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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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2025年02期目次

  • Sedimentary characteristics of coals in meandering river and braided river facies and during their transitions: A case study the Walloon Subgroup in the F8 block in the Surat Basin, Australia

    CUI Zehong;ZHAO Yibo;LI Zhihua;LI Shengli;LI Weiru;Petro China Research Institute of Petroleum Exploration & Development;School of Energy Resources,China University of Geosciences (Beijing);School of Education, Langfang Normal University;School of Earth Resources, China University of Geosciences;School of Electronic Information Engineering, Langfang Normal University;

    [Objective] Australia is recognized as the fourth largest producer and the second largest exporter of coals in the world. The Bowen-Surat Basin is the largest coal producing basin in this country. The Surat Basin exhibits coal-bearing layers of the Middle Jurassic Walloon Subgroup. This subgroup features a sedimentary environment of fluvial facies,necessitating clarifying the differential sedimentary characteristics and patterns of coal seams in braided river and meandering river facies and during their transitions. [Methods] Using comprehensive geological analysis methods, as well as seismic data, logs, and core data, this study established the sedimentary pattern of the study area. Using seismic horizon tracking and base-level cycles, this study divided the study area into six fourth-order stratigraphic cycles and categorized the log curves of 37 wells into five combinations based on the morphological characteristics of the curves and contact relationships. The observations of cores from 14 wells revealed six typical lithofacies in the Walloon Subgroup. In combination with the characteristics of log curves and lithofacies, this study determined two sedimentary facies: braided river to meandering river facies. The sedimentary facies can be further divided into eight microfacies. Using two horizontal and vertical cross-well sections, this study characterized coal distribution and analyzed the differential sedimentary characteristics of coal seams in the braided river and meandering river facies and during their transitions. [Results and Conclusions] In the case of a high base level, the study area was in a sedimentary environment of the meandering river facies. In this case, coals were well-developed, exhibiting the superimposition of multiple coal seams. As the base level dropped, the meandering river facies gradually transitioned to the braided river facies, with the lithofacies changing from fine-to coarse-grained rocks and the amplitude of bedding structures increasing. During this period, high-energy water flow washed away coal seams formed previously, leaving scattered coal deposits in braided river channels. When the base level approached its minimum, the study area exhibited a sedimentary environment of the braided river facies. This period witnessed the lowest level of coal development, with a minor presence of coals in overflow sands. As the base level rose, the braided river facies transitioned to the meandering river facies. During this period, the water body energy decreased, and the lithofacies varied, exhibiting Gm-St-Sp-SH-Fr/C sequentially. Meanwhile, an increasing number of coal seams were deposited. In the transition from the meandering river facies to the transition zone and then to the braided river facies, the three-dimensional coal distribution was characterized by increasingly reduced planar continuity and range, lateral continuity in sections, vertical stacking and thickness. As the base level changed, the sedimentary microfacies that was the most favorable for coal accumulation was coal swamps, followed by floodplains and overflow sands. The achievements of this study can serve as a guide for the analysis of the distribution range of coal seams. During well emplacement in the Surat block, the results of this study can help confirm the "sweet spots" of the targets for coal coalbed methane(CBM) production.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 3782K]

  • Relationship between continental chemical weathering trends in the North China Basin and the high-latitude glacial cycles from the Late Carboniferous to the Early Permian

    LING Ziyu;YANG Minfang;WANG Lei;WANG Ye;ZHANG Peixin;LIU Haoqing;SHAO Longyi;LU Jing;State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources, School of Geosciences & Surveying Engineering, China University of Mining & Technology (Beijing);Research Institute of Petroleum Exploration & Development,PetroChina;PetroChina Coalbed Methane Co., Ltd.;School of Civil Engineering, Shenyang Jianzhu University;Henan International Joint Laboratory for Green Low Carbon-Water Tr

    [Objective and Methods] The Late Paleozoic Ice Age(LPIA; ca. 360-254 Ma), the only period recording the transition from icehouse to greenhouse conditions throughout the geological history, can provide a deep-time perspective for glacier-environment-climate coevolution and future climate change. To gain a deep understanding of the potential relationship between the continental chemical weathering trends in low-latitude regions and the glacial cycles in the high-latitude Gondwana region from the Late Carboniferous to the Early Permian, this study investigated the mudstones of the Benxi-Taiyuan formations, Liujiang coalfield, North China Basin. Using multiple chemical weathering indices such as chemical index of alteration(CIA), chemical index of weathering(CIW), and plagioclase index of alteration(PIA) calculated from the elemental geochemical data of the mudstones, this study reconstructed the continental chemical weathering trends and paleoclimatic evolutionary characteristics of the Liujiang coalfield. [Results] The results indicate that the periodic changes of continental chemical weathering in the low-latitude Liujiang coalfield involved three weathering weakening stages(i.e., early-middle Bashkirian, Moscovian-Kasimovian, and early Asselian) and two weathering enhancement stages(i.e., late Bashkirian and Gzhelian). This cyclic alternation of weathering trends was closely associated with the glacial cycles of the high-latitude Gondwanaland. The weathering weakening stages represent shifts to relatively cool and dry climates, roughly synchronous with the glacial periods at high latitudes. In contrast, the weathering enhancement stages suggest changes to relatively warm and humid climates, coinciding with the interglacial periods at high latitudes. The comparative analysis reveals that frequent volcanic activity, increased atmospheric CO2 concentration, climate warming, enhanced hydrologic cycles, and sea-level rise during the interglacial periods jointly contributed to the reduced area of tropical rainforests and the enhanced continental chemical weathering, creating favorable conditions for the formation of bauxite. In contrast, the weakening volcanic activity, cooling climate, reduced atmospheric CO2 concentration, and increased rainforest area during the glacial periods led to weakened continental weathering, facilitating the formation of coals and organic-rich mudstones. [Conclusions] The results of this study reveal the relationship between the continental chemical weathering trends in the low-latitude North China Basin and the glacial cycles and the distributions of sedimentary minerals(e.g., coals and bauxite) in the high-latitude Gondwana region, providing a novel perspective for understanding the mechanisms underlying complex glacier-environment-climate interactions throughout the geological history.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1653K]

  • Geological-engineering integrated reconnaissance survey technology for skylights as a hidden disaster-causing factor

    DONG Mintao;CCTEG Xi'an Research Institute (Group) Co., Ltd.;

