore concentration area in China, as well as several concealed giant manganese deposits. Their research aimed to explore intelligent predictive methodologies and digital exploration techniques for deep-seated mineral resources, with the goal of cultivating and developing new quality productivity in the field of geological and mineral exploration. The team developed a big data-based metallogenic schema and exploration model, established a comprehensive geological big data resource system. They refined and widely promoted digital exploration technologies system, created a province-wide three-dimensional glass earth in Guizhou Province, and developed multi-scale, multi-objective progressive mineral prediction techniques. These efforts have significantly accelerated the digital transformation of geological and mineral exploration in Guizhou Province. Their efforts led to the discovery of multiple concealed exploration targets, including manganese, phosphate, bauxite, lead-zinc (germanium), barite, and newly identified altered limestone-type lithium deposits, contributing to significant advancements in Guizhou new round of prospecting breakthrough strategic action. The key outcomes indicate that the team’s research not only accelerates the digital transformation of geological mineral exploration but also fosters a deep integration with big data, cultivating and developing new quality productivity in the field of geological and mineral exploration and supporting breakthroughs in the exploration of concealed minerals. To further advance this digital transformation and develop a digital economy in geology, it is crucial to continue initiatives aimed at enhancing ‘Data cloud service, Deep integration of big data, and Enterprise intelligent transformation’ in exploration, strengthen the key technology research and development, and vigorously promote these applications, while continuously exploring, improving, and developing in practice. Figures and Tables | References | Related Articles | Metrics

Select

Analysis of oil and gas distribution and exploration potential in oil-rich depression: Taking Dongpu Depression as an example XU Tianwu, ZHANG Hong’an 2024, 31(6): 368-380.  DOI: 10.13745/j.esf.sf.2024.2.26 Abstract ( 445 )   HTML ( 6 )   PDF (9245KB) ( 41 )   The major oil fields in the Bohai Bay Basin have undergone long-term detailed exploration, yet the latest resource assessments still indicate a large potential for remaining resources in oil-rich depressions with high resource abundance. These areas will continue to be a long-term focus for exploration and development. Deepening the understanding of hydrocarbon accumulation patterns in oil-rich depressions is crucial for guiding future oil and gas exploration. This paper begins from the perspective of source rocks, clarifying the hydrocarbon generation characteristics of the Paleogene lacustrine shales in the Dongpu Depression and the coal-bearing source rocks of the Upper Paleozoic. It then integrates typical oil and gas reservoir analyses and reservoir evaluation units to establish a correspondence between source and reservoir. By combining this with other accumulation factors, it aims to develop hydrocarbon accumulation models and clarify the patterns of remaining oil and gas enrichment. The research indicates that the oil-rich depression in the Dongpu Depression is characterized by “proximity to source aggregation, continuous accumulation, and fault-controlled richness”. The hydrocarbons primarily originate from high-quality source rocks with TOC greater than 1.0%. The richness of oil and gas in the oil-rich zones is mainly due to the presence of multiple sets of high-quality source rocks, multiple oil and gas systems, and multiple stages of hydrocarbon accumulation, referred to as the “three multiplicities”. In the Dongpu Depression, coalbed methane is primarily distributed in areas where the thermal maturity level of coal-bearing source rocks (Ro) exceeds 1.3%, exhibiting both in-source and out-of-source accumulation modes. The findings of this study not only provide technical support for the exploration of conventional oil and gas reservoirs but also for the exploration of thin-layer tight oil and shale oil. Figures and Tables | References | Related Articles | Metrics

