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Characteristics and favorable area evaluation of deep coalbed methane accumulation in Fugu area of the Ordos Basin
GUO Guangshan, XU Fengyin, LIU Lifang, CAI Yidong, QIN Wei, CHEN Zhaohui, DENG Jimei, LI Zhuolun
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Abstract:
The Shenfu block on the eastern edge of the Ordos Basin is a typical deep coalbed gas field with abundant resources and enormous exploration and development potential. In October 2023, the Shenfu deep coal seam atmospheric field has successfully applied for a proven geological reserve of over 110 billion m3. The Fugu area is located in the central part of the Shenfu block and is the earliest experimental area for deep coalbed methane production. However, the understanding of its coalbed methane enrichment and accumulation patterns and exploration and development potential is still unclear. Comprehensive application of seismic, logging, drilling, and coal rock testing data to identify the geological characteristics, enrichment and accumulation patterns, and distribution of favorable areas of deep coalbed methane in the region. The results show that the main coal seams 4+5 and 8+9 have stable development and large thickness (4+5 coal:3.2-5.8 m; 8+9 coal:8.7-13.5 m), and favorable layers are mainly distributed in the middle and upper parts of the coal seam; The macroscopic coal rock type is mainly bright semi bright coal, and the coal body structure is mainly primary fragmented coal; Due to the influence of deep metamorphism, coal is mainly composed of gas coal, fat coal, and coking coal. The degree of coal metamorphism is at the peak of pyrolysis gas generation, and coal reservoirs exhibit medium to high gas content (4+5 coal:3.0~12.0 m3/t; 8+9 coal:7.5~18.5 m3/t) and gas saturation (35.0%~115%); The main coal seam belongs to a low-permeability reservoir (0.01~0.09) ×10-3 μm2), the pore structure is mainly composed of micropores and small pores. It is proposed that the coalbed methane in the Fugu area is enriched and accumulated in a "fold fault hydrodynamic" model, with the coalbed methane enrichment area located in the tectonic gentle zone and slope zone. Establish a dual sweet spot evaluation system for deep coalbed methane geology and engineering, and identify Class I geological engineering sweet spot areas located in the east and southwest, which are the preferred areas for deep coalbed methane exploration and development in the study area. Therefore, this research further enriches the theory of deep coalbed methane enrichment and accumulation, and has important guiding significance for the exploration and development practice of deep coalbed methane in the eastern edge of the Ordos Basin.
Genesis and accumulation mechanism of low rank coalbed methane in gas-rich depressions of Erlian Basin
LIN Haitao, LI Ling, TANG Shuling, TIAN Wengang, LI Jie, MENG Qin
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Abstract:
Inner Mongolia is rich in low rank coalbed methane (CBM) resources, and research on the genetic and accumulation mechanism of coalbed methane is crucial for the selection and evaluation of low rank coalbed methane resources. Taking the low rank CBM in the key gas rich depressions of the Erlian Basin as the research objective, the geochemical characteristics of CBM and coal seam water is analyzed and the genesis and accumulation mechanism of low rank CBM is revealed by using various experimental methods, including tests on composition and carbon/hydrogen isotopes of CBM water quality, hydrogen/oxygen isotopes, and radioactive isotopes 3H and 14C of coal seam water. The result shows that the CBM component in the Erlian Basin is dominated by CH4, which belongs to dry gas. The CH4 volume fraction increases with the increase of burial depth, while the CO2 volume fraction first increases and then decreases with the increase of burial depth, and it shows high values between 300 and 500 m. The carbon and hydrogen isotopes of CH4 in the research area are generally lighter, with and δ13C(CH4) ranges from -70.3‰ to -48.0‰ and δD(CH4) ranges from -285.5‰ to -189.0‰, and δ13C(CO2) varies between -37.6‰ and 1.94‰. The chemical types of coal seam water are mainly HCO3-Na type and Cl·HCO3-Na type, and the present water environment of coal seam is relatively stable, with weak hydrodynamic forces. The apparent age of coal seam water is about 1 020-47 490 years, mainly sourced from Quaternary atmospheric precipitation, and there is no or less current surface water supply. The CBM in the Erlian Basin is mainly primary biogenic gas, mixed with a small amount of early thermogenic gas. As the burial depth increases, the geological environment and types of methanogenic archaea change, and the production pathway of biogenic methane also changes. In the Jirgalangtu depression, the biogenic methane is mainly produced by acetic acid fermentation pathway in the early stage, and is converted to CO2 reduction pathway in the late stage, mixed with a small amount of low mature thermogenic gas. In both Bayanhua and Huolinhe depressions, acetic acid fermentation is the main pathway of biogenic gas production, and there is also a small amount of methyl fermentation biogenic gas in Huolinhe depression. The research area has the "three low" coal seam conditions suitable for biogenetic gas generation, including low geothermal temperature, low salinity, and low thermal evolution. The Jirgalangtu depression belongs to the graben type biogenetic gas accumulation model in shallow thick coal seam, while the Bayanhua and Huolinhe depressions belong to the semi-graben type biogenetic gas accumulation model in middle-deep confined areas with hydraulic sealing effect. Finding favorable target areas for the formation and enrichment of biogenic gas should be a key direction for the future exploration and development of CBM in the Erlian Basin, and it is also a practical guarantee for increasing the storage and production of low rank CBM in the Erlian Basin.
The coupling relationship between the depth effect of coalbed gas content and the formation process
CHEN Shida, HOU Wei, TANG Dazhen, LI Xiang, XU Hao, TAO Shu, LI Song, TANG Shuling
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Abstract:
Depth is a comprehensive factor influencing coalbed methane (CBM) enrichment, and the depth effect of gas content is an important basis for understanding the storage state and accumulation mechanism in both deep and shallow zones. Based on the current status of CBM exploration and analyzing the data from exploration wells in the eastern margin of the Ordos Basin, the coupling relationship between depth effects of gas content, adsorption capacity, gas saturation, and reservoir formation process were discussed using both conventional and unconventional petroleum geology theories. It is pointed out that the CBM formation is a coupled result of hydrocarbon generation during the structural subsidence phase and phase transformation and dissipation during the uplift phase, which is manifested as a deep coupling of self-sealing storage and buoyancy storage. The variation in gas content involves two critical depth thresholds:the turning point of saturated adsorption capacity and the depth of retained free gas. Importantly, these two thresholds do not exhibit absolute synchronicity:The saturated adsorption capacity is an intrinsic property of coal under specific temperature and pressure conditions, not strictly constrained by preservation conditions. Its dynamic evolution process controls the phase transition and is influenced by pressure gradients and rank compensation effects, leading to a noticeable lag in the turning depth (zone) of current regional saturation adsorption capacity. The accumulation of free gas is controlled by the covering conditions during the stratum uplift phase, involving the comprehensive impact of burial depth-structure-hydrology tri-coupling effects, as well as the effects of buoyancy, reservoir/caprock capillary force. Super-saturated gas reservoirs can form only with small uplift amplitude and the weak transformation intensity, while the weaker sealing capacity of shallow strata leading to widespread loss of free gas. In the area from Liulin to Yanchuannan in the eastern margin of Ordos Basin, the total gas content continues to increase with depth, with a gradual convergence trend in the deep zones being less pronounced. The theoretic turning depth of in-situ saturated adsorption capacity is in the range of 1600-2200 m, but the regional differentiation of coal rank results in a continuous increase in saturated adsorption capacity with depth. In Daning block, the critical depth of free gas retention is approximately 2000 m, the average gas saturation is 120% at 2500 m, and it is estimated to reach 136% at 3000 m. Different regions exhibit variations in the geological background and conditions, necessitating a specific analysis of the depth effects of gas content. The analysis should focus on the comprehensive impact of the spatial-temporal evolution of methane phase transitions and formation sealing conditions on the current distribution of gas and water. This is crucial for achieving zonal evaluation and efficient development design of deep CBM.
Deformation and collapse patterns of gas extraction boreholes and a precise monitoring technology
XIAO Peng, HUANG Xiaosheng, LIU Xiaoxiao, LI Bingkun, CHEN Liping, CHEN Zixi, ZHANG Chao, CHENG Renhui, ZHAO Yajie
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Abstract:
This study aims to promote the precise and intelligent monitoring of gas extraction boreholes. In the engineering background of a coal mine in Shanxi Province, this study conducted simulation experiments on the plugging of gas extraction boreholes under varying particle size ratios of simulated coal samples using distributed optical fiber monitoring and the Brillouin optical time-domain analysis (BOTDA). Then, this study established a mathematical model for calculating the borehole plugging rate of the test mine, revealing the deformation and collapse patterns of gas extraction boreholes. Furthermore, this study proposed a precise in-situ monitoring technology for the gas extraction boreholes in the test mine and verified its feasibility and accuracy through field tests. Key findings are as follows: (1) There existed a linear correlation between the strain measured by fiber couplers, the mass of simulated coal samples, and the deformation and collapse of the boreholes. With an increase in the coal sample mass, the strain exhibited similar variation trends, increasing sharply, generally, and sharply in sequence. A mathematical model for calculating the borehole plugging rate was established through segmented fitting; (2) The error analysis revealed that with an increase in the strain, the maximum absolute error between the actual and theoretical borehole plugging rates manifested a trend of initial increase, followed by decrease and then increase, equaling 19.48% in the middle collapse stage. Under complete borehole plugging in the late collapse stage, the local maximum of the coal sample mass closer to the average local maximum of the mass of coal samples with different particle size ratios corresponded to a smaller error; (3) Based on calculations using the mathematical model, this study revealed the boreholes’ collapse pattern during the borehole plugging simulation. Specifically, coal blocks first accumulated in a convex shape at the bottom of a borehole, then slid toward both sides, and finally accumulated at the borehole’s top. With strain values of 0, 45.95×10-6, and 72.19×10-6as critical values, this study determined the early, middle, and late stages of borehole collapse, developing the precise monitoring technology for the gas extraction boreholes in the test mine. As indicated by the analysis of in-situ strain monitoring results, fractures are prone to form around the boreholes in their unstable segments under the action of factors such as stress and disturbance, with borehole collapse intensifying over time. By combining the calculated plugging rates along the boreholes, this study determined the deformation and collapse along the boreholes. Comparison with the boreholes’ inside images reveals that the results obtained using the precise monitoring technology are roughly consistent with actual observations. Therefore, the precise borehole monitoring technology based on the distributed fiber optic coupler and the BOTDA is feasible and reliable, serving as a reference for advancing the precise and intelligent monitoring of gas extraction boreholes.