    [Objective] Skylights represent a primary hidden disaster factor in mines in the southern Yushen mining area within the Shanbei Jurassic coalfield, Shaanxi Province. Since they are hidden and difficult to detect, their distribution in the mining area remains unclear, posing pronounced safety hazards. This necessitates developing effective technical means to overcome challenges in the spatial exploration of skylights and ensure mine safety. [Methods] Focusing on a typical mine in the Yushen mining area as an example, this study explored the spatial distribution characteristics and types of skylights in the study area using the geological-engineering integrated reconnaissance survey technology that combines geological analysis, scientific assessment, and engineering exploration. [Results and conclusions] The results indicate that the formation and evolution of skylights in the study area are primarily governed by the paleochannels,while also exhibiting some inheritance from modern rivers. The high-density direct current electric method and micromotion exploration yielded distinct resistivity and acoustic signals of skylights in the study area, exhibiting significantly high resistivity and anomalous wave velocities. In contrast, the transient electromagnetic method yielded insignificant responses of physical properties. The developmental areas of skylights consist of lithologic assemblages formed by paleochannel sediments, exhibiting a distinct dual structure and lithologic assemblage characteristics of secondarily deposited laterites mixed or interbedded with sandy soil layers in channels. The developmental areas of laterites are characterized by borehole shrinkage, small fluid leakage in boreholes, and upright rock layers with distinct stratification. In the developmental areas of skylights, loess and laterites exhibit permeability coefficients of 2.21×10-2 m/d and 7.18×10-3m/d, respectively, suggesting that laterites have a higher capacity to block water flow than loess. Comprehensive geophysical prospecting allows for the quick identification of anomalous laterite areas on a horizontal plane, providing a basis for accurately delineating skylights using detailed exploration engineering. Concurrently, the detailed exploration results can verify the accuracy of the resistivity and acoustic signal characteristics of skylights derived using comprehensive geophysical prospecting. The results of this study can provide technical support for the reconnaissance survey and treatment of the skylights formed by the lacuna of laterites in the study area and serve as a guide of technical means for the effective exploration of skylights in mining areas with geological conditions similar to those in the study area,thus offering geological guarantee technology for safe, efficient, green, and intelligent coal mining.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2952K]

  • Characteristics and prediction methods of coal spontaneous combustion for deep coal mining in the Ximeng mining area

    MA Li;GAO Wenbo;TUO Longlong;ZHANG Pengyu;ZHENG Zhou;GUO Ruizhi;College of Safety Science and Engineering, Xi'an University of Science and Technology;Key Laboratory of Coal Fire Disaster Prevention and Control, Xi'an University of Science and Technology;Inner Mongolia Haosheng Coal Industry Co., Ltd.;

    [Objective] The mining of deep coal seams in the Ximeng mining area within the Ordos Basin is subjected to complex environmental conditions like high in-situ stress, large water inflow, and severe air leakage, which lead to the encountered with elevated risks and difficult prediction of coal spontaneous combustion and posing challenges in predicting spontaneous combustion. [Methods] Coal samples from the Yingpanhao and Shilawusu coal mines in the Ximeng mining area were selected for temperature-programmed spontaneous combustion experiments to determine the characteristic parameters of coal spontaneous combustion under different moisture contents and sulfur mass fractions.Based on these parameters, as well as with coal quality parameters from proximate analysis, a prediction database was established. Then, the hyperparameters of the random forest(RF) model were optimized using the crested porcupine optimizer(CPO) algorithm. Accordingly, the CPO-RF model was constructed to predict the degree of coal spontaneous combustion. [Results and Conclusions] The results indicate that the coal samples from the Yingpanhao and Shilawusu coal mines showed similar laws of variations in gas concentrations and oxygen consumption rates during oxidative heating. CO was identified as the dominant indicator gas, appearing initially at a temperature of about 30℃. The amount of gas produced increased with the sulfur mass fraction. However, as the moisture mass fraction increased, it decreased initially and then increased. The coal spontaneous combustion manifested critical temperatures ranging from 67.5℃ to 70.5℃and dry cracking temperatures from 113.5℃ to 115.4℃. The optimal tree depth and tree count of the RF model were automatically identified using the efficient global search capability of the CPO algorithm, avoiding local optimal solutions caused by improper settings and thus enhancing the generalization and robustness of the model. The constructed CPO-RF model significantly improved the prediction accuracy of coal spontaneous combustion. As a result, the predicted temperatures based on the test set coincided well with the actual values, with a mean absolute error of 0.762℃, a root mean square deviation of 1.014, and a coefficient of determination of 0.999 4. The comparison between the predicted results of the CPO-RF model and the characteristic temperatures of coal spontaneous combustion enabled the efficient discrimination of the risks of coal spontaneous combustion. Based on this, targeted fire prevention and extinguishing methods can be adopted. The results of this study serve as a reference for preventing coal spontaneous combustion for deep coal mining in mining areas.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1701K]

  • Geological condition assessment and selection of optimal favorable areas for deep underground coal gasification in the Yanchuannan block

    LI Xin;CHEN Zhenlong;GUO Tao;GAO Xiaokang;XIAO Cui;JIN Xiaobo;WU Caifang;WANG Fangfang;SINOPEC East China Oil & Gas Company;China Petrochemical Deep Coalbed Methane Exploration and Development Key Laboratory;Key Laboratory of Coalbed Methane Resources &Reservoir Formation Process, Ministry of Education, China University of Mining and Technology;School of Resources and Geosciences, China University of Mining and Technology;

    [Objective and Methods] Geological condition assessment for underground coal gasification(UCG) allows for considerably reducing the risk of UCG projects, while scientific siting serves as a prerequisite for the success of UCG projects. To achieve the geological condition assessment for deep UCG and the selection of optimal favorable areas in the Yanchuannan block, this study quantified the indices of coal quality, coal seam occurrence, surrounding rocks, hydrogeology, and structures in the No.2 coal seam in the study area. Employing the technique for order preference by similarity to an ideal solution(TOPSIS) method, this study performed mathematical assessments and grading of various exploitation units. Finally, this study obtained comprehensive assessment results of favorable, relatively favorable, and potentially favorable areas for UCG. [Results] The results indicate that the No.2 coal seam in the study area was formed in a sedimentary environment of the delta plain facies. This coal seam consists primarily of medium-rank coals, including coking, lean, and meagre coals, exhibiting low average moisture and low average ash contents and a high yield of volatile constituents. In terms of sulfur content, the No.2 coal seam contains low-to high-sulfur coals. Furthermore, the No.2coal seam manifests a considerable thickness, high stability, a low average gangue layer number, and low gangue coefficients(i.e., the ratio of the total gangue thickness to the total coal seam thickness), and simple structures, suggesting a stable moderately thick to thick coal seam with a relatively complete coal structure. The roof and floor of the No.2 coal seam are dominated by mudstones, and its surrounding rocks show high values of the comprehensive lithological index and high sealing performance. Faults in the coal seam exhibit moderate fractal dimension values overall, suggesting simple fault development and favorable conditions for exploitation. The study area exhibits surface water locally, with moderate hydrological fractal dimension values and high groundwater sealing coefficients. [Conclusions] Overall, the No.2 coal seam in the study area exhibits resource and geological conditions suitable for the implementation of UCG projects. Based on the distribution characteristics of structures, burial depths, rivers, and mine boundaries, as well as the description of geological exploration data, the No.2 coal seam can be divided into 11 exploitation units, with favorable areas for UCG primarily distributed in the northern part. Specifically, the most favorable areas consist of units Ⅴ and Ⅲin the north-central part, the relatively favorable areas include units Ⅰ, Ⅱ, Ⅳ, Ⅵ, Ⅶ, Ⅸ, and Ⅹ, and potentially favorable areas comprise units Ⅷ and Ⅺ.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 3046K]

