The structure of China’s coal-based energy consumption will not change in the short term. Coal resources are still being developed at a high intensity and with significant demand in China.It's necessary to pay close attention to China’s coal resource exploration efforts. This study essentially determines the state of coal resources by examining the distribution and preservation of coal resources in China. The distribution of China’s comparatively abundant coal resources is mostly governed by the “two horizontal” and “two vertical” tectonic bands that run east-west and north-south. The distribution of “nine palaces” resources is uneven in terms of their occurrence and development in the various regions. While there is little coal exploration and development in the western region despite its wealth of resources, there is a high level of coal development in the middle and eastern regions. The mining situation of coal resources in typical mines of main coal mining areas in China was investigated and calculated. The calculation method of coal resource recovery rate is studied. The resources mined by the majority of mines only make up 24.3% to 59.8% of the resource reserves found through exploration, which can essentially represent the actual mining situation of the coal resource reserves found in China under the current technical mining conditions. The majority of the coal resource reserves that have been identified in China’s present exploration and appraisal will be mined and occupied in 20 years, according to the research. The inability to reliably identify resource reserves necessitates drawing society’s attention to the exploration of coal resources and enabling proactive planning and formulation of focused solutions. In order to realize the ballast role of coal in ensuring the safe and stable development of China’s energy sector, it is necessary to strengthen the exploration of coal reserves in the old mining areas in the central and eastern regions; accelerate the westward shift of coal development strategy, the construction of coal base “Gemini”; and carry out fine exploration and evaluation of geological conditions in deep and complex areas.

The western loess-covered area is an important coal production base in China, with complex geomorphology and geological mining conditions, huge thickness of loess layer, mining subsidence with special characteristics different from other mining areas, large surface subsidence rate, small starting distance, more serious discontinuous damage such as mining cracks, and more complicated and changeable characteristics of the shape of the surface subsidence basin and the distribution of subsidence deformation. Under the current technical conditions, it is still difficult to carry out efficient monitoring and quantitative evaluation of surface subsidence. In recent years, multi-source remote sensing technologies such as Interferometric Synthetic Aperture Radar(InSAR), Unmanned Aerial Vehicle photogrammetry(UAV photogrammetry), and Light Detection and Ranging(LiDAR) have been developing rapidly, and with its features of non-contact observation, wide coverage, and high spatial and temporal resolution, it is able to realize the continuity, dynamics and comprehensive monitoring of surface subsidence. Through the fusion of multi-source observation data, it can provide a new technological way for the efficient monitoring of the mining subsidence in the western mining area. This paper summarizes the progress of the application of multi-source remote sensing technology in mining subsidence monitoring. The practical effects of lnSAR, UAV photogrammetry, and LiDAR for subsidence monitoring in mining areas on the Loess Plateau are explored through field experiments, and it is found that under the conditions of complex geomorphology, undulating topography, and vegetation cover, as well as large-gradient deformation of the ground surface, the lnSAR interferometric loss of correlation, atmospheric delays and other kinds of errors are too large. The 3D model constructed from UAV photogrammetry is affected by vegetation and terrain, resulting in insufficient elevation accuracy for the ground model. UAV laser scanning is affected by the combined effects of terrain slope, point cloud density, and horizontal movement of surface points leading to significant DEM modeling errors. As a result, multi-source remote sensing techniques under the current conditions all have their own advantages, limitations and technical bottlenecks. On this basis, the algorithmic process of ground point cloud extraction and surface 3D deformation information acquisition in the loess gully area is proposed; the technical path to realize accurate and efficient monitoring of mine subsidence 3D displacement based on the fusion of multi-source remote sensing data is pointed out; and the prospect of the application of constructing an intelligent system of multi-source remote sensing monitoring of mine subsidence is envisioned.

Strategic metal resources are irreplaceable for new materials, new energy, information technology, aerospace, national defense and other emerging industries, traditional strategic metal mineral resources have relatively few reserves and high supply risks. The Strategic metal resources in coal-bearing strata are used as an important supplement and have become an important direction of new strategic metal resources exploration, therefore, based on the basic characteristics of coal and strategic metal resources in coal-bearing strata, it is urgent to carry out research on collaborative exploration methods for coal and strategic metal resources in coal-bearing strata. This article is based on previous research results and focuses on coal and strategic metal resources in coal-bearing strata (uranium, lithium, gallium, germanium, niobium-zirconium-gallium-rare earth), the study has summarized the main combination types of coal and strategic metal resources in coal-bearing strata, and explored the cooperative exploration methods of coal and strategic metal resources in coal-bearing strata. From the perspective of the occurrence position of coal and strategic metal resources in coal-bearing strata, the main combination types of coal and strategic metal resources in coal-bearing strata are summarized, including coal-uranium deposits, coal-lithium deposits, coal-gallium deposits, coal-germanium deposits, coal-niobium-zirconium-gallium-rare earth deposits. According to the differences in physical properties of different rocks and minerals, the response principles and characteristics of different exploration techniques and methods were summarized. Based on distribution law and occurrence horizon of coal and strategic metal resources in coal-bearing strata, the geological, geochemical and geophysical conditions of coal and strategic metal resources in coal-bearing strata are discussed, the basic characteristics of the main combination types have been summarized. From the perspective of coordination of multi-mineral exploration and coordination of various exploration technologies, based on the exploration technology and method of coal and strategic metal resources in coal-bearing strata, following the principle of maximization of economic benefit and optimization of exploration methods, a reasonable cooperative exploration method for coal and strategic metal resources in coal-bearing strata is proposed. Based on the radioactive characteristics of uranium deposits, the cooperative exploration of coal-uranium deposits should strengthen the cooperative application of remote sensing, geological mapping, radioactive exploration methods (gamma total, gamma spectrum, radon and its daughter measurement and gamma logging), deep penetrating geochemical, ground geophysical prospecting (high-precision magnetic/seismic/electromagnetic), drilling engineering, logging and rock geochemical methods. Based on the dispersion and occurrence location of lithium and gallium, the collaborative exploration of coal-lithium and gallium deposits should strengthen the collaborative application of remote sensing, geological mapping, mountain engineering, high-precision seismic, drilling engineering, logging and rock geochemical methods. Based on the symbiotic minerals of coal-germanium and the occurrence of germanium in organic matter, the collaborative exploration of coal-germanium deposits should strengthen the collaborative application of remote sensing, geological mapping, mountain engineering, drilling engineering, logging and rock geochemical methods. Based on the high field intensity characteristics of niobium, zirconium, gallium and rare earth associated elements, the collaborative exploration of coal-niobium-zirconium-gallium-rare earth deposits should strengthen the collaborative application of remote sensing, geological mapping, mountain engineering, drilling engineering, logging (natural gamma) and rock geochemical methods.