Summary of underground coal gasification field tests and suggestions for industrial development
DONG Zhen, CHEN Yanpeng, KONG Lingfeng, WANG Feng, CHEN Hao, XUE Junjie, ZHANG Mengyuan, CHEN Shanshan, ZHAO Yufeng, YU Yueyu, GONG Wanxing, SUN Hongliang, WANG Xinggang
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Abstract:

China's underground coal gasification has entered a new historical development opportunity period, driven by the dual requirements of realizing the "carbon peaking and carbon neutrality goals" and ensuring national energy security. This paper analyzes the history of underground coal gasification in chronological order in order to scientifically formulate a technological breakthrough route and promote industrial development. The history is divided into three stages of development: mine type gasification, straight/directional well type gasification, and horizontal well type gasification. The underlying logic of promoting gasification technology innovation at different stages is explored. The reasons for the failure of industrialization are analyzed from the two aspects of technology and non-technology, and the countermeasures for industrialization are proposed. The findings of the study are as follows： (1)Horizontal well & controlled retracting injection point gasification process can not only effectively avoid the risks of shallow gasification in terms of surface subsidence and freshwater pollution, but also has the advantages of expanding the scope of vertical coal resource development, increasing the amount of coal control within two wells, improving the quality of crude gas, and ensuring continuous gasification. In the current and future period, this method is the mainstream technical route.(2)China has the longest field test period and has been in the stage of mine-type gasification for a long time. Although China's underground gasification of medium-deep coal test research is in the early stage, but due to the difficulty and low maturity of technology research, the major coal-rich countries in the medium-deep coal gasification technology research and development basically falls into the same pace. This technology has the potential to become a new track for China's drilling-type gasification technology to overtake the other countries. (3)Analysis shows that the poor applicability of technology is the main technical reason for the difficulty in industrialization of mine and vertical well gasification, and the low maturity of technology is the main technical reason that restricts the industrialization of horizontal well gasification. The long-term safety and high production issues have not been completely solved.(4)The low-cost development of conventional natural gas and the impact of the shale gas revolution, public concerns about environmental pollution caused by shallow gasification, and the government's policy shift towards underground coal gasification are the main non-technical reasons for the termination of foreign experiments; The long-term lack of development planning, relatively single scientific research and experimental subjects, insufficient scientific research investment, lack of industrial support policies, and lack of establishment of joint innovation mechanisms are non-technical reasons that hinder China's industrialization. The industrialization suggestion of UCG in China is put forward: it is necessary to fully understand the complexity and challenges of underground coal gasification technology in the new period. According to the two levels of “full accomplishment” and “high-quality accomplishment”， the core issues of "longterm stable production" and "high yield and excellent production" should be solved. Through synchronous promotion of scientific research and on-site experiments, the technological maturity should be continuously improved. On the production side, the cascade development method of "physical gas extraction followed by chemical gasification" should be adopted to avoid competition with the development of coalbed methane. On the utilization side, actively exploring the integration development mode with oil and gas, new energy and coal chemical industries to improve economic benefits.⑥As a subversive “artificial gas reservoir” development method, the success of underground coal gasification can provide technical reference for fluidization development of other mineral resources, and push China's unconventional fossil energy development technology to a new level.
Occurrence mechanism, environment and dynamic evolution of gas and water in deep coal seams
LI Yong, XU Lifu, LIU Yu, WANG Ziwei, GAO Shuang, REN Ci
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Abstract:

Accurately understanding of the occurrence states, relative content, and distribution characteristics of gas - water under deep conditions has important guiding significance for efficient exploration and development of coalbed methane. Based on the theoretical model, molecular simulation and systematic analysis of gas - water, the occurrence states of gas - water in coal seam is clarified, and the boundary and dynamic evolution process of gas - water dynamic migration and accumulation are revealed. Considering the coal - water interface interaction, the mobility and occurrence states of water, the coalbed water can be divided into movable water (gravity water and capillary water), bound water (adsorbed water, zeolite water, crystallization water and interlayer water) and structural water. The adsorbed water, capillary water and gravity water are dominated by pores, and zeolite water, structural water, crystallization water and interlayer water are dominated by minerals. The molecular simulation results show that water molecules are saturated and filled in 0.7 nm pores, with consistent adsorption and desorption processes, while weak adsorption layers and free states appear in larger pores. The adsorption process of water molecules is manifested in stages: single molecule oxygen-containing group adsorption, monolayer strong adsorption, multi-layer weak adsorption, water clusters formation, and pore filling. Methane molecules stably fill pores (1.5 nm) with 3 layers of adsorption, and coexist in monolayer adsorption and free state in the larger pore（s >1.5 nm）, resulting in the widespread presence of free state in pores above mesopores. According to the boundary between adsorption and free gas mentioned above, the theoretical calculation formulas for free gas and adsorption gas have been improved to provide new ideas for gas content calculation. Deep thermal coalbed methane is the residual gas generated after large-scale hydrocarbon generation and expulsion from coal. During the hydrocarbon expulsion process, the water is driven by methane and the evaporation diffusion process results in a small amount of residual water (bound water and structural water) remaining in the pores, which cannot be changed in the later stage. Assuming a static water pressure of 20 MPa, under reservoir pressures of 0, 5, 10, 15, and 20 MPa, the maximum pore size that external water can invade is 7, 9, 13, 27 nm and non-invasive. Controlled by differential preservation conditions, coal-derived gas not only forms overpressure and under pressure differential gas bearing systems, but also forms multiple types of gas bearing modes in coal measures. The above work has clarified the micro-occurrence mechanism and evolution mode of coalbed methane and water, which has guiding significance for the enrichment characteristics and efficient development design of deep coalbed methane.
Application of the horizontal seismic profiling-based advance detection technology to the excavation of rock roadways in coal mines using tunnel boring machines
ZHANG Sheng, CHEN Zhao, LU Song, YANG Zhanbiao, JI Panjun, HE Fei, LU Yiqiang, LIU Jiawei
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Abstract:
With the gradual application of full-face tunnel boring machines (TBMs) to the excavation of rock roadways in coal mines, there is an increasingly urgent need for the accurate and rapid advance prediction of unfavorable geological structures. This study analyzed the characteristics of active-source seismic wave-based advance detection methods and the applicability of the advance detection technology based on TBM seismic while drilling (TSWD) with TBM rockbreaking vibration as a seismic source. Then, by combining the geological and production conditions of coal mine roadways, this study proposed a horizontal seismic profiling (HSP)-based advance detection method applicable to the excavation of roadways in coal mines using TBMs. Then, the detection instrument with designed integrated explosionproof hardware was applied to a TBM-excavated bottom drainage roadway in the Shoushan No.1 Mine, Pingdingshan City, Henan Province. This study detected near-horizontal thin coal seams in the roadway by constructing a spatial observation method and optimized the array arrangement parameters of geophones in the narrow space of a double shield TBM-excavated roadway. Finally, this study processed the original signals and obtained images of detection results through time-frequency analysis, cross-correlation interferometric processing, and the joint inversion of reflection and scattering data. The results show that the spatial observation method can identify thin coal seams that obliquely intersect with the roadway at low angles, with the optimal identification results obtained when the distance between the seismic source and the first geophone was designed at 15 m. Unfavorable geological structures in surrounding rocks can be accurately inferred by extracting effective signals through time-frequency analysis, determining virtual seismic source channels and reflection characteristic curves through cross-correlation interferometry, and plotting the stratigraphic reflection energy distribution maps of the detected area through imaging based on the joint inversion of reflection and scattering data. The results revealed by in-situ excavation were highly consistent with the detection results, indicating that the HSP-based advance detection method can achieve non-destructive advance prediction of geological conditions within a range of 100 m in front of the tunneling face. Therefore, this method assists in increasing TBMs' tunneling speed for rock roadways in coal mines.
The development potential of deep-ultradeep coalbed methane resources in the Longtan formation of the upper permian in the Sichuan Basin
MING Ying, SUN Haofei, TANG Dazhen, XU Liang, ZHANG Benjian, CHEN Xiao, XU Chang, WANG Jiaxian, CHEN Shida
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Abstract:
The breakthrough in high-yield gas flow in the 1000-2500 m deep coalbed gas wells in the Junggar Basin, the DanningJixian and Yanchuan South blocks signifies the enormous potential for deep coal-bed gas development. The main buried depth of the thin to medium thick coal seam group (7-15 layers) in the Longtan Formation of the Upper Permian in the Sichuan Basin is 2000-4500 meters. In the central Sichuan region, there is a northward dipping monocline with locally developed low amplitude uplifts. The key development parameters such as coal seam gas content, gas saturation, and reservoir pressure are all better than those in the shallow part, which has strong potential to support the national natural gas development strategy of "increasing reserves and production". (1) The Longtan Formation coal seam has frequent coal mud interbedding, multiple coal seams, and a large cumulative resource. The lateral development of the 19 # coal seam is stable (average 3.2 m; >4 m favorable area of 700 km2). (2) The degree of thermal evolution of coal rock is high (2.53% -3.18%), with strong hydrocarbon generation ability. The total hydrocarbon content of coal measure gas shows good results, with a measured gas content of 16.64-17.61 m3/t at a depth of 2500 m, a gas saturation of 138% -151%, and free gas of about 4.84-5.6 m3/t. (3) The measured reservoir pressure coefficient at a depth of 800 m in southern Sichuan is greater than 1.1, and the predicted reservoir pressure coefficient in the central Sichuan area is greater than 1.8, indicating a potential abnormal ultrahigh pressure reservoir. Based on the resource endowment characteristics of coal seams in the Sichuan Basin, such as deep-ultra deep, overpressure, and supersaturation, and drawing on the successful experience of deep coalbed methane in the Daji area of eastern Hubei, taking the 19 # coal seam as the risk exploration target, implementing resource potential and gas reservoir characteristics, and exploring the construction of a three-dimensional exploration and development technology system for deep-ultra deep thin coalbed methane, it is of great significance for the large-scale production of - coalbed methane.