  • A method for intelligent information extraction of coal fractures based on μCT and deep learning

    HU Zhazha;ZHANG Xun;JIN Yi;GONG Linxian;HUANG Wenhui;REN Jianji;Norbert Klitzsch;Science and Technology R&D Platform of Emergency Management Ministry for Deep Well Ground Control and Gas Extraction Technology, School of Energy Science and Engineering, Henan Polytechnic University;School of Resources and Environment, Henan Polytechnic University;School of Energy, China University of Geosciences(Beijing);School of Computer Science and Technology, Henan Polytechnic University;Institute of Applied G

    [Objective] The fine-scale characterization of fractures in coal reservoirs is significant for the exploration and exploitation of coalbed methane(CBM) resources. Given that the size, orientation, and density of fractures directly affect the permeability of coal seams, the accurate information identification and extraction of fractures in coal seams plays a key role in revealing the formation and propagation mechanisms of fracture networks during reservoir volume fracturing. Conventional methods for fracture information extraction typically rely on manual labeling and feature extraction based on image processing techniques, exhibiting significantly limited accuracy and efficiency. [Methods] This study proposed a method for fracture information extraction of coals based on TransUNet and micro-computed tomography(μCT) images. TransUNet, integrating the advantages of both the Transformer modules and convolutional neural network(CNN), is capable of extracting global features and capturing local details in images, significantly enhancing the image segmentation accuracy and network robustness. First, the μCT images of coal samples were preprocessed, including improving the image quality using the difference method and increasing the sample size using data augmentation techniques. Subsequently, image segmentation was conducted using TransUNet to extract fracture features. Additionally,the image segmentation results of varying neural network models were compared. [Results and Conclusions] The results indicate that the proposed method exhibited superior performance on a given dataset. Specifically, the TransUNet model yielded an accuracy of 91.3%, precision of 89.5%, F1 score of 89.8%, and Intersection over Union(IoU) of84.0%, significantly outperforming other intelligent models like U-Net and U-Net++. Given the characteristics of finegrained μCT images, applying TransUNet to the fracture information extraction of coals emerges as an efficient and accurate approach. This study provides a novel philosophy for image processing in the field of CBM exploration and production.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2039K]

  • Theories, technologies, and prospects for the utilization of deep underground storage space

    WEI Hengfei;FANG Jie;SHI Junjie;LI Qiuyuan;YU Beibei;CHEN Jing;National Institute of Clean and Low-Carbon Energy;State Key Laboratory of Water Resource Protection and Utilization in Coal Mining;Research Institute of Exploration & Development,Dagang Oilfield Company,PetroChina;PipeChina Engineering Technology Innovation Co., Ltd.;

    [Background] The world's energy utilization has shifted from high-carbon, high-polluting, non-renewable energy to low-carbon, clean, renewable energy. In this process, the utilization of low-carbon, clean energy typified by natural gas, wind power, solar energy, and hydrogen energy needs to be coupled with deep underground storage space(DUSS) to offset their regional constraints and instability. Additionally, low-and zero-carbon technologies like carbon dioxide(CO2) geological storage also rely on DUSS. Therefore, investigating the theories, technologies, and prospects of DUSS utilization under the low-carbon background will provide significant guidance for efficient DUSS utilization in China. [Methods] Based on the investigation into the types and utilization history of global DUSS, as well as the current status of DUSS utilization in China, this study determined the historical stages of global DUSS utilization and provided a summary of the orientations and current status of diversified DUSS utilization, as well as the theoretical and technical status of the construction of underground storage facilities based on DUSS. Furthermore, this study analyzed China's theoretical and technical contributions to the construction of underground storage facilities, along with China's challenges and countermeasures in DUSS utilization. [Results and Conclusions] Generally, the DUSS utilization has been conducted for about 110 years, including three major stages: the initial development stage(1915-1945), the rapid development stage(1946-1998), and China's catch and synchronous development stage(1999-the present). Despite a short history of large-scale DUSS utilization, China holds the originality and leadership of the theories and technologies for the construction of layered salt rock reservoirs and underground water reservoirs in coal mines. Moreover, China has developed the theories and technologies for constructing underground gas storage(UGS) facilities under complex geologic conditions. At present, China holds only limited completed underground storage facilities with single types and application scenarios, lacking completed UGS facilities in aquifers. It is necessary to put more effort into achieving theoretical and technical breakthroughs in hydrogen, helium, and oil storage in salt caverns, as well as CO2 geological storage in saline aquifers. Besides, the resource allocation for DUSS requires enhanced top-level design by the Chinese government and the coordination of various departments. To reach the goals of carbon neutrality and peak carbon dioxide emissions, the DUSS utilization in China holds promising prospects. Underground storage facilities will provide significant support for the large-scale development of industries including natural gas, wind and solar power, green hydrogen, and carbon sequestration in China. The construction of underground storage facilities will reach a 100-billion industrial scale,holding the potential for fostering new technologies and industries and representing significant industrial innovation points for the development of new quality productive forces.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1672K]

  • Factors influencing the production of coalbed methane from deep reservoirs

    WANG Zhenzhi;FU Xuehai;PAN Jienan;JIN Yi;WANG Haichao;School of Resources and Environment, Henan Polytechnic University;School of Resources and Earth Sciences, China University of Mining and Technology;School of Geology and Mining Engineering, Xinjiang University;

