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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

  • A method for advance detection of underground concealed water hazards in coal mines based on borehole transient electromagnetic method and vector synthesis

    FAN Tao;HAO Yue;LI Ping;ZHAO Rui;LIU Zaibin;MA Liang;LI Peng;YAN Junsheng;CCTEG China Coal Research Institute;CCTEG Xi'an Research Institute (Group) Co.,Ltd.;CCTEG Xi'an Transparent Geology Technology Co.,Ltd.;National Key Laboratory of Intelligent Coal Mining and Rock Stratum Control;State Key Laboratory of Digital Intelligent Technology for Unmanned Coal Mining;

    [Background] The advance detection of underground concealed water hazards in coal mines is crucial to ensuring the safe and efficient roadway tunneling. The borehole transient electromagnetic(TEM) method allows for longdistance advance detection. However, due to the limitation of the spatial structure of boreholes, currently available techniques can only effectively identify low-resistivity anomalies(e.g., water-bearing structures) in the radial direction, leaving blind areas in the primary tunneling direction(i.e., the axial direction of boreholes). [Objective and Method] To address this challenge, this study proposed a method for the advance detection of concealed water hazards in the axial direction of boreholes using both the vector synthesis based on biorthogonal transmitter-receiver coils and a self-adaptive inversion algorithm. By designing vertical and horizontal orthogonal transmitter coils, this method excited dual-component primary fields using sequential current while collecting the time-domain signals of secondary fields in the corresponding direction. Based on the vector synthesis principle, data on dual-component anomaly fields extracted using the trend surface method were fused to produce multi-directional composite anomaly fields. The composite anomaly fields were then superimposed on the background field obtained from numerical simulation, yielding the total field with high signal-to-noise ratios(SNRs). This enables the fan-shaped advance detection of concealed water hazards in the axial direction of boreholes. During the inversion stage, a self-adaptive regularization algorithm with physical constraints, combined with the main direction angle of the synthesized field, was employed to achieve the 3D imaging of low-resistivity anomalies. [Results and Conclusions] Both the numerical simulation(achieved by constructing a 3D model with a lowresistivity anomaly using the FDTD method) and the physical simulation of a 1:100-scale flume(obtained by simulating a water-bearing structure using highly conductive media) indicate that the proposed method can accurately locate the anomaly, with the degree of match between imaging morphology and the pre-set model reaching up to 90 %. The proposed method was applied to the detection of a water sump in a horizontal roadway of a coal mine in Shanxi Province.The water hazard target was effectively identified by comparing images captured before and after water discharge. Furthermore, the method was employed to detect the water accumulation range in the goaf of mining face 15101 within the coal mine based on three verification boreholes. The inversion results reveal the presence of a stable low-resistivity anomaly zone in borehole intersection area, confirming the expansion trend of the water accumulation range in the goaf over time. The application results further demonstrate the reliability and engineering applicability of the proposed method in localizing concealed water hazards. The results of this study provide effective technical support for the long-distance, high-precision advance detection of underground concealed water hazards in coal mines, holding critical significance for ensuring the safe coal mining of mines.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 4833K]

  • Investigating surface-borehole transient electromagnetic responses from veined orebodies considering induced polarization effects

    LI Jianhui;WANG Yao;WANG Wenchuang;XIE Shaojian;ZHU Siwei;School of Geophysics and Geomatics, China University of Geosciences (Wuhan);

    [Objective] The observational data derived using the surface-borehole transient electromagnetic(TEM) method tend to feature complex curve morphologies, a problem posing significant challenges to data processing and interpretation. This study aims to ascertain the mechanisms behind the generation of such complex responses using forward modeling. [Methods] Using the vector finite element-based spectral method and the Cole-Cole model, this study developed a3D forward modeling technique incorporating the induced polarization(IP) effect. By constructing a typical theoretical model of low-resistivity veined orebodies, it systematically analyzed the electromotive force(EMF) responses excited by transmitter loops at different orientations. [Results and Conclusions] The results indicate that the induced EMF curves from surface-borehole TEM responses were characterized by complex morphologies, with multiple sign reversals commonly observed. These characteristics were jointly controlled by the relative locations between transmitter loops and survey points, the resistivity contrast between veined orebodies and surrounding rocks, and the IP effect. The sign reversals in the late delay stage arose primarily from the individual or combined effects of the IP effect and the resistivity contrast between veined orebodies and surrounding rocks, representing a significant indicator for identifying concealed veined orebodies. The results of this study provide a theoretical basis for the mechanistic analysis and geological interpretation of complex TEM responses.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 3597K]

  • A simulation study on a dual-borehole DC resistivity system for advance detection under varying angles

    ZHOU Guanqun;XU Shaotian;ZHANG Weixin;WANG Yafei;WU Xiaoping;HU Xiongwu;CHEN Xinghai;CAO Yu;School of Resources and Environmental Engineering, Hefei University of Technology;School of Earth and Space Sciences, University of Science and Technology of China;School of Earth and Environment, Anhui University of Science and Technology;Anhui Huizhou Geology Security Institute Co., Ltd.;

    [Significance] Mine direct current(DC) methods, an efficient geophysical exploration technique, can be used to identify and delineate underground electrical resistivity anomalies, serving as a critical means for the advance detection of water-bearing or hydraulically conductive structures ahead of the mining face. [Methods] By combining the water exploration and discharge boreholes commonly used in coal mining and making reference to the observation system of the ground-based cross-borehole DC resistivity CT method, this study devised a dual-borehole DC resistivity observation system for advance detection. Through numerical simulation using the COMSOL software, this study constructed a homogeneous full-space model, in which a low-resistivity ball was used to represent a water-rich zone. Three types of observation configurations were developed, namely single-borehole sounding, dual-borehole profiling, and cross-borehole observation, with the included angle between a borehole and the tunneling direction set at 22.5°, 30°, and 45°. The full potential matrix was obtained through simulation, followed by apparent resistivity calculation and inversion imaging.Accordingly, the impacts of varying observation configurations and the included angles on the detection of the low-resistivity ball were compared. [Results and Conclusions] In the case where the position of the anomaly was fixed, a larger included angle between a borehole and the tunneling direction corresponded to gentler apparent resistivity curves with less distinct extrema, making it difficult to identify the influence range of the low-resistivity ball. Conversely, a smaller included angle was associated with more pronounced local maximum and minimum values, suggesting more significant anomaly responses. The inversion results of numerical simulation show that a smaller induced angle corresponded to better alignment between the location of the low-resistivity anomaly and the actual position of the ball. Besides, it was also associated with greater consistency between resistivity and its preset values. Among various configurations, the cross-borehole observation yielded the highest detection performance. The inversion results from the physical simulation conducted using a water tank confirm that, as the induced angle decreased, the detection results of the observation configurations became gradually better in the order of single-borehole sounding, dual-borehole profiling, and cross-borehole observation with an increase in the size of data acquired. These findings are consistent with the results from the numerical simulation, further verifying the reliability of the proposed observation system. The results of this study provide new technical guidance for advance detection in roadway tunneling.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2403K]

  • Coal body structure identification method based on Bayesian-optimized CNN-BiLSTM-Attention

    BIAN Huiyuan;JI Jiajun;DUAN Chaowei;ZHOU Jun;LI Kun;MA Yuhan;College of Geology and Environment, Xi'an University of Science and Technology;China Petroleum Logging Co.Ltd.;