The research and demonstration of coalbed methane well location deployment and implementation plan is an important link in the formulation of coalbed methane block development plan. It is generally believed that the thickness, gas content, and burial depth of coal seams are the main controlling factors for the deployment of coalbed methane wells. In practice, it has been found that structures, inter well interference, and production processes also have a significant impact on gas production. The deployment of coalbed methane wells requires a systematic study of scientific rationality and full cost investment evaluation based on multiple factors such as exploration, development, and economic benefits. Therefore, this article focuses on analyzing and studying some important factors that are often overlooked in the geological conditions of the block, optimization of well spacing, and on-site construction process. ① This article proposes ideas and methods for the precise deployment and implementation of coalbed methane well locations. The precise deployment and scientific implementation of coalbed methane well locations require full consideration of multiple factors such as geological factors, development effects, economic benefits, and construction requirements. Overall planning, precise deployment, scientific construction, and dynamic adjustment of the development block are required. The fine deployment of coalbed methane well locations mainly includes three stages of tasks: pre development fine deployment stage, on-site scientific implementation stage, and post development dynamic adjustment stage. ② Structural changes have a significant impact on the gas production efficiency of coalbed methane wells. This article analyzes the impact of secondary structures such as small high points, small low points, small nose shaped, and small faults on gas production in a coalbed methane block in the southern part of Qinshui. Local small nose shaped structures are most conducive to the enrichment and high production of coalbed methane. Based on the characteristics of changes in different structural parts, 4 types of 13 well pattern classification were proposed considering different well types and micro structural changes, which are suitable for deployment of coalbed methane well pattern under different geological conditions. ③ This article simulates and studies the optimization plan of well spacing under the influence of multiple factors. By comprehensively considering the impact of inter well interference on gas production efficiency under different well spacing conditions, the difference in cumulative gas production between different well spacing, and the economic benefit difference between the number of development wells and gas production efficiency, the optimal well spacing size that can achieve good gas production efficiency and economic benefits is obtained. ④ This article proposes a new approach to the deployment and implementation of integrated geological engineering well locations. Process improvement and optimization adjustment of coalbed methane wells can be achieved through four steps: “geological block division, optimization of wellhead target coordinates, factory drilling, and “block fracturing” to enhance inter fracture interference. This method can improve drilling efficiency. At the same time, this method can improve the gas production efficiency of deployed wells, utilizing alternating fracturing of multiple wells to form inter fracture interference, generating larger and more complex fracture networks, and maximizing communication between reservoir fractures and pores. The research ideas and methods proposed in the article can be applied to the deployment and on-site implementation of coalbed methane blocks. By continuously improving and refining the deployment and implementation of coalbed methane well locations, we aim to improve the scientific and rational development plan of coalbed methane and maximize the exploitation and utilization of coalbed methane resources.

Coal and sandstone-type uranium deposits in the Mesozoic coal-bearing basins in Northern China often show the stratigraphic structure of “lower coal and upper uranium”, indicating a good co-occurrence relationship between coal and uranium deposit. In order to precisely restrict the role of sedimentary factors in coal accumulation and uranium enrichment, and to explore the sedimentary mechanism of coal and uranium co-occurrence, we selected the Zhundong coalfield and its adjacent areas in the eastern Junggar Basin, where there are two sets of “lower coal and upper uranium” strata, as the research object. Based on the stratigraphic sequence analysis and isochronous stratigraphic framework construction, detailed sedimentary characterization of coal measure strata and an in-depth discussion of sedimentary evolution law are carried out. The results show that the Jurassic strata in the Zhundong coalfield and its adjacent areas is a complete second-order sequence consistent of multiple third-order depositional cycles of retrogradation-progradation, and the top and bottom are limited by regional unconformities. The retrogradation-progradation sedimentary cycle is the main reason for the superposition of coal measure strata and uranium reservoir. It controls the change of sedimentary environment and the spatial configuration of materials by accommodating spatial changes, and progradation corresponds to stronger coal accumulation and better uranium reservoir sand body than retrogradation. Moreover, The second-order sedimentary cycle has stronger compulsion than the third-order sedimentary cycle, which restricts “lower coal and upper uranium” formation structure of Badaowan Formation in the regressive environment in the second-order cycle to be much smaller than that in Xishanyao-Toutunhe Formation in the progradative environment. All these results will provide a theoretical basis for the prospect prediction of uranium mineralization in other coal-bearing basins, especially for the identification of new uranium reservoirs and new prospect areas.

Coal-bearing sequences are important source for increasing strategic metal mineral reserves. There are abundant coal resources in Ningdong Coalfield,and strategic metals enrichment have been found in several coal-bearing sequences. The study selected coal-bearing sequences of Renjiazhuang Mine Field in Ningdong Coal Field as the research object, the coal samples, gangue, roof and floor plate of the main coal seam section were collected systematically. The mineralogical and geochemical tests were carried out by inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence spectroscopy and X-ray diffraction, and the distribution characteristics of major and trace elements were ascertained. The causes of strategic metal element enrichment and their provenance were analyzed.The results showed that the Permo-Carboniferous coal-bearing of late Paleozoic are the enrichment beds of strategic metal minerals in RenJiazhuang Mine Field. The enrichment of strategic metal elements in coal is common in Taiyuan and Shanxi formations, and the overall content of trace elements is high, which is characterized by Li-Ga-Zr(Hf)-Nb(Ta)-Th(U)-Pb,rare earth element and Yttrium(REY), co-enrichment. Moreover, strategic metal elements are more enriched in coal-bearing near the roof,floor and the gangue.Among them, Li and Ba are highly enriched, Rb and Zr are enriched in No.5 coal seam. Li is highly enriched in No.9 coal seam, while Zr, Hf and Th are enriched. The content of strategic metal elements in upper No.9 coal seam is relatively low and Cr is enriched. The concentration of trace elements in No.5 and No.9 coal is better than that in upper No.9 coal seam. Li and Ga of the ash foundation of No. 5 and No. 9 coal seam have reached the industrial grade, and REY of the ash foundation of No. 5 coal seam has also reached the industrial grade, which presenting a very promising potential for further exploration.Based on the comprehensive analysis of element occurrence characteristics, sedimentary environment and tectonic evolution, it is concluded that the strategic metal element enrichment in Renjiazhuang Mine Field is mainly influenced by the clastic supplying of the erosion source area, and the felsitic-neutral rock detrites from the northern Yinshan ancient landthe and the northwestern Alxa block in the western margin of Ordos Basin were transported into the peat swamp by palaeocurrent. It was enriched through interaction between organic matter and inorganic matter in specific sedimentary environment and geochemical environment, and formed the present distribution state and enrichment characteristics under the control of multi-stage tectonic evolution.