    [Objective] The production characteristics of coalbed methane(CBM) from deep reservoirs differ significantly from those of CBM from shallow reservoirs. Key challenges in deep CBM production include maintaining reservoir permeability or minimizing permeability loss, enhancing CBM(CH4) desorption efficiency, and accurately predicting the laws of CH4 diffusion. There is an urgent need to overcome these challenges through technological innovation and theoretical research. [Methods] This study systematically analyzed the advances in domestic and international research on coal reservoir permeability, CBM desorption, and CBM diffusion. By integrating the classification of production stages of deep coal reservoirs with the dominant CBM migration mechanisms of varying stages, this study summarized the mechanisms and influential factors of deep CBM production. [Results and Conclusions] The results indicate that deep CBM production can be divided into four stages: rapid production increase, relatively stable production, gradual production decrease, and low production. During the former two stages, reservoir pressure remains high, free gas serves as a primary gas source, and methane migration is dominated by seepage flow. Key influential factors of both stages include coal structure, developmental degrees of pores and fractures, reservoir temperature, in situ stress, and effective stress. At these stages, minimizing permeability loss is crucial, and direct fracturing should be avoided in reservoirs with a high proportion of granulated and mylonite coals. After the relatively stable production phase, an increase in the reservoir permeability caused by reservoir temperature will gradually increase with an enhancement in the slip effect.Controlling pressure drop and slow production can help to slow down the decline of reservoir permeability. In the lowproduction stage, the permeability loss rate caused by both primary and artificially induced fractures approaches 100%.However, the irreversible permeability loss rate remains significantly lower than that of shallow coal reservoirs, suggesting the feasibility of secondary reservoir stimulation for increased production. From the rapid production increase stage to the relatively stable production stage, the adsorbed gas begins to undergo gradual desorption. In this case, the primary objectives are to expand the desorption range, ensure the opening of seepage channels, and enhance the productivity of CBM wells. Compared to shallow reservoirs, the desorption of adsorbed gas in deep coal reservoirs occurs over a prolonged period, with the critical desorption pressure being challenging to determine accurately. Furthermore, the pathways for gas migration are prone to be compressed and close, leading to a limited desorption range. To achieve precise estimations of CBM recovery rates, it is necessary to adopt a stepwise depressurization desorption method in experimental research. Specifically, achieving a gradual decrease in the reservoir pressure using control measures during CBM production can effectively enhance the desorption rate of adsorbed gas in micropores. In the low-production stage, gas production primarily originates from desorbed gas in remote well areas. In this stage, the production of CBM wells is determined by methane diffusion, with the accurate measurement of the diffusion coefficient and the development of dynamic diffusion models playing a crucial role. Notably, the diffusion coefficient exhibits significant anisotropy, yet current CH4 diffusion models seldom account for the anisotropic characteristics of coal structure. It is necessary to develop a time-varying CH4 diffusion model while considering the CH4 diffusion patterns across multi-scale pores and microfractures in coals. Experiments on the fine-scale characterization of multi-scale pores and fractures, combined with hightemperature with high-pressure nuclear magnetic resonance imaging, allow for the characterization of variations in CH4density across different pore sizes. This systematic review integrates theories and practice, further laying a theoretical foundation for deep CBM recovery.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1744K]

  • Migration characteristics and storage forms of liquid and supercritical CO2 in saline aquifers

    PENG Xiyi;WANG Yanyong;LI Song;WANG Xiaoguang;CUI Guodong;HE Yongming;College of Energy, Chengdu University of Technology;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology;Tianfu Yongxing Laboratory;School of Engineering, China University of Geosciences;

    [Objective] CO_2 storage in saline aquifers serves as a critical technology used to dramatically reduce greenhouse gas emissions. Owing to the low-temperature marine environment and the pressure from overlying seawater, shallow offshore saline aquifers exhibit significantly different temperature and pressure conditions compared to onshore saline aquifers at equivalent burial depths, allowing CO_2 to occur in a liquid state. Compared to supercritical CO_2, liquid CO_2 features higher density, viscosity, and solubility in formation water, which affect the CO_2 migration and storage processes. Previous studies focus primarily on supercritical CO_2, lacking a deep understanding of the migration and storage patterns of liquid CO_2 in saline aquifers. [Methods] Considering the distinct characteristics of liquid and supercritical CO_2, this study constructed a mathematical model for CO_2 migration and storage under the action of buoyancy and capillary pressure. Using the high-precision numerical simulations of two-phase seepage, this study compared the laws of changes in the migration characteristics and storage forms of liquid and supercritical CO_2 in saline aquifers after gas injection. [Results and Conclusions] The results indicate that compared to supercritical CO_2, liquid CO_2 manifested reduced vertical migration rates and swept volumes under buoyancy-dominated conditions. After 25 a, the storage amounts of liquid CO_2 in different storage forms were significantly lower than those of supercritical CO_2, making it more difficult to fully leverage the storage capacity of saline aquifers. Among the different CO_2 storage forms, local capillary trapping, residual gas trapping, and solubility trapping represent 55%, 40%, and 5%, respectively, with the CO_2 phase states posing minor impacts on the storage forms. An increase in geothermal gradient enhanced the vertical migration and swept volume of liquid CO_2, the CO_2 storage amounts of different storage forms, and the utilization efficiency of the storage capacity of saline aquifers. At the same burial depths, supercritical CO_2 displayed significantly different migration characteristics and storage amounts in onshore and offshore saline aquifers. The inhibited vertical migration of supercritical CO_2 in offshore saline aquifers reduced the CO_2 storage amounts of local capillary trapping and residual gas trapping, hampering the effective utilization of the storage capacity of saline aquifers. The results of this study can serve as a guide for efficient CO_2 storage in onshore and offshore saline aquifers.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2038K]

  • Developmental patterns and formation and evolutionary mechanisms of surface cracks induced by the mining of shallowly buried coal seams

    HOU Enke;MU Jiaxin;XIE Xiaoshen;FENG Dong;YANG Lei;LI Yan;HE Tao;BAO Kangguang;CHEN Xiaosheng;College of Geology and Environment, Xi'an University of Science and Technology;College of Energy Engineering, Xi'an University of Science and Technology;Shenmu Hongliulin Mining Co., Ltd.,Shaanxi Coal Group;