    [Background] Coal-bearing basins contain primary and tectonically deformed coals due to multistage tectonic deformations. However, the gas-bearing properties of coal seams differ significantly due to varying pore and fracture densities, permeability, and mechanical properties. This makes coal structure assessment critical to coalbed methane(CBM) exploration and production. [Objective and Method] To enhance the accuracy and intelligence of coal structure identification, this study constructed a CNN-BiLSTM-Attention hybrid model that integrated a Bayesian optimization strategy. This model allowed for efficient fusion and representation of multi-scale log data by combining the local feature extraction capability of the convolutional neural network(CNN), the temporal sequence modeling strength of the bidirectional long short-term memory(BiLSTM), and the feature focusing ability of the Attention mechanism. Moreover,this model showed elevated stability and high training efficiency thanks to automatic parameter tuning through Bayesian optimization. Focusing on coal seams in the Shanxi and Benxi formations within the Ordos Basin, this study constructed a dataset of primary, primary-cataclastic, and cataclastic coals based on conventional log data, subjected to normalization, outlier removal, and interpolation of missing values, as well as data from cores. Then, the hybrid model was trained and assessed using the cross-entropy loss function. [Results and Conclusions] The CNN-BiLSTM-Attention hybrid model yielded an accuracy of 95.12%, outperforming isolated BiLSTM and CNN models. This hybrid model yielded precision and recall rates above 93% for various coal structures. Furthermore, it yielded a uniform error distribution, as indicated by the confusion matrices. This model was applied to well X2, demonstrating high consistency and discriminative ability for transition zones between varying coal structures. This significantly reduces misclassification between primary-cataclastic and cataclastic coals. Additionally, the hybrid model exhibits strong robust performance in processing noise in log data. This study offers a reliable and effective approach for fine-scale CBM assessment.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 3003K]

  • Logging-while-drilling azimuthal electromagnetic measurements for high-resistivity coal seams

    ZHAO Weina;ZHENG Dongfang;AI Weiping;XIE Xia;School of Science, Qingdao University of Technology;CNPC Engineering Technology R&D Company Limited;

    [Objective and Method] To determine the boundary detection capability of logging-while-drilling(LWD)electromagnetic azimuthal measurements for high-resistivity coal mines, this study simulated geosignal responses under varying operating frequencies, transmitter-receiver coil spacing conditions, and formation resistivity values. Then, key parameters for boundary detection for high-resistivity coal seams were optimized. Accordingly, this study proposed design schemes for LWD instruments with short(< 80 inches) and long(approximately 240 inches) transmitter-receiver coil spacing for short-distance(2.032 m) and long-distance(6.096 m) detection, respectively. [Results and Conclusions] LWD electromagnetic azimuthal measurements exhibit a significantly decreased depth of detection(DOD) in highresistivity coal seams compared to that in low-resistivity hydrocarbon reservoirs. Consequently, the existing methods for selecting the operating frequency and transmitter-receiver coil spacing are no longer applicable. In high-resistivity coal seams, increasing the operating frequency and transmitter-receiver coil spacing appropriately can enhance the strength and DOD of geosignals. Under transmitter-receiver coil spacing of 50-85 inches(1.270-2.159 m) and an operating frequency of(2-5) MHz, the DOD can reach 3 m, meeting the need for roof and floor detection. When the transmitter-receiver coil spacing increases to 5 m and the operating frequency decreases to 200-400 kHz, the DOD of electromagnetic signals in high-resistivity coal seams can extend to 10 m, offering a foundation for long-distance detection of low-resistivity anomalies.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2251K]

  • Self-adaptive inverse wavefield transform and derived pseudo-wavefield characteristics under roadway-borehole observation of transient electromagnetic data

    FAN Kerui;GUO Jianlei;WANG Ruoyu;ZHUANG Ming;FAN Fangze;XU Sheng;ZHAO Wentao;College of Civil Engineering and Architecture, Shandong University of Science and Technology;Key Laboratory of Engineering Geophysical Prospecting and Detection of Chinese Geophysical Society;CCTEG Xi'an Research Institute (Group) Co., Ltd.;Shandong Bainianhuitong Engineering and Technology Co., Ltd.;

    [Objective] To address the challenge of detecting aquifers outside the roadway excavation contour, this study combined the close-range detection via roadway-borehole transient electromagnetic(TEM) method with the wavefield transform. This will help simultaneously receive detection signals in front of the mining face and outside the roadway excavation contour while also highlighting the boundary information of aquifers. Moreover, to obtain a pseudo-wavefield featuring both reasonable kinematic characteristics and high sensitivity to changes in the electrical structures of strata, this study proposed a self-adaptive algorithm of inverse wavefield transform, thereby improving the accuracy and efficiency of the inverse wavefield transform of roadway-borehole TEM data. [Methods] The TEM wavefield transform faces some inherent limitations, such as a large dynamic range of the kernel function and high ill-posedness of the inverse transform equation. To address these challenges, this study, using the analytical solutions of the kernel function of wavefield transform over an infinite interval, proposed a method to automatically determine the interval of integration for inverse wavefield transform based on parameters such as the acquisition time of TEM data. The proposed method can minimize the dynamic range of the kernel function. Furthermore, using the precise integral method, this study developed an algorithm for solving inverse wavefield transform equations based on a self-adaptive step size of integration and iteration process, thus converting the solving of the ill-conditioned system of equations into solving an integral stably. For aquifers outside the roadway excavation contour, their TEM response signals were determined through forward modeling using the finite volume method. Accordingly, the pseudo-wavefield records of their vertical magnetic field components of TEM data were obtained. Moreover, the inverse wavefield transform of measured TEM data from boreholes was also conducted using the same algorithm. [Results] The results indicate that the obtained pseudo-wavefield records exhibited reasonable kinematic characteristics. The reflected wave trajectories in the pseudo-wavefield records were reasonably similar to the time-distance curves in the single-shot seismograms. Regarding numerical accuracy, the back substitution results of the pseudo-wavefield data were highly consistent with the forward modeling-derived or measured data, with the maximum relative errors all below 10%. [Conclusions] Under the roadway-borehole observation mode of TEM data, the proposed self-adaptive algorithm of inverse wavefield transform enables the acquisition of pseudo-wavefield records with clear physical significance and reliable numerical accuracy. Furthermore, the obtained pseudo-wavefield is highly sensitive to the aquifer boundaries with significant electrical contrasts, providing robust data support for further pseudo-wavefield imaging.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 10047K]

  • A method for interpretating acoustic reflection imaging logging data of fractured-vuggy reservoirs based on their theoretical response characteristics

    HUANG Ruokun;JIANG Kai;WU Xingneng;MA Kunyu;SU Yuanda;WANG Bing;CHEN Xu;Research Institute of Exploration and Development,Tarim Oilfield Company,PetroChina;School of Geosciences,China University of Petroleum;Xinjiang Key Laboratory of Ultra-deep Oil and Gas;State Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing);R&D Center for Ultra-Deep Complex Reservoir Exploration and Development,CNPC;