Acid mine drainage gushing from unknown source after coal mine closure is the key problem that puzzles the ecological restoration of mining areas. Due to the southern coal mining areas in China generally exist “complex terrain conditions, large mining base, multiple points and wide areas” and other problems, it is difficult to identify large-scale underground pollution sources. In order to investigate and study the water-rich space of coal mines in areas with complex terrain and trace the source of acid mine drainage gushing on the surface, the historical abandoned mine in Yanshi Town, Longyan City, Fujian Province, which is located in the depression zone of southwest Fujian Province was taken as an example. Use the semi-airborne transient electromagnetic method with Unmanned Aerial Vehicle, the low resistivity characteristics surrounded by high resistivity for detecting target and according to the resistivity difference between water-rich area and surrounding rock to detect the abnormal water content area within 300 m below the surface with multi-source data, analyze the water content of the abnormal area, and define the geographical location of the water-rich space, provide a scientific basis for the treatment of acid mine drainage in abandoned coal mines. The results show that: ① The semi-airborne transient electromagnetic detection technology has a high sensitivity to the detection of underground water-rich space, and the low-resistivity anomaly area covered by high resistance can effectively reflect the water content of underground space; ② Historical gob areas are widely distributed in the study area, but not all the historical gob areas are water-rich. Using semi-airborne transient electromagnetic detection technology and geological profiles, a total of 8 water-rich areas, a large number of nearly circular water-rich channels and 3 water-rich areas in fault zones are identified; ③ The historical goaf in the study area is not the main underground water-rich space. Compared with the water content of the goaf, the water content of the near-circular tunnel and the waterlogging zone of the fracture zone is also particularly important for the treatment of water gusher in the surface acidic mine.

Coal mining has caused the reduction of land productivity in mining areas and exacerbated the problem of ecological fragility, while microbial combined plant reclamation technology is a commonly used means of ecological restoration in mining areas, and the appropriate inoculation method of microbial agents is of great significance for accelerating the ecological restoration in mining areas.Dark Septate Sndophytes(DSE) are a group of endophytic fungi ubiquitously existing in plant root systems, whose metabolites could function as plant growth stimulants. TakingMedicago sativa L.as the research object, four treatments were set up, including DSE hypha (HD), metabolite (MD), hypha and its metabolite (HD+MD) and blank control (CK), to explore the mechanism of DSE and its metabolite promoting effect onMedicago sativa L., under two inoculation methods of root dipping and simulated soil cultivation. The results showed thatMedicago sativa L.co-treated with hypha and its metabolites under root dipping method had the best growth potential. Compared to the control group, the total biomass, total chlorophyll, root volume and total nitrogen content increased by 83.78%, 35.54%, 132.12% and 82.16%, respectively. The colonization rate of DSE in the root system ofMedicago sativa L.could achieve 68.89%, dominated by the colonization in the hypha mode. Under simulated soil cultivation, DSE metabolites performed a significant growth-promoting effect onMedicago sativa L., and the colonization was dominated by the microsclerotia mode. The correlation analysis showed that compared with the inoculation method, the DSE inoculation treatment was significantly positively correlated with hypha colonization rate, microsclerotia colonization rate, total colonization rate, root length, root surface area, root projected area (P<0.05), and highly significantly positively correlated with aboveground fresh weight, root fresh weight, total fresh weight, root volume, total nitrogen and total potassium (P<0.01). DSE and its metabolites could regulate the growth ofMedicago sativa L.through colonization rate and photosynthesis, providing a theoretical basis for the development and utilization of green microbial fertilizer for ecological restoration in mining areas.

The large-scale open-pit coal mining has seriously disturbed the landform and soil carbon cycling process of the mining areas. Restoration and improvement of soil organic carbon in open-pit mining areas is in line with the “dual carbon” goal, and is of great significance for improving soil fertility and self-sustaining ecosystems. To reveal the disturbance characteristics of soil organic carbon pool loss caused by open-pit mining, and grasp the influencing factors and improvement strategies of soil organic carbon recovery in mining areas, the Zhungeer mining area, largest open-pit coal mine group in China, was selected as the research area in this study. Sentinel 2 was used to extract the remote sensing images of the damaged area, and 149 soil samples were collected, as well as methods such as statistical interpolation and regression analysis of influencing factors were also adopted. The results indicated that there were significant differences in the physicochemical characteristics, and biological activity between the open-pit mine waste dump soil and natural soil in semi-arid areas. The soil organic carbon content of the newly reclaimed waste dump lacking natural topsoil coverage was extremely low, with an average of 0.19%. Due to non-standard natural topsoil stripping and disorderly mixed discharge, it was estimated that the cumulative loss of organic carbon in the surface soil of this area exceeded 620,000 tons. Regression analysis result showed that total nitrogen (0.559), reclamation period (0.225), and vegetation NDVI (0.172) were the positive factors affecting the recovery of mining soil organic carbon . The survey result also showed that the soil organic carbon content of the composite vegetation restoration model was significantly higher than that of the single vegetation restoration model, while the soil organic carbon content of the grass shrub community composed of sea-buckthorn, alfalfa, and sweet clover was close to the value of natural soil. Under the single vegetation restoration model, the restoration of soil organic carbon content was manifested as follows: shrubs mainly composed of Salix psammophila > trees mainly composed of Pinus tabulaeformis > small trees mainly composed of Rhus typhina > herbaceous plants mainly composed of Medicago sativa. The organic carbon content of the platform and slope soil in the reclamation area of the waste dump increased with escalation of reclamation years. After 5 years of reclamation, the organic carbon content of mining soil exhibited a rapid promotion. The continuous scientific improvement of soil organic carbon is the key to the successful ecological restoration of mining waste dump. Measures such as controlling erosion and fertilizer, adding materials to increase carbon, vegetation carbon sequestration, conservation tillage are the main technical ways to enhance the organic carbon content of mining soil in open-pit mining areas.

