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19 pages, 5802 KiB

Open AccessArticle

Advancing PetroChina’s Development Strategies for Low-Permeability Oil Reservoirs

by Jun Cao, Mingqiang Hao, Yujia Chen, Baozhu Li, Zhuo Liu, Yang Liu and Jinze Xu

Processes 2024, 12(2), 351; https://doi.org/10.3390/pr12020351 - 7 Feb 2024

Cited by 1 | Viewed by 1403

Abstract

Based on PetroChina’s status and situation of low-permeability oil reservoir development, this paper analyzes the key common issues in the production capacity construction of new oilfields, the stable production of old oilfields, and enhanced oil recovery, and, in connection with the progress made [...] Read more.

Based on PetroChina’s status and situation of low-permeability oil reservoir development, this paper analyzes the key common issues in the production capacity construction of new oilfields, the stable production of old oilfields, and enhanced oil recovery, and, in connection with the progress made in major development technologies and the results of major development tests for low-permeability oil reservoirs in recent years, puts forward the technical countermeasures and development directions. For optimizing the development of low-grade reserves, a comprehensive life-cycle development plan is essential, alongside experimenting with gas injection and energy supplementation in new fields. Addressing challenges in reservoir classification, multidisciplinary sweet spot prediction, and displacement–imbibition processes can significantly boost well productivity. In fine water flooding reservoirs, the focus should shift to resolving key technological challenges like dynamic heterogeneity characterization, and functional and nano-intelligent water flooding. For EOR, accelerating the application of carbon capture, utilization, and storage (CCUS) advancements, along with air injection thermal miscible flooding, and middle-phase microemulsion flooding, is crucial. This approach aims to substantially enhance recovery and establish a new model of integrated secondary and tertiary recovery methods. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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19 pages, 10297 KiB

Open AccessArticle

Mechanism of and Prevention Technology for Water Inrush from Coal Seam Floor under Complex Structural Conditions—A Case Study of the Chensilou Mine

by Qi Wang, Shitian Zheng, Zhiyuan Shi, Pei Wu, Huayong Lv and Gang Wang

Processes 2023, 11(12), 3319; https://doi.org/10.3390/pr11123319 - 29 Nov 2023

Cited by 1 | Viewed by 1042

Abstract

Based on the complex hydrogeological conditions of the Chensilou mine, numerical simulations and field validation methods were used to study the mechanism of water inrush from the floor of the coal seam, which has faults and cracks, as well as the regional advanced [...] Read more.

Based on the complex hydrogeological conditions of the Chensilou mine, numerical simulations and field validation methods were used to study the mechanism of water inrush from the floor of the coal seam, which has faults and cracks, as well as the regional advanced grouting reinforcement technology during the coal mining process. The evolution laws of the roof stress field, displacement field, crack field, and plastic area are revealed at different mining distances. The coupling mechanism of floor water inrush channel formation under complex conditions is analyzed. Advanced grout filling reinforcement technology in the ground area is proposed, the slurry diffusion law of different grouting layers under different grouting pressures is revealed, and the grouting effect is evaluated, which provides a research basis for selecting a reasonable grouting pressure. Finally, the application of regional advanced grouting reinforcement technology was carried out at the site, and the grouting reconstruction effect was verified by the transient electromagnetic and three-dimensional DC resistivity method. The results show that the apparent resistivity of the floor after the grouting reinforcement is high, and the water yield of the verification borehole is less than 10 m³/h. The area where the three-dimensional direct current resistivity is less than 12 Ω·m only appears in the lower part of the middle of the working face, and there is no water in the verification borehole. Through our underground supplementary treatment and verification process, the initial water inflow meets the requirements of being less than 10 m³/h. It indicates that the ground regional advanced treatment project achieved significant results. The results of our research can also provide references for water hazard control in similar mines. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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24 pages, 22303 KiB

Open AccessArticle

Surrounding Rock Deformation Mechanism and Control Technology for the Roadway in the Fault-Disturbed Zone under Special-Shaped Coal Pillars

by Chao Liu, Fangtian Wang, Zhenyu Zhang, Dongxu Zhu, Wenhua Hao, Tiankuo Tang, Xutong Zhang and Chenguang Zhu

Processes 2023, 11(12), 3264; https://doi.org/10.3390/pr11123264 - 22 Nov 2023

Cited by 2 | Viewed by 999

Abstract

In order to explore the impact of residual special-shaped coal pillars and fault disturbances on the lower layered roadway, this study takes the short-distance coal seam mining in Luwa Coal Mine as the engineering background to explore the surrounding rock deformation mechanism along [...] Read more.