Discussion on the coal measure gas co-mining method by the stratified pressure relief in surface wells
LI Rui, JIN Lihong, XIA Binwei, GE Zhaolong
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In order to further understand the restrictive factors of coal measure gas co-mining, and to improve the gas production contribution of each production layer of coal measure gas co-mining, based on power, passage and gas source conditions, the necessary factors of coal measure gas co-mining were analyzed. Based on the principle of changing the crustal stress state to improve the reservoir conductivity and changing the reservoir fluid pressure in different layers to meet the dynamic conditions of multi-layer co-mining, the coal measure gas development method by stratified pressure relief in surface wells was proposed. Through directional drilling on the surface, high-pressure water jet operation is carried out in the target reservoir, pressure relief spaces (slots, grooves, holes) are artificially created, the stress state is changed, with the effective stress damage the being reduced, and then the number and opening of reservoir diversion channels are increased, and the fluid pressure drop of the target reservoir is finally induced. When the reservoir pressure drops to meet the dynamic conditions of coal measure gas combined production, the combined layer drainage will be carried out, realize the coordinated multi-layer gas combined production, and improve the gas production contribution of each production layer of coal measure gas combined production. Compared with conventional reconstruction technologies, the method can reduce the damage of coal measure gas reservoirs under the effective stress action, improve the efficiency of inducing the pressure to promote the desorption and diffusion of coal measure gas, and reduce interlayer interference. On the basis of the above research, it is considered that the development mode of surface well delamination relief is mainly suitable for the coal measure gas reservoir with large in-situ stress and small spacing between production layers, and it is expected to be applied in the field of thin interlayer gas reservoir stimulation and the development of symbiotic coal measure reservoir with serious interlayer interference.
Characteristics and genetic mechanisms of geothermal reservoirs in the Neogene Guantao Formation, Qikou Sag
XIA Guo-chao, LOU Da, ZHAO Yan-ting, WANG Hui, DUAN Zhong-feng, SUN Xiao-lin, ZHANG Fei-peng, LUO Rong, GE Jia-cheng
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The Qikou Sag in the Huanghua Depression, Bohai Bay Basin boasts extremely abundant geothermal resources.Among them, the geothermal reservoirs of the Neogene Guantao Formation have the greatest potential for exploitation. To ascertain the properties of geothermal resources in this formation and rationally exploit these resources, it is significant to investigate the geothermal field, porosity, permeability, geothermal water circulation patterns, and genetic mode of geothermal reservoirs in the formation. Based on data from drilling, geophysical exploration, thermometry, and production of the study area, this study determined that the geothermal reservoirs of the Guantao Formation in the Qikou Sag constitute a conductive geothermal system of a sedimentary basin, with the heat flow from the deep mantle and the radioactive heat from the crust being transferred through heat conduction. The distribution of geothermal anomalies is subjected to wavy bedrock. Hightemperature geothermal anomalies with geothermal gradients up to above 5.0°C/hm are found near the Cangdong and Beidagang faults. The geothermal reservoirs of the Guantao Formation manifest high porosity and permeability in the north and south but low porosity and permeability in the central portion, with porosity greater than 26%, permeability above 400×10-3 μm2, and average single-well water yield of 60 m3/h overall. These suggest high-quality geothermal reservoirs. The geothermal water in the study area primarily originates from paleometeoric water. As the recharge source, the paleometeoric water from the Yanshan area in the north circulates deeply along strata while absorbing heat from the rock matrix, ultimately forming geothermal water. The geothermal reservoirs of the Guantao Formation in the Qikou Sag host geothermal resources of 41.81×1018 J, 95% of which are distributed in the Tianjin Binhai New Area and Huanghua City, Hebei Province. Their high match with demands makes geothermal resources in the study area have great potential for production and utilization.
Theory and application of setback distance from active faults
WEI Leiming, XU Xiwei, LI Feng, CAO Jun, REN Junjie, CHENG Jia, ZHANG Xianbing, JIA Qichao, CHEN Guihua, WU Xiyan
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Determining setbacks from active faults is the "last 1 km" from active fault surveys to their application to seismic disaster mitigation. It is also a technique for blocking the risk sources of earthquake-induced chains of geologic hazards. Field investigations and experimental studies have demonstrated that buildings and structures can be free from catastrophic destruction caused by coseismic ruptures and offset of active faults provided they are kept at a certain finite distance from the active fault traces. Therefore, determining setbacks from active faults serves as an ultimate goal of the surveys and precise localization of active faults. Based on the definitions and terminologies related to setbacks from active faults, this study systematically analyzes the width of earthquake rupture localization of various active faults, the hanging-wall effects of surface ruptures/disasters induced by dip-slip faults, and the shearing and tearing of buildings and structures caused by the coseismic ruptures and offset of active faults, which jointly shape the spatial distribution of destruction zones. These characteristics constitute the theory of setbacks from active faults. Accordingly, this study highlights the application scopes of standards for setbacks from active faults, the bases and ranges for delineating the regulatory zones of active faults, the positioning accuracy of setbacks from active faults required for construction sites, and the basic setback distance (D0) for general buildings and structures within the regulatory zones around active faults. This value can be used as the minimum distance for setbacks from the foot walls of nearly vertical strike-slip faults and dipslip faults. It is recommended that the setback distance from the hanging walls of normal faults with dip angles of about 60° and reverse faults with dip angles of about 30° should be approximately twice and 3 to 4 times D0, respectively. For particular buildings and structures, different from general ones, their safety directly influences social stability and national prosperity. Therefore, this study presents classified setback distances specific to these buildings and structures to ensure that they will not induce serious secondary disasters during earthquakes. Finally, this study briefly introduces domestic and international laws/regulations concerning setbacks from active faults, along with illustrative examples. As a scientific and effective technique for blocking earthquake-induced geologic hazards, determining setbacks for active faults can effectively determine setback means and distance for the anti-rupture of buildings and structures. Furthermore, this technology provides innovative technical support for ensuring the seismic safety of the sustainable economic and social development of China and the infrastructure construction of the Belt and Road Initiative proposed by the country.
Application of high-precision LiDAR technology in research on active fault-induced offset geomorphic features-A case study of the Juxian-Tancheng segment of the Yishu fault zone
YANG Bin, WANG Hualin, WU Hongbin, GE Fugang, ZOU Hao, SU Sili
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The Tancheng-Lujiang fault zone (also referred to as the TanLu fault zone), one of the most significant largescale active faults in eastern China, has great seismogenic potential while passing through several cities with the activities and accumulation of human beings. To investigate the geometric distribution and activity characteristics of the TanLu fault zone, this study focused on the Juxian-Tancheng segment of the Yishu fault zone-a part of the TanLu fault zone. Given the vegetation coverage in eastern China, airborne light detection and ranging (LiDAR) and terrestrial laser scanning were employed to collect high-precision topographic data of the Zuoshan (Yibujian), Zhonghuashan, Jishan, and Maolingshan segments of the Yishu fault zone, as well as the Jiangjialing area. Based on these data, this study analyzed the slip distribution of the faults. The measured point cloud data were processed through point cloud matching, mosaic, vegetation filtering, and triangulated irregular network (TIN)-based modeling. As a result, a digital elevation model (DEM) with a spatial resolution of 0.1 m was obtained. This model allowed for a high-definition three-dimensional reconstruction of the microgeomorphic features of faults. Furthermore, this study extracted the dextral horizontal offset amount of fault-controlled gullies and the vertical offset amount of fault scarps. Based on these data, as well as the validation and comparison with the paleo-earthquake events revealed by geological mapping and trenches, this study conducted a quantitative analysis of the fault activity characteristics in the Juxian-Tancheng segment of the Yishu fault zone. The results indicate that the horizontal and vertical offset amount along the Zuoshan (Yibujian), Zhonghuashan, Jishan, and Maolingshan segments of the Yishu fault zone exhibit grading characteristics, suggesting multi-phase (3-5 times) activities and multiple paleo-earthquake events since the Late Quaternary. The findings of this study will provide an important basis for further research on the kinematics and geometry of the Tan-Lu fault zone. They also demonstrate the wide application prospects of terrestrial laser scanning and airborne LiDAR in research on active faults.
Optimization of data acquisition parameters for deep seismic reflection surveys in complex terrain
YAN Yunxiang, LI Pei, ZHI Min, LIU Jianda, WANG Zichen, ZHANG Ying, PEI Gendi, LI Linyuan, MOU Qi, JIA Jin
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Fujian, located in the orogen region of the coastal areas of southeast China, exhibits well-developed structures and complex surface conditions, which make deep seismic reflection surveys challenging. In response to the diversity and complexity of seismogeological conditions in Fujian, this study optimized the seismic excitation means based on previous deep seismic surveys. Specifically, the combination of large, medium, and small guns was transitioned into the layout of normal guns (spacing of shot points:600 m) and large shots (spacing of shot points:15 km), leading to enhanced folds of large shots. Through simulation analysis, this study calculated the spacing of combined boreholes, aiming to concentrate the excitation energy and generate seismic elastic waves with the maximum efficiency. It optimized the dominant frequency of the nodal seismometers for data acquisition, reducing it from 10 Hz to 5 Hz to improve the resolution of data on the middle-deep crust in seismic records. Furthermore, this study increased the number of receiving channels from 1 200 to 2 400, achieving a maximum offset of 36 km. This value exceeds the depth of the Moho in Fujian, allowing for the acquisition of the reflection signals of deeper parts. After the optimization of the seismic acquisition parameters, the obtained original single-shot seismic records and initially stacked time sections featured high signalto-noise ratios. The optimization also contributed to clear reflected waves of the middle-deep crust and the Moho, as well as high imaging accuracy of the crustal structure. As a result, the expected geological survey effects were achieved. The newly obtained data parameters can provide a reference for deep seismic reflection surveys in similar areas.