A profound understanding of the derivative ecological damage effects of coal mining subsidence has become a key basic scientific issue and research hotspot for repairing ecological environment damage caused by mining in western coal mining areas. Grasping how coal mining subsidence in different geomorphic units affects soil microorganisms and enzyme activities is beneficial for the ecological environment protection and restoration of coal mining subsidence areas in the western region. The typical subsidence slope soil of the Yushuwan mine field (aeolian landform) and the north wing of the Ningtiaota mine field (loess landform) in northern Shaanxi coal mine area were selected as the research objects, while the soil samples from different slope parts (vertical depth of 0~60 cm) were collected, respectively. Absolute quantitative PCR and enzyme-linked immunosorbent assay (ELISA) methods were used to determine the number of soil bacteria, actinomycetes and fungi, as well as the activities of sucrase, catalase, urease and phosphatase, respectively. The spatial variation characteristics of soil microbial quantity and enzyme activity on subsidence slope were thoroughly analyzed, while the main physical and chemical soil properties were comprehensively integrated to reveal the impact of coal mining subsidence on soil microorganism and enzyme activity under different landform types. The results showed that: ① Coal mining subsidence in both aeolian landform and loess landform type unit could significantly reduce the number of soil microorganisms and enzyme activity on the subsidence slope. The decrease in soil microbial quantity reached 8.27%-42.39% and 11.53%-45.95%, respectively, while the decrease in soil enzyme activity reaches 6.52%-39.83% and 9.09%-42.42%, respectively. With the transition from the top of the slope to the middle of the slope and then to the foot of the slope, the reduction effect exhibited different variation characteristics for three soil microorganisms and four enzymes; ② The coal mining subsidence of loess landform type unit performed the most significant reduction effect on various soil microbial quantity and enzyme activity in “middle part of slope 0~10 cm soil layer”. Meanwhile, the coal mining subsidence of aeolian landform unit presented the most significant reduction effects on the soil actinomycetes quantity and invertase, urease and phosphatase activities in “middle part of slope 0~10 cm soil layer”, and soil bacteria and fungi quantity in “middle part of slope 10~20 cm soil layer”, as well as soil catalase activity in “middle part of slope 20~40 cm soil layer”. Therefore, it can be served as a targeted area for slope soil microbial remediation in coal mining subsidence areas of northern Shaanxi; ③ Whether in the units of aeolian landform or loess landform, the number of soil fungi and urease activity were the most sensitive indicators to coal mining subsidence, with decreases of 23.28%-45.95% and 22.78%-42.42%, respectively. Moreover, the two indicators can be used as markers to analyze the microbial characteristics of soil damaged by coal mining subsidence in northern Shaanxi mining area; ④ The correlation coefficients between soil available phosphorus and organic matter content and soil microbes and enzyme activities were the highest, exceeding 0.8 and 0.7, respectively, on both wind-sand and loess subsidence slopes. They can be served as key indicator factors for coal mining subsidence affecting soil microbial characteristics.

Single and multi-scene remote sensing data have been usually adopted to evaluate the ecological environment in mining areas, whereas these two types of data always presented the drawbacks of inconsistent time and inaccurate evaluation. To achieve the accurate monitoring of ecological environment in mining areas, the open-pit mine in Gobi desert and its surrounding environment was selected as the research object, and CFmask algorithm+Tmask algorithm were used to obtain pure pixel reflectance. The annual remote sensing data of study area was synthesized by the time series model, and then the pressure-state-response model was used for long-term ecological environment evaluation. The results show that: ① The difference between the predicted surface reflectance values based on time series model and the surface reflectance values observed by the satellite in the corresponding local area was small, while the difference between the true color image vision was relatively small. Meanwhile, the difference between the predicted reflectance value of the impeccable pixel position and the surface reflectance value of the surrounding pure pixel in true color image vision was small. The accuracy was verified by comparing the observed and predicted values of pure pixel reflectance of each band in the study area in 2022, and the results showed that the observed values were significantly correlated with the predicted values (with the correlation coefficients greater than 0.6). The correlation between the field investigation data and the ecological environment index obtained from the time series prediction data (R²=0.450) was better than that of the single-scene ecological index (R²=0.347) and the multi-scene ecological index (R²=0.386). ② From 2013 to 2021, the overall ecological environment of the study area was poor, presenting a spatial pattern of high in the south and low in the north, high in the west and low in the east. With the increasing time, the ecological environment in the south deteriorated more seriously. The change of ecological environment inside the mining area was more stable than that outside the mining area, with the ecological environment outside the mining area degenerating rapidly. ③ The annual change rates of poor, moderate and superior ecological areas were 0.005 /a, 0.002/a and −0.007/a, respectively. The status of each ecological grade performed a trend of decreasing landscape fragmentation, decreasing landscape heterogeneity, and increasing convergence over time. The ecological superiority patch moved towards ecological medium and poor patches, and the ecological poor grade gradually became the main ecological grade of the ecological environment in the study area. The proportion of each grade within the mining area was stable, while the proportion of ecological poor level outside the mining area increased year by year. When ecological restoration would be conducted in the research area, crops planting should be avoided in the direction of semi-sunny slopes as much as possible. Moreover, it is recommended to avoid planting crops with slopes greater than 17.5° in the direction of shady slopes, semi-shady slopes, sunny slopes and semi-sunny slopes.

The permafrost layer plays an important role in the ecological balance of high-altitude and cold regions, but the restoration and protection of permafrost layers are often overlooked in the ecological environment management of high-altitude and cold mining areas on the plateau, and corresponding research still has many gaps. Taking the comprehensive ecological environment improvement practice in Juhugeng Area of Muli Mining Area as an example, through the analysis of the planar distribution, vertical distribution, stratigraphic structure, and ground temperature changes of the original frozen soil layer, and targeting the ecological geological layer profiles of different research objects such as damaged soil layer, surface layer, frozen soil layer, and coal seam roof rock layer, following the idea of simulating the differences in seasonal frozen soil and permafrost changes and their ecological geological functions, Based on the construction of a binary structure frozen soil ecological geological layer profile model using artificial frozen soil layer and backfill layer, a repair technology for artificial frozen soil layer is proposed, which involves investigating the frozen soil overview, establishing the profile model, overlapping fusion, determining backfill time, designing surface water retention, laying interception and drainage ditches, and reshaping the terrain. This technology aims to achieve the material structure, underground aquifer structure, and hydraulic connection of the artificial frozen soil layer The functions of water source conservation and other aspects have basically reached the level of the original frozen soil layer, while providing more favorable conditions for frozen soil preservation. By using different methods such as pit exploration, drilling core sampling, and long-term monitoring of ground temperature inside the borehole, comparative experiments were conducted in the former slag mountainous area of the mining area and in the newly backfilled and repaired mining pit. It was confirmed that the permafrost top boundary in the original slag mountainous area is steadily rising, and new permafrost layers have begun to form in the newly backfilled area of the mining pit; By comparing the time and thickness of natural restoration of frozen soil layers in Zhashan District and artificial restoration of frozen soil layers in mining pits, it is shown that the construction of artificial frozen soil layers is more conducive to the rapid recovery of frozen soil in this area.

