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About the Journal

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Journal:
Coal Geology & Exploration
Establishment year:
1973
 
Periodicity:
Biomonthly
Supervised by:
Xi’an Research Institute Co. Ltd., China Coal Technology and Engineering Group Corp.
Sponsored by：
Xi’an Research Institute Co. Ltd., China Coal Technology and Engineering Group Corp.
Editor-in-chief:
 DONG Shuning
 
Associate E ditor-in-chief:

 LIU Cheng, James W. LaMoreaux 

 

Executive Editor-in-chief:
JIN Xianglan 

 

ISSN:
1001-1986
CN:
61-1155/P
Web:
www.mdkt.cbpt.cnki.net

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Article list

  • Geochemical nature of the geothermal water from Lanzhou Basin: Implications for the genesis of shallow helium-bearing fluids

    TANG Jianzhou;WANG Shuangming;ZHANG Zhicheng;LI Ke;LI Changpeng;College of Geology and Environment, Xi'an University of Science and Technology;Shaanxi Key Laboratory of Petroleum Accumulation Geology;School of Earth and Space Sciences, Peking University;College of Resources and Safety Engineering, Chongqing University;Gansu Coalfield Geological Bureau;

    [Objective and Methods] Investigations on the geochemical nature of geothermal water are vital to the comprehension of the origin of helium-rich fluids in shallow basins. To address this issue, this paper reports the results of the chemical analysis, H-O isotopes and 14C ages from geothermal water and soluble gas components from the well BY-1 in Lanzhou Basin, northeastern margin of Qinghai Tibet Plateau. Chemical analysis of geothermal water samples reveals that the chemical type of geothermal water is NaCl. The show δD value of-78‰, high δ~(18)O value(-8.7‰), low 3H value(<0.4TU), and old 14C age(20.50±0.92ka). The geothermal water has undergone evaporation-concentration and water-rock interactions, which originated from ancient atmospheric precipitation. Component analysis from 10 waterdissolved gas samples reveals an average helium concentration of 0.44%. The concentration of He meets the standard for helium-rich gas fields. Compositions of the dissolved gas and the geochemical nature of the groundwater jointly suggest that the associated helium in the geothermal water from this well is a product of the radioactive decay of Th-U elements in the basement rocks of the basin. Comprehensive analysis indicates that the upward migration and accumulation of ancient helium-bearing water from the basement into shallow geothermal reservoirs along fault zones under the background of tectonic uplift is the key process for the enrichment of associated helium in geothermal water in the Lanzhou Basin.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1794K]

  • Diffusion mechanisms of coal-measure helium and their implications for helium accumulation:A case study of the Taiyuan Formation, northern Qinshui Basin, China

    MA Yong;XIN Zhiyuan;CHEN Jianfa;LI Yuhong;ZHANG Xiutao;JIANG Haojie;CHEN Zeya;State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing);Xi'an Center of Geological Survey,China Geological Survey;PetroChina Research Institute of Petroleum Exploration and Development;

    [Objective] The global helium-rich gas reservoirs are dominated by conventional natural gas reservoirs. In recent years, helium-bearing natural gas has been discovered in the Carboniferous-Permian coal measures in the Ordos Basin and surrounding regions, revealing the resource potential of coal-measure helium. However, there is almost a total lack of studies on mechanisms underlying the diffusion and migration of coal-measure helium. This severely restricts further research on the accumulation patterns of coal-measure helium. [Methods] This study investigated a coal seam in the Taiyuan Formation in the northern Qinshui Basin and mudstones in the coal seam roof. Using physical diffusion experiments on coal-measure helium under different water saturations and gas concentrations, as well as the simulation of the regional sedimentary, burial, and hydrocarbon generation histories, this study calculated the helium diffusion fluxes in the coals and mudstones. Accordingly, the mechanisms behind the enrichment of coal-measure helium gas were determined. [Results and Conclusions] Under experimental temperature(20 ℃) and pressure(1 MPa), helium diffusion was dominated by Knudsen diffusion in pores with sizes less than or equal to 13.5 nm, with similar diffusion rates observed in the coals and mudstones. In contrast, helium diffusion shifted to Fick diffusion in pores with sizes greater than 13.5 nm. The diffusion of coal-measure helium gas was primarily affected by pore structure, water content, and gas concentration. Poorer pore connectivity, higher water saturation, and a lower helium concentration corresponded to slower helium diffusion and a higher sealing capacity. The coals exhibited a developed cleavage-fracture system, which contributed to high connectivity. As a result, the coals had a higher helium diffusion coefficient(1.1 × 10~(-8) m~2/s) than the mudstones(5.8 × 10~(-9) m~2/s). High water content reduced the helium diffusion rate by blocking pore pathways and changing the behavior of the gas-liquid interface. The influence of the gas concentration on the helium diffusion rate was principally related to both the partial pressures of gases and differences in physical properties between helium and methane. In combination with the physical and numerical simulation results, this study established a prediction model for the helium diffusion flux throughout geological history. The prediction results indicate that the helium diffusion fluxes in the coals and mudstones were 13.24 cm~3/m~2 and 5.05 cm~3/m~2, respectively under standard temperature and pressure conditions.Furthermore, the helium diffusion occurred predominantly in the early hydrocarbon generation stage with high gas concentrations, while the amount of helium escaping in the later stage can be ignored. Given the relatively weak helium generation capacity of the coal measures, the enrichment and accumulation of coal-measure helium resulted from the dynamic balance between exogenetic recharge and preservation. Deep faults facilitate the upward migration of deep helium. Meanwhile, the low gas concentration gradient, high water saturation, and low connectivity enhance the helium storage capacity by suppressing diffusion. Therefore, it is necessary to highlight the connectivity of deep fault systems and the sealing performance of cap rocks in the exploration of coal-measure helium.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1941K]

  • Mechanisms underlying differential helium enrichment in shale gas of varying structural styles in the southeastern Sichuan Basin