In order to explore the impact of residual special-shaped coal pillars and fault disturbances on the lower layered roadway, this study takes the short-distance coal seam mining in Luwa Coal Mine as the engineering background to explore the surrounding rock deformation mechanism along the mining roadway in the fault-disturbed zone under special-shaped coal pillars, it presents the roadway surrounding rock control technology and it conducts on-site industrial test verification. The study shows that the abutment pressures on the floor of special-shaped coal pillars are distributed as “three peaks and two ridges”. The part beneath coal pillars is mainly disturbed by vertical stresses, while the part below the coal pillar edge is co-affected by vertical stresses and shearing stresses, generating a stress concentration coefficient ranging from 1.26 to 1.38 in the lower coal seam. According to the superposed effects of special-shaped coal pillars and fault disturbance on the mining roadway, the mining roadway is divided into the lower section of goaf, the section crossing the coal pillar edge, the lower section of coal pillars, and the section obliquely crossing the coal pillar edge. According to the above sections, the segmental control strategies of “improving stress distribution on surrounding rock + reinforcing support on special sections” are proposed. A joint control technology of large-diameter drilling hole pressure relief and special section anchor cable reinforcement support was adopted to carry out on-site industrial testing and monitoring. Overall, the convergence rate on the roadway surrounding rock is controlled within 5%, and the deformation of roadway surrounding rock is under effective control. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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14 pages, 4279 KiB

Open AccessArticle

True Triaxial Test and Research into Bolting Support Compensation Stresses for Coal Roadways at Different Depths

by Jianwei Yang, Jian Lin and Pengfei Jiang

Processes 2023, 11(11), 3071; https://doi.org/10.3390/pr11113071 - 26 Oct 2023

Cited by 1 | Viewed by 880

Abstract

During the excavation and support construction process used in coal mine roadways, the stress path is the unloading of in situ stress and the compensation of support stress. The 150 mm × 150 mm × 150 mm coal mass samples were obtained in [...] Read more.

During the excavation and support construction process used in coal mine roadways, the stress path is the unloading of in situ stress and the compensation of support stress. The 150 mm × 150 mm × 150 mm coal mass samples were obtained in situ underground and prepared, the true triaxial loading–unloading–confining pressure restoring test method was used, and the mechanical response and deformation failure evolution characteristics of the coal seam during the excavation and support process of the shallow, medium depth, and deep coal roadways in the coal mine were simulated and studied. Based on the distribution law of the bolt and cable support stress field, the support compensation stress required for the stability of the surrounding rock after the excavation of the coal roadway with different burial depths was determined, and the corresponding roadways’ surrounding rock control technologies were proposed. This study’s results indicate that the compensation stress required for support in shallow coal roadways (with a burial depth of about 200 m) was much less than 0.1 MPa. A single rock bolt support can keep the surrounding rock of the roadway stable; the compensation stress required for support in the medium buried coal roadway (with a depth of about 600 m) is around 0.1 MPa, and the combined support of rock bolts and cables can meet the support requirements. Deep coal roadways under high stress (with a depth of about 1000 m) require support to provide compensation stress. Even if the compensation stress reaches 0.2 MPa, the surrounding rock of the roadway will experience varying degrees of creep. In this study, it was necessary to increase the support density and surface area of rock bolts and cables, the pre-tension forces of rock bolts and cables were improved, and in synergy with grouting modification, destressing and other technologies could control the large deformation of the surrounding rock of the roadway in 1000 m deep coal mines. This study’s results provide a theoretical basis for the selection of control technologies for use in coal roadways at different depths. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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21 pages, 5716 KiB

Open AccessArticle

Effects of Layering Angle and Prestress on Dynamic Load Energy Conversion and Damage Mechanism of Sandstone

by Wenbing Fan, Junwen Zhang, Yang Yang, Kailun Fang, Shaokang Wu and Yulong Xing

Processes 2023, 11(9), 2641; https://doi.org/10.3390/pr11092641 - 4 Sep 2023

Cited by 1 | Viewed by 1135

Abstract

Previously conducted studies have established the conversion relationship between incident energy, reflected energy, transmitted energy and absorbed energy of rocks under dynamic load. In this paper, the combined dynamic and static loading tests of sandstone under different prestress and different bedding angles are [...] Read more.

Previously conducted studies have established the conversion relationship between incident energy, reflected energy, transmitted energy and absorbed energy of rocks under dynamic load. In this paper, the combined dynamic and static loading tests of sandstone under different prestress and different bedding angles are carried out to explore the law of the influence of prestress and bedding angles on energy evolution and damage evolution. The purpose is to provide some reference for deep mining, rock engineering design and geological hazard assessment. The energy conversion and damage characteristics of sandstone in the whole process of deformation are studied, and the internal energy conversion mechanism of sandstone under dynamic load is proposed. It is found that the increase in prestress will lead to the increase in the initial energy value of sandstone and further affect the shape of the energy evolution curve. In addition, the relationship between strain and energy transformation is established, and it is found that the energy transformation in different stages is different. At the same time, the relationship between prestress and damage characteristics and bedding angle and damage characteristics is established, and it is found that bedding angle and prestress significantly affect the damage characteristics. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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17 pages, 20658 KiB

Open AccessArticle

Evaluating Fractal Damage and Acoustic Emissions of Soft Rock–Coal Combinations in a Deep Mining Area

by Bin Liang, Dong Wang, Yujing Jiang, Xiaoming Sun, Hengjie Luan, Changsheng Wang, Ling Dong and Lugen Chen

Processes 2023, 11(9), 2599; https://doi.org/10.3390/pr11092599 - 30 Aug 2023

Cited by 3 | Viewed by 1051

Abstract

Weakly cemented soft rock mines in the Ordos Basin are susceptible to mining disasters, including roof collapse and substantial deformation of surrounding rocks, during coal mining operations. Researching the damage characteristics of structures composed of low-strength “soft rock–coal” combinations is crucial for effectively [...] Read more.