    [Objective] During the exploration and development of fractured-vuggy carbonate reservoirs, acoustic reflection imaging logging technology enables the detection of fractured-vuggy bodies around wells. However, this technology suffers from unclear response characteristics and a strong multiplicity of solutions. Focusing on the Tarim Oilfield,this study aims to establish a tailored interpretation method by integrating geological and geophysical characteristics.The purpose is to enhance the identification accuracy and reliability of fractured-vuggy bodies in these reservoirs.[Methods] Based on the distribution characteristics of fractured-vuggy carbonate reservoirs in the Tarim Oilfield, this study established the numerical simulation models of three typical fractured-vuggy bodies: inter-breccia porous, faultcavity, and tectonic-fracture types. Then, the imaging results of acoustic reflection imaging logging data were optimized using Hilbert transform-based envelope extraction and vertical constraint-based data reconstruction technique. Using the finite-difference numerical algorithm, this study simulated the theoretical reflection wavefields of various fracturedvuggy bodies. Then, using the optimized procedure for the imaging results of acoustic reflection imaging logging data,this study processed the migration imaging results of different types of fractured-vuggy bodies and summarized their typical characteristics. Based on typical theoretical response characteristics, the imaging results of acoustic reflection imaging logging data can be interpreted. [Results and Conclusions] The imaging results of acoustic reflection imaging logging data, obtained using the optimized procedure, exhibited clearer features. Compared to the imaging response characteristics of forward modeling, the imaging results of acoustic reflection imaging logging data revealed the presence of three sets of reflectors in the target interval. These reflectors were characterized by clear and distinct imaging results, mutual independence, and the occurrence of arc-like pseudomorph caused by adjacent reflectors. These characteristics aligned with the imaging response characteristics of fault-cavity-type fractures, demonstrating that these extrawell reflectors at this well interval are of the fault-cavity type. The interpretation results corresponded well with conclusions from well tests, confirming the presence of high-productivity fault-cavity-type fractured-vuggy reservoirs at this interval. The processing results of actual data validated the reliability of the identification of fractured-vuggy carbonate bodies based on theoretical response characteristics. This method provides robust technical support for the precise identification and interpretation of near-well fractured-vuggy carbonate bodies in the Tarim Basin.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 4937K]

  • Application of long-distance tunneling and detection for advance detection in excavation using shield tunneling machines

    CHEN Chao;LI Ping;LI Wei;WEI Rong;Shanxi Tiandi Wangpo Mining Industry Co.,Ltd.;CCTEG Xi'an Research Institute (Group) Co.,Ltd.;China Coal Research Institute;China Coal Mine Hazard Prevention and Control National Key Laboratory-Sub-Laboratory for Mine Water Hazard Prevention and Control;State Key Laboratory of Intelligent Coal Mining and Strata Control;

    [Objective and Method] During the rapid excavation process using shield tunneling machines in coal mines,the advance detection of concealed geological anomalies encounters challenges of limited space and insufficient accuracy. To overcome these issues, this study investigated highly-located drainage roadway 3211 in the Tiandi Wangpo Coal Mine in Jincheng City, Shanxi Province using the long-distance tunneling and detection technology, the core of which is long directional boreholes combined with comprehensive borehole geophysical prospecting. This roadway is located in the roof of the No.3 coal seam, and it is necessary to conduct shield construction in the stable sandstone layer located from 15 m to 19 m above the coal seam. Therefore, highly accurate geological positioning is required. By establishing the technical system of long directional boreholes combined with comprehensive borehole geophysical prospecting and considering the actual geological conditions, this study conducted the numerical simulations of boreholes under heterogeneous media and cross-layer conditions. Accordingly, it analyzed the characteristics of geophysical prospecting signals under different geological scenarios, revealing the structural response patterns and the effectiveness of the technology. Specifically, the synergetic detection of low-resistivity anomalies, geological structures, and coal-rock interfaces was carried out using the retreating branch drilling technology, combined with borehole transient electromagnetic(TEM)method, borehole radar, and borehole gamma-ray(GR) logging. [Results and Conclusions] A long horizontal borehole was drilled at a directional drilling site adjacent to it. This horizontal borehole consisted of one main borehole and two branch boreholes, with a cumulative directional run length of 594 m and a reaming length of 440 m. Concurrently, comprehensive borehole geophysical prospecting was conducted. The detection results reveal the presence of one major lowresistivity anomaly and three structural anomalies. Furthermore, the spatial distributions of four sandstone intervals were accurately characterized. Field verification shows that the positioning deviations of the sandstone horizontals ranged from 0.01 m to 1.02 m, suggesting a significantly improved accuracy of geological interpretations and an effectively reduced multiplicity of solutions. The long-distance tunneling and detection technology applied in this study enables the synergy between continuous shield tunneling and comprehensive borehole detection, enhancing the accuracy and efficiency of advance detection under complex geological conditions while also providing significant technical support for safe and efficient shield tunneling in coal mines.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2884K]

  • Structural evolution and spontaneous combustion and activation mechanisms of coals treated under inert atmospheres in a coal mine goaf

    ZHANG Leilin;LI Wanting;WEN Chenchen;Key Laboratory of Safe and Effective Coal Mining,Ministry of Education,Anhui University of Science & Technology;School of Safety Science and Engineering,Anhui University of Science & Technology;

    [Objective] When used for the treatment of fire zones in deep coal mine goafs, low-oxygen and inertization techniques suffer from a scientifically blind spot, i.e., the fire prevention and control bottleneck caused by a high susceptibility to re-ignition of coals after being treated with high-temperature, low-oxygen(or inert) gas. To overcome this limitation, this study aims to systematically determine the mechanisms by which the evolution of the physical and chemical structures of coals after heat treatment under different atmospheres influences their spontaneous combustion and activation behavior. The purpose is to provide theoretical support for the treatment and safe opening of fire zones in a coal mine goaf. [Methods] This study investigated gas-bearing coals in the Zhujidong Coal Mine, Anhui Province. Using a series of techniques, such as the Fourier transform infrared spectroscopy(FTIR), specific surface area and pore size analyses, thermal conductivity tests, and thermogravimetric analysis, this study systematically investigated the evolution of the chemical functional groups and changes in the pore structures in coal samples after heat treatment under atmospheres of 13% O_2, N_2, and CO_2. In combination with low-temperature oxidation experiments, this study monitored the release patterns of indicator gases such as CO and C_2H_4, oxygen consumption rates, and exothermic intensities of these coal samples. Additionally, variations in the activation energy for coal spontaneous combustion were quantitatively assessed through kinetic parameter-based inversion. [Results and Conclusions] FTIR analysis revealed that coal samples after heat treatment under different atmospheres exhibited significantly decreased ― OH content and noticeably increased contents of C―O and C=O. Among these, samples treated under a CO_2 atmosphere showed the most prominent effect of functional group reconstruction. Pore structure analysis suggests that coal samples after heat treatment exhibited significantly increased pore volumes and micropore specific surface areas, as well as improved pore connectivity.Most especially, samples treated under a CO_2 atmosphere exhibited the most developed pores with pore sizes ranging from 2 nm to 50 nm, with a micropore volume increasing by 0.3 μL/g and micropore specific surface area reaching up to1.56 m~2/g. These samples were followed by those treated under a N_2 atmosphere and then those treated under a 13% O_2 atmosphere in this regard. The test results of thermophysical properties and low-temperature oxidation characteristics revealed a generally enhanced thermal conductivity and low-temperature oxidation activity of coal samples after heat treatment, as manifested by significantly increased volume fractions of CO and C_2H_4, elevated oxygen consumption rates,and enhanced exothermic intensities. Kinetic analysis demonstrated that the apparent activation energy of the coal samples treated under 13% O_2, N_2, and CO_2 atmospheres decreased by 8.3%, 17.6%, and 21.6%, respectively. Thermogravimetric analysis(TGA) further confirmed that the active temperature t_3 of coal samples after heat treatment dropped by 2-11 ℃. Furthermore, the mass loss rates in stages from t_3 to t_5 of the coal samples decreased in the order of those treated under CO_2, N_2, and 13% O_2 atmospheres. These findings suggest that although heat treatment under inert atmospheres(especially CO_2) can temporarily suppress oxygen, it could increase the tendency of coals to spontaneous combustion. In engineering, it is advisable to adopt N_2 injection or N_2-CO_2 co-injection, supplemented by measures including temperature control, heat insulation, and fire suppression agents, to establish a multi-element fire prevention and re-ignition control system. This will help enhance the safety and long-term stability of the fire zones of coal mine goafs.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2613K]