    XIN Zhiyuan;CHEN Jianfa;WANG Jie;MA Yong;State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing);College of Geosciences, China University of Petroleum;Wuxi Research Institute of Petroleum Geology,Petroleum Exploration and Production Research Institute,SINOPEC;

    [Objective] Shale gas reservoirs hold considerable helium reserves despite relatively low helium abundance,establishing them as a critical replacement for helium production growth. The southeastern Sichuan Basin exhibits diverse structural styles with varying preservation conditions, leading to an unclear understanding of the distribution characteristics and enrichment patterns of helium in shale gas. Determining the mechanisms behind the differential helium enrichment in shale gas is significant for the effective utilization of helium in shale gas. [Methods] Focusing on the typical shale gas reservoirs of different structural styles in the southeastern Sichuan Basin, this study explored the mechanisms underlying differential helium accumulation in shale gas in different structural styles and determined the potential play fairways for the exploration of helium in shale gas. [Results and Conclusions] The Wulong residual syncline,Baima fault-fold deformation zone, and the shallowly buried Dingshan faulted anticline, featuring unfavorable structural preservation conditions and normal formation pressure, have relatively high helium abundance, averaging 524×10-6,606×10-6, and 534×10-6, respectively and reaching the industrial helium extraction standards. In contrast, the Jiaoshiba broad gentle anticline, Baima syncline, and deeply buried Dingshan faulted anticline, with favorable structural preservation conditions and formation overpressure, show relatively low helium abundance, averaging 335×10-6, 381×10-6, and250×10-6, respectively. The shale gas in the Wufeng-Longmaxi formations of different structural styles in the southeastern Sichuan Basin primarily holds crust-derived helium, exhibiting great helium-generating potential. However, shales of different structural styles show nonsignificantly different helium-generating potential. The calculations of helium production based on the uranium and thorium decay theories, as well as the helium and argon isotope analyses, demonstrate that the helium in shale gas reservoirs in the southeastern Sichuan Basin is primarily of an endogenous origin, suggesting self-sourced helium reservoirs. The differences in shale gas dilution intensity, caused by the differential preservation conditions of different structural styles and resulting differential dissipation behavior of the shale gas-helium system,serve as a key factor in helium accumulation of varying structural styles in the southeastern Sichuan Basin. Additionally,the synergistic effects of the diffusion and enrichment effects of helium in micro/nano pores and the physical clogging of migration pathways with methane molecules are identified as another significant factor governing helium enrichment in shale gas. Based on the investigation of the mechanisms behind helium enrichment in shale gas of different structural styles in the southeastern Sichuan Basin, it is predicted that secondary low-pressure zones with low shale gas grades outside the basin-such as the Qijiang, Wulong, Baima, and Pengshui blocks-are potential play fairways for helium enrichment in shale gas. This study is expected to open up an entirely new direction for the exploration and production of helium in shale gas.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2143K]

  • Advances in research on noble gas as tracers of geofluids and helium enrichment

    GAO Yu;LIU Quanyou;ZHU Dongya;WU Xiaoqi;LI Pengpeng;Institute of Energy, Peking University;Petroleum Exploration and Production Research Institute,SINOPEC;Wuxi Research Institute of Petroleum Geology, Petroleum Exploration and Production Research Institute,SINOPEC;

    [Background] Noble gases emerge as significant tools for tracing the sources and evolutionary processes of geofluids due to their chemical inertness and different isotopic compositions across varying reservoirs. Helium serves as a noble gas tracer and a scarce resource, and its enrichment mechanisms and exploration potential have attracted wide attention. [Methods] Based on a summary of the geochemical data of typical gas reservoirs, volcanic gases, and surface hot springs at home and abroad, this study analyzed the interfering factors and end-member value screening in the source apportionment of noble gases. Furthermore, it summarized the applications of noble gas isotopes in multiple scenarios such as constructing reservoir models and reconstructing fluid distribution. Accordingly, the helium accumulation theory was generalized based on the generation potential of helium, as well as its migration and accumulation mechanisms.[Advances and Prospects] By combining case studies, this study proposed three helium enrichment types: tectonic activity enhancing helium flux type(e.g., the Lhasa Block in the Qinghai-Tibet Plateau), the self-sealing-based helium accumulation in deeply buried high-pressure shale(e.g., the Cambrian and Silurian shale gas reservoirs in the Sichuan Basin), and helium accumulation based on the coupling of alkane gases and the precipitation of helium dissolved in water(e.g., the Hetianhe gas field in the Tarim Basin). The crust-derived helium flux in the Lhasa block shows a theoretical value 221 to 78 056 times the global average, with numerical simulations yielding 6 392 to 9 284 times, establishing this block as an ideal region for helium accumulation. Since the high-pressure nanopore system can significantly inhibit helium diffusion and an earlier hydrocarbon generation peak corresponds to a prolonged sustained helium enrichment stage, this study posits that the deeply buried ancient shale gas reservoirs possess ideal conditions for helium accumulation. Additionally, when the alkane gases accumulating in the late stage migrated toward traps, they can extract helium from widespread ancient formation water, leading to helium enrichment. Therefore, it is considered that these reservoirs also represent an ideal helium accumulation type.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1730K]

  • Physical simulation experiments on competitive dissolution of helium in helium-containing to helium-rich gas reservoirs

    ZOU Yi;LUO Qingyong;CHEN Jianfa;ZOU Huayao;DU Tao;LIU Xiaoqiang;CAI Xinyong;YU Chengming;FANG Zilong;Hainan Institute of China University of Petroleum (Beijing);College of Geoscience, China University of Petroleum (Beijing);Faculty of Petroleum, China University of Petroleum-Beijing at Karamay;

