scholarly journals Stress Relief and Stimulation of Coal Reservoir by Hydraulic Slotting

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xiaoyang Cheng ◽  
Qinghua Zhang ◽  
Zhigang Zhang ◽  
Yunlong Zou ◽  
Guo Junjie
Keyword(s):  
Coal Seam ◽  
Extraction Efficiency ◽  
High Stress ◽  
Great Influence ◽  
Stress Relief ◽  
Borehole Diameter ◽  
Gas Extraction ◽  
Geological Conditions ◽  
Coal Reservoir ◽  
Selection Of

Coal seam permeability is one of the key factors influencing the gas extraction efficiency, which is of great significance to reduce coal and gas dynamic disasters in gassy coal mines. Hydraulic slotting technique is an effective method to stimulate the coal reservoir, but the selection of slotting key parameters has great impact on gas extraction efficiency. For this reason, the hydraulic slotting model was established by using FLAC3D software to analyze the stress distribution before and after slotting. Then, the influence of borehole diameter, slotting width, and slotting length on coal seam stress relief is also discussed. The results show that the slotting width has a great influence on the stress relief of the coal seam, while the borehole diameter and slotting length have no obvious influence on that. Based on the results of numerical simulation, field tests were carried out in Sangshuping NO.2 coal mine. The results show that the coal seam stress can be fully released, resulting in the improvement of coal seam permeability. The gas extraction efficiency can be highly enhanced by hydraulic slotting. This research achievement provides the guidance basis for high-stress water jet slotting technology with adaptive selection of slotting parameters in different geological conditions.

scholarly journals Study on Borehole Arrangement Methods for Gas Extraction by Hydraulic Slotting in Long-Distance Through-Coal Seam Tunnel

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Cunfang Zhu ◽  
Shuang Cai
Keyword(s):  
Numerical Simulation ◽  
Coal Seam ◽  
Simulation Models ◽  
Gas Production ◽  
Gas Extraction ◽  
Long Distance ◽  
Pressure Relief ◽  
Coal Deposits ◽  
Geological Conditions ◽  
Rapid Pressure

How to quickly eliminate outburst in long-distance through-coal seam tunnels is one of the major challenges faced by the tunnel industry in mountainous areas. Compared with coal mine rock crosscut coal uncovering, the work surrounding the rock of through-coal seam tunnels has a high degree of breakage, large cross-section of coal uncovering, and tight time and space. In this paper, a method of networked slotting in long-distance through-coal seam tunnels for rapid pressure relief and outburst elimination is proposed. Based on this method, the corresponding mathematical governing equations and numerical simulation models have been established. The optimal borehole arrangement spacing and the slot arrangement spacing obtained by numerical optimization are 2.85 m and 3.1 m, respectively. Field gas production data of through-coal seam tunnels show that compared with the traditional dense-borehole gas extraction, the method of networked slotting in long-distance through-coal seam tunnels for rapid pressure relief and outburst elimination can shorten the extraction time by about 66%, the net quantity of peak extraction is increased by 3.55 times, and the total quantity of gas extraction when reaching the outburst prevention index is increased by 1.26 times, which verifies the feasibility of this method and the reliability of numerical simulation results. This study could be used as a valuable example for other coal deposits being mined under similar geological conditions.

scholarly journals The Drainage Horizon Determination of High Directional Long Borehole and Gas Control Effect Analysis

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yuqi Shang ◽  
Guiyi Wu ◽  
Qinzhi Liu ◽  
Dezhong Kong ◽  
Qiang Li
Keyword(s):  
Numerical Simulation ◽  
Coal Seam ◽  
Gas Extraction ◽  
Control Effect ◽  
Coverage Area ◽  
Gas Concentration ◽  
Fracture Evolution ◽  
Geological Conditions ◽  
Field Practice ◽  
Gas Control