  • Fructure mechanisms and fracture distribution patterns of main roofs in goaves within abandoned mines

    TAO Xuefeng;SHI Biming;HUA Xinzhu;LIN Baiquan;YUE Jiwei;LIANG Yuehui;ZHANG Chengcheng;QIN Hao;YANG Yong;XUE Yonglin;School of Safety Science and Engineering, Anhui University of Science and Technology;School of Safety Engineering, China University of Mining and Technology;

    [Objective] In abandoned mines, the storage zones of free gas are closely associated with overburden fractures in goaves. To accurately estimate free gas resources in abandoned mines, it is necessary to thoroughly investigate the rupture mechanisms of blocks in main roofs in goaves, as well as the overburden fractures and rupture trace morphologies in goaves. [Methods] Based on the masonry beam theory, this study established a mechanical model for the primary cantilever beam of a main roof. The analytical solutions of the stress components in the primary cantilever beam were analyzed using the stress inverse method, and the mathematical expression of periodic rupture traces was derived based on the Mohr-Coulomb failure criterion. Using the general rock mechanical parameters of the main roofs of goaves of various coal seams in the Panyi Mine in the Huainan mining area, Anhui Province, this study analyzed the stresses and strains of the primary cantilever beam, along with the strain energy density of the beam under different elastic moduli and Poisson's ratios. The rupture traces were calculated and plotted using the Maple software, and the influences of the internal friction angle and cohesive force on the rupture traces were analyzed. By constructing the experimental platform for physical simulation of mining face 1252-1 in the Panyi Mine using similar materials, this study analyzed the fracture network in the overburden in the goaf using the ImageJ software. [Results and Conclusions] The results indicate that the rupture of the primary cantilever beam of a main roof was primarily affected by horizontal and shear stresses,with tensile-shear failure predominating. The primary cantilever beam fracturing occurred initially in the compressed zone on its upper surface and then propagated toward the compressed zone on its lower surface. Substituting the overburden parameters of goaves in the Panyi Mine into the rupture trace expression yielded two parallel L-shaped rupture traces(i.e., rupture traces I and II). The rupture traces extended vertically from the top of the simulated block downward until inflection points and then propagated back downward to the bottom of the block. With an increase in the cohesive force,the number of rupture traces increased from two to three. Fracture traces I and II exhibited an L-shaped pattern, extending to the right side, whereas rupture trace III gradually extended vertically to the bottom of the block. The scanning results of overburden fractures in the goaf obtained using ImageJ software revealed that zones I-1 and I-2 were median-elevation gas enrichment areas, while zones II-1 and II-2 were high-elevation gas enrichment areas. The results of this study provide a scientific basis for designing the locations of gas drainage boreholes in an abandoned mine while also offering a reference for similar mines.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 3706K]

  • Numerical simulations of dynamic rock damage under laser-induced shock waves

    XU Yuelin;QIN Enwei;LI Wei;WANG Ying;School of Intelligent Equipment, Suzhou Vocational Institute of Industrial Technology;

    [Objective] Traditional laser thermal rock breaking technologies suffer from high energy consumption and a limited damage depth. To overcome these challenges, this study proposed a novel mechanical rock breaking method based on high-pressure plasma shock waves induced by short pulsed lasers, aiming to transform a thermodynamics-dominated rock breaking mechanism into a dynamics-dominated mechanism. [Methods and Results] Under the Abaqus/Explicit explicit dynamics framework, this study constructed a finite element model to simulate the interactions between nanosecond laser-induced shock waves and rocks. The accurate loading of shock wave pressure in the spatial and temporal domains was achieved using the VDLOAD user subroutine. Under the typical parameter combination-a peak pressure of 3 GPa, a pulse width of 20 ns, and a spot diameter of 4 mm, this study systematically simulated and revealed the dynamic behavior of the propagation of laser-induced shock waves in rocks, along with the two-stage mechanisms of dynamic rock damage. Specifically, in the shock wave loading stage, an instantaneous high stress(Mises stress: up to 2706 MPa) was generated on the rock surface; in the stress wave propagation stage, the reflection and superposition of the waves within rocks led to cumulative damage and ultimately rock material scaling. Furthermore, multiple comparative simulations were designed by systematically adjusting the peak pressure(1-5 GPa), pulse width(20-200 ns), and spot diameter(2-6 mm). With the damage volume as the assessment metric, the sensitivity of these parameters to the rockbreaking effect was investigated. The results reveal that under the typical parameter combination, a single laser shock led to the formation of a nearly conical damage zone on the rock surface, with a diameter of 4.3 mm, a depth of 5.8 mm, and a damage volume of 27.8 mm~3. The parameter sensitivity analysis indicates that the peak pressure exhibited a limited impact on the damage volume(increase rate: below 5.5%). In contrast, the pulse width and spot diameter exerted significant influence, representing dominant factors controlling the rock-breaking efficiency. [Conclusions] The rock-breaking efficiency of laser-induced shock waves depends predominantly on the spatiotemporal distribution and control of the stress wave energy. The collaborative optimization of the pulse width and spot diameter can effectively regulate the rock damage under similar single-pulse energy, thereby achieving low energy consumption and high efficiency in rock breaking. Overall, this study provides a novel approach for the exploitation of deep hard rock resources.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2026K]

  • A novel model for calculating in situ stress within deep coal seams considering microstructural characteristics and its application

    ZHAO Haifeng;SHI Hongwei;XIE Fei;WANG Chengwang;WANG Zongfei;CHEN Gaojie;College of Petroleum Engineering, China University of Petroleum (Beijing);Institute of Engineering and Technology,Coalbed Methane Company Limited, PetroChina;

    [Objective] Research on in situ stress serves as a bridge between geological and engineering analyses. Accurate insights into in situ stress regimes are crucial for ensuring engineering efficiency and development benefits.However, microstructures are well developed in deep coal seams, for which no effective model is currently available for calculating in situ stress. [Methods and Results] By classifying structures into macrostructures and microstructures, this study established a novel model for calculating in situ stress in deep coal seams while considering microstructural characteristics. In the novel model, the horizontal in situ stress was decomposed into three components: the horizontal components induced by vertical stress and macroscopic and microscopic tectonic stresses. The novel model allows for the simultaneous calculation of the magnitude and orientations of in situ stress through stress tensor decomposition. This model was applied to calculate in situ stress in two vertical wells. The calculated magnitudes and orientations of in situ stress were compared with acoustic emission experimental data and log interpretation data, respectively, yielding maximum relative errors of 8.20% and 4.58%. Based on the novel model and the data from adjacent wells, the magnitudes and orientations of in situ stress in three unlogged horizontal wells were calculated in a staged manner. The predicted in situ stress orientations were validated using microseismic monitoring results, yielding relative errors ranging from 0.29% to13.89%. Based on the calculated in situ stress, the propagation morphologies of simulated fractures in a horizontal well were predicted. The prediction results aligned well with microseismic monitoring results. The novel model provides a new approach for calculating in situ stress, enabling fine-scale determination of in situ stress within individual wells.[Conclusions] The fine-scale calculation results of in situ stress hold great values in applications in two aspects in the field of petroleum engineering:(1) in drilling engineering, accurate in situ stress parameters help significantly enhance the reliability of wellbore stability analysis, optimize drilling fluid density design, and mitigate the risks of wellbore collapse and lost circulation;(2) In reservoir fracturing, single-well in situ stress profiles can provide guidance the design of fracturing stages and clusters to effectively mitigate stress shadowing effects and enhance the complexity and conductivity of fracture networks, thereby achieving efficient reservoir stimulation and production growth.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2477K]