New evidence for Holocene activity of the northern segment of the Puqian-Qinglan fault in northern Hainan Province
LIU Huaguo, LI Feng, JIA Qichao, WANG Zhicheng, ZHANG Pan, LIN Zhen, ZHANG Jiehan, SHI Chunhua, ZHANG Yanbo, JIA Wei, LI Changlong
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The Puqian-Qinglan fault, located in northern Hainan Province, is closely related to the judgment of the seismogenic structure of the Qiongshan M7.5 earthquake in 1605. To accurately determine the latest activity characteristics of this fault, this study, adopting artificial shallow seismic exploration with large-tonnage seismic sources combined with small-spacing cross-well stratigraphic correlation, investigated the sedimentary geological conditions of the Quaternary basalt cover and significantly thick marine sand layers in northern Hainan Province through exploration at Qishantou and Dongzhai villages in the Sanjiang Town, Jiangdong New Area, Haikou. Key results are as follows:(1) the PuqianQinglan fault dislocates multiple marker strata, with the shallowest dislocation occurring in the silt layer of the Holocene Yandun Formation and upper fault contacts' burial depths of approximately 10 m. As revealed by drilling, the fault surface exhibits significant strike-slip and thrusting properties, suggesting a large-scale fault zone with a certain width, multiple branches, and multi-stage activity; (2) Within the depth range revealed by the cross-well stratigraphic correlation, the displacement of the dislocated strata increases with depth. The Puqian-Qinglan fault has been active since 8 346- 7 153 a cal BP. It exhibited a cumulative vertical displacement of 4-5 m during the Holocene, with vertical displacement rates of 0.53-0.63 mm/a. Accordingly, it can be inferred that the Puqian-Qinglan fault serves as the seismogenic fault of the Qiongshan M7.5 earthquake in 1605. The new evidence for the Holocene activity of the Puqian-Qinglan Fault obtained in this study provides a scientific basis for spatial land planning and regional seismic hazard assessment.
Revealing the upper crustal structure in the Fujian region using deep seismic profiling
LI Pei, REN Congrong, LI Haiyan, WANG Shanxiong
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The Fujian region, located along the southeastern margin of the Chinese continent, constitutes an active tectonic belt along the coastal area in southeast China, with complex formation and evolution histories. To understand the characteristics of upper crustal structures and basement structures in the Fujian, this study collected the Pg travel time data from four NE-trending deep seismic sounding (DSS) survey lines in the region. Employing finite-difference tomography, this study obtained the fine-scale velocity structure of the upper crust along the four profiles, revealing the lateral variations in the upper crustal velocity structure, basement structures, and shallow fault characteristics in the region. Key findings are as follows:(1) The velocities along the four profiles range between 4 700 and 6 100 m/s, gradually increasing from west to east. They exhibit noticeable lateral variations in basement velocities on either side of tectonic unit boundaries; (2) The burial depth of crystalline basement interface along the four profiles varies between 1.0 and 6.0 km, deepening from north to south. The undulations in the basement surface correspond to the structural uplifts and depressions; (3) The upper structures in the uplift zone in northwest Fujian exhibit overall high velocities and shallow burial depths, which are related to the metamorphic basement; (4) Regarding the upper crust in the depression zone in southwest Fujian, its structures exhibit significant variations velocities, and its interface morphology displays alternating patterns of deep and shallow parts. These correspond to the geological structures characterized by fault basins and depressions interlacing with uplifts in the region; (5) The upper crust of the Mesozoic magmatic zone along the coastal area in southeast China exhibits high and greatly varying velocities, indicating that stronger tectonic activity in the eastern part of South China Continent compared to its western part; (6) The NW-trending fault zone where the DSS profiles pass through cut through the basement, showing dominant strikes consistent with those of the geological structures and tectonic deformations in Fujian. This finding reflects the NW-directed subduction-collision compression from the Paleo-Pacific Plate. These findings provide shallow seismic evidence for obtaining significant depth relationships of NW-trending structures along the coastal area in southeast China.
Critical links and development trends of research on active tectonics
YUAN Daoyang, WANG Youlin, LI Shuwu, WANG Wanhe, LI Linyuan, ZOU Xiaobo, WEN Yameng
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Following a brief introduction of the general characteristics of active tectonics in China, this study analyzed two new features of large earthquakes with Ms ≥ 7 that have struck continental China since the beginning of the 21st century:(1) Large earthquakes occur primarily in clusters along the boundary fault zone of the Bayanhar active tectonic block-part of the Qinghai-Tibet active tectonic block; (2) Reverse fault-fold earthquakes have occurred multiple times within active basins or at basin-mountain boundaries. In response to the new seismic activity features and the new demand for disaster prevention and mitigation of engineering construction and the public, this study delved into the critical links or understudied aspects of research on active tectonics and explored the development trends and technical approaches for further strengthening related studies. First, research on active tectonics should highlight theoretical advancements and applications, including fine-scale research on the geometry of active faults. Furthermore, it is necessary to focus on the kinematics of active faults by combining their activity behavior with rupture segmentation and practically enhance the complementary study of paleoseismic trenches and offset microgeomorphic features. Most importantly, we should practically enhance the cross-disciplinary integration and applications of research on active tectonics with disciplines such as tectonic geomorphology, geophysical prospecting, crustal deformation, and seismology. Second, it is necessary to enhance research on regional active tectonics and the understanding of the cluster migration patterns and dynamic mechanisms of large earthquakes. The purpose is to elevate a holistic comprehension of large earthquake-related tectonic activity within active tectonic blocks and their boundary fault zones. To this end, we should organize and analyze the seismogenic structural environments and mechanisms of cluster earthquakes in active tectonic blocks across China. Furthermore, we should identify potential active or seismic structural zones susceptible to earthquake cluster activity by synthesizing detailed research findings from historical earthquakes and paleo-earthquakes. The aim is to provide scientific and technological support for dealing with the risks of violent earthquakes faced by potential seismic migration areas after major seismic activity in the Bayanhar active tectonic block. Third, particular attention should be directed toward under-studied aspects such as research on structures of reverse fault-fold earthquakes. Besides conventional techniques for research on active structures, it is necessary to examine the geomorphic deformation characteristics by combining tectonic geomorphology. Additionally, we should conduct deep seismic structure exploration and seismological studies. The purpose is to obtain deep structural features and comprehensively analyze the relationships between deep and shallow structures, construct deformation modes, and explore seismogenic mechanisms. Overall, we should focus on the above critical technical links and future development trends, thus providing a reference for in-depth research on active structures and disaster prevention and mitigation.
Activity variations of the Shanzuokou-Sihong fault within the Jiangsu segment of the Tancheng-Lujiang fault zone and their origins
ZHANG Hao, LI Wei, LI Limei, YAN Yunxiang, JIANG Xin, WANG Jinyan, ZHAO Qiguang, GU Qinping, XU Hangang
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Abstract:
The Shanzuokou-Sihong fault, having undergone the entire evolutionary process of the Tancheng-Lujiang fault zone (also referred to as the Tancheng-Lujiang fault zone), exhibits segmentation during the latest activity epoch. Determining the location and origin of its activity segmentation will provide a significant reference for exploring the activity variations of its branch faults and their origins. This study investigated the activity of the Shanzuokou-Sihong fault using a three-dimensional approach combining field geological surveys, shallow seismic exploration, and crosswell stratigraphic correlation. The results show that the Shanzuokou-Sihong fault is a Late Pleistocene active fault on the east side of the North Maling Mountain and a Middle Pleistocene fault in Xinyi City. Moreover, a Late Pleistocene-Early Holocene active fault has been discovered recently at the Zhangcang Primary School in Xinyi City (also known as the Zhangcang Primary School fault). With the intersection of this newly discovered fault and the Shanzuokou-Sihong fault (northeast of Zhangcang Village) as demarcation, the Shanzuokou-Sihong fault can be divided into northern and southern segments, which are a Late Pleistocene active fault and an Early-Middle Pleistocene fault, respectively. Since the Late Pleistocene, the northern segment has extended southward to the Zhangcang Primary School fault due to fault activity. The North Maling Mountain is a bedrock massif within the Tan-Lu fault zone, distributed along the strike of the fault zone. Its continuous uplift since the Quaternary has a certain coupling relationship with the activity variations of the Shanzuokou-Sihong fault. This study will provide a valuable reference for understanding both the activity variations of other branch faults and the formation mechanism of hills and mountains in the Tancheng-Lujiang fault zone.
Revealing fine-scale crustal structure and tectonic features in the Xiong'an New Area and its periphery using deep seismic reflection profiling
YUE Hangyu, WANG Kai, WANG Xiaojiang, ZHANG Baowei, ZHANG Kai
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As an effective method to accurately reveal the deep geological structures and tectonic features of the Earth, deep seismic reflection profiling has been increasingly applied to the exploration of the continental and oceanic crusts, as well as the upper mantle of the lithosphere, making it internationally recognized pioneer technique for deep Earth exploration. This study examined the deep seismic reflection profile spanning across the Xiong'an New Area in Hebei Province, aiming to reveal the crustal structure and tectonic features of the study area. Key findings are as follows:(1) The crust in the study area can be divided into the upper and the lower crusts, with average thicknesses of approximately 18 km and 16 km, respectively and an average Moho depth of around 34 km; (2) In the upper crust, the sedimentary strata above the crystalline basement exhibit high stratification, strong reflected energy, and intricate structural characteristics. Faults are well-developed in the upper crust, exhibiting various morphologies and dislocation depths, with no deepseated faults. The major faults encompass the Niudong, Niubei, Rongdong, Rongcheng, and Rongxi faults and the Taihang Mountain piedmont fault from southeast to northwest; (3) In the lower crust, the northwestern and southeastern portions of the deep seismic reflection profile are subjected to different tectonic stresses. Consequently, the northwestern and central segments manifest relatively simple seismic reflection features, reflecting relatively stable overall tectonics in the Xiong'an New Area. In contrast, the southeastern segment of the profile exhibits pronounced imbricate reflections, mirroring the lateral heterogeneity and local activity of the lower crust. These results will provide reliable data support for the overall planning and construction of the Xiong'an New Area and for the building of geological information platform Transparent Xiong'an, which involves survey depths of 10 000 m.
Mechanical behavior and fracture response characteristics of hard sandstone considering bedding dip angle
SONG Zhanping, LIU Hongke, ZHENG Fang, CHENG Yun, SUN Yinhao, SONG Wanxue
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Aiming at the mechanical behavior and fracture response characteristics of hard sandstone considering bedding dip angle, uniaxial compression tests of hard sandstone with different bedding dip angle were carried out to explore the influence of bedding dip angle on the mechanical behavior of hard sandstone and the relationship between bedding dip angle and fractal characteristics of fragments. The test results show that the bedding dip angle has no significant effect on the type characteristics of the stress-strain curve of hard sandstone, but when the dip angle is small (0°, 22.5°, 45°), the curve shows the law of single peak. When the dip angle is large (67.5°, 90°), the curve shows the law of multi-peak, and the fluctuation position of the curve is mainly near the peak value. Both peak stress σd and peak strain εd reach the minimum values 46.25 MPa and 9.80×10-3 when the dip angle is 67.5° (the most unfavorable bedding structural plane). The effect of bedding dip angle on the stress of hard sandstone is obviously greater than that of strain. Affected by bedding dip angle, the degree of anisotropy of hard sandstone is 1.32-1.64, showing the characteristics of low anisotropy. The bedding dip angle has a significant influence on the failure mode of hard sandstone. With the increase of bedding dip angle, the hard sandstone shows the damage failure evolution law of shear failure-shear tension compound failure-bedding structural plane shear failure-splitting failure. Under uniaxial compression, the quality and fractal characteristics of hard sandstone are obvious, the hard sandstone fragments are mainly distributed in middle blocks, and the bedding dip angle has little influence on the mass distribution of fine-grained fragments, and the value of fractal dimension is in 1-2. A large proportion of fragments are distributed in the range of large size distribution. The research results can provide theoretical reference for the stability of rock with bedding structural plane and the disaster prevention and control of underground space engineering.