In order to effectively solve the problem of gas concentration overrun in the upper corner of goaf and tailentry during the mining of panel 9303 in Anshun Coal Mine, based on the advantages of controllable trajectory and wide coverage area of directional drilling technology, high directional long boreholes are arranged in tailentry 9303 to extract pressure relief gas. Firstly, the principle of high directional long borehole drainage technology is introduced, and the fracture evolution of overlying strata is obtained through using numerical simulation, theoretical calculation, and field practice, and the fracture evolution range is determined to be 6–12.69 m, and rationality of fracture height obtained by theoretical analysis and numerical simulation is verified by the method of field borehole peep observation. Through the analysis, it is concluded that the best location of the final hole is within the range of 6–12.69 m of the roof of coal seam 9#. The field practice has proved that the final hole position of the high directional long borehole is arranged at 12 m from the roof of coal seam 9#, and the average gas extraction concentration can reach 40%–50% after the borehole enters the stable extraction stage, the purity of gas extraction is up to 8.5 m3/min, and the gas concentration in the upper corner of panel 9303 is stable below 0.5% during mining, which achieves good gas drainage and control effect and provides a new way for gas control under similar geological conditions.

Numerical Simulation Study on Ground Stress Distribution around Thrust Fault

2013 ◽  
Vol 838-841 ◽  
pp. 773-778
Author(s):  
Lu Sheng Song ◽  
Shu Gang Li ◽  
Ting Xu Yan
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Principal Stress ◽  
High Stress ◽  
Physical And Mechanical Properties ◽  
Thrust Fault ◽  
Maximum Principal Stress ◽  
Geological Conditions ◽  
Ground Stress ◽  
Stress States

Based on geological conditions of working face 25110 in YiMa coal mine, the ground stress distribution around thrust fault is simulated by using FLAC3D. In the fault profile, the intersection of fault footwall profile and the middle of coal seam tendency dip profile, ground stress distribution are analyzed. Distress is not continuous because of faults. Coal and rock show different stress states under high stress because of different physical and mechanical properties, and the maximum principal stress and the minimum principal stress distribute consistently with the z axis and the x axis. It provide basis on optimal design of outburst prevention of coal seam with impulsion pressure risk.

scholarly journals Simulation of the Extraction Efficiency of Coalbed Methane under Water Injection: A Gas-Liquid-Solid Coupling Model

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Hai Pu ◽  
Liqiang Zhang ◽  
Xu Dong ◽  
Tao Jing ◽  
Xu Junce
Keyword(s):  
Elastic Modulus ◽  
Coal Seam ◽  
Coalbed Methane ◽  
Extraction Efficiency ◽  
Water Injection ◽  
Free Water ◽  
Coupling Model ◽  
Experimental Results ◽  
Gas Extraction ◽  
Gas Drainage

Coalbed methane is always a major hidden danger that affects mining safety in coal mines. In the study of coal seam water injection to control gas disaster, the increase of free water content is helpful to destroy the integrity of coal seam and to promote the flow of gas in fractures. However, when the free water fills the fracture space, it will increase the flow resistance of gas, and then will reduce the gas extraction efficiency. At present, there is currently no mathematical model describing the effects of coal seam water injection that combines these two aspects on gas drainage. In this study, a series of experiments were conducted to study the differences in mechanical property changes under wetting conditions with different coal samples. The experimental results show that the elastic modulus and compressive strength decrease as an exponential function with increasing water pressure. Based on the experimental results, a gas-liquid-solid coupling model including effective stress change and gas desorption is established and used to predict a field gas extraction application. According to the results of the numerical model, In the plastic failure zone of coal seam, the permeability increases, the elastic modulus drops and gas migrates faster. In the water wetting zone, the free water occupies the fracture space, which blocks the gas migration channel. The overall effect of water injection on gas extraction depends on which impact plays a dominant role. The established gas drainage model is validated by field data and can reflect the pattern of borehole damage and gas drainage under water injection.

scholarly journals A New Width Measurement Method of the Stress Relief Zone on Roadway Surrounding Rocks