  • Differences in gas-bearing properties of deep and shallow coal reservoirs and their implications for coalbed methane production in the western section of the southern margin of the Junggar Basin, Xinjiang

    MI Julei;ZHAO Changyong;YANG Zhaobiao;WANG Pengli;LI Erting;ZHANG Baoxin;BAI Haifeng;GAO Xiuwei;WANG Jianan;PetroChina Xinjiang Oilfield Company;Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology;

    [Background] In recent years, breakthroughs have been constantly achieved in the production of coalbed methane(CBM) at burial depths exceeding 2 000 m in China, with the gas-bearing properties of coal reservoirs identified as a primary geological parameter controlling the CBM production. The western section of the southern margin of the Junggar Basin(also referred to as the study area) hosts abundant CBM resources. In this section, the burial depths of extensive coal seams exceed 2 000 m. However, limited explorations of deep coal reservoirs have restricted a systematic understanding of the gas-bearing properties of coal reservoirs in the study area. [Methods] Coal samples were collected from the Middle Jurassic Xishanyao Formation at burial depths ranging from 2 400 m to 2 600 m in well QX-1-a typical deep CBM test well in the study area. These deep coal samples were tested for lithotypes and coal quality, gas content, and geochemical characteristics of CBM. Based on the test results and previous data on shallow CBM, this study presented a summary of the differences in gas-bearing properties between deep and shallow coal reservoirs. Furthermore,it revealed the geological factors controlling the differences in the gas content, occurrence state, and composition between deep and shallow coal reservoirs. [Results and Conclusions] The deep coal samples showed measured gas content(on an air-dried basis) ranging from 10.28 m~3/t to 18.99 m~3/t, with an average of 14.95 m~3/t. The adsorbed gas saturation generally exceeded 100%, indicating that CBM occurs in both adsorbed and free states, with an average free gas proportion of 36.56%. Regarding the gas composition, CH_4 accounted for a volume fraction close to 90% in most samples, while N_2 and CO_2 exhibited average volume fractions of 5.72% and 1.78%, respectively. Compared to those of the shallow coal reservoirs, the gas-bearing properties of the deep ones exhibited a slight increase in total gas content, a pronounced increase in the free gas proportion, but a notable decrease in the volume fractions of CO_2 and N_2. The deep coal reservoirs exhibit elevated organic matter maturity, coupled with changes in temperature and pressure, which changed the adsorbed and free gas distribution patterns. These lead to differences in the gas content and occurrence state.Moreover, the deep strata feature an enhanced sealing performance and a configuration consisting of old source rocks and young reservoirs, representing the primary causes of differences in gas-bearing properties between deep and shallow coal reservoirs. Analysis of the gas production characteristics and performance of shallow and adjacent deep CBM wells reveals that the high gas content and free gas proportion and low volume fractions of non-hydrocarbon components in deep coal reservoirs in well QX-1 collectively suggest the considerable potential for gas production. The key to high and stable production while avoiding rapid depletion of the deep coal reservoirs lies in unraveling the release patterns of CBM in different occurrence states and, accordingly, formulating a dynamic pressure control regime. The results of this study provide a critical theoretical basis in terms of basic geology for deep CBM production in the study area.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 1910K]

  • Technique for water-preserved coal mining based on zonal height limits along mining face and mechanisms behind overburden failure

    SUN Xueyang;CAO Hongyi;LI Peng;HAN Dehao;LUO Qiyao;LIU Kuan;LI Jihong;YIN Xu;College of Geology and Environment, Xi'an University of Science and Technology;Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation;Geological Research Institute for Coal Green Mining, Xi'an University of Science and Technology;CCTEG Xi'an Research Institute (Group)Co., Ltd.;

    [Objective] The exploitation of shallow coal seams under water bodies faces a contradiction between water resource preservation and overburden disturbance. In this case, achieving safe mining while preventing water-conducting fracture zones from affecting key aquifers and exploring techniques that place equal emphasis on water preservation and efficient resource recovery have emerged as popular research topics. [Methods] An integrated aquifer-overburdencoal seam model was constructed using 3D geological visualization technology. This model, combined with the principles for the setting up of waterproof coal pillars, enabled accurate delineation of zones with water inrush risks. Accordingly, a technical scheme for mining based on zonal height limits along a single mining face was proposed. By introducing bending moment and shear force continuity conditions at mining height transition boundaries, this study derived the deflection curve equations for both full-seam and height-limited mining zones using the theory of beams on elastic foundations. The heights of water flowing fractured zones were determined by comparing the maximum bending deflection-induced subsidence of hard rock layers with their free-space height. Furthermore, by combining the 3D geological modeling with FLAC3D-based numerical simulation, this study systematically investigated the overburden failure characteristics and stress evolutionary patterns under the condition of mining based on zonal height limits. [Results] This study proposed a zonal mining scheme for mining face 200 in the Shuanglong Coal Mine, Shaanxi Province. In the zonal mining schemes, the mining heights for the full-seam and height-limited mining zones were set at 3.2 m and 2.5 m, respectively. The results indicate that in the early mining stage, the development of the water flowing fractured zone in the height-limited mining zone exhibited significant spatiotemporal lags. Theoretical analysis reveals that the height of the water flowing fractured zone decreased from 83.6 m to 68.9 m as the mining face advanced from 45 m to 100 m. In contrast, the numerical simulation indicates that the height decreased from 86.8 m to 69.5 m as the advancing distance reached 50 m. The reduction in the mining height significantly enhanced the concentration effect of coal support pressure in front of the mining face. Specifically, the coal support pressure increased sharply from 12.0 MPa to 15.2 MPa(growth rate: 26.7%) at an advancing distance of 50 m, decreased to 8.7 MPa at an advancing distance of 250 m, and finally reverted to 10.9 MPa after mining completion. Therefore, the coal support pressure generally exhibited a dynamic evolutionary pattern from a sharp increase to a gradual decrease and then to a gradual increase. [Conclusions] The mining technology based on zonal height limits can effectively inhibit the development of local water flowing fractured zones and reduce damage to aquifers caused by the overburden disturbance, thereby achieving water-preserved coal mining. Furthermore, this study reveals the stress redistribution patterns in coals following a reduction in mining height,along with the mechanisms behind the lagged response of the development of water flowing fractured zones. The results of this study will provide a theoretical basis and technical reference for the zoning parameter optimization and support design for water-preserved mining under water bodies in similar geological conditions.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 4541K]

  • Macro-mesoscopic developmental patterns of cracks in surrounding rocks of rectangular roadways under true triaxial stresses