    [Objective] Surface cracks are recognized as one of the most common geologic hazards in coal mining areas in northern Shaanxi Province. These cracks directly cause damage to surface ecosystems. Furthermore, those penetrating fractures in the overburden act as primary channels for surface water to burst underground, threatening the safe production underground. [Methods] This study aims to further reveal the developmental patterns of surface cracks induced by the mining of shallowly buried coal seams and elucidate their formation and evolutionary mechanisms. To this end, this study investigated mining face 15218 and 25213 in the Hongliulin Coal Mine in northern Shaanxi. Specifically, the surface cracks in the mining face were comprehensively examined using methods including surface crack mapping, dynamic monitoring of cracks, and numerical simulations. [Results and Conclusion] The results indicate that the surface cracks caused by the mining of shallowly buried coal seams exhibited a C-shaped distribution overall. The developmental characteristics and locations of the surface cracks were closely related to landform types. Under the same mining conditions, the proportion of cracks with widths greater than 5 cm in areas with loess gullies was 2.15 times that in areas with sandy beaches, suggesting a significantly higher developmental degree of cracks in the former areas than in the latter areas. Besides, the boundary cracks of the mining face exhibited a significantly higher developmental degree than cracks within the mining face. Surface cracks induced by the mining of shallowly buried coal seams manifested two dynamic developmental characteristics: ahead of and lagging behind mining positions. Among them, the formation of surface cracks induced by mining along mining face 25213 lagged behind the mining position, with a lag distance of 6.49m. In contrast, surface cracks induced by mining along mining face 15218 were formed ahead of the mining position,with a lead distance of 20.07 m. Cracks within the mining face exhibited four activity characteristics, while the boundary cracks only showed an activity characteristic of cracking, increase in length, and stability sequentially. The surface cracks exhibited overall activity time ranging from 4 days to 14 days. Compression zones, tension-compression transform zones, and tensile zones were formed near the surface of the goaves. As the mining face advanced, movement deformation and failure zones within the roof strata and on the surface constantly expanded forward. The surface subsidence-induced basins were slightly larger than the goaves, with a maximum subsidence coefficient of 0.82. Non-penetrating cracks were primarily formed when the tensile deformations of soils along the margins of surface moving basins exceeded their limited values. In contrast, penetrating cracks were formed by the connection between upgoing cracks within the overburden and surface cracks or by the direct connection between the upgoing cracks and the surface. As the mining of the mining face advanced, the cycle rupture of the main roofs caused the surface cracks to continuously expand forward. The characteristics of variations in the surface crack width were closely related to the complex movement of blocks on both sides of the cracks. The results of this study can serve as an important reference for the prevention and control of surface cracks in the mining areas of shallowly buried coal seams.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2975K]

  • Deformation characteristics and influential factors of the surface uplift of closed mines

    LUO Jin;LI Yingming;GUO Qingbiao;ZHAO Guangming;State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines, Anhui University of Science and Technology;School of Mining Engineering, Anhui University of Science and Technology;School of Spatial Information and Geomatics Engineering, Anhui University of Science and Technology;

    [Objective] The residual surface deformations of closed mines exhibit prolonged duration and complex evolutionary processes, potentially leading to unconventional phenomena like surface uplift, which affects the re-exploitation and reutilization of closed mines. [Methods] This investigated a mining area in Huainan, Anhui Province as an example to explore the deformation mechanisms, characteristics, and influential factors of the surface uplift of closed mines. Through numerical simulations, this study analyzed the propagation process of surface uplift with an increase in the groundwater level. Accordingly, this study investigated the quantitative impacts of the mining height, groundwater level, and rock strength of the caving zone on the characteristics of the surface uplift. The results indicate that the pore water pressure in rock layers above the goaf increased with the groundwater level. Specifically, as the groundwater level increased from 30 m to 150 m, the pore water pressure in the central portion of the goaf increased from 5.99 × 102 kPa to2.17 × 102 kPa, while that in the surrounding area decreased. Within the mining height threshold, the amplitude of overburden rebound and surface uplift increased with the mining height. The deeply buried rock layers exhibited significant rebound, while the surface uplift occurred after four months of seepage, suggesting a lag effect. An increase in the groundwater level exerted a direct influence on the overburden rebound and surface uplift. The increasing groundwater level resulted in an overall rebound trend of the overburden generally. However, the rebound trend became weak as the groundwater level increased further. Notably, the rebound effect lessened when the groundwater level exceeded 146 m.The attenuation of the modulus of elasticity of the caving zone significantly intensified the surface uplift, with the amplitude of the surface uplift exhibiting a linear positive correlation with the degree of the attenuation. Specifically, the amplitude of the surface uplift was 86.4 mm before the attenuation of the modulus of elasticity and was 160 mm as the degree of the attenuation increased to 50%. The findings of this study determine the deformation characteristics and propaganda mechanisms of surface uplift under different conditions, providing a significant reference for further research on the surface uplift of closed mines caused by an increase in the groundwater level.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 4030K]

  • Anisotropy in non-Darcy flow in individual rough-walled rock fractures

    ZHU Yinbin;LIAO Zhen;LI Changdong;LIU Hongbin;JIANG Xihui;School of Engineering, China University of Geosciences;Yajiang Clean Energy Science and Technology Research (Beijing) Corporation Limited;Badong National Observation and Research Station of Geohazards, China University of Geosciences;

    [Objective] Investigating the flow behavior of fluids in individual rough-walled rock fractures is fundamental for fully understanding the seepage characteristics of fluids in rock fracture networks. [Methods] Rock fractures were artificially synthesized based on the fractal theory, and numerical simulations of seepage along these fractures were performed using the COMSOL Multiphysics software. Then, fracture specimens with the same geometric characteristics as numerical models of fractures were prepared using 3D printing technology. In combination with the self-designed equipment for seepage experiments, this study conducted seepage experiments on these fracture specimens under different injection flow rates to investigate the impacts of varying injection directions on the microscopic and macroscopic behavior of non-Darcy flow in 3D individual rough-walled fractures. [Results and Conclusions] The results indicate that the differences in the surface roughness of rock fractures under different injection directions significantly influenced the seepage characteristics of fractures, with greater flow resistance, flow path tortuosity, and non-Darcy flow effect occurring in the injection direction with higher fracture surface roughness. The developmental degree of eddies in fractures was positively correlated with the fracture surface roughness. Specifically, eddies in the injection direction with higher fracture surface roughness manifested a higher developmental degree compared to those in the direction with lower surface roughness. The Forchheimer equation did not apply to the entire range of Reynolds numbers when describing non-Darcy flow in fractures. Instead, it was sufficiently accurate only in the case of the sufficient occurrence of non-Darcy flow.The higher anisotropy in the surface roughness, non-Darcy flow was more prone to occur along fractures in the direction with higher surface roughness, accompanied by more pronounced differences in flow behavior between both injection directions. Quantitative characterization models for describing the relationships of the critical Reynolds number with the anisotropy factor in the fracture surface roughness and average fracture aperture were established based on the seepage simulations of 3D fractures. The effectiveness of the established models was verified using seepage experiments. The results of this study serve as a reference for more comprehensive research on the anisotropy in non-Darcy flow behavior in rough-walled fractures.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2404K]

  • Strength and damage characteristics of cemented gangue backfill during saturated immersion

    YU Xiang;YANG Ke;HE Xiang;HOU Yongqiang;WEN Zhiqiang;ZHANG Lianfu;School of Mining Engineering, Anhui University of Science and Technology;Institute of Energy,Hefei Comprehensive National Science Center;Joint National-Local Enginering Research Centre for Safe and Precise Coal Mining;