    [Background and Purpose] Helium is widely applied in high-tech and scientific research fields due to its unique physicochemical properties. Formation water plays a key role in helium migration and enrichment. Typically, in the form of dissolved gas, helium is transported in pores or fractures by formation water. When helium-rich fluids migrate to shallow natural gas reservoirs, helium will experience dissolution and desorption exchange with other gases.This process is affected by formation temperature, pressure, and water salinity, as well as the competitive dissolution between helium and other gases. However, there is a lack of studies on the mechanisms underlying the competitive dissolution between helium and other gases under formation conditions, along with the impact of these mechanisms on helium enrichment in helium-containing and helium-rich natural gas reservoirs. [Methods] This study investigated the Jinqiu gas field in the Sichuan Basin-a helium-containing to helium-rich gas field discovered recently. Based on actual geological data on gas reservoirs in this gas field, this study conducted physical simulation experiments by setting varying temperature, pressure, and water salinity conditions. Accordingly, delved into the mechanisms behind the competitive dissolution between helium and other gases, as well as the impact of these mechanisms on helium enrichment in natural gas reservoirs. [Results and Conclusions] Under pressure and temperature ranges of 10–60 MPa and 20–150 ℃, respectively, helium solubility in formation water with identical salinity initially decreased and then increased with rising temperature but kept increasing with pressure. Under a pressure of 25 MPa and a temperature of 70 ℃, the helium solubility decreased significantly with an increase in formation water salinity(0-300 g/L). Furthermore, under pressures ranging from 10 MPa to 60 MPa, temperatures varying from 20 ℃ to 150 ℃, and a formation water salinity of 84.5 g/L, a higher proportion of helium in mixed gases of helium and nitrogen corresponded to a higher helium solubility in the formation water. The helium accumulation in gas reservoirs in the Jinqiu gas field is primarily affected by the following factors:(1) Decreases in the formation temperature and pressure, combined with hydrocarbon enrichment attributable to hydrocarbon generation from organic matter, jointly decrease helium solubility in formation water, leading to helium exsolution from the formation water.(2) Hydrocarbon gases transport helium to shallower reservoirs. During the migration,further decreases in the formation temperature and pressure accelerate helium exsolution from the formation water. The resulting helium, together with hydrocarbon gases, recharges shallow gas reservoirs. This process results in higher helium content in shallow reservoirs compared to deep ones.(3) Gas reservoirs with anomalously low pressures exhibit lower gas recharge intensity than those with anomalously high and normal pressures, producing a smaller helium dilution effect. Moreover, these reservoirs exhibit lower pressure than their surrounding strata, thus facilitating helium enrichment. Consequently, shallow natural gas reservoirs with anomalously low pressures in the Sichuan Basin have the potential to emerge as play fairways for helium enrichment.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1697K]

  • Dominant factors causing helium deficiency in coal-measure natural gas in the Kuqa Depression, Tarim Basin

    LIU Jiarun;LIU Quanyou;LI Pengpeng;GAO Yu;Lü Jiahao;Institute of Energy, Peking University;State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences;University of Chinese Academy of Sciences;

    [Background] Helium is identified as a scarce strategic resource, having found widespread applications in high-tech fields such as high-end manufacturing, aerospace, and national defense due to its stable chemical properties and low boiling point. The Kuqa Depression in the Tarim Basin is a significant natural gas production base in China. Determining the distribution characteristics and controlling factors of helium in coal-measure natural gas in the Kuqa Depression holds great significance. [Methods] Using two helium resource assessment methods and geological data, this study explored the dominant factors causing helium deficiency in the coal-measure natural gas in the Kuqa Depression.[Results and Conclusions] The natural gas in the Kuqa Depression exhibits helium content(Volume fraction) ranging from 22×10~(-6) to 93×10~(-6)(average: 57.6×10~(-6)), suggesting helium-deficient natural gas. Its ~3He/~4He ratios range from3.33×10~(-8) to 11.24×10~(-8), indicating crust-derived helium. Helium in the natural gas originates primarily from the Jurassic coal-measure source rocks, with minimal contribution from the basement. The helium deficiency is predominantly governed by the regional structural evolution and the coupling effect of the helium-and hydrocarbon-generating intensities of coal-measure source rocks. In terms of structural evolution, differing from the discovered helium-rich gas fields,the Kuqa Depression has experienced continuous stratigraphic burial since the Himalayan, hindering the desorption and migration of helium. Regarding helium accumulation, the high hydrocarbon-generating intensity of coal-measure source rocks exerted a strong dilution effect on helium. Consequently, gas fields located in the hydrocarbon kitchen have a significantly lower helium content than those in the slope zone. The exploration of helium resources in coal-measure natural gas should focus on helium source rocks connecting the ancient basement, areas with strong regional tectonics and significant uplift of strata, and areas with weak natural gas charging and dilution. Exploration targets should be rationally selected according to helium accumulation conditions.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1676K]

  • Resource potential and extraction technique design for helium in coal measures

    WANG Lei;TANG Maoyin;PetroChina Coalbed Methane Company Limited;State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources,College of Geoscience and Surveying Engineering,China University of Mining and Technology-Beijing;

    [Back ground] Helium is an important strategic scarce resource. Presently, helium used in industry originates primarily from natural gas. In contrast, helium in coal measures, generally emerging as coalbed methane(CBM)with a high helium content, serves as a vital supplement to conventional helium resources. In industry, helium extraction from boil off gas(BOG) during natural gas liquefaction is recognized as an important way to obtain helium resources.However, existing studies on helium in coal measures mostly focus on the genesis, enrichment patterns, and geochemical characteristics of helium, while there is a lack of studies on its resource characteristics and extraction techniques.[Methods] This study investigated the helium resources in coal measures in the Sanjiaobei Block along the northeastern margin of the Ordos Basin as an example to analyze the characteristics of regional helium resources. Furthermore, a technique for helium extraction from natural gas in the block was designed based on a existing liquefied natural gas(LNG) plant in the block. [Results] The results indicate that the Sanjiaobei Block features abundant coal-measure gas but relatively low helium resources. Crust-derived helium is identified in this block, with molar volumetric fractions ranging from 0.01% to 0.30%(average: 0.07%). This establishes the Sanjiaobei Block as the low-helium area. Nevertheless,the helium resources in this block prove stable generally, with geological reserves and cumulative production reaching up to 11.145 6 million m~3 and 0.700 7 million m~3, respectively. Therefore, these helium resources can be treated as a feed gas source for helium extraction. This study conducted helium extraction from BOG produced during LNG production.The low-temperature helium extraction technique was selected, for which the two-tower separation technique combining pre-expansion refrigeration and nitrogen cycle refrigeration was employed. The helium extraction process consisted of six units: gas filtration, catalytic dehydrogenation, dehydration and drying, helium extraction, helium charging, and liquid oxygen catalysis. [Conclusions] The design proposed in this study adopts a nitrogen circulation system(NCS) for efficient refrigeration and optimizes energy recovery, reducing the dependence on direct compression of feed gas. Furthermore, this design provides a stable low-temperature environment that is insensitive to helium concentration fluctuations, enabling the rational and full utilization of BOG gas produced in the plant. This renders the design especially suitable for efficient extraction of low-abundance helium resources produced in the plant. The findings of this study will play a positive and significant role in improving both the technique for helium extraction in coal measures and the economic benefits of relevant enterprises.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1596K]