    SHI Wenbao;XU Qingzhao;CHANG Jucai;LI Chuanming;QIAO Longquan;MIAO Zhuang;YAN Aoyun;Joint National-Local Engineering Research Centre for Safe and Precise Coal Mining, Anhui University of Science and Technology;Anhui Province Joint Key Laboratory of Intelligent and Green Mining of Deep Coal Resources, Anhui University of Science and Technology;School of Mining Engineering, Anhui University of Science and Technology;

    [Objective and Method] This study aims to investigate the relationship between the stress environment and the deformation and failure responses of surrounding rocks, thereby unraveling the inherent mechanisms underlying the deformation and failure. With cement, river sands, and gypsum as raw materials, rectangular roadway model specimens measuring 200 mm × 200 mm × 200 mm were prepared. Using a large-scale true triaxial seepage coupling testing machine, this study conducted triaxial loading tests on the rectangular roadway specimens under different lateral pressure coefficients. Using microcameras and an acoustic emission system, it monitored the whole process of the macroscopic deformation and failure, along with the evolutionary characteristics of internal damage, of the surrounding rocks of the rectangular roadway specimens. In combination with the PFC~(3D) numerical simulation, the distribution patterns of microcracks within the rectangular roadway specimens were determined. [Results and Conclusions] During the deformation and failure of the roadway surrounding rocks under stress loading, the failure of the sides of the rectangular roadways was primarily caused by tangential stress concentration. Under continuous stress loading, the maximum bending moment was prone to occur in the middle parts of the roadway sides, resulting in tensile failure of roadways, characterized by the scaling of arc-shaped thick sheets(thick in the middle and thin at both ends). The scaling failure expanded gradually inward and formed a macroscopic V-shaped failure groove, showing pronounced layered failure characteristics.With a gradual increase in the axial load, the thickness of fragments generated by layered scaling failure decreased progressively. Concurrently, the arc-shaped thick sheets transitioned into arc-shaped thin sheets and partially scaled arcshaped thin sheets, while the cumulative acoustic emission energy shifted from a gentle growth to stepped and then steep increases. The development of microcracks in the roadway surrounding rocks was inherently related to the stress environment. The increase in the lateral pressure coefficient inhibited the development of microcracks within the roadway surrounding rocks, with the proportion of tensile microcracks decreasing from 80.424 1% to 76.637 9%. During failure,the internal microcracks exhibited a butterfly distribution pattern. The results of this study provide an experimental reference for the stability control of the surrounding rocks of deep mining roadways.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 4262K]

  • Performance and migration path tracing of magnetic grouts for fractured rock masses

    SHANG Hongbo;WANG Hao;WANG Xiaodong;QIAO Wei;WANG Tiantian;SUN Junqing;SUN Jie;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;

    [Objective] For coal mining areas in the middle reaches of the Yellow River basin, sealing mining-induced fractures via grouting serves as an effective approach to preventing water inrushes from coal seam roofs while also protecting groundwater resources. However, accurately identifying the migration paths of grouts remains a bottleneck for the further application of grouting modification technology to fractured rock masses. [Methods] This study investigated a coal mine threatened by both water inrushes from the coal seam roof and a short supply of water resources within the Jurassic coalfield in the middle reaches of the Yellow River basin, focusing on the magnetic tracing of the migration paths of grouts in fractured rock masses within the coal seam roof. Employing a range of techniques, includ-ing laboratory tests and analysis, physical simulations using similar materials, and theoretical calculations, this study ana-lyzed the performance, microstructures, and magnetic responses of magnetic grouts. Furthermore, using magnetic particles as a tracer, this study carried out tracing experiments on the migration paths of grouts in fractured rock masses and exam-ined the distribution of magnetic intensity along the paths. [Results and Conclusions] The performance test results indicate that the optimal mix ratios of the magnetic grouts included a water-cement ratio of 1.0∶1.0, along with a mass fraction of 15% and a particle size of 0.2 μm for magnetic particles. The grouts prepared using such mix ratios exhibited both the magnetic properties of solid magnetic particles and the properties of ordinary cement grouts. The analytical results reveal that the migration paths of grouts in the specimens of fractured rock masses, as plotted in the magnetic intensity monitoring diagrams, were roughly consistent with the fracture locations and shapes in the physical diagrams and the fracture localization maps derived using acoustic emission tests. Such consistency demonstrates that the magnetic intensity monitoring can be used to characterize the migration paths of grouts in fractured rock masses. Using the proposed method for calculating the magnetic intensity of grouts migrating in fractured rock masses, the magnetic intensity at various points of the centers of the fractured rock masses was determined. Furthermore, the calculated migration paths of grouts were largely consistent with the actual flow paths observed in the grouted specimens, further verifying that it is relia-ble to characterize the migration paths of grouts in fractured rock masses based on magnetic intensity. The results of this study help address the challenge of accurately identifying the migration paths of grouts in fractured rock masses,providing a basis for the parameter design and performance evaluation of grouts for these rock masses.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 14784K]

  • Sensitivity analysis of factors influencing water redistribution in vadose zones under coal mining disturbance in ecologically vulnerable areas

    WANG Ao;LIU Shiliang;WANG Shanlin;ZHENG Yusheng;WANG Tengye;WANG Zuzhen;MAO Deqiang;School of Civil Engineering, Shandong University;

    [Objective] Coal mining-induced disturbance leads to water redistribution in the vadose zones of mining areas. The sensitivity analysis of the factors influencing this redistribution holds critical significance for the reconstruction of eco-geological environments and the sustainable economic development in mining areas. [Methods] Against the engineering background of the Yushen mining area characterized by wind-blown sandy terrain in northern Shaanxi Province, this study analyzed the primary factors influencing water redistribution in the vadose zone under coal mining disturbance. Accordingly, 18 COMSOL Multiphysics numerical models for water redistribution in the vadose zone under coal mining disturbance were constructed through orthogonal experiments. Using these models, the theoretical average saturation along three monitoring lines at burial depths of 6.2 m, 7.0 m, and 7.8 m was derived to recover the coal mining disturbance of the pre-mining stage. Through the range analysis and multiple linear regression analysis, this study clarified the sensitivity of the factors influencing water redistribution in the vadose zone under coal mining disturbance and further determined the weights of the primary influential factors using the analytic hierarchy process(AHP).[Results and Conclusions] From the perspective of stratigraphic structure, hydrogeological conditions, and mining conditions, the primary factors influencing water redistribution in the vadose zone under coal mining disturbance included the ratio of the sandy loam thickness to the sandy clay thickness(a), initial porosity(p), initial number of fractures(l),the matrix permeability coefficient of the vadose zone(K_1), fracture permeability coefficient(K_2), and coal seam mining height(b). Under coal mining disturbance, the overall water redistribution in the vadose zone was primarily influenced by factors a and K_2, along with minor influence from factors l, b, and K_1. Based on the range analysis and multiple linear regression analysis of the orthogonal experimental results, the sensitivity of these factors decreased in the order of a, K_2,p, b, l, and K_1. Following the sensitivity ranking of these factors, the weights of the primary factors were determined at38.25%(a), 25.04%(K_2), 15.96%(p), 10.06%(b), 6.41%(l), and 4.28%(K_1) using the AHP. The sensitivity ranking was consistent with the weight ranking, with both substantiating each other. The results of this study hold great significance for reconstructing the ecological security patterns and constructing green mines in ecologically vulnerable areas within western China.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 1811K]

  • Simulation of groundwater flow field evolution and water inrush risks under the deep-well reinjection of high-TDS mine water