Weakly cemented soft rock mines in the Ordos Basin are susceptible to mining disasters, including roof collapse and substantial deformation of surrounding rocks, during coal mining operations. Researching the damage characteristics of structures composed of low-strength “soft rock–coal” combinations is crucial for effectively preventing and controlling disasters in deep soft rock mining. To investigate the fractal damage characteristics of soft rock–coal combinations with different height ratios, uniaxial compression tests were conducted on specimens containing soft rock percentages of 20%, 40%, 50%, 60%, and 80%. The results show that the uniaxial compressive strength and modulus of elasticity of the soft rock–coal combinations increased with increasing proportions of soft rock. The soft rock–coal combination was clearly segmented, and the 40%, 50%, and 60% soft rock–coal combinations had good self-similarity. The fractal dimensions were 2.374, 2.508 and 2.586, which are all within the interval [2, 3]. When the percentage of soft rock was 20%, the specimen damage yielded flaky coal bodies with smaller grain size, whereas the coal–rock interface was spalled by small conical rock bodies. As the soft rock proportion increased, the percentage mass of fragments with particle size greater than 20 mm increased from 83.34% to 94.15%. The failure mode in soft rock–coal combinations is primarily attributed to the partial tensile splitting of the coal body. As the proportion of soft rock increased, there was a gradual reduction in the extent of coal body damage. Moreover, the acoustic emission absolute energies and counts decreased as the proportion of soft rock increased. The acoustic emission energy was reduced from 2.46 × 10⁹ attoJ to 3.41 × 10⁸ attoJ, and the acoustic emission counts were reduced from 18,276 to 7852. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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18 pages, 8778 KiB

Open AccessArticle

Investigating the Mechanism of Continuous–Discrete Coupled Destabilization of Roadway-Surrounding Rocks in Weakly Cemented Strata under Varying Levels of Moisture Content

by Lihui Sun, Zhixin Jiang, Yaxin Long, Qingfeng He and Haiyang Zhang

Processes 2023, 11(9), 2556; https://doi.org/10.3390/pr11092556 - 26 Aug 2023

Cited by 2 | Viewed by 1007

Abstract

This study examines frequent disasters, including large-scale deformation and collapse, caused by underground mining in weakly cemented strata in Western China. The weakly cemented rock’s unique characteristics, including low strength and easy disintegration, demonstrate a different damage pattern than that traditionally seen in [...] Read more.

This study examines frequent disasters, including large-scale deformation and collapse, caused by underground mining in weakly cemented strata in Western China. The weakly cemented rock’s unique characteristics, including low strength and easy disintegration, demonstrate a different damage pattern than that traditionally seen in the central and eastern regions. Using Fast Lagrangian Analysis of Continua-Particle Flow Code (FLAC2D-PFC2D) coupling, we model the strata, focusing on the 3-1 coal seam roadway at Hongqinghe mine. This study investigates the damage–rupture–destabilization progression in the peripheral rock under varying levels of moisture content. Our findings indicate that a water content of ω = 5.5% is the threshold for roadway damage, and moisture content <5.5% yields minimal rock deformation. However, moisture content >5.5% abruptly increases cracks and shifts the rock’s force chain, causing significant deformation and affecting the ceiling the most. Moreover, higher levels of moisture content weaken the anchor solid’s performance, with two primary failure modes: anchor interface slippage (comprising five stages: elasticity, elasticity–shear hardening, elasticity–shear hardening–decohesion, shear hardening–decohesion, and decohesion) and shear damage. These insights are vital for improving numerical simulations of underground mining, obtaining a more accurate understanding of mineral pressure disasters in weakly cemented strata mining regions in Western China, and developing a solid foundation for the better control of such strata. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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23 pages, 13357 KiB

Open AccessArticle

Large Eddy Simulation of Cavitation Jets from an Organ-Pipe Nozzle: The Influence of Cavitation on the Vortex Coherent Structure

by Zhenlong Fang, Wenjiang Hou, Zhifan Xu, Xiaofeng Guo, Zenglei Zhang, Ruichao Shi, Yunan Yao and Yong Chen

Processes 2023, 11(8), 2460; https://doi.org/10.3390/pr11082460 - 16 Aug 2023

Cited by 7 | Viewed by 1406

Abstract

High-speed water jets are widely used in deep mining and the in-depth study of jet characteristics helps to improve drilling efficiency. Three-dimensional Large Eddy Simulation is used to simulate turbulent flows generated by an organ-pipe nozzle. The simulation is validated with existing experimental [...] Read more.

High-speed water jets are widely used in deep mining and the in-depth study of jet characteristics helps to improve drilling efficiency. Three-dimensional Large Eddy Simulation is used to simulate turbulent flows generated by an organ-pipe nozzle. The simulation is validated with existing experimental data and is focused on the evolution and interaction of cavitation bubbles and vortices. Dynamic mode decomposition is performed to extract structural information about the different motion modes and their stability. Results show that the dominant fluid frequency is positively correlated with inlet pressure while unrelated to the divergence angle. Meanwhile, jets’ oscillation is amplified by a large divergence angle, which facilitates the occurrence of cavitation. Results about the flow field outside of an organ-pipe nozzle advance the understanding of the basic mechanism of cavitation jets. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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21 pages, 16283 KiB

Open AccessArticle

Coal Pillar Size Determination and Surrounding Rock Control for Gob-Side Entry Driving in Deep Soft Coal Seams

by Zaisheng Jiang, Wenke Guo and Shengrong Xie

Processes 2023, 11(8), 2331; https://doi.org/10.3390/pr11082331 - 3 Aug 2023

Cited by 5 | Viewed by 1052

Abstract

In response to the large-scale instability failure problem of designing coal pillars and support systems for gob-side entry driving (GSED) in high-stress soft coal seams in deep mines, the main difficulties in the surrounding rock control of GSED were analyzed. The relationship between [...] Read more.