    [Objective] Under the influence of backfill slurry, water inrushes in mining face, and water accumulation in goaves, the water content in cemented gangue backfill varies with the immersion time, thus altering the bearing performance of the backfill. Investigating the strength and damage characteristics of cemented gangue backfill during saturated immersion is crucial for maintaining the stability of the backfill and ensuring the safety of coal mines. [Methods] Using uniaxial compression tests and scanning electron microscopy(SEM) of cemented gangue backfill during saturated immersion, this study analyzed the law of changes in the backfill strength under varying immersion times. Based on the statistical distribution of microelement strength, this study established a piecewise damage constitutive model for the cemented gangue backfill in the pre-peak stage. Using SEM, this study revealed the mechanism underlying the strength weakening of the cemented gangue backfill during saturated immersion. [Results and Conclusions] The results indicate that during saturated immersion, the cemented gangue backfill under uniaxial compression exhibited significant fourstage stress-strain curves. In the compaction and closure stage of pores and fractures, the maximum strain/stress and the strain at the peak stress point were positively correlated with the immersion time, while the peak stress and modulus of elasticit y were negatively correlated with the immersion time. With an increase in the immersion time, the primary failure morphologies of the cemented gangue backfill transitioned from shear failure to tension-shear conjugate failure, finally shifting to longitudinal tensile failure, with the failures concentrated in the central part of the cemented gangue backfill. This study established a piecewise damage constitutive model for the cemented gangue backfill in the compaction and closure stage of pores and fractures that considered the maximum stress and strain, modulus of elasticity, peak stress, and strain at the peak stress point. This model was verified using test data, indicating that the model-derived theoretical curves were roughly consistent with the test curves. Subjected to the surface tension and lubrication of water, as well as mineral dissolution, the cemented gangue backfill during saturated immersion manifested a three-stage strength weakening mechanism. As the cemented gangue backfill was saturated with water, its strength continued to decrease at a decreasing rate. The results of this study will provide certain data for coal mining based on cemented gangue backfill in environments with water-rich goaves.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2763K]

  • Response characteristics of the orthogonal antennas of electromagnetic azimuthal resistivity measurement while drilling(MWD) tool for coal mining

    CHEN Gang;CCTEG Xi'an Research Institute (Group) Co., Ltd.;

    [Objective and Methods] This study aims to determine the factors influencing the detection performance of the electromagnetic azimuthal resistivity measurement while drilling(MWD) tool for coal mining in horizontal wells.Through finite element numerical simulations, this study conducted boundary detection using orthogonal coupling coils with multiple frequencies and coil pitches. This allowed for determining the optimal asymmetric arrangement of coils, as well as the optimal working parameters of frequency, source-detector separation distance, and coil pitch suitable for highresistivity coal seams. [Results and Conclusions] The comparative study of orthogonal and inclined coils reveals that in the case of directional signals of inclined coils, although the amplitude ratio signals were theoretically enhanced with an increase in the coil pitch, the actual amplitude of induced electromotive force in inclined coils decreased. This complicates signal acquisition. This study designed an orthogonal coil array structure for electromagnetic azimuthal resistivity measurement for coal mines, enabling concurrent resistivity and interface detection for high-resistivity coal seams. Furthermore, this study obtained the optimized parameters of frequency, source-detector separation distance, and coil pitch for mining of these coal seams. The results of this study provide a basis for electromagnetic azimuthal detection along coal seams in wells in underground coal mines.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1828K]

  • A method for high-accuracy localization of microseismic sources in mines based on finite element simulation

    NING Dianyan;ZHU KaiPeng;ZHU Yongsheng;YUAN Shuxia;ZHOU Zhenfang;CCTEG Xi'an Research Institute (Group) Co., Ltd.;State Key Laboratory of Coal Mine Disaster Prevention and Control;School of Mechanical Engineering, Xi' an Jiaotong University;School of Mechanical Engineering, Xi'an Shiyou University;

    [Objective and Methods] Microseismic monitoring technology for mines can reflect the deformations and failure of rock layers by capturing low-frequency vibration signals their internal structure generated during the stress-induced deformation and failure of them. Accordingly, water inrush warnings and geologic hazard prediction can be achieved. Acoustic source localization, allowing for the localization of energy release and the early warning of potential hazards, plays a key role in this technology. Presently, when used for acoustic source localization, the time difference of arrival(TDOA) method is facing issues including high algorithmic complexity, significant impacts of probe arrangement on the localization accuracy, and low adaptability to complex stratigraphic structures. Using the finite element method, this study simulated the elastic wave propagation in various stratigraphic structures. Considering the transmission, reflection, and diffraction effects at various stratigraphic boundaries, this study investigated the impacts of various inversion models and probe arrangements on the localization accuracy. [Results and Conclusions] The results indicate that the point source control models can effectively simulate the elastic wave propagation in rocks, with the orthogonal probe arrangement delivering superior performance in the acoustic source localization. In planar homogeneous materials,compared to the probe sets arranged in double triangles, the probe sets arranged in a single square exhibited a decrease of0.6% in the localization error, while probe sets arranged in double squares displayed an increase of 1.69% in the localization accuracy. In a planar layered structure, compared to uniform velocity inversion, the transmission inversion increased the localization accuracy by 15% in the case of probe sets with a double triangle arrangement and by 14.9% for a probe set with a double square arrangement. In a three-dimensional layered structure, compared to uniform velocity inversion, the transmission inversion increased the localization accuracy by 14.5% in the case of the probe set arranged in a trirectangular tetrahedron. Overall, the inversion method produces more significant impacts on the localization accuracy than the probe arrangement, and the proposed numerical method enables high-accuracy, rapid acoustic source localization using the TDOA method and transmission inversion. The results of this study provide a valuable reference for optimizing microseismic monitoring and early warning systems for mines.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1999K]

  • Frequency-domain induced polarization responses of water-bearing anomalous bodies in the roadway tunneling direction in coal mines

    HU Xiongwu;HU Yuanrong;WU Rongxin;YU Hao;School of Earth and Environment, Anhui University of Science & Technology;