The Ningdong Coalfield is located in the arid and semi-arid region of northwest China, which is one of the 14 approved large-scale coal bases with a reserve of over 100 million tons in China. Currently, it faces challenges such as a large volume of highly-mineralized mine water, mature but costly treatment technology, and a low comprehensive utilization rate. To achieve the low-cost efficient reinjection and storage of highly-mineralized mine water in the Ningdong Coalfield and to protect the hydrological and ecological environment, this study, based on the typical characteristics of high mineralization in the mine water of 13 coal mines in the Ningdong coalfield, proposes a technical approach for the reinjection and storage of highly-mineralized mine water in depleted petroleum reservoirs in the coal and oil resources overlapping area. This approach utilizes the valuable unconventional water resource by making use of the pore-fracture dual structure and water storage space in the depleted petroleum reservoirs, the initial reservoir pressure vacuum during the shutdown of the oilfield, and the low-cost disposal of highly-mineralized mine water after resource utilization. The study systematically elaborates on the selection of depleted petroleum reservoirs, reinjection processes, water storage potential, pre-treatment water quality requirements, and the feasibility analysis of the environment. It also outlines prospects for fundamental theoretical research, legal regulations, policies, and real-time monitoring and control. The results indicate the feasibility of the proposed reinjection and storage technology in depleted petroleum reservoirs, which can achieve the low-cost efficient treatment of highly-mineralized mine water in the Ningdong Coalfield. “How to finely characterize the water injection seepage process” is identified as a bottleneck issue in the reinjection treatment technology. In essence, it involves the evolution mechanism of water injection and seepage in the pore-fracture scale of the depleted petroleum reservoir under the coupled chemical action of highly-mineralized mine water and sandstone. Furthermore, there is an urgent need for improvement in related legal regulations, policies, and real-time monitoring and control to ensure the smooth implementation of the reinjection and storage technology in depleted petroleum reservoirs. This study aims to provide new insights into efficiently reinjecting and storing highly-mineralized mine water and to offer references for the protection of secondary water resources in the development of coal, oil, and gas resources.

The variation degree of ecological water level in ecologically fragile areas is very important for ecological geological environment protection. Ecological water level inevitably undergoes variation under coal seam mining. The current research focuses on the decline of ecological water level under mining induced groundwater leakage, with little consideration given to the ecological water level restoration degree under non leakage of groundwater or disturbance of coal mining subsidence. For this reason, methods such as groundwater dynamics, groundwater level measurement, mathematical statistics, and comprehensive analysis are adopted, and an analytical method was proposed based on the idea of “distinguishing the leakage status of groundwater under coal seam mining → measuring the ecological water level changes in the coal mining face → establishing an ecological water level restoration degree well flow analysis model → predicting different ecological water level restoration times → comparing the analytical and measured values of different ecological water level restoration times” to study the degree of ecological water level restoration under the disturbance of coal mining subsidence in ecologically fragile areas. The results are as follows. ① Based on “key strata layer location + thin plate theory + soil arch effect + descending fissure”, a calculation method for the water-conducting fissure development height under overburden bedrock and soil structure is established, which overcomes the insufficient prediction accuracy caused by the existing empirical formula not considering the soil layer effect. Furthermore, combines the relationship between the thickness of the residual water-retaining layer and the aquifer seepage state, the aquifer seepage state is confirmed. ② Under the disturbance of coal mining subsidence, the measured ecological water level shows a change law of “rapid decline first, slow recovery, and stabilization”, but the ecological water level after coal mining can’t completely recover to the premining state. ③ An analytical model of the recovery degree of ecological water level under the disturbance of coal mining subsidence is established. The analytical values of the recovery time of three different recovery degrees of ecological water level are estimated, and the time errors of both are less than 10% compared with the measured values. ④ The reasons for the incomplete recovery of postmining ecological water level to pre-mining state are discussed from the perspectives of surface topography, atmospheric rainfall recharge, recharge and drainage of phreatic aquifers, and underground water drainage in mining areas.

Water conservation restoration and protection has always been a weak link in the whole life cycle management and ecological environmental protection from open-pit mining to pit closure, which involves more complex water problems in the complex environment of multidisciplinary and multi-circle environments in alpine permafrost areas, among which the analysis and research of interconnected hydrological processes is a huge challenge. On the basis of a brief analysis of the influencing factors of water transport and conservation in the natural environment and alpine permafrost environment and the impact of mining activities on water transport and conservation, this paper focuses on the analysis of the water transport and conservation mechanism in three cases: the impact of water transmission and conservation in the natural environment, the damage impact of open-pit mine production activities, and artificial restoration and protection.Based on the idea of comprehensive contact analysis and problem finding and the principle of comprehensive system governance, the concept of water transmission and conservation system is proposed, and the model construction of open-pit mine water transmission and conservation system is proposed from three basic frameworks: ① from the treatment area to more than 20 combination modes connected with natural water systems and the basic applicable conditions of different types of objects, the construction of surface water system connection and overlapping top-level system is proposed; ② According to the positioning of functional units such as approximate in-situ conservation, catchment transmission, water transmission, and transmission and drainage channels, the construction of ecological interception and drainage network was proposed from the spatial distribution style of ecological interception and drainage ditches, different interception and drainage ditches, and the partitioning of water transmission and drainage backbone network, catchment branch network, and functional units. ③ The underlying design of the in-situ water conservation system reconstruction is supported by the concepts of micro-geomorphic shaping, surface capillary network and vertical multi-ecological geological layer reconstruction. Based on the above research, taking Well No. 5 as an example, it is planned to be divided into 10 functional units, so as to realize the readjustment and distribution of the spatial distribution of surface water recharge and discharge under the guidance of zoning, and finally form a new surface water transmission and conservation system of Well No. 5. The purpose of this study is to provide a new systematic thought and method support for the restoration and protection of open pit in the high frozen soil area.