In response to the large-scale instability failure problem of designing coal pillars and support systems for gob-side entry driving (GSED) in high-stress soft coal seams in deep mines, the main difficulties in the surrounding rock control of GSED were analyzed. The relationship between the position of the main roof breaking line, together with the width of the limit equilibrium zone and a reasonable size for the coal pillar, were quantified through theoretical calculations. The theoretical calculations showed that the maximum and minimum widths of the coal pillar are 8.40 m and 5.47 m, respectively. A numerical simulation was used to study the distribution characteristics and evolution laws of deviatoric stress and plastic failure fields in the GSED surrounding rock under different coal pillar sizes. Theoretical analysis, numerical simulation, and engineering practice were comprehensively applied to determine a reasonable size for narrow coal pillars for GSED in deep soft coal seams, which was 6.5 m. Based on the 6.5 m coal pillar size, the distribution of deviatoric stress and plastic zones in the surrounding rock of the roadway, at different positions of the advanced panel during mining, was simulated, and the range of roadway strengthening supports for the advanced panel was determined as 25 m. The plasticization degree of the roof, entity coal and coal pillar, and the boundary line position of the peak deviatoric stress zone after the stability of the excavation were obtained. Drilling crack detection was conducted on the surrounding rock of the GSED roof and rib, and the development range and degree of the crack were obtained. The key areas for GSED surrounding rock control were clarified. Joint control technology for surrounding rock is proposed, which includes a combination of a roof channel steel anchor beam mesh, a rib asymmetric channel steel truss anchor cable beam mesh, a grouting modification in local fractured areas and an advanced strengthening support with a single hydraulic support. The engineering practice showed that the selected 6.5 m size for narrow coal pillars and high-strength combined reinforcement technology can effectively control large deformations of the GSED surrounding rock. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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23 pages, 8971 KiB

Open AccessArticle

Study on Mechanical Behavior and Mechanism of Sandstone under the Coupling Effect of Water Content and Dynamic Load

by Yang Chen, Ting Kang and Chao Wu

Processes 2023, 11(8), 2318; https://doi.org/10.3390/pr11082318 - 2 Aug 2023

Cited by 3 | Viewed by 915

Abstract

In the process of underground engineering construction, rock mass often faces the dual influence of dynamic load disturbance and groundwater, it is therefore essential to investigate the mechanical response of the rock mass under the coupling effect of dynamic load disturbance and water [...] Read more.

In the process of underground engineering construction, rock mass often faces the dual influence of dynamic load disturbance and groundwater, it is therefore essential to investigate the mechanical response of the rock mass under the coupling effect of dynamic load disturbance and water content. In this paper, dynamic load impact tests were carried out on sandstone with bullet velocities of 5 m/s, 10 m/s, and 15 m/s and water content of 0, 0.3, 0.6, and 0.9, and the mechanical behavior and mechanism response of water content to sandstone were investigated. The research findings indicate that this study has made significant contributions in quantifying the along grain and trans-grain fractures of microcracks. It has explored the influence of water content and dynamic loading on the strength mechanism of sandstone. It was discovered that the dynamic loading and water content significantly affect the ratio of along grain and trans-grain fractures, thereby influencing the dynamic behavior of sandstone. The findings suggest a negative association between rock strength and water content and that its peak strength rises as the bullet velocity rises. The fracture characteristics of rock are influenced by water content and bullet velocity. The sample’s fracture degree increases with an increase in water content, its particle size distribution map is evident, and there is a positive relation between bullet velocity and fractal dimension. The energy conversion mechanism of the rock is influenced by the water content, as the bullet velocity increases, the absorbed energy density of the rock becomes higher. Furthermore, the correlation between the absorbed energy intensity and density and its fractal dimension is quantified. It is found that energy density and strength are positively correlated. The greater the fractal dimension, the higher the energy density absorbed. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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26 pages, 14184 KiB

Open AccessArticle

Energy Dissipation and Fracture Mechanism of Layered Sandstones under Coupled Hydro-Mechanical Unloading

by Zhixiang Song, Junwen Zhang and Shaokang Wu

Processes 2023, 11(7), 2041; https://doi.org/10.3390/pr11072041 - 7 Jul 2023

Cited by 4 | Viewed by 1071

Abstract

Rock burst is easy to occur in the water-rich roadway of coal mines, which is closely related to the energy dissipation and fracture mechanism of rocks under coupled hydro-mechanical (H-M) unloading. Therefore, in combination with the triaxial loading and unloading process and H-M [...] Read more.