    [Objective] A frequency-domain induced polarization(FDIP) method enables the observation of critical electrical parameters such as frequency dispersivity and complex resistivity of geological bodies, mitigating the multiplicity of solutions in the interpretations of electrical anomalies. This method has emerged as a primary technique for electric method-based advance water detection during roadway tunneling in coal mines. However, the FDIP method primarily focuses on data observation in the direction opposite to roadway tunneling, exhibiting a limited capacity to capture geoelectric information in the roadway tunneling direction. This leads to practical challenges such as unclear orientations of water-bearing anomalous bodies. Therefore, exploring the advance response characteristics and anisotropy of the FDIP parameters of roadways holds critical theoretical and practical significance for improving data observation methods and further enhancing the identification accuracy of water-bearing anomalous bodies. [Methods] First, a method for observing triaxial apparent IP parameters was developed based on the practical conditions of a coal mine roadway. Second,the response expressions of the triaxial parameters were derived by using an infinitely large tabular body in the whole space as the model of water-bearing bodies in the roadway tunneling direction. Third, the variations in the triaxial parameters with the model's attitude like azimuth, dip angle, and distance from the field source were analyzed using numerical calculations and theoretical analysis. [Results] The results indicate that the curves of apparent frequency dispersivity and complex resistivity along the axial direction of the roadway exhibited K-type(low-high-low) and H-type(high-lowhigh) patterns, respectively, independent of changes in the model parameter, with electrical anomalies consistently demonstrating low resistivity and high dispersivity. The curves of apparent frequency dispersivity perpendicular to both sides of the roadway presented a K-type pattern when the model was set directly ahead of the roadway, and they appeared to be inversely proportional functions in other cases. The apparent complex resistivity curves displayed K-and Htype patterns when the model was arranged near the left and right sides of the roadway, respectively. The curves of apparent frequency dispersivity perpendicular to the roof and floor of the roadway exhibited a K-type pattern in the case where the model was upright, and they appeared to be inversely proportional functions in other cases. The apparent complex resistivity curves presented K-and H-type patterns when the model was inclined towards the front and rear of the roadway, respectively. The anomaly amplitude and detection ranges of the triaxial apparent IP parameters were significantly influenced by the model parameters. Notably, the detection ranges at extreme or step points changed significantly with the distance from the field source. [Conclusions] The triaxial apparent IP parameters demonstrated pronounced anisotropic responses to the tabular water-bearing anomalous body model. The apparent IP parameters in the axial direction of the roadway manifested a relatively low sensitivity to the model's attitude, proving to be a primary cause of low detection of electrical anomaly accuracy. In contrast, the apparent IP parameters perpendicular to both sides of the roadway were sensitive to the model's azimuth, while those perpendicular to the roadway roof and floor are susceptible to the dip direction of the model. Compared to current observation methods, the triaxial observation method provides richer electrical information for detecting water-bearing anomalous bodies in the roadway tunneling direction, thereby enhancing the spatial positioning accuracy of water-bearing anomalous bodies.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 9677K]

  • Distributed optical fiber acoustic sensing-based optimization of microseismic source localization in the hydraulic fracturing for coalbed methane production

    HUA Hao;CHENG Bingjie;XU Tianji;YAN Zhenqian;GAO Bo;HE Cheng;Key Laboratory of Earth Exploitation and Information Techniques, Ministry of Education, Chengdu University of Technology;School of Resources and Environment, University of Electronic Science and Technology of China;Energy Geology Survey and Research Institute of Sichuan Province;

    [Objective] To achieve safe and efficient hydraulic fracturing, it is necessary to conduct timely and accurate microseismic monitoring in the reservoir stimulation process. The purpose is to analyze and assess the fracturing effects.[Methods] Using a permanently deployed fiber-optic cable outside the casing of a coalbed methane(CBM) well, this study employed distributed optical fiber acoustic sensing(DAS)for full-borehole, wide-azimuth, and high-density realtime monitoring of microseismic events induced by the hydraulic fracturing of coal seams. Furthermore, this study proposed a novel method for localizing microseismic sources based on information about wave travel time and a sourceconstrained mapping algorithm. First, effective microseismic events were identified by calculating the interchannel similarity coefficient from optical fiber data. Second, the incidence locations of microseismic sources in the fiber were obtained based on the P-and S-wave peaks. Third, the wave travel time differences derived using the short term averaging/long term averaging(STA/LTA) algorithm were used to determine the spatial distances between microseismic events and the fiber. Finally, the constrained mapping and localization of microseismic sources were performed by combining the incidence locations in the fiber and the distances from microseismic sources to the monitoring fiber. [Results and Conclusion] The results indicate that DAS exhibited a strong directional sensitivity to seismic waves in the acquisition process of optical fiber data. Specifically, DAS was sensitive to P-waves with an incidence angle of 0° and Swaves with an incidence angle of 45°but almost insensitive to P-waves with an incidence angle of 90° and S-waves with an incidence angle of 90°. In the case of consistent noise intensity, the sampling effects in the seismic wavefield based on various gauge lengths exhibited decreasing significance in the order of 1 m, 10 m, and 100 m. In the case of a noise intensity of 300%, the spatial sampling data based on a gauge length of 1 m still displayed relatively continuous waveforms, highlighting the seismic source wavelets of 50 Hz. The predicted fracture networks primarily exhibited NNWSSE-directed distributions, aligning with the direction of the regional maximum principal stress, and prediction errors of within 10 m mostly. The application in wellfield M of the Chuannan coalfield in the Sichuan Basin indicates that the constrained localization algorithm yielded prediction results consistent with the experimental verification results and can effectively indicate the fracture network zones of coal seams. Therefore, this study holds great significance for enhancing the exploitation efficiency of tight hydrocarbon reservoirs with low porosity and permeability.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2628K]

  • A model predictive control method for directional borehole trajectories in underground coal mines

    LI Hao;YAO Ningping;LU Chengda;ZHANG Jinbao;WEI Hongchao;WU Jiajun;LI Jinyu;CCTEG China Coal Research Institute;CCTEG Xi'an Research Institute (Group) Co., Ltd.;School of Automation, China University of Geosciences;

    [Objective] It is challenging to control the borehole trajectories during directional drilling in complex strata in underground coal mines, resulting in significant deviations from the designed trajectories. Given this, this study proposed a method for tracking and controlling directional borehole trajectories based on model predictive control(MPC).[Methods] Focusing on the directional drilling process conducted using a screw drill, this study investigated the movement patterns of the directional screw drill by analyzing the characteristics of directional drilling in complex strata in underground coal mines. Based on the kinematic theory, this study developed a borehole trajectory extension model for sliding directional drilling. Then, the model linearization was processed using Taylor series expansion, aiming to eliminate the coupling relationships between state variables such as dip angle and azimuth. Accordingly, this study constructed a borehole trajectory prediction model and an objective function with the minimum trajectory deviation as the control target. The steady-state errors of the prediction model were reduced using feedback correction. Furthermore, this study designed a model predictive controller with functions of predictive modeling, rolling optimization, and feedback correction. As a result, the optimal control variable for the borehole trajectory-toolface angle-was recommended. Accordingly, the optimized control for tracking directional borehole trajectories was achieved. Finally, the control algorithm was validated using the drilling data from a coal mine in Hancheng City, Shaanxi Province. [Results and Conclusions]The results indicate that the linearized borehole trajectory extension model simplifies the design process of the controller while effectively preserving the characteristics of the original model. The improved MPC method with the feedback correction mechanism for predicting directional borehole trajectories removes the impacts of model adaptation and steady-state errors. Compared to the human experience-controlled decision-making method based on the deflection rules of a screw drill, the improved MPC method reduces the average absolute errors of the dip angle and azimuth by79.5% and 70.5%, respectively, providing a novel control algorithm for directional borehole trajectories in complex strata.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1651K]

  • Analyzing in-situ stress response characteristics of coals based on optimized measurement-while-drilling parameters