Application of integrated geophysical surveys in the identification of hidden fire sources in spontaneous combustion zones in coal seams
MA Zijun, YANG Haiyan, LI Wenyu, XU Yunlei, HE Yunlan, LIU Zhuoming, LI Peng, HUANG Jiu
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Spontaneous combustion in coal seams, a factor influencing the development of many mining areas in China, can cause severe coal resource loss and environmental pollution. The positioning and distribution identification of hidden fire sources can provide an important basis for coal mine enterprises to prepare prevention and control measures. They are also a hot research topic and challenge in the field of coal fire disasters. Suitable channels for ventilation and oxygen supply are necessary for spontaneous combustion in coal seams. When the oxidative heat release rate of coals exceeds the heat dissipation rate, coal temperature will rise until the occurrence of spontaneous combustion in coal seams. Therefore, the primary task for coal fire surveys is to pinpoint the combustion centers of coal fire zones and identify the burning-out areas and caving zones. This study investigated the Gongwusu open-pit coal mine in Wuhai City, Inner Mongolia. Based on the correlation analysis of coal seam resistivity and temperature, this study conducted surveys of the coal fire locations and their distribution range using the ground penetrating radar (GPR) and conical source-based transient electromagnetic (CSTEM) methods. Then, by combining the surface smoking positions, this study acquired the geophysical characteristics of the underground channels of the fire zones and further ascertained the distribution range of the coal fire channels. The results indicate that:(1) Both the protolith and sintering zones exhibited relatively consistent physical stability, with their top boundaries present as distinct reflection events in radar images and as transversely continuous resistivity distribution in the CSTEM outcomes; (2) The underground hidden fire channels, caused by factors like rock fragmentation and the presence of pores and fissures, exhibited weak, discontinuous in-phase echoes in the GPR profiles. In contrast, they show transverse concaves or dislocations of resistivity contours in the CSTEM pseudosections; (3) Along the survey lines, the apparent resistivity range varied with the elevation drop. Therefore, to determine the distribution patterns of geophysical anomalies in the protoliths, it is necessary to delve into the localized changes in physical property along survey lines based on the analysis of overall resistivity across the study area. As indicated by these results, potential spontaneous combustion in coal seams and its distribution range can be pinpointed by integrating the CSTEM and GPR methods, thus providing a basis for delineating coal fire zones and analyzing coal fire patterns.
A method for evaluating aquiclude stability in the water conservation-based mining of shallowly buried coal seams in ecologically vulnerable areas in Northwest China
LI Heng, HE Tao, GUO Bin
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Water conservation and coal mining are both critical to Northwest China. Water conservation-based coal mining is an important technology for the coordinated development of coal and water resources in this region. In this technology, the evaluation of aquiclude stability is critical. Due to the shallow depth of coal seams, intense topographic cutting, and complex changes in near-surface aquifers in the ecologically vulnerable areas in Northwest China, there exist large errors between traditional methods for aquiclude evaluation and the actual hydrological observations in these areas. To address this challenge, this study develops using the 3D geological modelling combined with numerical simulation to accurately evaluate the aquiclude stability in the water preservation-based mining of shallowly buried coal seams. First, an intuitive and reliable 3D geological model is constructed based on the exploration information and topographic contour maps. The purpose is to finely characterize topographic cutting and the complex changes in shallow aquifers. Then, numerical simulations of damage to the rocks overlying coal seams are performed by selecting several typical mining faces, aiming to determine the heights of the hydraulically conductive fissure zones at various coal seam points in the 3D model. Finally, using the 3D geological block model, the differences between the heights of the hydraulically conductive fissure zones and the thicknesses of overburden rocks’ aquifers were calculated for various coal seam proof points from the full 3D angle. These differences were employed to evaluate the aquiclude stability in water conservation-based coal mining. This study investigated the Mandura coal mine in Ordos. Based on the collected stratigraphic columns of 36 boreholes in the coal mine and its topographic and geological maps, this study established a fine-scale 3D geological model and evaluated the aquiclude stability. As indicated by the comparison of the observations of two underground waterlogged areas in the Mandura coal mine, the unstable aquiclude zones calculated using traditional methods failed to accurately reflect the area filled with water on the southern mining face. In contrast, the unstable aquiclude zones calculated using the new method was more fine-scale, adequately reflecting the effects of topographic cutting, weathering, and denudation on the Quaternary aquifers. As indicated by the results of this study, compared to traditional evaluation methods, the method for evaluating the aquiclude stability of shallowly buried coal seams based on 3D geological modeling can characterize the effects of the mining of shallowly buried coal seams on aquifers more intuitively and accurately and exhibits higher adaptability. Furthermore, the new method can provide fine-scale evaluation indices for water preservation-based coal mining.
Evaluation of water quality and identification of pollution factors in mining subsidence area with high phreatic water level
HU Lin, CHEN Yongchun, XU Yanfei, LI Bing, WANG Jin, AN Shikai, CHEN Chen, SUN Hongjie, MIAO Wei
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Huainan mining area is characterized by a high phreatic water level, as well as a wide range and large area of coal mining subsidence areas, with the water quality monitoring data missing and prominent water environment. Therefore, the evaluation of water quality monitoring and identification of pollution factors in large subsidence area is of great significance to regional water environmental governance. Specifically, the water quality of the subsidence area was evaluated with the Nemerow pollution index method by testing the water samples collected from 175 sampling points in the study area. Meanwhile, the nutritional state of water bodies was evaluated with the comprehensive nutritional status index method. The results show that: (1) For the open subsidence areas, the water quality level is evaluated to be excellent in terms of Cu, As and Cr, good in terms of DO, COD, NH4-N, Hg and F-, and relatively good in terms of TN and TP. For the closed subsidence area, the water quality level is evaluated to be excellent in terms of Cu and Cr, good in terms of the NH4-N, Hg, As and DO, relatively good in terms of COD and TN, and poor in terms of TP and F- according to Level-III standard of surface water. However, the water quality level is evaluated to be excellent in terms of NH4-N, Hg, As, Cu and Cr, good in terms of DO, COD, TP and TN, and relatively good in terms of F- according to Level-V standard of surface water. (2) The comprehensive nutritional status index of the study area is ranged within 40‒90, and the average nutritional status index is sized 68.61. Therefore, the study area is in moderate eutrophication, which shows that the water body in the subsidence area is at moderate nutrition level. Among the 175 water samples, 8.57% of the samples are in light eutrophication, 51.43% in moderate eutrophication, 2.29% in medium nutrition, and 37.71% in severe eutrophication. (3) According to the Standard for Environmental Quality of Surface Water, few samples have DO and NH4-N exceeding the level-V value, but most samples have COD, TP and TN exceeding the level-V value, and there are no excessive heavy metals in all waters of the study area, with excellent test results. Besides, a large number of samples have the inorganic anion index F- greater than the level-V value. Generally, the water quality of open subsidence area is better than that of the closed subsidence area. (4) For the water, TP and F- are poor for Zhangji and Panyi subsidence areas. For the closed water, the TP of Pan Yi, Pan San, Guqiao, Gubei and Zhangji subsidence areas are poor. The distribution of F- pollution shows the geographical characteristics, which is generally poor in north of Huai River and good in south. The indexes of Cr, Cu, Hg, As, NH4-N, TN, COD and DO in all waters are in the “excellent- relatively good” range. The F- and TP indexes of all the open subsidence areas are also in the “excellent-relatively good” range. But the F- of the closed water in Panji area and TP in Fengtai-Yingshang area are in the “poor” range. The regional pollution level is shown as Fengtai-Yingshang area>Panji area>old Mining area. (4) In order to protect the ecological environment of coal mining area, the pollution factors of coal mining subsidence area in Huainan mining area are determined to be COD, TP, TN and F-, with comprehensive consideration to the characteristics of two identification methods of pollution factors. The results provide important support for local ecological and environmental protection.
Mechanical properties and strength deterioration mechanism of soil in inner dump of open-pit coal mine under the action of freeze-thaw cycles
ZHANG Heyong, WANG Xuedong, ZHU Yongdong, WANG Haipeng, QI Lihui
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In order to investigate the influence mechanism of freeze-thaw cycle on the structure and mechanical properties of soil, the typical clay soil in the inner dump of Yuanbaoshan open-pit coal mine in Inner Mongolia was taken as the research object, and the simulation analysis of the internal temperature, moisture and stress fields of the soil was carried out through laboratory freeze-thaw cycle tests and MatDEM numerical simulation. The results show that: freeze-shrinkage occurs to the soil in the dump after the freezethaw cycle, and the stress-strain curve shows the trend of strain softening at low confining pressure for shear failure, and the trend of strain hardening at the increased confining pressure for dilative failure. The deterioration of shear strength was most significantly affected by the first three freeze-thaw cycles, and reached the lowest value in the third cycle. The temperature transfer process can be divided into four stages: rapid temperature drop, slow phase transition, continuous cooling and temperature stabilization. Moisture migration mainly occurs in the first two stages of temperature transfer, with more in the second stage. The overall radius of the particles decreases and the dispersion increases after freeze-thaw. The expansion and contraction of particles caused by temperature transfer and moisture migration, the ice-water phase transition and the formation of cryostructures lead to the repeated changes in particle size, position, connection state and interparticle stress, which together drive the irreversible structural damage to the soil, resulting in strength deterioration. Moisture migration not only provides water conditions for the formation of cryostructures, but also produces dissolution and erosion damage to them, which together with the phase transition of moisture is the main reasons for the structural adjustment and stress field change of soil under the action of freeze-thaw cycle. The simulation of freeze-thaw cycle by discrete element method is helpful to understand the mechanical properties and strength degradation mechanism of soil, and provides a reference for the stability study of dump slopes and other engineering constructions in open-pit coal mine in frozen areas.