Rock burst is easy to occur in the water-rich roadway of coal mines, which is closely related to the energy dissipation and fracture mechanism of rocks under coupled hydro-mechanical (H-M) unloading. Therefore, in combination with the triaxial loading and unloading process and H-M coupling effect, the mechanical test of layered sandstones under coupled hydro-mechanical unloading (TLUTP) was conducted. The energy dissipation and fracture mechanism were revealed. The results show that: (1) The influence of layered angles on the peak volumetric strain is more sensitive than that of confining pressure under conventional triaxial loading with H-M coupling (CTLTP). On the contrary, the influence of confining pressure on the peak volumetric strain is more sensitive than that of layered angles under TLUTP. (2) With increasing layered angles, the peak elastic energy density under CTLTP shows the “W” shaped evolution characteristic, while that of under TLUTP shows the “N” shaped evolution characteristic. (3) The “Energy Flow” chain is proposed. Meanwhile, combined with the domino effect and the structural evolution theory, the energy dissipation and fracture mechanism of layered sandstones under coupled hydro-mechanical unloading are both revealed. The conclusions obtained can provide certain fundamental theoretical references for the effective prevention of rock burst in a layered water-rich roadway. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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13 pages, 3229 KiB

Open AccessArticle

Reasonable Size Design and Influencing Factors Analysis of the Coal Pillar Dam of an Underground Reservoir in Daliuta Mine

by Zihan Chen, Xidong Zhao, Zhou Han, Yue Ji and Zhongjin Qiao

Processes 2023, 11(7), 2006; https://doi.org/10.3390/pr11072006 - 4 Jul 2023

Cited by 3 | Viewed by 1220

Abstract

Underground reservoir water storage technology has become one important way to achieve efficient coal mining and water resource protection in the western mining areas of China, and the width of coal pillar dams is an important factor affecting the safe operation of underground [...] Read more.

Underground reservoir water storage technology has become one important way to achieve efficient coal mining and water resource protection in the western mining areas of China, and the width of coal pillar dams is an important factor affecting the safe operation of underground reservoirs. In order to study the limitations on the reasonable size of a coal pillar dam, Daliuta Mine was selected as the engineering background and a theoretical formula for the reasonable width of a coal pillar dam was proposed. By combining theoretical analysis with numerical simulation analysis, the main influencing factors of the coal pillar dam were compared and analyzed. The research results indicated that changes in the mining height and coal parameters can cause a sharp change in the width of the plastic zone of the dam body. Then, mine water will have an impact on the width of the plastic zone and the width of the elastic core. Moreover, when the width of the coal pillar is smaller than the theoretically calculated width of the coal pillar dam body, the deviator stress and vertical stress inside the dam will significantly increase, and the plastic zone of the dam will significantly expand. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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15 pages, 11440 KiB

Open AccessArticle

Characteristics and Geological Impact Factors of Coalbed Methane Production in the Taiyuan Formation of the Gujiao Block

by Gang Wang, Yiwei Xie, Huizhen Chang, Liqiang Du, Qi Wang, Tao He and Shuaiyi Zhang

Processes 2023, 11(7), 2000; https://doi.org/10.3390/pr11072000 - 3 Jul 2023

Cited by 2 | Viewed by 1027

Abstract

The coalbed methane resources of the Gujiao Block are abundant, and the exploration degree is high. The gas production and water production of different CBM (coalbed methane) wells vary greatly. The average gas production of CBM wells in the study area is mostly [...] Read more.

The coalbed methane resources of the Gujiao Block are abundant, and the exploration degree is high. The gas production and water production of different CBM (coalbed methane) wells vary greatly. The average gas production of CBM wells in the study area is mostly less than 1000 m³/d, while the average water production is mostly less than 5 m³/d. The gas production of CBM wells near the core of the Malan syncline is relatively high. A series of large faults exist in the central and eastern parts of the study area, and CBM wells nearby produce more water but less gas. The salinity of water discharged from CBM wells ranges from 810.34 to 3115.48 mg/L, which is consistent with the trend of a gradual increase from north to south. The gas content distribution follows this same gradually increasing north to south trend. Coal thickness and buried depth have little effect on gas production, but have some effects on water production. The endogenous fracture system in the coal reservoir is extremely developed and the porosity and permeability of the reservoirs are low, which is not conducive to the migration and recovery of coalbed methane. The adsorption capacity of the coal sample is strong. However, the continuous uplift and denudation of the stratum from the middle Yanshanian to the Himalayan region are not conducive to the preservation and enrichment of coalbed methane. In addition, a series of large faults exist in this area, and the coal structures are broken. A large amount of coalbed methane is continually being released. Generally, structural and hydrological conditions affect the porosity, permeability, and gas content of coal reservoirs, thereby affecting the productivity of coalbed methane wells. The comprehensive analysis shows that the Xingjiashe well field in the southern part of the study area is a favorable area for CBM exploration and development. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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16 pages, 7304 KiB

Open AccessArticle

Study on Slurry Flow Characteristics and Diffusion Law of Superfine Cement-Based Composite Grouting Material

by Tongqiang Xiao, Zihao Yu, Fayi Liu, Xiaoliang Dai and Jianwei Sun

Processes 2023, 11(7), 1906; https://doi.org/10.3390/pr11071906 - 25 Jun 2023

Cited by 3 | Viewed by 1263

Abstract

The soft surrounding rock of deep roadways is in the state of “micro-fracture and low permeability”. In order to solve the problem of grouting reinforcement of micro-fractures surrounding rock in deep roadways, the influence characteristics of auxiliary materials and additives on slurry flow [...] Read more.