Select

Discovery of “detachment-core complex type” basins offshore the northern South China Sea and their oil and gas geological conditions:A case study of the Kaiping sag in the northern South China Sea XU Changgui, GAO Yangdong, LIU Jun, PENG Guangrong, CHEN Zhaoming, LI Hongbo, CAI Junjie, MA Qingyou 2024, 31(6): 381-404.  DOI: 10.13745/j.esf.sf.2024.7.1 Abstract ( 339 )   HTML ( 7 )   PDF (16260KB) ( 91 )   Kaiping sag in the Pearl River Mouth Basin is located in the crustal thinning zone offshore the northern South China Sea. It is a typical “detachment-core complex type” basin (sag) newly discovered around the world. It has a unique lithospheric extension-thinning-fracture process. It is of great significance to study its structural type, genetic mechanism and oil and gas geological conditions.This article is based on the detailed interpretation of three-dimensional seismic data and comprehensive geological research, discovering a new type of basin offshore the northern South China Sea called “detachment-core complex”, revealing its basin formation and hydrocarbon generation process, promoting new understanding of depression structure, hydrocarbon source distribution, and reservoir formation mode, and discovering a large oil field for the first time in this type of sag.The research results indicate that: (1) Kaiping sag is a typical “detachment-core complex type” sag developed under the strong extensional continental margin background offshore the northern South China Sea, and its formation process is influenced by horizontal extensional superimposed metamorphic core complex vertical uplift; The sedimentation period of the Wenchang Formation went through two major stages of basin formation and evolution: early faulting, late detachment, and uplift and transformation of core complex rocks, forming a depression structure of “north faulting and south overtaking”; (2) The source rocks of the Wenchang Formation have a coupled hydrocarbon generation mechanism of “fault detachment controlling basin-early depression late slope-high temperature heating”. The high-quality source rocks of the semi-deep lake and deep lake facies in the fourth section of the Wenchang Formation have undergone deformation and displacement to the southern slope zone under the combined action of detachment and core complex uplift. At the same time, they are affected by the high temperature field and magma heating, showing high heat and fast maturation characteristics, with a shallower hydrocarbon expulsion threshold, significantly enhancing the resource potential of the Kaiping sag; (3) The southern slope zone of Kaiping sag has a reservoir formation model of “basin controlled by fault detachment, combined control of hydrocarbon transport by fault ridges, multi-stage episodic filling, and nose shaped structure controlled accumulation”.The discovery of Kaiping South Paleogene oil field has opened up a new area of deep oil and gas exploration in the the Pearl River Mouth Basin, becoming the first successful case of commercial discovery of continental margin “detachment-core complex type” sag in the world, which is expected to provide important reference for oil and gas exploration of similar sag structures at home and abroad. Figures and Tables | References | Related Articles | Metrics

Select

Experimental study on the sensitivity of hydraulic permeability of fine-grained sediments sampled from a gas hydrate distribution area in the northern South China Sea SONG Dekun, LIU Lele, WANG Dong 2024, 31(6): 405-414.  DOI: 10.13745/j.esf.sf.2024.4.25 Abstract ( 338 )   HTML ( 3 )   PDF (3344KB) ( 30 )   Natural gas hydrates are mainly distributed in fine-grained marine sediments containing clay minerals. For instance, the sediments in the northern region of the South China Sea contain a large amount of illite. Understanding the changes in permeability during the depressurization extraction process is crucial for effectively regulating the production of gas from hydrates. This study utilized remolded soil samples taken from the target hydrate test-production area in the northern South China Sea and conducted limit water content tests, drained consolidation tests, and steady-state seepage tests under different pore fluid concentration conditions. Data on the liquid limit, plastic limit, plasticity index, permeability coefficient, and permeability were obtained. The stress sensitivity and chemical sensitivity of the permeability of South China Sea sediments were analyzed. The results indicated that the limit water content parameters of the South China Sea sediments decreased as the pore fluid concentration increased. The permeability of the sediments increased with the pore fluid concentration, while it decreased with increasing stress. Moreover, the degree of stress sensitivity increased as the pore fluid concentration rose, whereas the degree of chemical sensitivity diminished with increasing stress. The fitting relationship of the permeability coefficient obtained using the normalized void ratio was found to be unaffected by pore fluid concentration, making it convenient for engineering applications. Figures and Tables | References | Related Articles | Metrics

Select

The interaction between the opening of the Drake Passage and global paleoceanographic-paleoclimatic change ZHANG Mengwei, GAO Liang, ZHAO Yue, PEI Junling, YANG Zhenyu, GUO Xiaoqian, HU Xinwei 2024, 31(6): 415-435.  DOI: 10.13745/j.esf.sf.2024.5.29 Abstract ( 446 )   HTML ( 5 )   PDF (9536KB) ( 72 )   The opening of the Drake Passage has been influenced by the tectonic movements and evolutionary processes of the southern part of South America and the northern part of the Antarctic Peninsula, leading to the eventual formation of the Antarctic Circumpolar Current and today’s ocean circulation pattern, which is one of the key factors for understanding global changes during the Cenozoic era. Previous studies have investigated the opening of the Drake Passage and the formation of the Antarctic Circumpolar Current through methods related to paleocontinental reconstruction and paleoceanography. This paper summarizes previous research findings and integrates data on the Cenozoic tectonic evolution of the northern Antarctic Peninsula and southern South America, as well as δ18O, δ13C values of global deep-sea benthic foraminifera, global dissolved oxygen content, atmospheric CO2 concentrations, and changes in global ocean productivity. It proposes three critical stages of the opening of the Drake Passage and the strengthening of the Antarctic Circumpolar Current occurring around 40—35 Ma, 30—25 Ma, and 20—18 Ma. These events happened during key tectonic evolutionary phases of the northern Antarctic Peninsula and southern South America, with the latter two stages occurring after the formation of the Atlantic Meridional Overturning Circulation, corresponding to periods of low δ13C values in global deep-sea benthic foraminifera, low atmospheric CO2 concentrations, low dissolved oxygen levels in the deep sea, high paleoproductivity in the Southern Ocean, and low paleoproductivity in equatorial sea regions. Accordingly, we propose that the tectonic events related to the northern Antarctic Peninsula and southern South America caused the strengthening of the Antarctic Circumpolar Current, which dominated the paleoceanographic and paleoclimatic changes during these periods. This understanding helps clarify the significant stages of the evolution of the Drake Passage and its impact on global changes. Figures and Tables | References | Related Articles | Metrics