Analogue modeling of Love type channel wave and its response to faults
LIU Qiang, HU Jiwu, WANG Pan, JIA Qian
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Channel wave seismic exploration has been widely used in the exploration of hidden disaster-causing bodies in underground coal mines because of its high resolution and small energy attenuation. However, the accuracy of channel wave seismic exploration at this stage cannot meet the requirements of mine intelligence. In order to improve the detection accuracy, a lot of research has been carried out in numerical simulation. At present, the subject of channel wave analogue modeling is mostly Rayleigh channel wave under the condition of two-dimensional model, and the research of Love channel wave in three-dimensional channel wave analogue modeling is less. In order to master the propagation rule of Love-type channel wave, the analogue modeling of Love type channel wave was carried out. Based on the propagation and particle vibration characteristics of Love type channel wave field, the Love type channel wave in analogue modeling is successfully observed through the construction of analogue modeling platform, the design and manufacture of analogue modeling model, and the solid ultrasonic analogue modeling, and the wave field dispersion curve is consistent with the theoretical value. At the same time, the research and development found that the frequency components of the wave field before and after the fault have undergone a significant conversion with the Airy phase as the boundary, and the channel wave energy is almost completely attenuated after passing through the fault. The research results will provide basic platform support for acquisition, processing and interpretation methods for subsequent quantitative and refined seismic channel exploration.
Thermal stress field of high-temperature spray wellbore for underground coal gasification
TANG Yang, XIE Na, XIONG Haoyu, HE Yin, HUANG Shunxiao
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As a supplement to traditional physical coal mining technology, Underground coal gasification(UCG) is a new generation of chemical coal mining technology. During the gasification process, the wellbore is subjected to a combination of high temperature and internal pressure loads. Aiming at the structural characteristics of the wellbore of UCG production wells, based on the heat transfer theory, the calculation model of the transient temperature of the wellbore under the cooling condition of annular spray water injection is established. Based on the wellbore pressure model, the calculation model of the wellbore is established according to the theory of elasticity and the wall cylinder. The calculation model of the temperature stress field of the casing-cement sheath-formation rock combination is established, and the engineering calculation software of the thermal stress field is formed, and the influence law of different factors on the stress of the casing-cement sheath is analyzed. At high temperature, the stress of each part of the wellbore increases due to the limitation of thermal expansion or thermal shrinkage. Under the condition of natural cooling, the theoretically calculated maximum stresses of the casing and cement sheath are 2 640.6 MPa and 151.3 MPa respectively, which exceed the allowable compressive stress of the material itself. The axial stress of casing and cement sheath is only 28.4 MPa and 15 MPa respectively, which is far less than the result when the temperature is considered. Under the cooling mode of annular water injection, the wellbore stress can be effectively reduced by controlling the temperature of the spray chamber. With the increase of casing internal pressure, the wellbore stress also increases, and the change of casing internal pressure will cause the stress direction of casing and cement sheath to change, and it needs to be discussed on a case-by-case basis when checking its strength. The stress drop at the intersection of both sides of the cement sheath is generally larger, and the performance parameters of the ratio increases, the stress of the casing-cement sheath decreases, that is, the cement sheath material with good bonding performance, high toughness, and high Poisson's ratio can reduce the casing-cement sheath stress. The above results can provide a reference for the structural design and production process of UCG production wells.
Characteristics and genetic mechanism of low sulfate in high-salt groundwater of Permian sandstone in Fudong mining area
JIANG Chunlu, HUANG Wendi, FU Xianjie, ZHENG Liugen, CHENG Shigui, SHAN Chonglei
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Hydrogeochemistry research of groundwater in coal mining areas is of great significance to the prevention and control of mine water and the comprehensive utilization of water resources. In terms of the low surfate of Permian sandstone water in Fudong mining area of Huainan coalfield, the hydrochemical characteristics, water-rock interaction and low sulfate genesis of sandstone water were studied through water sampling and test by multivariate statistical method, in combination with the hydrogeological condition analysis and the sulfur and oxygen isotope technology. The results show that the Permian sandstone water in the study area is weakly alkaline, with an average TDS of 1 842.35 mg/L, which belongs to brackish water. The main hydrochemical types are Cl-Na type, HCO3-Na type and Cl·HCO3-Na type. The average concentration of SO42- is 37.48 mg/L, which is significantly lower than that in the Permian sandstone water in the eastern Panxie mining area of Huainan Coalfield and Huaibei coal field. The main water-rock interaction is the dissolution of evaporite (chloride and sulphate rock) and silicate rock minerals, with the alternating adsorption of cations. The Permian sandstone aquifer is a closed to semi-closed hydrogeological unit formed by the surrounding relative water-blocking boundary, which is cut by the boundary water-blocking fault. The aquifer is deeply buried, with weak water yield, poor hydrodynamic conditions and strong sulfate reduction environment, which is conducive to sulfate bacteria reduction. This results in obvious sulfate reduction, high δ34S and low sulfate content in the sandstone water. The research results could provide a basis for identifying the water inflow source in mining areas with similar conditions.
Numerical simulation study on the influence of laminar characteristics on the fracture propagation law of hydraulic fracturing in oil shale
LI Yanwei, ZHU Chaofan, ZENG Yijian, SHUI Haoche, FAN Cunhan, GUO Wei
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Hydraulic fracturing is one of the main technical means for oil shale reservoir development at present, and the difference of oil shale laminar characteristics plays a major role in influencing the post-pressure fracture morphology, and most of the current research focuses on the influence of the laminar development degree on fracture extension, ignoring the influence of the laminar thickness itself on hydraulic fracture extension. Taking the oil shale in Xunyi area of Ordos Basin as the research object, based on the theory of linear elastic fracture mechanics, we constructed a stress-damage-seepage model of hydraulic fracture fracture extension, and adopted the numerical simulation method of global FEM-CZM, to analyze the influence of the thickness of the laminae, the spacing of laminae, and the stress field on the extension of hydraulic fracture fracture, and to compare the type of damage of the fracture, length of the fracture, and the laminar communication area under different influencing factors. The results show that: (1) the thickness of the laminae affects the intercepting ability of hydraulic cracks on the laminae, when the thickness of the laminae is larger, it will lead to a stronger tendency of crack extension on the laminae, and more tensile damages will occur, which corresponds to a larger length of the cracks and laminae communicating area; (2) the spacing of laminae influences the time for hydraulic cracks to reach the laminae, a smaller spacing of laminae will lead to the cracks to penetrate through the laminae, and a larger spacing increases the extension of cracks, and the length of cracks will increase. Smaller spacing of the laminae will directly penetrate the laminae, larger spacing of the laminae will increase the resistance of crack extension, along with the larger spacing of the laminae, more tensile damage occurs, and the length of the hydraulic cracks and the laminae communicate with the larger area; (3) the ground stress field determines the direction of the expansion of the hydraulic cracks, the vertical stress will have a compaction effect on the laminae when there is a larger difference in the vertical ground stress, which will lead to the expansion of the laminae easier to penetrate the laminae. When the vertical ground stress difference is small, the hydraulic fracture extension at the layer surface will be bent and branched, and the corresponding fracture length and layer communication area will increase. It is suggested that the location of fracturing construction should be selected in the area with larger thickness of laminae, larger spacing of laminae and smaller vertical stress field, which is more favorable for the formation of highly efficient seepage and heat transfer channels, and this study can provide guidance for the hydraulic fracturing construction in oil shale in the Xunyi area.
Dynamic prediction method of tunnel water inflow based on detailed depiction of complex geological bodies
DU Yajun, LI Qingbo, WAN Weifeng, YANG Fengwei, LI Yazhe, QIAN Hui
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It is a challenge to accurately characterize the irregular geological bodies and underground structures such as inclined faults and inclined tunnels during the numerical simulation of tunnel water inflow prediction, and the prediction generally assumes that the tunnel excavation is completed instantaneously, without considering the construction progress. A dynamic prediction method for tunnel water inflow based on precise characterization of complex geometric bodies was proposed by addressing the non-self-intersection and watertight issues required in the coupling process of three-dimensional (3D) geological models and three-dimensional groundwater numerical models. Specifically, a sealed boundary interface of inclined tunnels, shafts, inclined faults and irregular geological bodies is firstly constructed in 3D geological modeling software. The inclined tunnels and shafts need to be segmented according to the excavation progress, and then a 3D geological model is established. Subsequently, the 3D geological model data is imported into the 3D groundwater simulation software Feflow in ml file format. Then the fully unstructured grid function of Feflow is used to achieve the fine gridding of the complex geometric bodies. Finally, the tunnel boundary is set as the third type boundary based on the detailed gridding of complex geometric body in Feflow. Thus, tunnel water inflow can be predicted dynamically by setting the exchange coefficients and reference water heads, with consideration to the tunnel excavation progress and construction techniques (such as grouting, lining, etc.). The method is applied to the calculation of water inflow of inclined tunnels and shafts in an underground project, with good practical effect.
A method of operation processes identification for intelligent drilling rig base on analytic hierarchy process
ZHU Qianxiang, LUO Pengping, WANG Longpeng, XING Wang, WANG Tianlong
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Abstract:
The limited variety and quantity of sensors deployed on drilling rigs make it difficult to identify the current execution process during the intelligent construction process of coal mine drilling rigs, therefore, an operation processes identification method is proposed, which includes hierarchical modeling of drilling rig operation and probability inference of current execution process. Firstly, the coupling process among the components of different granularity is described and modeled based on the hierarchical analysis method, which reveals the interactive characteristics between equipment, function and system during the execution of each process. Secondly, Bayesian network is introduced to establish a process execution probability inference model based on the above hierarchical model of the drilling operation process, which analyzes the causal relationship between different granularity components and the drilling processes. Then, the collected sensing data is processed and provided as a realtime evidence to the probability inference model, thereby obtaining the execution probability of each drilling process. Finally, the hydraulic pressure value, the rotational speed and the movement speed of the drilling head are provided as input to the probability inference model to obtain the execution probability of drilling process, and the accuracy of the result reaches over 81%. The experiment proves that the method proposed in this paper is practical and feasible. The above research provides a hierarchical decoupling method for the drilling processes and an analysis method for the interaction process between different granularity components of drilling rigs, providing technical support for the research on intelligent control methods of drilling rigs and the development of advanced intelligent geological equipment.