The soft surrounding rock of deep roadways is in the state of “micro-fracture and low permeability”. In order to solve the problem of grouting reinforcement of micro-fractures surrounding rock in deep roadways, the influence characteristics of auxiliary materials and additives on slurry flow were analyzed, and the composition and proportion of superfine cement-based composite grouting materials were determined: superfine cement accounted for 89.4%, superfine coal ash accounted for 5%, ultrafine mineral powder accounted for 5%, naphthalene water reducing agent accounted for 3~5‰, and lignin sulfonate calcium accounted for 1~3‰. The effects of water–cement ratio and water reducer content on slurry viscosity and water bleeding rate were tested by laboratory experiments. Based on the fracture characteristics of surrounding rock and the “Liu Jiacai Formula”, the influence law of fracture opening, grouting pressure and slurry viscosity on the slurry diffusion radius was analyzed. The results show that the slurry viscosity decreases with the increase of water–cement ratio and water reducer content, but the bleeding rate increases obviously with the increase of the two factors; when the water–cement ratio is 1.0 and the water reducer content is 3‰, the slurry has the advantages of “strong permeability, strong flow and low water bleeding rate”; the smaller the fracture opening is, the greater the required grouting pressure and the lower the required slurry viscosity. Aiming at the “micro-fracture zone” of surrounding rock in deep roadways, when the dynamic viscosity of the slurry is 2.0 mPa·s, the reasonable grouting pressure should be 12 MPa to meet the needs of grouting reinforcement engineering. The high-pressure grouting test of surrounding rock in the “micro-fracture zone” was successfully carried out by using the superfine cement-based composite grouting material. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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18 pages, 9027 KiB

Open AccessArticle

Study on the Stability of Coal Pillars in a Gob-Side Two-Entry Arrangement of Different Layers in Fully Mechanized Caving and the Zonal Linkage Control of “Heteromorphic” Surrounding Rock

by Hui Li, Sheng Gao, Dongdong Chen, Shengrong Xie, Yiyi Wu, Shaohua Feng, Zaisheng Jiang and Fangfang Guo

Processes 2023, 11(6), 1806; https://doi.org/10.3390/pr11061806 - 14 Jun 2023

Cited by 1 | Viewed by 896

Abstract

To solve the problem of considerable deformation of the tailgate in a fully mechanized caving face, the position of the main roof fracture line is first obtained by theoretical calculation, combined with the results of a similar simulation test and numerical simulation analysis. [...] Read more.

To solve the problem of considerable deformation of the tailgate in a fully mechanized caving face, the position of the main roof fracture line is first obtained by theoretical calculation, combined with the results of a similar simulation test and numerical simulation analysis. The width of the section coal pillar in the tailgate is determined to be 11.5 m. Based on the distribution characteristics of deviatoric stress and the plastic zone of surrounding rock, combined with the location characteristics and geological conditions, a new zoning control design approach is proposed, a “two pillars, three zones, and three parts” arrangement for the surrounding rock of the tailgate. The targeted two-entry support design is carried out following common engineering practices. Mine pressure monitoring data were used to verify the results of the new two-entry design. The comparison shows that the supporting technology can effectively control the considerable deformation of the surrounding rock, improving stability for regular mining production. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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26 pages, 17036 KiB

Open AccessArticle

Study on Failure Mechanism of Roadway Surrounding Rock and Hierarchical Continuous Support Technology in Unidirectional Fault Area

by Zhengzheng Xie, Fengchun Mu, Feng Guo, Nong Zhang, Yongle Li, Ruiji Chen and Qinghua Chen

Processes 2023, 11(5), 1453; https://doi.org/10.3390/pr11051453 - 11 May 2023

Cited by 1 | Viewed by 1476

Abstract

A fault is a common geological structure in coal mining. Large deformation or even instability and collapse often occur in roadways in fault areas, which restricts the safe and efficient production of mines. With the track roadway of the 5206 working face of [...] Read more.

A fault is a common geological structure in coal mining. Large deformation or even instability and collapse often occur in roadways in fault areas, which restricts the safe and efficient production of mines. With the track roadway of the 5206 working face of Xin’an Coal Mine as the engineering background, this study aims to explore the failure mechanism of surrounding rock under the influence of fault structures. Field investigation and numerical simulation were used comprehensively to analyze the failure characteristics of the surrounding rock under the influence of a unidirectional fault structure. Based on the principle of thick-layer transboundary anchorage, the hierarchical continuous support technology of transboundary anchoring in the fault structure area was proposed. The results show that the stress near the fault area is relatively concentrated, and the rock mass strength is low, which may easily cause the deformation and failure of the surrounding rock under the dynamic stress response. Using the new technology to reconstruct the bearing structure of the broken surrounding rock mass, the deformation of the surrounding rock can be effectively restrained. According to the monitoring feedback, the roadway deformation in the roof and two sides is reduced by 68.5% and 35.4%, respectively; and the maximum evolutionary depth of the roof crack is reduced to 3.5 m from 7.5 m in the original support scheme. Moreover, this study also explored the necessity of wedge anchorage for corner anchor cables and the deformation characteristics of surrounding rock at different fault dip angles. These results provide an important reference for the maintenance and control of coal roadways under the influence of unidirectional fault structures. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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14 pages, 5998 KiB

Open AccessArticle

Experimental Study on Ratio Optimization of Similar Materials for Underground Mining of Shendong Coalfield: A Case Study of Shangwan Coal Mine

by Yingming Yang, Hao Yue, Yongqiang Zhao, Shen Zhang, Jian Zhang, Zhaohui Wang and Wenqiang Yang

Processes 2023, 11(5), 1352; https://doi.org/10.3390/pr11051352 - 27 Apr 2023

Cited by 4 | Viewed by 1420

Abstract

Physical simulation is one of the effective methods to study mining problems, but the selection and proportion of simulation materials are greatly affected by the regional environment. This paper is based on a multilevel orthogonal design test scheme using sand, lime, and gypsum [...] Read more.