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Pengfei Cui ◽  
Banghua Yao ◽  
Yong Liu ◽  
Jianping Wei ◽  
Zhihui Wen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Field Test ◽  
Measurement Method ◽  
Extraction Efficiency ◽  
Stress Relief ◽  
Gas Pressure ◽  
Gas Extraction ◽  
Drilling Depth ◽  
Width Measurement ◽  
Different Depths

Determining the width of the stress relief zone on roadway surrounding rocks is the premise to optimize drilling borehole effect and increase gas extraction efficiency. In this study, a new width measurement method of the stress relief zone on the roadway surrounding rocks was proposed, which determined the width according to gas pressure attenuation speeds in roadway boreholes at different depths. Then, the variation curve of the gas pressure in boreholes at different depths with the time was gained through a field test. On this basis, laws of the gas pressure attenuation and the gas transmission and loss in boreholes at different depths were explored through a numerical simulation based on COMSOL Multiphysics, thus concluding the stress on roadway surrounding rocks, the distribution of plastic zones, and the stress-permeability relation. The scientificity of the proposed method was illustrated theoretically. Finally, the proposed method was verified by the field test data and numerical simulation results of the gas extraction at different sealing depths. Research results demonstrate that the pressure in boreholes attenuates in the logarithmic function pattern. The attenuation speed decreases with the increase of the drilling depth. The width of the stress relief zone on roadway surrounding rocks in the studied area was determined to be about 11 m according to the proposed method. Both the numerical simulation and the field test of the gas extraction efficiency prove the feasibility and validity of the proposed method in determining the sealing depth of the borehole for the gas extraction. Research conclusions are of important significance to enrich width measurement methods of the stress relief zone on roadway surrounding rocks and to optimize sealing parameters of underground boreholes for gas extraction.

scholarly journals Elimination of Coal and Gas Outburst Dynamic Disasters in Dengfeng Coalfield through Gas Extraction Based on Extremely Thin Protective Coal Seam Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Haibo Liu ◽  
Xucheng Xiao ◽  
Zhihang Shu
Keyword(s):  
Coal Seam ◽  
Coal And Gas Outburst ◽  
Comprehensive Treatment ◽  
Cross Layer ◽  
Gas Extraction ◽  
Pressure Relief ◽  
Gas Outburst ◽  
Geological Conditions ◽  
Fracture Development ◽  
Seam Mining

No. 21 coal seam is a full-thickness structured soft coal in Dengfeng coalfield. The coal seam gas-bearing capacity is high, and the permeability is poor, thus resulting in serious coal and gas outburst dynamic disasters. According to the gas geological conditions of Baoyushan Mine, No. 17 coal seam without outburst danger, which is 0.5 m thick and 23.4 m under No. 21 coal seam, was mined in advance as the lower protective seam. At the same time, a gas extraction roadway was constructed in No. 21 coal seam floor. Cross-layer boreholes were constructed to extract the pressure relief gas of No. 21 coal seam for comprehensive treatment of mine gas. The mobile deformation of the overburden coal and rock mass after mining No. 17 coal seam, the fracture development characteristics of No. 21 coal seam, the pressure relief gas migration of the coal seam, the gas extraction, and the outburst danger elimination were studied. The research findings showed the following: (1) after mining No. 17 coal seam, the overburden hard and extremely thick limestone roof sagged slowly, albeit leading to no craving zone. (2) The permeability of No. 21 coal seam was increased by about 394 times, from 0.0012 mD to 0.4732 mD. (3) After the extraction of pressure relief gas through the gas extraction roadway on the floor through the cross-layer borehole, the gas pressure of No. 21 coal seam decreased from 1.17 MPa to 0.12 MPa, while the gas content decreased from 9.74 m3/t to 3.1 m3/t, which suggested that the coal and gas outburst dynamic danger of No. 21 coal seam was totally eliminated and the goal of safe and efficient mining in the mine was realized.

scholarly journals A Comprehensive Coal Reservoir Classification Method Base on Permeability Dynamic Change and Its Application