Intelligent optimization method for tunnel rotary drilling based on drill string state estimation
YAO Ningping, WEI Hongchao, ZHANG Jinbao, LU Chengda, LIHao, YAO Yafeng, KE Yougang, ZHANG Youzhen
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Abstract:
The operating parameter optimization decision-making is the key to improve the efficiency of nearly horizontal rotary drilling of underground tunnels of coal mines. But it is difficult to obtain the downhole drilling parameters by Measurement While Drilling in current studies, and the accuracy is low for the rotary drilling optimization based on the hole opening data only. To address this problem, an intelligent optimization method for nearly horizontal rotary drilling in tunnels based on the drillstring state estimation was proposed by constructing a state observer to estimate the downhole drilling parameters. Firstly, an optimization objective evaluation method of Rate of Penetration (ROP) and bit wear was proposed by analyzing the rotary drilling characteristics of the underground tunnel in the coal mine, with consideration to the actual drilling constraints. Then, a lumped-parameter dynamic model of the drill string was established in axial and torsional dimensions, and a state observer was designed to estimate the motion state of the drill bit at the bottom of the hole. Finally, the NSGA-II multi-objective optimization algorithm was used to optimize the power head speed and feed pressure by integrating the data collected at the hole opening and the downhole state estimation, which was verified using actual drilling data from a coal mine in Huainan, Anhui Province, China. The results show that the optimized ROP based on the estimated downhole information of the drill string state is increased by 32.47%, which is more advantageous than the optimized ROP increased by 15.04% using only the measured data of the hole opening. It has important theoretical and practical significance for the realization of automatic and intelligent rotary drilling of tunnels in coal mine.
Numerical simulations and wavefield analysis of in-seam wave advance detection in viscoelastic media
HE Dixiu, JI Guangzhong, JIAO Wenjie, ZHANG Yawei, YU Kun
, Available online  
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Abstract:
In-seam waves are commonly applied to the advance detection of hidden faults in front of mining faces. However, coal seams, which have viscoelasticity actually, imposing absorptive and attenuation effects on in-seam waves. To investigate the wave field characteristics and propagation patterns of in-seam waves in viscoelastic coal seam media, this study built a three-dimensional geological model of coal measures with faults based on Kelvin-Voigt’s first-order velocity-stress equation. Using this equation, three-dimensional finite-difference numerical simulation was carried out. The results indicate that (1) for reflected in-seam waves in viscoelastic media, which exhibit high energy attenuation, their propagation and attenuation characteristics are more consistent with the actual situation of coal seams than those of reflected in-seam waves in completely elastic media; (2) High Q values of coal seams correspond to better advance detection effects of in-seam waves. By contrast, too low Q values are associated with poor advance detection effects. In this case, the x component of reflected shear waves and the z component of the P-S waves can be used for advance detection; (3) When the fault throw is less than the coal thickness, the y and z components of in-seam waves can yield great advance detection effects. When the fault throw is greater than the coal thickness and above, the y component of in-seam waves can be employed for advance detection; (4) When the angle between a fault plane and the tunnel is greater than 60°, the y and z components of in-seam waves can be employed for advance detection. When the angle is less than 60°, the x and y components of in-seam waves can be used for advance detection. The results of this study can provide theoretical support for the in-seam wave advance detection of coal mines.
Study on migration characteristics of chromium contaminated site and Dual-Frequency IP method monitoring technology
WEI Kaiyao, LIU Zhimin, LIANG Chen, ZHANG Jie, MA Qiang
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Abstract:
In view of the fact that the migration process of chromium contaminated sites can be affected by a variety of uncertainties, its migration characteristics and monitoring process are difficult to study experimentally. Based on the basic law of groundwater flow and the migration mechanism of pollutants, COMSOL software was used to simulate and analyze the migration characteristics of chromium contaminants in static reserves and their changing rules. The reliability and accuracy of numerical forward simulations are verified by conducting physical modeling experiments of static earth tanks. The chromium pollution source migration model is used as the basic model for geoelectric monitoring. Based on the theory of dual-frequency induced polarization(IP) method, the intermediate gradient detection device and symmetrical quadrupole sounding device are used for pollution source migration monitoring to analyze the influence of terrain undulation and the orientation of the measurement point on the monitoring effect. The results show that during the migration of chromium pollutants, the permeable layer with a high permeability coefficient shows a strong adsorption effect on the heavily polluted area, and at the same time, it will intensify the lateral spreading of polluted areas in a short period of time. Correspondence of excitation anomalies between the peak apparent amplitude frequency and the trough of apparent resistivity is better for profiling than for bathymetric surveys. For symmetrical quadrupole sounding, a measuring point in the center of the projected edge of the contaminated field allows for more effective contamination monitoring. The presence of valleys may trigger "multiple peaks" in the excitation curve during profiling and bathymetric soundings. By setting up power supply electrodes on the mountain frontiers on both sides of the raised peaks and comprehensively mapping the apparent amplitude frequency and apparent resistivity curves of the chromium contamination field, whcih is effective in determining the exact location of the heavily contaminated area. The research results enrich the theory of monitoring heavy metal soil pollution field by dual-frequency IP method, whcih promote the ecological environmental protection.
Genetic type and gas-generation potential of coalbed methane in Bayanhua Sag of the Erlian Basin
MENG Qin, LI Ling, LI Jie, TIAN Wenguang, LIN Haitao, LI Heng
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Abstract:
The Bayanhua Sag in Erlian Basin is a key experimental area for the development of low-rank coalbed methane(CBM) in Inner Mongolia. However, the exploration degree is relatively low and the understanding of CBM genesis is insufficient, which restricts exploration and development to a certain extent. Through carried out laboratory experiments of gas components, stable isotope, hydrochemical and radioisotope dating of CBM well gas samples and water samples in Bayanhua Sag. And comprehensive use the classical natural gas to clarify genesis. Further analyze potential and identify the key elements of gas-generation. The results show that C1/C1-5>0.99, CDMI is basically less than 5%, the drying coefficient C1/C2+ is between 224 and 5 540. The volume fraction of CH4 is high, while heavy hydrocarbons and CO2 is low. The δ13C(CH4) ranging from -51.80‰ to -67.70‰, δD(CH4) ranges from -226.20‰ to -291.00‰, and δ13C(CO2) ranges from -20.30‰ to -37.60‰, indicating a terrestrial biogenic gas characteristic. In the identification chart, most samples are located in the regions of biogenic gas, indicating that methane pathways are acetic acid fermentation and methyl fermentation, and CO2 is mainly the associated product of microbial methanogenesis. Coal seam water comes from atmospheric precipitation, mainly NaHCO3 type weakly alkaline water, δ13CDIC value is -2.6‰, δ18O is -16.4‰. Combined with 14C chronology shows that the water is quaternary water, non-primary water, but modern mixed water. Based on the analysis of geological structure and hydrogeological conditions in the whole area, the runoff area is conducive to acetic acid fermentation to produce gas, while the slow flow area is conducive to biogas enrichment and accumulation. The low-rank coal reservoir has good porosity and permeability, suitable temperature reservoir and superior hydrogeological conditions, which are conducive to the generation of biogas and the development of hydraulic plugging type biogas in the pressurized area. Hydrogeological conditions are the key to the formation of biogas, and should be paid more attention to the exploration area of CBM.
Geological characteristics and development potential of deep coalbed methane resources in Shenmu-Jiaxian Block, Ordos Basin, China
LI Guoyong, YAO Yanbin, WANG Hui, MENG Lingjian, LI Peijie, ZHANG Yongchao, WANG Jianwei, MA Limin
, Available online  
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Abstract:
China possesses abundant deep coalbed methane (CBM) resources with significant exploration and development potential, referring to depths greater than 2000 m. Deep CBM differs significantly from shallower formations in terms of accumulation and development patterns, necessitating detailed research for key blocks. The Shenmu-Jiaxian Block, situated in the northeastern part of the Ordos Basin, is currently in the early stages of deep CBM exploration, and its enrichment characteristics and development potential remain uncertain. In this study, we conducted a comprehensive analysis of the fundamental geological features of coal reservoirs in the study area using recent seismic data, well logs from over 300 wells, and analytical data from four core wells. We identified the main controlling factors and accumulation mechanism of CBM, and analogically assessed the development potential of deep CBM in the region. The targeting No. 8 deep coal, has the vitrinite reflectance of 0.7%~1.8%, indicating the coalification in the most parts of the study area is currently in the peak stage of thermogenic gas generation. The region exhibits considerable coal thickness, stable development, relatively simple tectonics, well hydrodynamic sealing, and favorable roof and floor sealing conditions, providing favorable conditions for widespread and continuous CBM accumulation. Among them, the southern area of Jiaxian demonstrates the most favorable CBM resource conditions. Compared to other deep blocks in the eastern Ordos Basin, the study area exhibits a notably higher proportion of free gas in coal seams. It is suggested that the adsorption gas in coals is mainly controlled by adsorption pressure, whereas the free gas is subject to dual controls of capillary pressure and buoyancy-gravity differentiation. These two trapping mechanisms jointly determine the vertical zonation and regional distribution of gas content in the deep coal seams. Taking the southern area of Jiaxian as an example, we summarized a typical enrichment pattern of deep CBM. Comparative analysis with the Linxing and Daning-Jixian Blocks indicates that the Shenmu-Jiaxian Block possesses a solid foundation of CBM resources, favorable reservoir alteration, and high production potential, hinting at promising prospects for large-scale development of deep CBM in this region. In addition, the Daning-Jixian block is characterized by high-rank coals, whereas the Shenmu-Jiaxia block consists of medium-rank coals. Therefore, this study contributes to the enrichment and refinement of the theory of deep coalbed methane accumulation, which holds significant instructive implications for the exploration and development of deep coalbed methane in China.