Physical simulation is one of the effective methods to study mining problems, but the selection and proportion of simulation materials are greatly affected by the regional environment. This paper is based on a multilevel orthogonal design test scheme using sand, lime, and gypsum as the materials in the Shangwan coal mine in the Shendong coalfield, with the sand to cement ratio, paste to ash ratio, and maintenance days as variables. The effect of the polar difference method on the strength and density of gypsum was used as a reference for physical simulation in the Shendong coalfield. The sensitivity analysis of each factor was carried out by the polar difference method, and the influencing factors on density were, in descending order, sand to mortar ratio, mortar to ash ratio, and the number of maintenance days; the influencing factors on strength were, in descending order, mortar to ash ratio, maintenance days, and sand to mortar ratio. The sand cement ratio was negatively correlated with strength and density, the paste to ash ratio was positively correlated with strength and density, and the number of maintenance days was positively correlated with strength and negatively correlated with density. The multivariate non-linear regression analysis of sand to cement ratio and paste to ash ratio identified similar material proportioning test equations for the Shendong coalfield, which can improve the accuracy of physical simulation and be used to guide physical simulation experiments in the Shendong coalfield. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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25 pages, 13413 KiB

Open AccessArticle

Control Mechanism and Support Technology of Deep Roadway Intersection with Large Cross-Section: Case Study

by Zaisheng Jiang, Shengrong Xie and Dongdong Chen

Processes 2023, 11(5), 1307; https://doi.org/10.3390/pr11051307 - 23 Apr 2023

Cited by 1 | Viewed by 1469

Abstract

Conventional bolt–shotcrete support technology is usually single-layered, which does not meet the requirements of strength and stiffness for roadway support. Therefore, in this paper, new combined support technology, including a multiple-layered staggered dense arrangement of bolts, multiple-layered laying of steel meshes, multiple-layered pouring [...] Read more.

Conventional bolt–shotcrete support technology is usually single-layered, which does not meet the requirements of strength and stiffness for roadway support. Therefore, in this paper, new combined support technology, including a multiple-layered staggered dense arrangement of bolts, multiple-layered laying of steel meshes, multiple-layered pouring of shotcrete, strengthening support of long cables, and full cross-section grouting, is proposed. Specifically, the following new combined support technology process is proposed: first layer of shotcrete (80 mm), first layer of mesh, first layer of bolt, second layer of shotcrete (50 mm), second layer of mesh, second layer of bolt, reinforced cable, third layer of shotcrete (50 mm), and grouting. The results show the following: (1) In the system of a superimposed coupling strengthening bearing arch, compared to a cable bearing arch, changing the support parameters of the bolt bearing arch can significantly vary the bearing capacity. A range of bolt spacing between 0.4 m and 0.7 m is more conducive for a high performance of the bearing capacity of the superimposed coupling strengthening bearing arch. (2) With the increase in the single-layer shotcrete thickness (from 50 mm to 100 mm), the bearing capacity of the shotcrete structure increased rapidly in the form of a power function. (3) After the multi-level bolt–shotcrete support structure was adopted, the ring peak zone of the deviatoric stress of the surrounding rock at the roadway intersection was largely transferred to the shallow part, and the plastic zone of the surrounding rock of the roadway was reduced by 43.3~52.3% compared to that of the conventional bolt–shotcrete support. The field practice model showed that the final roof-to-floor and rib-to-rib convergences of the roadway intersection were 114 mm and 91 mm after 26 days, respectively. The rock mass above the depth of 3 m of the roadway’s roof and sides was complete, the lithology was dense, and there was no obvious crack. The new technology achieves effective control of a deep roadway intersection with a large cross-section. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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17 pages, 5364 KiB

Open AccessArticle

Research on the Failure Mechanisms and Strength Characteristics of Deeply Buried Mudstone under the Interaction of Water and Stress

by Yuedong Liu and Dongpan Wang

Processes 2023, 11(4), 1231; https://doi.org/10.3390/pr11041231 - 16 Apr 2023

Viewed by 1270

Abstract

Mudstone is a widely occurring type of rock in deep mining, and it is crucial to understand its failure mechanisms and strength characteristics under the interaction of water and high stress to ensure the stability of deeply buried engineered mudstone. In this study, [...] Read more.