Select

Mechanism of carbon cycle and source-sink conversion and quantitative carbon exchange model in critical zone of wetland ZHOU Nianqing, GUO Mengshen, CAI Yi, LU Shuaishuai, LIU Xiaoqun, ZHAO Wengang 2024, 31(6): 436-449.  DOI: 10.13745/j.esf.sf.2024.6.36 Abstract ( 474 )   HTML ( 2 )   PDF (2758KB) ( 50 )   The transformation mechanism and quantitative relationship between carbon source and sink conversion in critical zone of wetland are key scientific issues that need to be explored and addressed in the study of wetland carbon cycle. Carbon (C) is one of the main elements that constitute living organisms and plays an extremely important role in the material cycle and energy flow processes of ecosystems. As the most active part of the Earth’s critical zone, the critical zone of wetland contains a large amount of information interchange. It is necessary to study the mutual feedback mechanism of carbon cycle and its migration and transformation information through information extraction and interpretation. Carbon has the function of a “source” and “sink” in wetland ecosystems, which involves the effects of atmosphere, soil, vegetation, water and microorganisms. Carbon cycle in critical zone of wetland plays a crucial role in promoting wetland ecological environment protection. Based on the biogeochemical cycle characteristics of C in critical zone of wetland, this paper analyzed the occurrence patterns and the migration and transformation processes of C at vegetation, atmosphere, root, soil interfaces. The main control factors of migration and transformation and coupling mechanisms affecting carbon cycle were also explained in critical zone of wetland. Further exploration was conducted on the positive role of dual driving forces of “carbon reduction source” and “carbon increase sink” in achieving the goal of “carbon peak” and “carbon neutrality”. Finally, the future research directions were proposed, which should focus on strengthening the comprehensive analysis of the spatiotemporal evolution of C and the impact mechanism of biogeochemistry cycle in critical zone of wetland, constructing a quantitative carbon cycle model, accurately measuring the flux changes during the transformation process of “carbon source” and “carbon sink” to quantify the surplus of “carbon sink” in critical zone of wetland and evaluating its contribution to “carbon peak” and “carbon neutrality”. Figures and Tables | References | Related Articles | Metrics

Select

Simulation and prediction of inland river runoff based on CMIP6 multi-model ensemble LIANG Wenxiang, LUO Zhen, CHEN Fulong, WANG Tongxia, AN Jie, LONG Aihua, HE Chaofei 2024, 31(6): 450-461.  DOI: 10.13745/j.esf.sf.2024.5.30 Abstract ( 363 )   HTML ( 4 )   PDF (4130KB) ( 32 )   The runoff series of inland rivers with glacier melt as the main supply source has changed significantly with the influence of global climate change and human activities. Predicting the runoff change of inland river basins under future climate change is of great significance for regional water disaster prevention and rational utilization of water resources. A decomposing, simulation-optimization-reconstruction model was constructed and coupled with eight kinds of GCMs data from the multi-model ensemble Average (MME) to predict and analyze the runoff response characteristics in the Manas River Basin under different climate scenarios from 2024 to 2030. The results show that R2>0.86 and TPE<0.28 in the runoff simulation stage of the Model.VLE Model has the smallest simulation error and the best stability. The runoff simulation effect of GCMs data through spatial downscaling, deviation correction, and Model.VLE Model coupling is the best in the historical period, which can provide reliable results for runoff prediction. Compared with the historical period (2000—2014), the runoff water abundance in the Manas River Basin in the future (2024—2030) has a significant increase trend, and the future annual runoff change is related to the future temperature and precipitation, and there is no significant difference in the future runoff under the three climate scenarios (2024—2030). Figures and Tables | References | Related Articles | Metrics