    LIU Qi;SUN Yajun;FAN Jianguo;TAN Xianfeng;XIAO Shengxin;YANG Chuanwei;CHEN Weiyang;CHEN Ge;School of Resources and Geosciences, China University of Mining and Technology;Fundamental Research Laboratory for Mine Water Hazards Prevention and Controlling Technology;Shandong Energy Group Co., Ltd.;Shandong Hi-speed Construction Management Co., Ltd.;Shandong Provincial Lunan Geology and Exploration Institute (Shandong Provincial Bureau of Geology and Mineral Resources No.2 Geological Brigade);Enginee

    [Objective] The deep-well reinjection of mine water results in a regional groundwater level rise to varying degrees, possibly inducing hydrogeological hazards such as floor water inrushes or water inrushes along faults. In this context, determining the evolutionary pattern of the groundwater flow field under long-term mine water reinjection and conducting reinjection safety assessments play a critical role in ensuring both the safety of mine water reinjection and water conservation-based coal mining. [Methods] This study examined the reinjection of mine water in a coal mine within the Juye coalfield, North China. Based on the geological conditions for mine water reinjection in the study area, this study selected the target aquifer for reinjection by referring to indices including mining safety, water quality security, water circulation condition, water exploitation and utilization, and reinjection potential. Using the groundwater modeling system(GMS) software, this study constructed a 3D numerical model of the Ordovician limestone aquifer. Using this model, this study simulated and predicted the regional groundwater level rise, cumulative water storage, and water storage efficiency during long-term mine water reinjection. Accordingly, the primary water inrush patterns that were likely induced by groundwater level rise were determined. In combination with the formulae provided in the Regulations for Mine Water Prevention and Control(also referred to as the Regulations) and the numerical simulation results derived using the FLAC~(3D) model, this study assessed the impact of the maximum groundwater level rise on mining safety under long-term mine water reinjection. Finally, a safety assessment system for deep-well mine water reinjection was proposed. [Results and Conclusions] The mine water in a coal mine within the study area features elevated water inflow and high total dissolved solids(TDS), which leads to high water treatment costs. A comparative analysis reveals that the deep Ordovician limestone aquifer was suitable to use as the optimal reinjection target for minimally treated mine water.Furthermore, the basis for the siting of reinjection boreholes was proposed. The GMS-based simulation results reveal that over a reinjection period of 10 years, single-borehole reinjection at a rate of 200 m~3/h led to a maximum groundwater level rise of 10.02 m. In contrast, reinjection using four boreholes with a spacing of 400 m and a reinjection rate of800 m~3/h yielded a maximum groundwater level rise of 25.83 m. The single-borehole reinjection could achieve an annual reinjection volume of up to 1.72 × 106 m~3, suggesting considerable potential for groundwater storage and a huge cost advantage of water treatment. Among various water inrushes, those along faults are the most likely triggered by groundwater level rise in the study area. The formulae in the Regulations and the simulation results derived using the FLAC~(3D)model demonstrate that under conditions where coal pillars are retained as required, the reinjection-induced groundwater level rise will not destroy the structural stability of impermeable rocks, and normal mining activity is less prone to induce secondary water inrushes during mine water reinjection. In this case, safe mining can be maintained. The safety assessment system established for deep-well mine water reinjection underscores that ensuring both water quality safety and mining safety is necessary for the implementation of a deep-well mine water reinjection technology. The results of this study provide critical theoretical and practical guidance for assessing the reinjection safety of mine water in coal mines with typical hydrogeological structures in North China.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 8123K]

  • An experimental study on the deterioration characteristics of sandstone masses with rock bridges under cyclic freezing and thawing

    ZHANG Huimei;LI Zengle;CHEN Shiguan;YUAN Chao;ZHENG Shihang;College of Science, Xi'an University of Science and Technology;School of Architecture and Civil Engineering, Xi'an University of Science and Technology;Xi'an Kedagaoxin University;

    [Objective] To determine the deformation and failure mechanisms of fractured rock masses with rock bridges in alpine regions, this study conducted mechanical property tests on rock samples with varying lengths of rock bridges subjected to cyclic freezing and thawing. [Methods] Through experiments, this study summarized the characteristics of the static strength deterioration of rock masses under the combined effects of different numbers of freezing and thawing cycles and varying rock bridge lengths. By combining acoustic emission signal monitoring and scanning electron microscopy, this study thoroughly explored both the evolutionary characteristics of fractures and rock rupture modes. Accordingly, it revealed the macroscopic and microscopic failure mechanisms of rock masses with varying lengths of rock bridges under cyclic freezing and thawing. [Results] The results indicate that with an increase in the number of freezing and thawing cycles, the rock sample with a shorter rock bridge exhibited greater loss rates of both mass and P-wave velocity. As the number rose, the peak strengths and moduli of elasticity of the rock samples gradually decreased, with their deterioration rates significantly decreasing. In the case of the same number of freezing and thawing cycles, a smaller distance between the bottom of a rock sample and fractures in the lower part of the rock bridge of the sample led to a lower overall rock mass strength. The peak stresses of rock samples with different lengths of rock bridges decreased in the order of the intact sample, and samples with rock bridge lengths of 50 mm, 60 mm, and 40 mm sequentially. Acoustic emission tests demonstrated that the sample with a 50-mm-long rock bridge exhibited the highest cumulative ringing count, while that with a 40-mm-long rock bridge showed the lowest count. The ringing count of the rock samples showed a positive correlation with peak stress but a negative correlation with the number of freezing and thawing cycles.The b-value in the acoustic emission tests fluctuated generally. Cyclic freezing and thawing caused the b-value to decline earlier, corresponding to the formation of large fractures in rocks. Macroscopically, the rock samples showed a more random microcrack direction distribution at the rock bridge tips after cyclic freezing and thawing. Consequently,penetration failure of the rock bridges occurred more rarely, with the failure mode shifting from single failure to tensileshear hybrid failure. Microscopically, the damage mode evolved from cement damage to the breakage of mineral grains,with the fragmentation zone expanding progressively. These findings indicated that with an increase in the number of freezing and thawing cycles, the tightness of rock sample structures decreased significantly. As a result, intergranular fractures became interconnected to form networks and penetrated, leading to the significant denudation of cemented minerals and causing a systematic loss of inter-particle bonding force. [Conclusions] Adjusting the rock bridge length plays a key role in enhancing rock masses' resistance to freezing and thawing in alpine regions, with the optimal rock bridge length contributing to effectively reduced ranges of stress concentration zones at fracture ends and slow deterioration caused by cyclic freezing and thawing. In engineering practices, the rock bridge length should be appropriately adjusted to achieve a balance between freeze resistance and mechanical stability. Furthermore, it is necessary to enhance the monitoring of fracture tips to restrict the rapid degradation induced by stress concentration.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 3077K]

  • Current status and future trend of research on underground borehole measurement technology for coal mines

    CHEN Long;YANG Dongdong;LI Quanxin;CHU Zhiwei;ZHANG Jiguan;CHEN Xiang;CCTEG Xi'an Research Institute (Group) Co.,Ltd.;School of Emergency Management and Safety Engineering,China University of Mining and Technology (Beijing);China Coal Research Institute;