  • Effectiveness assessment and spatial distribution characteristics of helium source rocks in the Shixi Block along the eastern margin of the Ordos Basin

    CHANG Yangmei;LIU Chao;SUN Beilei;College of Geological and Surveying Engineering, Taiyuan University of Technology;Key Laboratory of Coal Science and Technology, Ministry of Education, Taiyuan University of Technology;

    [Background] Helium gas serves as a significant rare strategic resource. In China, helium resources are relatively scarce and dependent heavily on imports. Therefore, there is a pressing need for the exploration and exploitation of helium resources. Helium source rocks provide a material basis for the formation of helium resources. The Zijinshan pluton serves as a principal source of coal-measure helium along the eastern margin of the Ordos Basin. Previous studies reveal that helium in natural gas within the Shixi Block originates primarily from the decay of radioactive elements in the deep part of the Jianjiagou-Zijinshan plutons. However, there is a lack of reports on the discovery of helium-rich natural gas in the Linxing Block, which is closer to the Zijinshan pluton. [Methods] This study investigated the Linxing and Shixi Blocks as study areas. Utilizing the geochemical parameters and mineralogical characteristics of helium source rocks in these blocks, this study quantitatively analyzed the helium-generating intensities of the helium source rocks, assessed their effectiveness, and calculated their helium generation volumes. In combination with log data, this study investigated the spatial distribution characteristics of potential helium source rocks in the Shixi Block along the eastern margin of the Ordos Basin. [Results and Conclusions] The potential helium source rocks in the Shixi Block exhibit uranium(U) content ranging from 0.25×10~(-6) to 9.19×10~(-6) and thorium(Th) content from 0.56×10~(-6) to 21.0×10~(-6). In contrast, potential helium source rocks in the Linxing Block manifest U content ranging from 1.29×10~(-6) to 207×10~(-6) and Th content from 8.19×10~(-6) to 438×10~(-6). Within the Shixi and Linxing blocks, U and Th occur predominantly as isomorphism in the basement granites. In bauxites, mudstones, coals, and sandstones, U and Th occur primarily in adsorbed and complexed forms, associated with organic matter and clay minerals. The Shixi and Linxing blocks have total helium generation volumes ranging from 4.92×10~8 m~3 to 6.94×10~8 m~3 and from 75.7×10~8 m~3 to 110.4×10~8 m~3, respectively. Primary helium source rocks in the Shixi Block include the metamorphic series and granites in the basement, followed by dolomites, sandstones, mudstones and coals. In contrast, primary helium source rocks in the Linxing Block encompass the metamorphic series and granites in the basement, along with the Zijinshan pluton, succeeded by dolomites,sandstones, mudstones, coals, and bauxites. Given the lack of log data, this study failed to analyze the spatial distribution characteristics of helium source rocks in the Linxing Block. However, the calculated helium generation volumes suggest the exploration and exploitation potential throughout the Linxing Block. The helium source rocks in the Shixi Block(except for the basement) are thick in the western and thin in the eastern portions. Notably, both sandstones in the lower Shihezi Formation and most strata in the Shanxi Formation exhibit high helium generation volumes. Therefore,these strata should be highlighted in the exploration and exploitation of helium resources.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2601K]

  • Backfill-strip mining and CO2 mineralization sequestration in coal mine goaves: A synergetic method and its key technologies

    ZHU Mengbo;LIU Lang;WANG Shuangming;WEI Baoning;RONG Ruoyu;ZHANG Wenzhong;ZHUANG Dengdeng;JIA Qifeng;College of Energy and Mining Engineering, Xi'an University of Science and Technology;Geological Research Institute for Coal Green Mining, Xi'an University of Science and Technology;College of Geology and Environment, Xi'an University of Science and Technology;CCTEG Xi'an Research Institute(Group) Co., Ltd.;

    [Objective] Coals serve as both the cornerstone of China's energy security and important industrial raw materials. However, their mining and utilization tend to cause ecological and environmental problems such as CO_2 emissions, the generation of solid wastes, and land subsidence. This necessitates reforming coal mining methods to promote the green, low-carbon, and sustainable development of China's coal industry. [Methods] Through the comparative analysis of the conditions of CO_2 sequestration in goaves corresponding to the caving, room-and-pillar(also known as knifepillar), and backfill mining methods, this study developed a synergetic method for backfill-strip mining and CO_2 mineralization sequestration in goaves by combining the current status of technologies for geologic CO_2 sequestration and coal mine backfill mining. With a typical coal mine in Shaanxi Province as a case study, this study conducted numerical simulation experiments on damage to the overlying low-permeability, thick mudstone layer during backfill-strip mining.Based on the continuous and the foundation beam models, this study established a mechanical model of the cap rocks and a model for the mining-induced fracture heights. Additionally, key technologies for the synergetic method were proposed. [Results and Conclusions] Goaves formed under the caving and room-and-pillar mining are characterized by poor reservoir and cap rock conditions for CO_2 storage, which tend to pose high leakage risks. In contrast, the backfill mining method can effectively protect cap rock integrity. However, it is necessary to reserve storage spaces if this method is applied. The numerical simulation results indicated that the maximum subsidence of the upper boundary of the lowpermeability, thick mudstone layer No.3 above the goaf were determined at 1 230 mm, 520 mm, and 105 mm, respectively under backfilling rates of 0, 50%, and 80%. As the backfilling rate increased, the low-permeability, thick mudstone layer exhibited decreased subsidence amplitude and substantially reduced plastic deformation areas. Therefore, the integrity of the cap rocks can be ensured by optimizing the process and parameters of the strip-backfill mining. The mechanical model of a non-horizontal continuous beam with six spans under the condition of three mining-backfilling cycles was established, and the expressions for reaction forces and bending moments at pivot points were derived. Additionally, the model for the mining-induced fracture heights was constructed. To achieve the practical application of the synergetic method, it is necessary to make breakthroughs in key technologies including geological siting, the building and stability-orientated regulation of underground gas storage(UGS) facilities for CO_2 sequestration, CO_2 mineralization combined with desulfurization/denitrification for backfilling material preparation, and CO_2 charging simulation and optimization, followed by the development of comprehensive schemes. This will offer new approaches for the green, lowcarbon development of China's coal industry.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2150K]