Select

Hydrochemical characteristics of surface water and genetic mechanism of high fluorine water in Qingshui River Basin in Ningxia ZHAO Zengfeng, WANG Chuyou, QIU Xiaocong, ZHOU Ruijuan, YANG Qiangqiang, ZHAO Ruizhi 2024, 31(6): 462-473.  DOI: 10.13745/j.esf.sf.2023.12.36 Abstract ( 266 )   HTML ( 2 )   PDF (5989KB) ( 55 )   The most representative samples were collected three times at 30 points in the Qingshui River Basin in Ningxia in level period(May), wet period(July) and dry period(December) of 2022 in order to explore the hydrochemical control factors and the causes of high-fluorine water in the Qingshui River Basin. The spatial and temporal distribution characteristics of hydrochemical components and fluorine was analyzed, the formation and enrichment mechanisms of high fluorine water were analyzed, and the contribution of different factors to the hydrochemical components of surface water in the basin was calculated by APCS-MLR. The results show that the surface water in Qingshui River Basin is weakly alkaline, the anion concentration was {\mathrm{SO}}_4^{2-}>Cl-> {\mathrm{HCO}}_3^{-}, and the cation concentration was Na+>Mg2+>Ca2+>K+. The F- concentration was dry period > wet period > level period, tributary > reservoir > trunk stream. The main hydrochemical type of surface water is SO4-Cl-Na type, followed by SO4-Cl-Ca-Mg type. The formation of high fluorine water is controlled by evaporation and concentration, rock weathering, mineral dissolution and precipitation, cation exchange and adsorption, and the enrichment of high fluorine water is controlled by climate, terrain and hydrochemical composition. Natural factors are the key driving factors for the hydrochemistry of surface water in Qingshui River Basin, contributing 77.56% to the hydrochemical components of surface water in the study area, and human activities mainly contribute TP (59%), {\mathrm{SO}}_4^{2-} (10%) and Ca2+ (10%).The contribution of natural sources to the hydrochemical components of surface water in the study area is as follows: sulfate mineral weathering > silicate mineral weathering > carbonate mineral weathering > rock salt weathering, and the main contribution source of F- is sulfuric acid rock mineral weathering (56%). Figures and Tables | References | Related Articles | Metrics

Select

Bioaccumulation of rare earth elements, uranium and thorium in plant-rhizosphere soil in Xiangshan uranium tailings areas DONG Shu, LIU Haiyan, ZHANG Yifan, WANG Zhen, GUO Huaming, SUN Zhanxue, ZHOU Zhongkui 2024, 31(6): 474-489.  DOI: 10.13745/j.esf.sf.2024.2.18 Abstract ( 422 )   HTML ( 2 )   PDF (8049KB) ( 46 )   Eight dominant plants and their rhizosphere soils were collected from different parts of the Xiangshan uranium tailings areas (in the tailing pond, on the dam, and downstream of the tailing pond). The bioaccumulation behavior and spatial isomerism characteristics of rare earth elements (REEs), uranium (U), and thorium (Th) in the roots, stems, leaves, spikes, and rhizosphere soils of the plants were studied through field investigation and laboratory analysis. The results showed that the total REE (∑REEs) contents were highest in the rhizosphere soils, followed by the roots, stems, and leaves (spikes). REE normalization indicated that, for plants in the pond, the roots exhibited similar patterns to the rhizosphere soils, showing enrichment of heavy rare earth elements (HREEs) and a negative europium (Eu) anomaly. In contrast, for plants collected from the dam and downstream of the pond, the roots and rhizosphere soils had relatively flat patterns with a negative cerium (Ce) anomaly, while the stems, leaves, and spikes showed enrichment of light rare earth elements (LREEs). This indicated that fractionation of REEs occurred during the transport from soils to roots in the soil-root systems and within the plant tissues. A DTPA extraction experiment with the rhizosphere soils showed that HREEs were preferentially taken up by plants compared to LREEs, and the bioavailability of gadolinium (Gd) was lower than that of other REEs. Pearson correlation analysis revealed that soil pH, Fe/Mn mineral adsorption, and organic matter were important factors affecting the bioavailability of REEs. Grey correlation analysis showed that the grey correlation coefficients of U, Th, and REEs were generally higher between rhizosphere soil and root as compared to those between rhizosphere soil and leaf, stem, and spike, reflecting that the influence of soil U and Th concentration on REEs was greater in root than that in leaf stem, and spike. The REEs Bioconcentration Factor (BCF=6.09) and Translocation Factor (TF=8.25) of Dicranopteris dicthotoma leaves were both greater than 1, and BCF and TF of its stems and roots were also higher than other plants. This indicated that Dicranopteris dicthotoma could be used as an accumulator for REEs. The rice roots were strongly accumulated with REEs, Th and U, which meat that rice could be considered as the candidate for joint-contamination phytoremediation. Figures and Tables | References | Related Articles | Metrics