Mudstone is a widely occurring type of rock in deep mining, and it is crucial to understand its failure mechanisms and strength characteristics under the interaction of water and high stress to ensure the stability of deeply buried engineered mudstone. In this study, the composition and the structure of mudstone were obtained, and triaxial tests were conducted on mudstone under five different water contents and four different confining pressures using a triaxial servo press. The variation rules for the peak strength and residual strength were obtained, and the applicability of the strength criteria was analyzed through fitting. The results showed that both the peak strength and the residual strength decreased linearly with increasing water content, with the peak strength decreasing more rapidly. Both the peak strength and the residual strength increased with increasing confining pressure, with the residual strength increasing more rapidly. The decrease in strength was primarily due to the decrease in cohesion, with the cohesion of the peak strength decreasing from 8.40 MPa to 0.94 MPa and the cohesion of the residual strength decreasing from 1.75 MPa to 0.82 MPa. The internal friction angle did not change much, with the internal friction angle of the peak strength decreasing from 41.57° to 37.29° and the internal friction angle of the post-peak strength increasing from 32.35° to 33.28°. For dry and low-water-content mudstone, the peak strength conformed to the Mohr–Coulomb criterion, while for mudstone with a higher water content, the peak strength conformed to the Hoek–Brown criterion. The residual strength conformed to the Hoek–Brown criterion. Under low and medium confining pressures, water played a dominant role in the damage pattern for the fractures produced by the initial damage to the mudstone. Under a high perimeter pressure, water played a guiding role for the fractures produced by the initial damage to the mudstone. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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22 pages, 12436 KiB

Open AccessArticle

Optimization of Destressing Parameters of Water Jet Slits in Rock Burst Coal Seams for Deep Mining

by Yingyuan Wen, Anye Cao, Chuanhong Ding, Yang Hu, Chengchun Xue, Yujie Peng and Shikang Song

Processes 2023, 11(4), 1056; https://doi.org/10.3390/pr11041056 - 31 Mar 2023

Cited by 4 | Viewed by 1387

Abstract

Mining in deep coal seams is characterized by high ground stress, often accompanied by coal and rock dynamic disasters such as rock bursts. High-pressure water jet slotting technology can relieve pressure and reduce the stress concentration on the coal seam, which is one [...] Read more.

Mining in deep coal seams is characterized by high ground stress, often accompanied by coal and rock dynamic disasters such as rock bursts. High-pressure water jet slotting technology can relieve pressure and reduce the stress concentration on the coal seam, which is one of the effective pressure relief measures in rock burst coal seams for deep mining. Reasonable pressure relief parameters are an important influence on the effectiveness of pressure relief achieved by a high-pressure water jet. This paper uses theoretical analysis and numerical simulation to analyze the principle of high-pressure water jet pressure relief and rock burst prevention, and a theoretical calculation model of six key pressure relief parameters is constructed. The optimal values of each pressure relief parameter are obtained, and good pressure relief effect is achieved in a certain rock burst risk area. The research results showed that (1) parameters such as drilling spacing–slit radius, drilling depth–slit length, and slotting cutting spacing–slotting cutting width have a great influence on the pressure relief effect, and there is a significant interaction between the parameters, while the strength of the coal seam also has a significant effect on the selection of the parameters and the pressure relief effect. (2) The displacement, vertical stress, plastic zone, elastic energy, impact risk index, and the cost of pressure relief can be used to comprehensively evaluate the quality and economy of the pressure relief effect, and the optimal pressure relief parameters of high-pressure water jet slotting under specific physical force properties of the coal seam can be obtained. (3) High-pressure water jet technology with optimal pressure relief parameters was applied to No. 3 connecting the roadway in the 730 mining area of a mine studied, and field monitoring showed that indicators such as microseismic frequency, total energy, and spatial concentration significantly decreased. Moreover, the accuracy of the theoretical model of high-pressure water jet slotting pressure relief parameter optimization is reliable in the relevant technical parameters of coal seam slotting. It is believed that the model can be used to design the high-pressure water jet slotting pressure relief parameters in deep rock burst coal seams. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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Review

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25 pages, 15124 KiB

Open AccessReview

Stope Structural Parameters Design towards Green and Deep Mining: A Review

by Xin Zhou, Xingdong Zhao, Qingdong Qu and Jingyu Shi

Processes 2023, 11(11), 3125; https://doi.org/10.3390/pr11113125 - 31 Oct 2023

Cited by 3 | Viewed by 2768

Abstract

A reliable design of stopes is critical to ensure both safety and efficiency in mining operations. The evolving mining methods and technologies as well as increasing mining depth dictate the need to continually improve stope designs. This paper presents a comprehensive review in [...] Read more.

A reliable design of stopes is critical to ensure both safety and efficiency in mining operations. The evolving mining methods and technologies as well as increasing mining depth dictate the need to continually improve stope designs. This paper presents a comprehensive review in order to compare and consolidate various stope design methods. This review covers various aspects of stope design, including design principles, factors to consider, and the diverse range of design methods available. The results led to the classification of various methods encompassing engineering analogies, fundamentals, numerical simulations, and industrial tests. Of particular significance, the review furnishes detailed insights into the research conducted on each method, as well as each method’s practical performance in engineering applications. Furthermore, the review highlights the inherent limitations in current design methods and suggests potential avenues for future research. Finally, by comprehensively considering the functional roles and advantages of each design method, it overcomes the limitations of relying solely on a single method for stope structural parameter design, and a general process is proposed. Full article

(This article belongs to the Special Issue Advanced Technologies of Deep Mining)

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