  • Analyzing the permeability enhancement effect of hydraulic slotting for low-permeability coal seams based on a stress-diffusion-seepage coupling model

    ZHANG Hongtu;ZHOU Tian;WANG Dengke;LI Botao;LUO Yong;PAN Rongsheng;TANG Jiahao;LU Weiyong;School of Safety Science and Engineering, Henan Polytechnic University;State Key Laboratory Cultivation Base for Gas Geology and Gas Control;Collaborative Innovation Center of Coal Work Safety and Clean High Efficiency Utilization;Sichuan Furong Chuannan Construction Engineering Co., Ltd.;Department of Resources and Mechanical Engineering, Lüliang University;

    [Objective and Methods] This study aims to improve the permeability enhancement effect of coal seams for gas drainage. Targeting the soft, low-permeability coal seams with complex gas occurrence conditions in the Baiping mining area and considering the impacts of effective stress, gas migration, actual gas effects, and tortuosity, this study constructed a stress-diffusion-seepage coupling model based on the pore-fracture dual medium assumption. Using the coupling model, this study simulated the variation patterns of gas content in coal seams during gas drainage under varying gas contents and borehole spacings. Through field tests under different permeability enhancement measures and unloaded coal amounts across borehole intervals, this study compared the permeability enhancement effects of hydraulic flushing, hydraulic slotting, and mechanical reaming to determine the optimal permeability enhancement technique.[Results and Conclusions] The stress-diffusion-seepage coupling model enables accurate characterization of the diffusion behavior and flow paths of gas in coal seams. The coal seam thickness and gas content produce significant impacts on the gas drainage effects, with a thicker coal seam and higher gas content associated with a smaller borehole spacing required to achieve effective gas drainage. Under gas contents of ≤7 m3/t, >7-8 m3/t, and >8-9.35 m3/t, borehole spacings sshould not exceed 11 m, 9 m, and 8 m, respectively in the case of coal seam thicknesses ≤1 m, should not exceed 10 m, 9 m, and 7 m, respectively if coal seam thicknesses range from > 1 m to 5 m, and should not exceed 10 m,8 m, and 7 m, respectively if coal seam thicknesses vary from > 5 m to 9 m. Field tests indicate that hydraulic flushing,hydraulic slotting, and mechanical reaming all reduce the volume fraction of methane in coal seams and increase the effective gas drainage radius. Notably, these effects prove especially significant in the early drainage stage, while gradually tending to be gentle in the later stage. Under the same technical conditions, hydraulic slotting can deliver optimal performance, reducing the volume fraction of methane by 64.74 % and increasing the effective gas drainage radius by0.35 m after 90 days of gas drainage.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 3289K]

  • Influencing patterns of low-temperature nitrogen on the pore structure and oxidation characteristics of lignite

    XIE Shuliang;WANG Gang;QU Qingdong;LIU Hao;SUN Lulu;College of Safety and Environmental Engineering, Shandong University of Science and Technology;Shandong University of Science and Technology, Mining Disaster Prevention and Control-Ministry of State Key Laboratory Breeding Base;The Commonwealth Scientific and Industrial Research Organisation;

    [Objective] During fire prevention and extinguishment for mines, injecting normal-temperature nitrogen into goaves can only play an inerting role. Meanwhile, the preparation of liquid nitrogen is complicated and costly. Therefore, in the Wudong Coal Mine in Xinjiang, low-temperature gaseous nitrogen of -40 ℃ was prepared using nitrogen cooling devices and then injected into goaves to prevent the spontaneous combustion of residual coals. However, the influencing patterns of low-temperature nitrogen on the pore structures and oxidation characteristics of residual coals in goaves remain poorly understood. This tends to affect the prediction and forecast of the secondary oxidation of residual coals in goaves after low-temperature nitrogen injection ends. [Methods] Using experiments with an ultra-depth 3D digital microscope and a confocal laser scanning microscope(CLSM), nitrogen adsorption experiments, and temperatureprogrammed heating experiments, this study examined the surface morphologies, pore structures, and oxidation characteristic parameters of coals following sample processing using low-temperature nitrogen. [Results and Conclusions]After being processed using low-temperature nitrogen, the surface structures of coal samples were destroyed. With an increase in the processing time, the coal samples exhibited more developed reticular pore structures, and coal sample surfaces displayed distinct undulations. The arithmetic mean height of various points on the surfaces gradually increased from 9.562 1 μm to 21.904 5 μm, with an increase of 1.29 times. Concurrently, the average height difference of all undulations rose from 81.321 0 μm to 193.146 5 μm, representing an increase of 1.36 times. Low-temperature nitrogen primarily affected the distribution of micropores and mesopores in the coal samples, especially 2-4 nm mesopores. With an increase in the sample processing time, micropores in the samples trended upward and then downward, while mesopores therein showed an opposite trend. As a result, the total pore volume increased by 0.004 3 cm~3/g, with the 2-10 nm mesopores identified as the largest contributor, and the specific surface area of coal samples determined using the Brunauer–Emmett–Teller(BET) theory increased by 0.049 3 m~2/g. After sample processing using low-temperature nitrogen,the CO production, heat release intensity, and oxygen consumption rates significantly increased during coal sample oxidation. Notably, their increments increased with the sample processing time. Specifically, the CO production, oxygen consumption rate, and maximum heat release intensity increased by 5.02×10~4 μL/L at maximum, 2.33×10~(-8) mol/(cm~3·s),and 2.25×10~(-2) J/(cm~3·s), respectively. Additionally, the characteristic temperature of oxidation reactions in the coal samples decreased. The results of this study reveal that low-temperature nitrogen can destroy the pore structures of coals and enhance their oxidation performance. In the case where low-temperature nitrogen of -40 ℃ is injected into a goaf,its macroscopic dominant effect of inerting and cooling can effectively suppress the spontaneous combustion of coals.When oxygen is restored after nitrogen injection ends, coals show a higher tendency for spontaneous combustion after being treated due to the microscopic side effect of low-temperature nitrogen, enhancing the secondary oxidation intensity.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2024K]

