Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology.In this work,the No.5 coal seam in the Hancheng block was taken as the research object.Based on the findings ...Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology.In this work,the No.5 coal seam in the Hancheng block was taken as the research object.Based on the findings of true triaxial hydraulic fracturing experiments and field pilot under this technology and the cohesive element method,a 3D numerical model of indirect fracturing in the roof of broken soft coal seams was established,the fracture morphology propagation and evolution law under different conditions was investigated,and analysis of main controlling factors of fracture parameters was conducted with the combination weight method,which was based on grey incidence,analytic hierarchy process and entropy weight method.The results show that“士”-shaped fractures,T-shaped fractures,cross fractures,H-shaped fractures,and“干”-shaped fractures dominated by horizontal fractures were formed.Different parameter combinations can form different fracture morphologies.When the coal seam permeability is lower and the minimum horizontal principal stress difference between layers and fracturing fluid injection rate are both larger,it tends to form“士”-shaped fractures.When the coal seam permeability and minimum horizontal principal stress between layers and perforation position are moderate,cross fractures are easily generated.Different fracture parameters have different main controlling factors.Engineering factors of perforation location,fracturing fluid injection rate and viscosity are the dominant factors of hydraulic fracture shape parameters.This study can provide a reference for the design of indirect fracturing in the roof of broken soft coal seams.展开更多
Based on the different deformation and failure laws of coal and rock materials under tensile or compressive loads,the damage variable was defined to divide three phases from the damage and rupture point of view in ord...Based on the different deformation and failure laws of coal and rock materials under tensile or compressive loads,the damage variable was defined to divide three phases from the damage and rupture point of view in order to reveal the fissured field evolution characteristics and spatial distribution of coal and rock in the single coal seam mining with low permeability and rich methane.According to the corresponding damage constitutive equations,the secondary development of the finite element program was completed.The fissures field evolution law of a coal mine with single coal seam mining was calculated and analyzed by this new program and the distribution areas and failure degree of the surrounding coal and rock structures with damage,fissure or rupture are given on the condition of mining.This paper provides a scientific basis for quantitative research and evaluation of the safe simultaneous production of coal and gas.展开更多
Grouting is an important method to reinforce soft coal roadway,and the presence of primary cracks in the coal body has an important influence on the grouting effect.With the discrete element simulation method,the grou...Grouting is an important method to reinforce soft coal roadway,and the presence of primary cracks in the coal body has an important influence on the grouting effect.With the discrete element simulation method,the grouting process of the soft coal seam was simulated.The mechanism of primary cracks on grouting was revealed,while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed.The results demonstrated that grouting in the soft coal seam involves the stages of seepage,rapid splitting,slow splitting,and stability.Due to the presence of primary cracks,the grouting diffusion radius increased significantly.Under the slurry pressure,the tensile stress concentration was formed at the crack tip,and the slurry split the coal once the splitting pressure was reached.In addition,the distribution characteristics of fractures are found to have a great influence on the grouting effect.It is observed that smaller fracture spacing is associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips.The fracture angle affects the direction of fracture propagation.The secondary fracture formed by splitting is a tensile fracture,which is more likely to extend along the direction parallel to the maximum principal stress.Overall,these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.展开更多
Based on the analyses of sulfur and 41 other elements in 8 channel samples of the No. 11 coal seam from Antaibao surface mine, Shanxi, China and 4 samples from the coal preparation plant of this mine, the distribution...Based on the analyses of sulfur and 41 other elements in 8 channel samples of the No. 11 coal seam from Antaibao surface mine, Shanxi, China and 4 samples from the coal preparation plant of this mine, the distribution of the elements in the seam profile, their geo-chemical partitioning behavior during the coal cleaning and the genetic relationships between the both are studied. The conclusions are drawn as follows. The coal-forming environment was probably invaded by sea water during the post-stage of peatification, which results in the fact that the contents of As, Fe, S, etc. associated closely with sea water tend to increase toward the top of the seam, and that the kaolinite changes into illite and montmorillonite in the coal-sublayer near the roof. These elements studied are dominantly associated with kaolinite, pyrite, illite, montmorillonite, etc., of which the As, Pb, Mn, Cs, Co, Ni, etc. are mainly associated with sulfides, the Mo, V, Nb, Hf, REEs, Ta etc. mainly with kaolintie, the Mg, Al etc. mainly with epigenetic montmorillonite, and the Rb, Cr, Ba, Cu, K, Hg, etc. mainly with epigenetic illite. The physical coal cleaning is not only effective in the removal of ash and sulfur, but also in reducing the concentra-tion of most major and trace elements. The elements Be, U, Sb, W, Br, Se, P, etc. are largely or partly organically bound showing a relatively low removability, while the removability of the other elements studied is more than 20%, of which the Mg, Mn, Hg, Fe, As, K, Al, Cs, and Cr associ-ated mostly with the coarser or epigenetic minerals show a higher removability than that of ash. The distribution of the elements in the seam profile controls their partitioning behavior to a great degree during the coal cleaning processes.展开更多
基金National Natural Science Foundation of China(11672333).