To explore the distribution of microbial communities in different functional zones of coal mine and their response to hydrogeochemical characteristics, a coal mine in Ordos was taken as the research object. 24 water samples were collected from six typical functional zones involved in the whole process of the mine water source, formation, collection and discharge. Hydrochemical components detection and high-throughput sequencing of microbial 16S rRNA genes were carried out. and multivariate statistical methods were used for sequence data processing. The results showed that the hydrochemical type of mine water was high salinity SO₄-Na type, which directly inherited the supplied water-source, while the concentration of characteristic pollutant${\rm{SO}}_4^{2 - }$was highest in coal roadways and surface water pools. The compositions of microbial communities in different functional zones presented significant differences. The dominant bacterial genera detected at the genus level includedThiothrixand sulfur oxidizing bacteria that could oxidize sulfides (i.e.,ThiothrixandSulfuricurvum), as well as newSphingobacteriaandShortwave Monocmonasthat can degrade organic matter (i.e.,NovosphingobiumandBrevundimonas), while they distributed relatively high in coal tunnels and goafs. The abundances of aerobicUliginosibacteriumandAcinetobacterwith strong adsorption and organic degradation, was highest in rock roadways. Bacteria related to nitrogen cycle (i.e.,HydrogenophagaandRhodobacter) accounted for the higher proportion in water sumps and surface water. Microbial communities were sensitive and closely related to the hydro-chemical processes. The distribution of microbial communities in underground coal mine was not only related to nutrients such as C, N, Ca and Mg, but also closely interrelated to redox sensitive substances such as Fe, COD and${\rm{SO}}_4^{2 - }$. Coal roadways and goafs are the key zones for groundwater pollution prevention and control. After mining disturbance, the low valent sulfides associated with coal have generated a large amount of${\rm{SO}}_4^{2 - }$through the chemical oxidation and catalytic oxidation of sulfur oxidizing bacteria. However, it is worth noting that when the working pannel stopped for six months to three years, the characteristic pollutant${\rm{SO}}_4^{2 - }$was reduced by 15%-34% due to the physical or chemical adsorption, precipitation (dominated in the early stage), and the reduction of sulfate reducing bacteria (dominated in the later stage). This result indicated that the goaf had a certain degree of self-cleaning ability. In summary, the research results could provide theoretical supports for the engineering applications of mine water pollution prevention and control, which was reflected in the following two aspects: on the one hand, to reduce the generation of${\rm{SO}}_4^{2 - }$from the source by maintaining the anaerobic condition on the working pannel through nitrogen gas supply; on the other hand, after screening and cultivating the sulfate-reducing bacteria and organic matter degrading bacteria, they would be produced into bio materials, and added to the underground for in-situ remediation of groundwater pollution.

The contradiction between coal and water has become the main factor restricting the safe, efficient and green mining of coal in Yushenfu Mining Area. In order to alleviate the contradiction and effectively protect water resources and ecological environment, a typical coal mine in Yushenfu Mining Area is taken as an example. This research reveals the characteristics of coal water occurrence, establishes the water loss model of mining-influenced aquifer, and preliminarily explores the overall strategy and technology of water resources protection. The study indicates that there are two types of water resources in the Yushenfu Mining Area: surface water and groundwater. The surface water exists in the form of lakes, surface runoff and springs, while groundwater includes the Sa’la Wusu Formation confined water, metamorphic rock water, and weathered bedrock water. Based on the relationship between aquifers and water-conducting fracture zones, two types of aquifers are identified: low-level aquifer and high-level aquifer. The water loss model for low-level aquifers is characterized by leakage through connecting pathways. For high-level aquifers, there are two water loss models: non-conductive vertical seepage and seepage overflow evaporation. The former occurs in high-pressure confined aquifers, while the latter is mainly for high-level phreatic aquifers. For low-level aquifers, protection involves the development of height-controlled technology in water-conducting fracture zones and post-mining roof grouting reinforcement technology. For high-level aquifers, protection measures include the construction of artificial water barriers, separation grouting, and coordinated mining technology. In cases where water cannot be protected in situ and flows into mined-out areas, comprehensive water utilization technologies such as underground water storage, purification, recycling, and deep injection can be employed to indirectly achieve water resource protection in the mining area.

With the improvement of mine water discharge standards, the demand for technological innovation in mine water treatment and resource utilization has been further enhanced. Reducing the discharge of mine water, especially high salt mine water, and improving the availability of mine water are important guarantees for improving coal production safety, accelerating green mine construction, and promoting sustainable development of coal enterprises. Focused on the problems of high water inflow, high salinity and high cost of treatment and utilization during deep mining of Zhangshuanglou Coalmine, a treatment technology system of mine water emission reduction in high salt mine with “reduction, storage and purification” as the core was put forward: Blocking the water inflow points through the floor water inflow blocking reduction technology to reduce the discharge of high salt mine water from the source; Through the deep reinjection technology of mine water, some mine water will be transferred and stored in depth to realize the “zero discharge” and water conservation of mine water; Through the technology of coal and rock self-purification in goaf, the high-salt mine water is carried out by regulation and storage; Through surface deep desalting treatment technology, high salt mine water purification treatment, resource utilization or standard discharge can be realized. Further, combined with the hydrogeological background of the mine, the law of mine water gushing and the status quo of mine water treatment and utilization, the feasibility of the application of the above technology in the mine was comprehensively analyzed and evaluated: Through the implementation of floor water gushing plugging reduction technology, the reduction treatment of 188 m³/h floor four ash gushing water was realized; Through deep reinjection technology, 200 m³/h recharge storage and water conservation restoration of Ordovician limestone aquifer can be realized in the west wing mining area;  About 1.65 million m³ of mine water can be stored in the east wing mining area through self-cleaning pretreatment of coal and rock in goaf and regulation storage technology, and the underground pretreatment of characteristic components can be carried out; Through the surface deep desalination treatment technology, the mine water treatment capacity reaches 700 m³/h, and the annual salt discharge can be reduced by 14 271.5 t. Finally, the comprehensive technical idea of water emission reduction treatment of high salt mine in Zhangshuanglou Coalmine is put forward. The proposal of the water emission reduction treatment technology system of the high-salt mine in Zhangshuanglou Coalmine can provide a theoretical basis and technical reference for the water reduction treatment and resource utilization of high-salt mine in Zhangshuanglou Coalmine and other similar deep mining coal mines.