  • Chemical temporary plugging-based full-bore reconstruction technology for old wellbores for the collaborative production of tight-sand gas and deep coalbed methane

    YANG Fan;TAN Zhanglong;HU Jiachen;AN Qi;LI Yu;YANG Ruiyue;LIN Junwen;SUN Zening;JING Meiyang;China United Coalbed Methane Corporation Ltd.;CNOOC Energy Development Co., Ltd.Engineering Branch;State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing);

    [Objective] In China, the Ordos Basin boasts abundant coal-measure gas resources, holding considerable potential for resource development. As the development deepens, the proportion of depleted, stripper, and inefficient wells for tight-sand gas in coal measures has gradually decreased year by year. The collaborative production of tight-sand gas and deep coalbed methane(CBM) has emerged as a significant approach to effectively releasing production capacity.[Methods] To achieve the reconstruction of old wellbores and commingled production of new and old layers, this study proposed a technology of chemical temporary plugging-based full-bore reconstruction of old wellbores of tight-sand gas combined with the large-scale production of deep CBM. Specifically, a chemical temporary plugging material system was developed based on the concept of dynamic chemical temporary plugging through large-particle bridging, mediumparticle filling, and adaptive powder plugging. In combination with the fractal theory and the plugging layer instability criterion, this study constructed a multi-purpose calculation model for the permeability and strength of plugging layers.Accordingly, it proposed an optimized ratio of particle sizes 3-4 mm, 1-2 mm, and 0.15 mm at 1:2:4 to plug low-productivity and inefficient old layers. This created favorable conditions for the fracturing and stimulation of deep coal seams. The proposed technology was applied to the field test conducted in the Linxing-Shenfu Block in the Ordos Basin,validating the rationality and feasibility of the proposed wellbore reconstruction technology and composite temporary plugging material system. [Results and Conclusions] Field implementation of the optimized composite temporary plugging agent achieved full-bore wellbore reconstruction based on chemical temporary plugging, effectively plugging the stimulated reservoirs in the old well, with the pressure born by the plugging layer exceeding 60 MPa. The fracturing process using smooth casings, integrated variable-viscosity slickwater, and temporary plugging knots was employed to stimulate the deep coal seams. The pressure was maintained stable in the proppant injection stage, with no leakage sites or fracturing liquid division observed. Therefore, large-scale volume fracturing of the deep coal seams lying below the tightsand gas layer was successfully achieved. The results of this study are expected to provide technical support for both the succeeding production of tight-sand gas pay zones in old wells and the collaborative production of tight-sand gas and CBM.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2069K]

  • Prediction of geological and engineering integrated sweet spots of deep coalbed methane

    CHEN Zhengrong;LIU Wei;ZHU Xueshen;TIAN Yongjing;XIE Xin;College of Petroleum Engineering, China University of Petroleum (Beijing);State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing);CNOOC Research Institute Co., Ltd.;

    [Objective] Deep coalbed methane(CBM) has emerged as a hot topic in CBM resource development.However, deep CBM has characteristics such as great burial depths, complex stress environments, and strong reservoir heterogeneity, which seriously restrict sweet spot prediction and accurate well location deployment in its large-scale exploitation. [Methods] This study investigated a deep CBM field along the eastern margin of the Ordos Basin. Using sonic, density, and caliper logging, this study developed a coal structure index model for deep coals. By introducing the coal structure index based on the coal structure differences in deep coal seams and combining factors including overburden formation pressure, tectonic stress, and pore pressure, this study established an adaptive horizontal in-situ stress difference model for deep coal seams. Based on the rock strength parameter, the enlargement rate of wellbore diameter, and the fracture toughness of rocks, a natural fissure index model was constructed. By integrating these three models, as well as the six indices of geological and engineering sweet spots, this study developed an intelligent prediction model of geological and engineering integrated sweet spots of deep CBM using support vector machine(SVM). [Results] The results indicate that the intelligent prediction model of geological and engineering integrated sweet spots yielded a prediction accuracy of 88.2%. Classes I, II, and III sweet spots were identified in the study area, with areas of 117.4 km2(14.0%),258.4 km2(30.8%), and 463.1 km2(55.2%), respectively, and average predicted production of 6 478.6 m3/d,5 076.7 m3/d, and 4 022 m3/d, respectively. [Conclusions] Based on the results of this study, it is recommended to focus on Class I sweet spots, actively explore Class II sweet spots, and proactively avoid Class III sweet spots in the well location deployment for deep CBM in the study area. The fine-scale prediction of geological and engineering integrated sweet spots can provide valuable guidance for reserve growth and production addition of deep CBM along the eastern margin of the Ordos Basin.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2127K]

  • Construction and application of a TCN-LSTM-SVM-based time series prediction model for water inflow in coal seam roofs