Dual-frequency transmission radio wave-based exploration method and its application
FU Xianjie, HU Ze'an, WU Rongxin, LI Peng
, Available online  
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Abstract:
Coal seams can act as the guided wave layers of high-frequency electromagnetic waves, and radio wave perspective technology can be used to detect geological structures within coal seams of a working face. Presently, radio wave perspective methods usually use a single frequency, leading to some problems such as improper frequency selection and limited detection accuracy in the exploration of mining faces. In response, this study developed a dual-frequency transmission radio wave-based exploration method. Based on theoretical analysis, as well as the field strength of dual-frequency perspective and attenuation coefficient, this study derived the calculation formula for the absorption factor γ of coals based on the measurement data of dual-frequency radio waves. Furthermore, using the finite element numerical simulation method, this study simulated and analyzed the conditions of coal seams bearing no anomalous geological structures and those containing faults. The experimental results show that the dual-frequency absorption factor was more sensitive to the geological anomalies of coal seams, verifying the effectiveness of the dual-frequency transmission radio wave-based exploration method. The comparison between the field experimental data and the mining drilling results also verified that the dual-frequency absorption factor γ exhibited better responses to geological anomalies than the single-frequency attenuation coefficient. The above experimental results show that the dual-frequency transmission radio wave-based method can improve the detection effects of geological anomalies within coal seam mining faces, providing a new method and idea for radio wave-based finescale exploration and the ascertainment of mine geology.
Experimental study on MICP restoration law and influencing factors of coal mining ground fissures
LI Tao, GAO Ying, YAN Jingwang, ZHANG Jiarui, KOU Guigui, MA Tengfei, MEI Aoran
, Available online  
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Abstract:
The coal mining ground fissures in the northwest loess covered area cause shallow water resource leakage and soil instability. Therefore, the experimental study on MICP (micro induced carbon precision) restoration of coal mining ground fissures in the loess covered area were conducted. Taking the Ningtiaota Coal Mine in northern Shaanxi as the research background, the characteristics of mining ground fissures were observed and the development characteristics of mining induced ground fissures were revealed. Based on the observation of mine pressure, the types of ground fissures in loess mining were classified. Based on the classification and characteristics of coal mining ground fractures, the mechanical and hydraulic parameters of two types of fractured loess MICP restoration samples were compared and tested using unconfined compression tests, triaxial compression tests, variable head permeability tests, and triaxial permeability tests. Based on the pH value of the restoration body, MICP calcium carbonate production, and scanning electron microscopy test results, analyze the influencing factors of MICP restoration for coal mining loess ground fissures. The results indicate that coal mining ground fissures in loess covered areas can be divided into two types: boundary ground fissures and internal ground fissures. Under the condition of boundary ground fissures, the optimal ratio of bacterial solution to cementitious solution is 1.2:1. Under the conditions of internal ground fissures, the optimal ratio of sand and loess to fill the fissures is 1:1, and the optimal ratio of bacterial solution and cementitious solution is 1.0:1. The difference in the opening of different types of coal mining ground fissures in loess covered areas results in a 31.2% difference in the yield of calcium carbonate. Therefore, the optimal MICP repair solution for boundary ground fissures accounts for a larger proportion of the cementitious fluid components compared to internal ground fissures. When the ratio of windblown sand and loess in the crack filling material is 1:1, the pH value of the mixture of filling material and repair fluid is 9.2. The yield of calcium carbonate in this pH value environment can reach 88%, promoting the efficient operation of MICP. The research results provide a reference for the repair of coal mining ground cracks in loess covered areas.
Prediction of rockburst intensity grade based on convolutional neural network
LI Kangnan, WU Yaqin, DU Feng, ZHANG Xiang, WANG Yiqiao
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Abstract:
Rockburst is one of the urgent problems to be addressed in the process of deep resource extraction. In order to predict the rockburst disasters safely and efficiently, a rockburst intensity grade prediction model (MICE-CNN) based on the Multiple Imputation by Chained Equations (MICE) and Convolutional Neural Network (CNN) was proposed. Specifically, a predictive indicator system was established based on the main influencing factors and the acquisition conditions of rockburst. A total of 120 sets of raw data from rockburst cases were collected, with the outliers processed by pauta criterion. Then, the missing data were interpolated with the four interpolation models of RF, BLR, ET and KNN, which were selected using MICE. Besides, data interpolation was performed with the optimal model selected according to RMES, in combination with the two traditional interpolation methods (Mean and Median), resulting in a complete data set. In addition, the data were flattened into a 6×1×1 one-dimensional image data as the input layer, and the sizes of the convolutional kernel and pooling kernel were calculated to be 3×1 based on the size of the input layer. Moreover, zero-padding was applied for the feature edge processing. Batch normalization layers were added to improve the model stability and convergence speed. Thus, ReLU activation function and SGDM optimizer function were selected. Further, the CNN prediction model was trained, with accuracy rates of 100% for the training set and 91.67% for the validation set. Meanwhile, the RBF, SVM and PNN models were established for the comparison and verification of their test set data with that of the CNN model. Generally, the CNN model shows higher accuracy (91.67%) than the other models. By comparing the confusion matrix of the PNN model with the CNN model, it is found that the CNN model tends to overestimate the degree of rockburst compared to the actual results, indicating better safety after misjudgment. This demonstrates the feasibility of the MICE-CNN prediction model of rockburst intensity grade.
Water-blocking performance of laterite in weak deposition areas of Neogene Baode Formation and significance of resource exploitation
ZENG YIfan, BAO Han, WU Qiang, MENG Shihao, HUA Zhaolai, MIAO Yanping, ZHANG Ye, BU Wenyang
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Abstract:
The in-depth study on the water-blocking performance of red clay in the weak deposition areas of the key aquiclude is of significant importance for mine production safety and ecological water resource protection. Specifically, the borehole data were reoptimized based on the regional sedimentary characteristics, the thickness distribution pattern of laterite deposit in Yushen mine area was studied, and the micro-engineering characteristics and control factors related to the water-blocking performance of laterite were explored. The results show that the deposition thickness of laterite gradually increases from northwest to southeast, the distribution of laterite becomes extremely uneven with the evolution of rivers, and the area of laterite missing zone reaches 48.80%. The particle size analysis and permeability test show that the water-blocking performance of laterite increases vertically with the increase of laterite deposition depth. The microstructure and material composition analysis show that the water-blocking performance of laterite is not in a simple linear relationship with its deposition thickness in the horizontal direction, and the water-blocking performance of laterite in the weak zone decreases sharply with the decrease of its deposition thickness. Based on the concept of stable Darcy flow rate, the critical thickness of laterite in the weak zone with non-complete water-blocking performance was calculated, and the waterblocking performance of laterite in Yushen mine area was classified through multi-source data fusion. The systematic study of engineering characteristics and water-blocking performance of laterite in Yushen mine area could provide important theoretical basis for identifying the potential geological factors that may cause hacards in the mines within the weak laterite area, realizing the protection and reconstruction of key aquiclude and guiding the practice of coal-water dual-resource cooperative co-mining engineering.
Multipoint sources-based high-resolution electrical detection of the water-rich areas near mining faces of coal mine roadways
WU Rongxin, XU Hui
, Available online  
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Abstract:
To accurately explore the water-rich areas near mining faces of mine roadways, this study proposed a multipoint sources-based high-resolution electrical detection technology. A multi-channel electrode observation system was arranged behind a roadway mining face, with electrodes at a distance of 1/4 measuring lines behind the mining face as point source electrodes sequentially. Data were collected using a monopole-dipole device, with the obtained apparent resistivity considered the sounding data of multipoint sources-based electrical detection. The images of multipoint sources-based electrical sounding allow for quickly determining the presence of water-rich areas and their locations relative to the mining faces of mine roadways. Specifically, the detection range was divided into a series of target units. Then, the multipoint sources-based electrical sounding data were processed using the matched filtering method for abnormal targets, yielding the correlation imaging results of the detection range. Among them, the ranges of high correlation values can accurately reflect the distribution locations of rich-water areas in front of or behind the roadway heading mining faces. A theoretical template curve was obtained through the fitting of measured electrical sounding data. Subsequently, the multipoint sources-based sounding ratio data obtained using the ratio method can effectively eliminate the influence of factors such as roadway cavities and laminated strata. As indicated by the detection results of a mining face in the Pansan Mine of the Huainan Mining Group, the multipoint sources-based high-resolution electrical method can accurately detect the locations of water-rich areas near the mining faces of mine roadways, thus effectively guiding the prevention and control of water disasters during roadway tunning.
Study on suspension and migration law of proppant in long-distance pipeline for ground-coalmine combined hydraulic fracturing
LI Haozhe, JIANG Zaibing, SUN Siqing, ZHU Chuanyong, FAN Yao, GUO Yong, CHENG Bin
, Available online  
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Abstract:
Ground-coalmine combined hydraulic fracturing is one of the development trend of staged fracturing of long boreholes in underground coal mines. After the fracturing fluid is pressurized by the ground fracturing pump, it enters the long boreholes in underground coal mines through the through-well and long pipeline to conduct large-pump-rate fracturing. The suspension and migration law of proppant in the long pipeline is of great significance for optimizing the sanding parameters and avoiding sand blockage in the pipeline. The rheological properties and sand carrying properties of fracturing fluid were evaluated by laboratory tests. Then, based on the Euler-particle flow theory, a numerical simulation model was constructed to study the transport law of proppant in horizontal pipe. The flow pattern of fracturing fluid and the calculation model of critical settlement velocity were discussed. The results show that the addition of 1% friction reducer can increase the viscosity of active water fracturing fluid by 3~5 times. The smaller the proppant density, the larger the fracturing fluid viscosity and sand concentration, and the smaller the settling velocity of proppant in fracturing fluid. The flow of proppant in horizontal pipe is affected by many factors. The smaller the flow rate of fracturing fluid, the larger the density and particle size of proppant, and the more serious the deposition of proppant at the bottom of the pipe, and the worse the sand carrying effect is. With the increase of pipeline diameter, the maximum volumetric concentration of proppant at the outlet moves from the middle and lower part of the pipeline to the bottom of the pipeline, and the flow of proppant aggravates the wear of the pipeline. The larger the sand concentration is, the stronger the interaction between proppants is, and the sand carrying capacity of fracturing fluid is reduced. The model recommended by dredging technical specification is preferred to calculate the critical settling velocity of proppant under the condition of active water fracturing fluid. With the increase of pipeline diameter, the required critical sand carrying pump rate increases exponentially. Increasing the viscosity of fracturing fluid can reduce the critical sand carrying pump rate. According to the critical pump rate model of sand carrying migration, the pipeline diameter and fracturing fluid pump rate can be optimized and matched. The research results can provide theoretical support for ground-coalmine combined hydraulic fracturing.

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