Mining tremors is an inevitable dynamic phenomenon in deep mine mining, in view of the current situation that strong mining tremors occurs frequently in the Erdos mining area under mining near goaf in deep mine with extremely thick strata, we used techniques such as ground detection holes and surface stratum movement monitoring, combined with Reissner Thick Plate Theory and the relative moment tensor inversion method, to study the characteristics of strata rupture transport and the evolution of rupture-induced mining tremors source rupture pattern at the working face, and revealed the occurrence mechanism of strong mine tremor in deep coal with the Cretaceous extremely thick strata under goaf mining. The results show that: during the in the retreating period with no goaf nearby, extremely thick strata has no obvious fissures and the surface settlement is stable, with a maximum settlement of about 0.23 m; during the In the retreating period along with goaf, the fissures develop to a maximum height of 444.8 m above the coal seam in the extremely thick strata, and the surface always reaches the maximum settlement at the source of the mining tremor first, and the maximum settlement of the surface increases rapidly before the strong mining tremor occurs, which is more than 60% higher than the recent one. This indicates that the fracturing and movement of the extremely thick strata was the source of the strong mining tremor and that the instability of the extremely thick strata caused the surface to settle rapidly again as a result of the disturbance of the strong mining tremor. The initial fracturing step of the extremely thick strata is 331.82 m, which is consistent with the actual advance of the working face, and supports that the strong mining tremor was induced by the initial fracture of the extremely thick strata; the initial fracturing step increases gradually with the increase of the thickness of the extremely thick strata; the initial fracturing step increases linearly with the increase of the working face length, and the initial fracture of the extremely thick strata transforms from horizontal “O-X” shape to vertical “O-X” shape. The bottom-up rupture of the rock layer induced by the bottom-up rupture of the mining tremors source changed from compressional and shear rupture to compressional and tensional rupture; with the further increase of the mining area of the working face, the fissure extended to the extremely thick strata, and the tensional rupture of the unstable extremely thick strata was the root cause of the “8•20” strong mining tremor. The findings of the study can provide references for the prevention and control of strong mining tremors under mining near goaf in deep mine with extremely thick strata.

The paper aims to determine the reasonable layout and stability control scheme of the mining roadway under the influence of remnant coal pillars in the multi-slice longwall mining of the extra thick coal seam in Laogong Yingzi Coal Mine. Combining field monitoring, theoretical analysis and numerical simulation, the stress distribution characteristics of the remnant coal pillar and the coal in the lower slice are studied to compare and analyze the stress states of the surrounding rock of roadways at different locations, the roadway layout across the remnant coal pillar is proposed, and a mechanical model of the floor slip line field is established. The model takes the width of the stress increasing area as the width of the bar-shaped foundation, the roadway layout scheme of 4 m horizontal distance from the remnant coal pillar iss determined. Combining with the roadway layout characteristics, the active and passive combined support scheme of “I-beam steel sets + cable bolts + shotcrete + shallow hole low-pressure grouting” is proposed. The results show that there is a double peak stress concentration both within the remnant coal pillar and the lower coal slice after mining on both sides of the upper slice. Inside the coal pillar is the vertical stress concentration zone, and at the edge of the coal pillar is the shear stress concentration zone.  External spaced overlapped roadway is influenced both by vertical and shear stresses. The stress concentration of external spaced overlapped roadway is the highest followed by vertical overlapped roadway and increases with the increase of the outer staggered distance. The influence of the shear stress is more obvious for vertical overlapped roadway. The influence of the vertical stress and shear stress on the roadway layout across the remnant coal pillar is significantly reduced, and the peak value of the vertical stress stabilizes at 34.1 MPa. The peak shear stress stabilizes at 6.7 MPa, and the stress concentration is the lowest and decreases with the increase of the interval of the two roadways. Field application results show that the deformation of roadway surrounding rock across the remnant coal pillar is small, and there is no intensive pressure observed, which meets the requirements of safety production.

The technology of roof cutting by dense drilling is mainly through the transformation of the surrounding rock structure of the lateral roof of the stope, and the use of overburden load and roof weight to cut off the basic roof can effectively reduce the roof pressure of the roadway. This paper analyzes the key parameters of drilling and the effect of retaining roadway by analyzing the roof cutting and pressure relief by dense drilling technology along the empty roadway in some mines in China, and studies the main influencing factors of the key parameters of roof cutting by dense drilling. The results show that the technology of roof cutting by dense drilling is suitable for coal seams with different thicknesses, and the effect of roof cutting depends on whether the cutting height, cutting angle, drilling diameter and spacing are reasonable. Because the roof is not completely broken before recovery when the roof is cut by dense drilling, after recovery, the greater the thickness of the coal seam, the greater the tensile stress generated by the roof subsidence and rotation around the drilling, the more easily the roof with the dense drilling is to break, and the increase of coal thickness is conducive to the independent breaking of the roof. The roof cutting height of dense drilling increases with the increase of coal thickness and main roof thickness. With the increase of coal thickness, the influence of drilling angle on roof cutting gradually decreases, and the drilling angle shows a decreasing trend. The combined effect of dense drilling aperture and spacing affects the fracture effect of roof with dense drilling. The D / B value (the ratio of drilling spacing to drilling diameter) increases with the increase of coal thickness within a certain range, and decreases with the increase of main roof strength. According to the statistical results, the engineering analogy method is adopted, and combined with the research results of the main influencing factors of roof cutting by dense drilling, the method for determining the key parameters of roof cutting by dense drilling is put forward. The test of roof cutting by dense drilling and retaining roadway is carried out in the return laneway of 11210 working face in Zhaojiazhai Mine. The effect of roadway retaining is good, which proves that the method is practical and effective, and has certain engineering reference value.

Aiming at the special characteristics of underground coal mine operation environment and the deficiency of existing support technology, heap spraying technology was proposed, technological parameters were determined, heap spraying admixture (S2) was developed, the mechanism of S2 was revealed, and a complete set of heap spraying construction technology was formed and applied to gob-side entry retaining. The results show that: ① Heap spraying technology can be used to construct the supporting structure according to need, which is not restricted by operating space and the operator is far away from the danger zone, so that the surrounding rock can be controlled safely and efficiently. ② Heap spraying material tide mixing and conveying pipeline segmentation with water process, wetting materials in advance, can promote material hydration, enhance adhesion and workability, reduce dust and rebound rate. ③ The accelerating components of S2 include NaAlO₂, Al₂(SO₄)₃, NaF, Al(OH)₃ and fast-hardening sulfoaluminate cement (SAC-42.5), and the viscosifying and anti-cracking components are silica fume (GS), polymer propylene fiber (JB), S2 improves the compressive strength of the supportintg structure material and has micro-expansion properties. ④ Uniaxial compressive strength of the standard specimens molded by heap spraying is 12.0 MPa at 1 d, 18.0 MPa at 3 d, 27.5 MPa at 7 d, 42.1 MPa at 28 d and 42.3 MPa at 90 d, with high strength supporting capacity, and late strength does not shrink, the strength growth process is divided into three stages: the initial rapid growth stage (age 0−14 d), the medium sustained growth stage (age 14−28 d), and the later stable stage (age>28 d). ⑤Heap spraying technology can build the isolation wall along roadway to realize gob-side entry retaining, having a positive effect on expanding the construction method of supporting structure.