    LIU Xuan;JI Yadong;ZHU Kaipeng;ZHAO Chunhu;LI Kai;LI Chaofeng;YUAN Chenhan;LI Panpan;YAN Pengzhen;China Coal Research Institute;CCTEG Xi'an Research Institute (Group) Co., Ltd.;State Key Laboratory of Coal Mine Disaster Prevention and Control;Shaanxi Key Laboratory of Prevention and Control Technology for Coal Mine Water Hazard;

    [Background] The accurate prediction of mine water inflow plays a significant role in the prevention and control of water hazards and the safe and efficient production in coal mines. [Methods] To construct a prediction model of water inflow in mines under threat of water hazards from extremely thick sandstones aquifer in West China, this study investigated a typical mine(also referred to as the studied mine) severely affected by such water hazards in the Binchang mining area of Shaanxi Province. The correlation between the mining footage and water inflow of the mining face was selected as the characteristic variable for the time series prediction of mine water inflow. Accordingly,this study proposed a prediction model for water inflow along the mining face in the studied mine based on the temporal convolutional network(TCN), long short-term memory(LSTM), and support vector machine(SVM)-the TCN-LSTM-SVM model. First, by raw data processing using the TCN framework, this model extracted the dependency between mining footage and water inflow and its dynamic characteristics. Subsequently, the extracted characteristics were output to the LSTM-SVM model to further capture the time series relationship between mining footage and water inflow and its characteristics. [Results] The training and prediction results indicate that the TCN-LSTM-SVM model yielded mean absolute errors(E MA) ranging from 56.02 m~3/h to 129.89 m~3/h, mean absolute percentage errors(EMAP) from 3 % to 7 %, root mean square errors(ERMS) from 82.60 m~3/h to 162.61 m~3/h, and coefficients of determination(R 2) from 0.81 to 0.98based on the training, validation, and test sets. This model exhibited more accurate prediction results compared to the commonly used prediction models like backpropagation neural network(BPNN), random forest(RF), and Transformer while avoiding excessive errors produced by most of these models on the validation and test sets. The results indicate that the TCN-LSTM-SVM model integrated the parallel processing advantages and multi-scale feature extraction capacity of the TCN model while also enjoying the excellent prediction performance and generalization capability of the LSTM-SVM model. Compared to previously developed models, the TCN-LSTM-SVM model demonstrated certain superiority and applicability in the prediction of water inflow along the mining face in the studied mine. [Conclusions] The results of this study provide a new approach to water inflow prediction for mines with similar geological conditions to those in the Binchang mining area. Therefore, this study holds practical implications for water inflow prediction and water prevention and control in mining faces with similar geological conditions to those in the studied mine.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1732K]

  • The borehol wall image digital description method of the overlying rock structural planes evdution process in deep mining

    WANG Jinchao;ZOU Junpeng;LI Shenghai;WANG Chao;LI Xiaobin;State Key Laboratory of Water Resource Protection and Utilization in Coal Mining;State Key Laboratory of Geomechanics and Geotechnical Engineering Safety, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences;Faculty of Engineering, China University of Geosciences (Wuhan);Jining Engineering Research Center for Complex Hard Rock Drilling, Shandong Provincial Lunan Geology and Exploration Institute (Shandong Provincial Bureau of

    [Objective] In China, as mineral resource mining is increasingly expanding towards the deep parts of the Earth, the safe and efficient exploitation of deep resources has become a major strategic and technological challenge at the national level to be addressed urgently. Understanding the movement patterns of mining-affected strata in deep environments will assist in improving the intelligent prevention and control of mine disasters, thereby ensuring the safe and efficient exploitation of deep resources. [Methods] Targeting the complex and diverse forms of the overburden's structural planes in deep mining, as well as a lack of characterization methods tailored to the evolutionary process of the structural planes, this study proposed a digital characterization method based on borehole wall images. First, by leveraging the structural information of rock masses derived from borehole wall images, this study developed a method for describing characteristic points that reflect the spatial morphologies and locations of structural planes. This allowed for the digitization of the three-dimensional spaces of the overburden's structural planes. Second, based on the typical evolutionary characteristics of the structural planes, this study established a characterization system for the evolutionary process of the overburden's structural planes, which involved the linear movement, torsional movement, and thickness evolution of the structural planes. Last, the proposed method was applied to a practical case, demonstrating its superiority in the fine-scale characterization of the evolutionary process of key zones of the structural planes compared to traditional simple image-based characterization methods. [Results and Conclusions] The proposed method can present the evolutionary characteristics of the structural planes of rock masses at different deep locations in the form of three-dimensional point cloud coordinates. Compared to traditional image display, the scatter plots of spatial characteristic points present more detailed change processes, enabling a more fine-scale characterization of the evolutionary process of key zones and the rapid search of typical characteristic zones of rock movement. The proposed method provides a more convenient digital basis for revealing the variation patterns of internal rock movement in the mining process, serving as a new digital method to characterizing evolutionary processes in research on the movement of strata during mine exploitation.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2046K]

  • Impacts of metakaolin and fly ash on the performance of cement-based grouting materials in anchoring engineering

    CHENG Zhiyuan;YANG Junpeng;XUE Wei;WEI Daidong;WANG Yimin;School of Civil Engineering and Transportation, South China University of Technology;Guangzhou Chemical Grouting Co.Ltd., CAS;