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 644 ◽  
Author(s):  
Xinlu Yan ◽  
Songhang Zhang ◽  
Shuheng Tang ◽  
Zhongcheng Li ◽  
Yongxiang Yi ◽  
...  
Keyword(s):  
Coalbed Methane ◽  
Dynamic Change ◽  
Initial Permeability ◽  
Gas Production ◽  
Gas Desorption ◽  
Reservoir Permeability ◽  
Geological Conditions ◽  
Production Stages ◽  
Productivity Potential ◽  
Coal Reservoir

Due to the unique adsorption and desorption characteristics of coal, coal reservoir permeability changes dynamically during coalbed methane (CBM) development. Coal reservoirs can be classified using a permeability dynamic characterization in different production stages. In the single-phase water flow stage, four demarcating pressures are defined based on the damage from the effective stress on reservoir permeability. Coal reservoirs are classified into vulnerable, alleviative, and invulnerable reservoirs. In the gas desorption stage, two demarcating pressures are used to quantitatively characterize the recovery properties of permeability based on the recovery effect of the matrix shrinkage on permeability, namely the rebound pressure (the pressure corresponding to the lowest permeability) and recovery pressure (the pressure when permeability returns to initial permeability). Coal reservoirs are further classified into recoverable and unrecoverable reservoirs. The physical properties and influencing factors of these demarcating pressures are analyzed. Twenty-six wells from the Shizhuangnan Block in the southern Qinshui Basin of China were examined as a case study, showing that there is a significant correspondence between coal reservoir types and CBM well gas production. This study is helpful for identifying geological conditions of coal reservoirs as well as the productivity potential of CBM wells.

scholarly journals Strain Accommodations among Twin Variants in Ti and Mg

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 453
Author(s):  
Ping Zhou ◽  
Guo-Zhen Zhu
Keyword(s):  
Mechanical Property ◽  
Great Influence ◽  
Local Strain ◽  
Deformation Texture ◽  
Variant Selection ◽  
Slip Systems ◽  
Twinning Shear ◽  
Active Variant ◽  
Shed Light ◽  
Selection Of

The selection of twin variants has a great influence on deformation texture and mechanical property in hcp metals where slip systems are limited and twinning types are abundant during deformation. Local strain accommodations among twin variants are considered to shed light on variant selection rules in Ti and Mg alloys. Five kinds of strain accommodations are discussed in terms of different regions that are affected by the twinning shear of primary twin. These regions contain (I) the whole sample, (II) neighboring grain, (III) adjacent primary twin in neighboring grain, (IV) adjoining primary twin within the same parent grain, and (V) multi-generation of twinning inside the primary twin. For a potentially active variant, its operation needs not only relatively higher resolved shear stress but also easily accommodated strain by immediate vicinity. Many of the non-Schmid behaviors could be elucidated by local strain accommodations that variants with relatively higher SFs hard to be accommodated are absent, while those with relatively lower SFs but could be easily accommodated are present.

Reasonable Entry Layout of Lower Seam in Multi-Seam Mining Based on Numerical Simulation

2013 ◽  
Vol 295-298 ◽  
pp. 2980-2984
Author(s):  
Xiang Qian Wang ◽  
Da Fa Yin ◽  
Zhao Ning Gao ◽  
Qi Feng Zhao
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Coal Seam ◽  
Coal Mine ◽  
Abutment Pressure ◽  
Surrounding Rock ◽  
Geological Conditions ◽  
Seam Mining

Based on the geological conditions of 6# coal seam and 8# coal seam in Xieqiao Coal Mine, to determine reasonable entry layout of lower seam in multi-seam mining, alternate internal entry layout, alternate exterior entry layout and overlapping entry layout were put forward and simulated by FLAC3D. Then stress distribution and displacement characteristics of surrounding rock were analyzed in the three ways of entry layout, leading to the conclusion that alternate internal entry layout is a better choice for multi-seam mining, for which makes the entry located in stress reduce zone and reduces the influence of abutment pressure of upper coal seam mining to a certain extent,. And the mining practice of Xieqiao Coal Mine tested the results, which will offer a beneficial reference for entry layout with similar geological conditions in multi-seam mining.

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