Protective layer mining is the most effective technical means to prevent and control coal mine gas disaster, which is applicable to multiple coal seams (groups) with protected seams available for mining. With the influence of multiple factors such as increasing mining depth, mining intensity and more complex tectonics, the stress and gas coupling type of disaster for a single strong protrusion coal seam without protective layer has become the dominant. In order to eliminate the risk of coal and gas protrusion, the current measures such as mechanical reaming, hydraulic punching, water jet cutting and hydraulic fracturing can better improve the extraction effect, but fail to achieve uniform pressure relief, uniform penetration and eliminate stress anomalies, there are certain limitations to the elimination of protrusion. How to achieve efficient gas extraction and high-efficiency outburst elimination is the main technical bottleneck that has long curbed the safe and efficient mining of this type of coal seam. The study combined the engineering practice of “zero-distance protective layer” stratified mining and unloading pressure and increasing penetration of penetrating boreholes to enhance the extraction and eliminate outburst in prominence mine belonging to Henan Energy Group. The effect of pressure-releasing enhancement and outburst elimination was investigated by optimizing the design of penetrating boreholes, reasonably selecting the pressure releasing measures and accurately metering the amount of coal hollowed out. The effect of pressure releasing to eliminate outburst was strengthened, the uniform pressure releasing in a large area was realized, and a way of eliminating outburst by constructing a similar protective layer in the coal seam was formed. The “construction of inner protective layer technology” was proposed to achieve strong and uniform pressure relief, efficient extraction and rapid outburst elimination in coal seam. Summarizing the development history and experience of gas management technology in protruding mines represented by Henan Energy Coking Coal Company, the research on the “construction of inner protective layer technology” for single thick coal seam was carried out, the scientific connotation of “constructing inner protective layer” to eliminate outburst was explained, the mechanism of eliminating outburst was revealed, and the constructing method was formed. The effect evaluation technology of inner protective layer to eliminate outburst was developed, a technology system for eliminating outburst in the inner protective layer of a single coal seam with strongly outburst was constructed, and the related enterprise standard was formulated. The proposed concept of actively constructing the inner protective layer to eliminate outburst in a single coal seam with strongly outburst has innovated the connotation and extension of protective layer mining, and provided a more complete technical system and a more solid theoretical basis and technical means for the efficient outburst elimination in a single coal seam with strongly outburst.

In order to prevent coal mine gas accidents and realize efficient and accurate gas extraction, spraying gas sustained-release agent in local high concentration gas area has become one of the important means to prevent and control gas overlimit. The self-developed multi-factor influencing coal gas desorption and spraying experiment platform, built based on the similarity ratio model of coal mine driving working face, was used to study the law of different factors affecting the peak concentration distribution of desorbed gas under spraying gas sustained-release agent. The effects of APG solution mass fraction, atomizing pressure, coal sample particle size, equilibrium pressure, ambient temperature, wind speed and other factors on the peak concentration distribution of desorbed gas were analyzed. The Pearson correlation coefficient method was used to obtain the correlation between the factors and the peak gas concentration in different areas after spraying gas sustained-release agent. The results shown that, the peak gas concentration declined rapidly with increasing mass fraction for APG solution mass fraction less than 0.10%, and the decline rate decreased when it exceeded 0.10%. Under the effect of sustained-release agent, the peak gas concentration shown negative linear and negative exponential relationship with atomization pressure and coal sample particle size, respectively. The peak gas concentration decreased with the increase of atomization pressure and coal sample particle size, and the maximum gas reduction rate was observed when the coal sample particle size was 5-10 mm. The peak gas concentration shown linear and exponential relationship with equilibrium pressure and ambient temperature, respectively. The peak gas concentration increased with the increase of equilibrium pressure and ambient temperature, and the growth rate of peak gas concentration was the highest when the ambient temperature was 35 °C. The peak gas concentration at the center and corners of the working face model decreased with increasing wind speed, and the reduction rate of peak gas concentration decreased when the wind speed exceeded 12.7×10⁻³ m³/s. The peak gas concentration was reduced by 4.3%-8.0% with multiple factors compared to a single factor. Using the correlation coefficient method, the maximum factors affecting the peak gas concentration at the upper and lower corners of the inlet, upper and lower corners of the outlet, and the center of the model were obtained as atomization pressure, atomization pressure, equilibrium pressure, ambient temperature and equilibrium pressure, respectively.

In order to solve the technical bottleneck problem of downward directional drilling coal cuttings blockage and gas drainage with concentration but no flow, the nitrogen foam power law multiphase flow slag carrying and unblocking technology of downward directional drilling was proposed. Theoretical analysis, numerical simulation, om-site industrial experiments and other methods were used to research the causes of coal cuttings blockage caused by downward directional drilling gas drainage in coal mines, and the theory and practical application of nitrogen foam power law multiphase flow slag carrying in downward directional drilling annular. Numerical simulation was carried out by a turbulence model containing wall function coupled with gas flow and coal deformation, and the elastic displacement of the borehole wall caused by the fluid pressure after drilling extraction was analyzed. Numerical simulation with a three-dimensional Coulomb failure criterion model solved for the pressure changes caused by extraction, as well as the stress, strain, and displacement changes induced by the pressure changes, and the collapsing risk of downward directional drilling. The stability of nitrogen foam, the fluidity of foam in drill pipe, at the drill bit, in the annulus, the suspension performance of coal powder in foam, the pressure loss of foam slagging in the annulus, and the upward slagging stress on the foam were analyzed by the power law multiphase flow theory. Based on the theoretical analysis of downward directional drilling annulus nitrogen foam power law multiphase flow slag carrying theory, the stable nitrogen foam generator, foam generating injecting system, downward directional drilling nitrogen foam drilling process, and gas drainage drilling nitrogen foam secondary unblocking process were designed, and the downward directional drilling nitrogen foam slag removal on-site industrial experiment was conducted. The results indicated that, the frictional drag force of the borehole wall and the centrifugal force at the bends could cause the aggregation of coal particles and increase the risk of borehole wall collapse. The coal powder particles carried by the gas will collide with the borehole wall to deform or detach the borehole wall, which would lead to the collapse and blockage of the extraction borehole. The theoretical system of downward directional drilling annulus nitrogen foam power law multiphase flow slag carrying and unblocking technology, which included nitrogen foam stability, fluidity, coal powder suspension performance, annular space foam pressure loss, and analysis of slag removal force, can well provide theoretical support for downward directional drilling nitrogen foam slag removal. In the on-site industrial experiments, the initial mixing and pure amount of the nitrogen foam slag removal drilling hole increased by 6.5 and 6.4 times, respectively, compared with the water drainage drilling hole, and the mixing and pure amount increased by about 10 times in 40 days, which indicated that the nitrogen foam slag carrying and unblocking technology can significantly improve the gas drainage efficiency of the downward directional drilling hole.