    [Background] Underground borehole measurement emerges as a core technology for the safe production of coal mines. Its multi-parameter measurements, data accuracy, data transmission rate, and reliability directly influence the timeliness of early warning for disasters, the operating stability of instruments, the accuracy of borehole assessment, and the scientific rigor of intelligent decision-making under complex deep geological conditions. [Advances] So far, the measurement while drilling(MWD) and post-drilling borehole visualization techniques have developed into a diversified technological system. Specifically, the MWD technique has achieved a leap from wireline to wireless transmission,obviating the reliance on wireline drill rods in traditional measurement methods and enabling the collaborative development of the real-time monitoring of borehole trajectory parameters, stratigraphic information, and drilling conditions. For this technique, the gyroscope-based MWD system effectively addresses the issue of magnetic interference, significantly enhancing the timeliness and accuracy of measurements; the geosteering MWD system enables precise identification of coal-rock interfaces; and the engineering parameter MWD system, by integrating sensors for vibration, drilling pressure,and other parameters, provides comprehensive engineering parameters for the drilling process. By developing storagetype, push-rod-type, and drill-rig-propelled equipment, the visualization technique for post-drilling borehole measurement allows for fine-scale assessment of borehole trajectories and geological information. [Prospects] To address issues of borehole measurement techniques, such as low accuracy, insufficient multi-parameter fusion, and low data transmission rates, against the backdrop of intelligent coal mine construction, future research should focus on the collaborative optimization of high-precision sensors and intelligent algorithms, as well as technologies for the rapid acquisition and transmission of multiple types of data within boreholes, the intelligent optimization and control of borehole trajectories,and dynamic real-time correction of errors in post-drilling borehole measurement. These research efforts will provide core support for precise steering and safe, efficient drilling under complex underground geological conditions in coal mines, thereby driving the transition of the coal industry toward a safe, efficient, and green intelligent mining mode.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2186K]

  • Intelligent lithology identification while drilling using BiLSTM integrating attention mechanism

    WANG Xi;PENG Fengjia;LI Siyang;GUO Xiao;ZHANG Feifei;RAN Xiaofeng;ZHANG Cong;Hubei Key Laboratory of Oil and Gas Drilling and Production Engineering (Yangtze University);National Engineering Research Center for Oil & Gas Drilling and Completion Technology, School of Petroleum Engineering, Yangtze University;Changqing Drilling Company, CNPC Chuanqing Drilling Engineering Company Limited;Huabei Oilfield Company,PetroChina;School of Mechanical Engineering,Yangtze University;

    [Objective] Vibration signals while drilling reflect the physical properties and microstructural characteristics of rocks, providing a valuable basis for real-time lithology identification. However, existing models suffer from limited accuracy and robustness due to the low dimensionality of signal features and the class imbalance induced by variations in the rock layer thickness. [Methods] To overcome these limitations, this study proposed a novel lithology identification method based on a bidirectional long short-term memory(BiLSTM) network that integrates attention mechanism(also referred to as the BiLSTM-Attention). This approach incorporates automated feature extraction and class weight adjustment strategies to enhance both the classification performance and generalizability of the model. First, triaxial vibration acceleration signals were acquired using a custom-designed measurement sub. Subsequently, a wide range of statistical,time-domain, and frequency-domain features were automatically extracted utilizing Tsfresh-a Python package. Key features were then selected through feature importance evaluation, followed by the construction of a high-quality feature space. Afterward, temporal dependencies inherent in the time-series data were modeled using the BiLSTM network.Meanwhile, attention mechanism was introduced to enhance critical features through weighting, thus improving the sensitivity to lithological variations of the resulting model. In addition, a class weight calculation mechanism was adopted to reduce the adverse impact of class imbalance, thereby enhancing the ability of the model to accurately identify a minority of lithologies. [Results and Conclusions] The experimental results indicate that for the dataset treated with feature engineering using Tsfresh, the proposed BiLSTM-Attention model yielded a training accuracy of 99.59% and a low loss value of 0.012 5, which increased by 12.35% and decreased by 0.391 5, respectively compared to raw data without feature engineering. The proposed model yielded precision ranging from 98.31% to 100.00%, recall from 98.99% to100.00%, and F_1 scores from 99.15% to 99.73%, increasing by 4.23% to 6.89%, 4.46% to 5.13%, and 4.7% to 5.38%, respectively compared to those of the GRU, LSTM, BiLSTM, and LSTM-Attention models. Furthermore, the proposed method outperformed traditional models in terms of feature representation and classification accuracy. Notably, it exhibited enhanced robustness and stability in identifying a minority of lithologies. Overall, this study provides a novel approach for intelligent lithology identification while drilling.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2725K]

  • An automated attitude control method for the rotary steerable system and its validation through hardware-in-the-loop simulation

    ZHANG Nan;REN Bai'an;LI Fei;LIU Ziqi;LYU Fangxing;College of Petroleum Engineering, Xi'an Shiyou University;School of Electronic Engineering, Xi'an Shiyou University;Directional Drilling Laboratory of CNOOC Key Laboratory of Well Logging and Directional Drilling;Xi'an Key Laboratory of Intelligent Equipment for Oil,Gas and New Energy Development;

    [Objective] The traditional manual control mode of a rotary steerable system(RSS) faces challenges, including response delay and low control efficiency. To address these challenges, this study proposed a closed-loop automated attitude control method for the RSS and verified its effectiveness through hardware-in-loop(HIL) simulation. [Methods]This study focuses on the drilling process of a point-the-bit RSS. In the case of deviations between measured and target attitudes, the control parameters were calculated based on the deviation signals using a closed-loop controller, driving the RSS actuator to conduct trajectory correction. Afterward, the actual attitude was yielded and then entered the input end of the RSS through the feedback of the measurement unit, thereby forming a closed-loop control structure. To further validate the effectiveness of the proposed control algorithm, this study developed a HIL simulation platform consisting of(1) a digital twin model that integrated a model describing the movement of the drilling tool and a virtual attitude sensor model,(2) a real-time simulator, and(3) a physical main control unit of the RSS. This platform enables real-time interactions among the control algorithm, the movement model of the drilling tool, and the virtual attitude sensor model.In this manner, the high-precision simulation of complex downhole conditions can be achieved in a laboratory environment. Using the HIL simulation platform, this study conducted tests and experiments on manual and automated control modes of drilling, along with anti-disturbance tests on the holding interval under the control of analytical formulas and proportional integral derivative(PID). [Results and Conclusions] Compared to manual control, the automated control mode exhibited significantly reduced overshoot, steady-state errors, and settling time. For the inclination interval, the automated control mode reduced the overshoot from 23.92% to 1.96% and the average settling time by 72.33% compared to the manual control model. For the azimuth interval, the automated control mode reduced the overshoot from23.31% to 2.04% and the average settling time by 53.45%. To verify the robustness of the automated attitude control method, anti-disturbance tests were conducted under azimuthal disturbances with a mean of zero and a variance of 0.2.The results reveal that the automated attitude control method, combined with PID control, reduced the settling time by18.9% reduction in the holding section. Therefore, the proposed closed-loop automated control method can significantly enhance the attitude control performance of the RSS, the stability of drilling trajectories, and response efficiency, providing a feasible technical pathway for achieving the automated RSS control under downhole conditions. The digital twinbased HIL simulation platform offers an efficient environment for verifying the iterative optimization of the downhole closed-loop control algorithm, effectively avoiding the high cost and risks associated with tests in the actual downhole environment. This accelerates the iterative optimization of the downhole closed-loop automation algorithm of the RSS and its transformation to engineering implementation.

    2025 11 v.53;No.335 [Abstract][OnlineView][Download 2378K]