文摘Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology.In this work,the No.5 coal seam in the Hancheng block was taken as the research object.Based on the findings of true triaxial hydraulic fracturing experiments and field pilot under this technology and the cohesive element method,a 3D numerical model of indirect fracturing in the roof of broken soft coal seams was established,the fracture morphology propagation and evolution law under different conditions was investigated,and analysis of main controlling factors of fracture parameters was conducted with the combination weight method,which was based on grey incidence,analytic hierarchy process and entropy weight method.The results show that“士”-shaped fractures,T-shaped fractures,cross fractures,H-shaped fractures,and“干”-shaped fractures dominated by horizontal fractures were formed.Different parameter combinations can form different fracture morphologies.When the coal seam permeability is lower and the minimum horizontal principal stress difference between layers and fracturing fluid injection rate are both larger,it tends to form“士”-shaped fractures.When the coal seam permeability and minimum horizontal principal stress between layers and perforation position are moderate,cross fractures are easily generated.Different fracture parameters have different main controlling factors.Engineering factors of perforation location,fracturing fluid injection rate and viscosity are the dominant factors of hydraulic fracture shape parameters.This study can provide a reference for the design of indirect fracturing in the roof of broken soft coal seams.
基金supported from the State Key Basic Research Program of China(Nos.2010CB226804 and 2011CB201200)the National Natural Science Foundation of China(Nos.10802091and 50974125)
文摘Based on the different deformation and failure laws of coal and rock materials under tensile or compressive loads,the damage variable was defined to divide three phases from the damage and rupture point of view in order to reveal the fissured field evolution characteristics and spatial distribution of coal and rock in the single coal seam mining with low permeability and rich methane.According to the corresponding damage constitutive equations,the secondary development of the finite element program was completed.The fissures field evolution law of a coal mine with single coal seam mining was calculated and analyzed by this new program and the distribution areas and failure degree of the surrounding coal and rock structures with damage,fissure or rupture are given on the condition of mining.This paper provides a scientific basis for quantitative research and evaluation of the safe simultaneous production of coal and gas.
基金The authors acknowledge the financial support provided by the National Natural Science Foundation of China(No.51604094 and 51674098)the Shandong Provincial Natural Science Foundation(No.ZR2020QE118).
文摘Grouting is an important method to reinforce soft coal roadway,and the presence of primary cracks in the coal body has an important influence on the grouting effect.With the discrete element simulation method,the grouting process of the soft coal seam was simulated.The mechanism of primary cracks on grouting was revealed,while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed.The results demonstrated that grouting in the soft coal seam involves the stages of seepage,rapid splitting,slow splitting,and stability.Due to the presence of primary cracks,the grouting diffusion radius increased significantly.Under the slurry pressure,the tensile stress concentration was formed at the crack tip,and the slurry split the coal once the splitting pressure was reached.In addition,the distribution characteristics of fractures are found to have a great influence on the grouting effect.It is observed that smaller fracture spacing is associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips.The fracture angle affects the direction of fracture propagation.The secondary fracture formed by splitting is a tensile fracture,which is more likely to extend along the direction parallel to the maximum principal stress.Overall,these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.
文摘Based on the analyses of sulfur and 41 other elements in 8 channel samples of the No. 11 coal seam from Antaibao surface mine, Shanxi, China and 4 samples from the coal preparation plant of this mine, the distribution of the elements in the seam profile, their geo-chemical partitioning behavior during the coal cleaning and the genetic relationships between the both are studied. The conclusions are drawn as follows. The coal-forming environment was probably invaded by sea water during the post-stage of peatification, which results in the fact that the contents of As, Fe, S, etc. associated closely with sea water tend to increase toward the top of the seam, and that the kaolinite changes into illite and montmorillonite in the coal-sublayer near the roof. These elements studied are dominantly associated with kaolinite, pyrite, illite, montmorillonite, etc., of which the As, Pb, Mn, Cs, Co, Ni, etc. are mainly associated with sulfides, the Mo, V, Nb, Hf, REEs, Ta etc. mainly with kaolintie, the Mg, Al etc. mainly with epigenetic montmorillonite, and the Rb, Cr, Ba, Cu, K, Hg, etc. mainly with epigenetic illite. The physical coal cleaning is not only effective in the removal of ash and sulfur, but also in reducing the concentra-tion of most major and trace elements. The elements Be, U, Sb, W, Br, Se, P, etc. are largely or partly organically bound showing a relatively low removability, while the removability of the other elements studied is more than 20%, of which the Mg, Mn, Hg, Fe, As, K, Al, Cs, and Cr associ-ated mostly with the coarser or epigenetic minerals show a higher removability than that of ash. The distribution of the elements in the seam profile controls their partitioning behavior to a great degree during the coal cleaning processes.