    [Objective] The filling of grouting materials plays a significant role in ensuring the performance of anchoring structures. This study aims to further enhance the fluidity of grouting materials, reduce their dry shrinkage in the curing process, and ensure complete filling. This will help improve the bonding property between the anchoring body and the rock and soil mass to be reinforced. [Methods] Using cement as the primary material, as well as fly ash and metakaolin as admixtures, this study designed and prepared 20 groups of binary and ternary mixtures and one control group.Through tests of the fluidity, bleeding ratios, and mechanical strengths of these mixtures with different mix ratios, this study determined the impacts of metakaolin and fly ash on the performance of cement-based grouting materials. In combination with the X-ray diffraction(XRD) analysis and scanning electron microscopy, this study revealed the mechanisms underlying the regulation of metakaolin and fly ash for the performance of cement-based grouting materials. Finally, this study proposed the optimum mix ratio of grouting materials while considering the fluidity and filling ability of grouts, as well as the load-bearing capacity of the anchoring body. [Results and Conclusions] With the metakaolin and fly ash contents were controlled at approximately 6% and 15% to 20%, respectively, the resulting grout exhibited a reduced viscosity of 0.16 Pa·s and a reduced bleeding rate of 2% at γ = 100 s-1 compared to pure cement grout. Furthermore, its compressive strength increased to approximately 30 MPa at day 7 and about 32.7 MPa at day 28. In this case,the cement-based grouting material delivered the optimal overall performance. The XRD and SEM analyses indicate that metakaolin and fly ash exhibited significant synergistic effects when mixed into the ternary mixtures, as evidenced by a faster hydration rate, a more even distribution of hydration products, and a denser microstructure. The results of this study provide a scientific basis for enhancing the performance of cement-based grouting materials by using metakaolin and fly ash as admixtures, offering a valuable reference for the design and applications of grouting materials in anchoring engineering.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1926K]

  • Current status and future trends of seismic prediction and assessment technology for coalbed methane reservoirs

    WU Haibo;ZHANG Pingsong;XU Shi'ang;HUANG Yaping;DONG Shouhua;CHENG Yan;LI Donghui;ZHANG Sheng;ZHANG Min;School of Earth and Environment, Anhui University of Science and Technology;State Key Laboratory of Digital Intelligent Technology for Unmanned Coal Mining, Anhui University of Science and Technology;School of Resources and Geosciences, China University of Mining and Technology;China National Administration of Coal Geology;College of Safety Science and Engineering, Henan Polytechnic University

    [Background] The seismic prediction and assessment technology for coalbed methane(CBM) reservoirs has undergone rapid development for over three decades, playing an indispensable role in CBM exploration. [Methods] This study reviews the development history and current status of core technologies within the seismic prediction and assessment technical system for CBM reservoirs, including seismic-petrophysical tests, modeling and inversion, seismic wavefield simulation, seismic amplitude versus offset(AVO) inversion and seismic attribute inversion, and integrated seismic prediction of the sweet spot areas of CBM reservoir resources and engineering. Furthermore, this study delves into the impacts and limitations of the characteristics of CBM reservoirs, such as adsorbed gas, pore-fracture dual system,viscoelasticity, and thin layers, on the accuracy and resolution of seismic prediction and assessment technology for CBM reservoirs. Finally, this study proposes future prospects for the development trends and directions of seismic prediction and assessment technology for CBM reservoirs from two perspectives: the shift in the targets for CBM reservoir exploitation and the technological iteration of critical seismic exploration links. [Prospects] In the future, seismic prediction and assessment technology for CBM reservoirs will closely follow the development direction of deep CBM exploitation and the multi-gas commingling production from coal measures. Breakthroughs are to be achieved in the following technical aspects: fine-scale petrophysical characterization of reservoirs, numerical modeling and simulation, high-precision exploration data acquisition, target-oriented fine-scale processing, multi-parameter high-precision intelligent inversion,and comprehensive identification of sweet spot areas. This will promote a leap forward in the field of CBM exploration.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 1922K]

  • A method integrating a non-stationary random field for constrained inversion of CSAMT data

    DAI Qianwei;GUO Luyao;WU Yun;XIONG Zhexian;DUAN Dan;BAO Zhonglin;WU Hongfei;HAO Fengyun;School of Geosciences and Info-physics,Central South University;Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Ministry of Education,Central South University;Zhengyuan International Mining Co.,Ltd.;Altay Zhengyuan International Mining Co.,Ltd.;

    [Objective] The inversion of controlled-source audio-frequency magnetotelluric(CSAMT) data remains challenging due to two key issues: computational efficiency and resolution. To tackle these two issues, especially the oversmoothing effect caused by traditional regularization methods in estimating complex geological structures, this study proposed an improved regularization inversion method to reflect the spatial distribution characteristics of subsurface physical property parameters more accurately. [Methods] The proposed method was developed using the method for establishing the stochastic partial differential equation(SPDE) based on the Matérn covariance function. By introducing vector fields and the shape parameters of a range ellipse, this method fully considered both variations in the inclination of strata and the non-stationary nature of physical property distribution. Accordingly, this study developed a model covariance matrix meeting the non-stationary assumption. Then, inversion was conducted using the model covariance matrix as the regularization constraint. From the perspective of inversion results, residuals, relative residuals of apparent resistivity, and uncertainty, this study compared the proposed method with traditional maximum smoothness-constrained inversion and covariance-constrained inversion based on the stationary assumption. In addition, the proposed method was applied to measured data from the exploration of the Ye'erkeman-Jinba gold deposit in Habahe County, Xinjiang to validate its practical application effects. [Results] The results from the theoretical model indicate that the four experiments with the non-stationary constraint yielded residuals ranging from 20.47% to 21.29%, which were lower than those of experiments with the stationary constraint(21.25% and 22.83%) and those of experiments using traditional maximum smoothness-constrained inversion(32.46%). Furthermore, the proposed method could characterize geological structures more accurately and delineate geological boundaries more distinctly. The results from measured data show that the covariance-constrained CSAMT inversion based on the non-stationary assumption delivered significantly higher imaging performance than the conventional Occam-type(smoothness constrained) inversion, achieving a 51.47% reduction in data fitting residuals. The proposed method exhibited a remarkably enhanced capacity to identify complex geological structures and reduced the uncertainty in the inversion results of deep areas, thereby effectively improving the overall reliability of inversion results. [Conclusions] The non-stationary assumption-based inversion method with the Matérn covariance function as the regularization constraint provides a novel technical solution for addressing the issues of the insufficient computational efficiency and resolution of CSAMT inversion. This method holds great significance for advancing geophysical inversion technology.

    2025 06 v.53;No.330 [Abstract][OnlineView][Download 2930K]
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