    ZHANG Kun;WANG Ke;REN Jianxi;FENG Shangxin;CHANG Pengbo;ZHAO Yutao;MIAO Yanping;HU Jian;School of Civil Engineering and Architecture, Xi'an University of Science and Technology;Xiashijie Coal Mine, Shaanxi Tongchuan Coal Mine Construction Co., Ltd.;Shenmu Hongliulin Mining Co., Ltd.,Shaanxi Coal Group;Shenmu Zhangjiamao Mining Co., Ltd.,Shaanxi Coal Group;

    [Background] The spatial distribution of stress in coals in underground coal mines is a significant factor influencing the safe production of mines and the optimization of mining processes. The quantitative, advanced prediction of in-situ stress in coals is significant for the precise regulation of the underground stress field and the classification of areas with rock burst risks. [Methods] Using the self-developed monitoring-while-drilling system, this study conducted indoor coal drilling experiments under different drilling conditions and explored the laws of effects of drilling conditions on drilling parameters(e.g., torque and drilling displacement) under varying stresses. Furthermore, this study developed a method for determining coal stress based on drilling parameters and verified this method through the in-situ engineering application in an underground coal mine. [Results and Conclusions] The results indicate that the monitoring-while-drilling system could monitor the drilling parameters in real time in the presence of disturbance to the drilling process. In the drilling process, the drilling rate negatively correlated with the weight on bit(WOB) but positively correlated with the torque. The functional relationship between the drilling indices and the stress in coals exhibited a high goodness of fit(R2 = 0.92). The in-situ engineering application revealed that the differences between the stress in coals predicted based on drilling parameters and the actual stress were less than 10%, suggesting relatively high consistency.This study demonstrates that it is reliable to determine the stress in coals based on drilling parameters and also provides a scientific reference for the development of in-situ digital drilling technology for determining stress in coals.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 3084K]

  • A temporal fusion method for modeling the rate of penetration during deep geological drilling

    ZHOU Yang;LU Chengda;WU Min;CHEN Xin;YAO Ningping;SONG Haitao;ZHANG Youzhen;School of Automation, China University of Geosciences;Hubei Key Laboratory of Advanced Control and Intelligent Automation for Complex Systems;Engineering Research Center of Intelligent Technology for Geo-Exploration, Ministry of Education;School of Future Technology, China University of Geosciences;CCTEG Xi'an Research Institute (Group) Co., Ltd.;CCTEG China Coal Research Institute;

    [Objective] Given that the rate of penetration(ROP) serves as a key indicator of drilling efficiency, constructing an accurate ROP model holds great significance for optimizing drilling processes and reducing drilling costs.However, deep geological drilling faces challenges such as nonlinearity, non-convex optimization, multiple operating conditions, and temporal variations. Consequently, traditional modeling methods are difficult to adapt to complex geologic environments. [Methods] To address these challenges, this study proposed a fusion method combined with temporal regulation for ROP modeling: the SVR-MDBO method. Initially, a basic ROP model was constructed using support vector regression(SVR) to solve the nonlinear problem caused by ROP changes. To solve the non-convex optimization problem encountered in model parameter design, a modified dung beetle optimizer(MDBO) algorithm was designed through weight fusion, modified echolocation, modified iterated local search, and the re-updating strategy of the optimal solution. To adapt to the temporal variations of the ROP, a temporal regulation method based on fuzzy C-means clustering and the Mann-Kendall trend test was employed to conduct the temporal regulation of the model output. [Results and Conclusions] The results indicate that the MDBO algorithm yielded satisfactory results in the tests of 11 benchmark functions, suggesting that the MDBO algorithm can effectively solve the problem encountered in model parameter design. The simulation results based on actual drilling data demonstrate that the ROP model constructed in this study achieved optimal results in two well sections. Post-temporal regulation, the ROP model yielded more accurate predicted trends for both well sections, with respective prediction accuracy reaching up to 80% and 87.5%. The tests of the microdrilling experimental system reveal that the constructed ROP model yielded the highest accuracy under different rock samples. Overall, the constructed ROP model can effectively cope with changes in complex geologic environments, laying a solid foundation for controlling the process of deep geological drilling.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 1648K]

  • Design and simulations of a balancing device with a hydraulic circuit for a fully hydraulic top drive drilling system for a drilling rig capable of 10 000-m-deep drilling

    LUO Chaochun;WANG Qingyan;FAN Liming;LI Haoxuan;ZHONG Weiling;GUO Naiming;College of Construction Engineering, Jilin University;Key Laboratory of Drilling Technology for Complex Conditions of the Ministry of Natural Resources;Drilling & Production Research Institute of CNPC Chuanqing Drilling Engineering Company Limited;

    [Objective] The balancing device for a fully hydraulic top drive drilling system(TDDS), an important part of a drilling rig capable of 10 000-m-deep drilling, is designed to dynamically and accurately regulate the axial load in the screwing and unscrewing processes. This helps protect the threads of drill rod connectors from damage, thereby ensuring the stability and safety of drilling operations. [Methods] This study designed a balancing device with a hydraulic circuit for the SP.TD-01A fully hydraulic TDDS, aiming to achieve the balancing and bouncing functions required during the application of the TDDS. First, this study determined the structure and principal operating parameters of the hydraulic circuit of the balancing device for the TDDS. Then, using the Matlab/Simulink/SimScape simulation platform, this study constructed dynamic simulation models for the hydraulic circuit and for the screwing and unscrewing mechanisms of the spindle and drill rod of the TDDS. Using these models, this study simulated and tested the axial load change and displacement characteristics of the spindle protection connectors of the TDDS in the screwing and unscrewing processes,as well as the flow and intensity of pressure characteristics and energy consumption indicators of the hydraulic circuit.[Results and Conclusions] The results indicate that the balancing device designed for the TDDS demonstrates a reasonable functional structure and high dynamic regulation performance. At a spindle speed of 10 r/min, screwing and pretightening were completed within 24 s, and unscrewing and releasing consumed 26 s. During the screwing operation,the pressure on the threaded surface reached a maximum of 11.2 kN, stabilizing at around 550 N. During the unscrewing operation, the pressure on the threaded surface exhibited a maximum of 3.5 kN and an average of about 1.2 kN. After the unscrewing operation, the TDDS bounced off the drill string for a distance of 76.5 mm. The designed balancing device for the TDDS and its hydraulic circuit were applied to the SP.TD-01A fully hydraulic TDDS, yielding satisfactory application results and playing a vital role in protecting the threads of drill rod connectors. The spindle protection connectors of the TDDS were replaced only four times for safety reasons during the drilling of well SK-2. This study can serve as a guide for the further research and development of TDDSs.

    2025 02 v.53;No.326 [Abstract][OnlineView][Download 2587K]