Effect Of Fault Structure And Its Stress Environment On Coal And Gas Outburst

Coal and gas outburst is a complex geological dynamic disaster affecting the safety production of coal mine,which is considered the comprehensive effects of geostress,coal bed methane and physical and mechanical properties of coal.It is also a problem that gas geology research faces all the time.Geological structures have an obvious effects on coal and gas outburst,especially fault structures are frequent zones of coal and gas outburst disasters.Tectonic stress plays an important role in the power source of coal and gas outburst.Therefore,studying the control effect of tectonic stress environment on coal and gas outburst in fault zone has major practical significance for the prevention of coal and gas outburst disasters.Guided by gas geology theory,this paper studies by means of field investigation,laboratory testing,theoretical analysis and numerical simulation to carry out systematic research on the control effect of stress environment on coal and gas outburst in fault zone.Firstly,based on the investigation of structural feature and the analysis of characteristics,combined with mechanical mechanism of the formation of structural feature and dominant occurrence of structural planes,the tectonic stress environment in the study area is reconstructed by using stereographic projection method.Secondly,a three-dimensional geological model is established for the coal and gas outburst belt,and different characteristics of stress environment in the fault zones are simulated by FLAC 3D.The spatial variation of stress components in the study area is revealed and the influence of different fault patterns on the stress environment is discussed.The dynamic response law of different fault patterns under mining disturbance is analyzed.In addition,the relationship between tectonic stress environment and development,fracture distribution and damage degree of tectonic coal are analyzed on the basis of transformation of different tectonic stress environment on coal reservoirs,and the control effect of tectonic stress environment on the tectonophysical characteristics of tectonic coal is discussed.Based on the theory of fault zone sealing,a comprehensive quantitative evaluation system for faults in different seal types is established.Combined with the distribution characteristics of gas,the relationship between the sealing property of fault zone and gas enrichment is discussed.From the three aspects of working face fault,planar fault and vertical fault,it is verified that the sealing of fault area is evaluated by the shale gouge ratio and the reliability of the gas enrichment area is delineated.Finally,through the study of structural distribution characteristics and coal and gas outburst characteristics,the fault structure and stress environment for coal and gas outburst are discussed from five aspects:fault combination type,tectonic coal distribution,terrain curvature,coal thickness and dip angle and stress.The role on coal and gas outbursts provides the basis for prevention and control of coal and gas outburst.The research content of the thesis is divided into the following five aspects:(1)Tectonic stress environment reconstruction based on stereographic projection methodThe application of stereographic projection method to the tectonic stress environment is studied based on the basic principles of stereographic projection and projection network.Tectonic stress environment in the study area is reconstructed by the investigation and analysis of conjugate shear joint and slickenside using stereographic projection method,combining with mechanical mechanism of the formation of structural feature and dominant occurrence of structural planes.The results of conjugate shear joint reconstruction show that there are four directions of tectonic stress,which are NEE-SWW,NW-SE,NE-SW and NNE-SSW.The results of slickenside reconstruction show that there are four directions of tectonic stress,which are NNE-SSW,NNW-SSE,NEE-SWW and NW-SE.According to developmental scale,intersection relationship,extension length and penetration analysis of conjugate shear joint and the spatial cutting and recombination of slickenside,tectonic stress environment order in the study area is clarified.Compared with the research results of tectonic stress activities in north China,tectonic stress environment period is determined by the overall consideration of two structural features.Tectonic stress environment in the study area is divided into three phases.The maximum principal stress in the Indosinian period is NE-SW,the maximum principal stress in the Yanshanian period is NW-SE,and the maximum principal stress in the Himalayan period is NEE-SWW.(2)Tectonic stress environment and mining response law in fault zoneIn order to improve the pertinence of the numerical simulation of tectonic stress environment in the fault zone,the distribution law of coal and gas outburst in the study area are surveyed in detail.The NW direction structural belt of Guozhuang anticline,Niuzhuang syncline,Niuzhuang reverse fault and Yuan 11 mine reverse fault and structural belt of Xindian normal fault and Zhangwan normal fault are selected to establishe three-dimensional geological model.The software FLAC 3D is used to simulate the stress environment in the fault zone and the spatial variation of the principal stress magnitude show a linear relationship that increases with increasing burial depth.Also,the distribution characteristics of the principal stress in the block between faults and the outer block of faults are analyzed by slice processing of strike profile on different levels.The magnitude of stress rises and then decreases in the block between faults,and the magnitude of the stress increases linearly with the distance from faults in the outer block of faults.The principal stress orientation near the fault zone is significantly deflected by the principal stress vector analysis.It is found that stress distribution characteristics in the fault zone with inverted trapezoidal zone on the section.When the two faults are close,the block between faults shows obvious stress increase.In the fault zone with trapezoidal zone on the section,when the distance between the two faults is relatively close,the block between faults shows evident stress drop.When the working face is greater than 90m from the fault,normal stress and shear stress remain stable.In the interval of 20-90m from the fault,normal stress and shear stress are obviously affected by the mining disturbance.When the working face is less than 20m from the fault,normal stress and shear stress are complex and the risk of unstable slip in the fault zone is the highest.The model 1 is prone to unstable slip under the mining disturbance and there is no unstable rotation.The model 2 may occur unstable slip and unstable rotation under mining disturbance.With the advancement of the working face to the fault,sliding zone of the fault surface is extended from overlying strata to basement strata and slip displacement of model 1 is larger than that of model 2.(3)Effects of tectonic stress environment on tectonophysical features of tectonic coalBased on the evolution characteristics of regional tectonic stress environment in the study area,the selection of research parameter of tectonic stress environment is completed.According to distribution characteristics of the principal stress,the evolution of stress regime is analyzed with thickness of overlying bedrock.The quantitative analysis of tectonic coal of C and E coal seam is formed by underground observation combining with geophysical logging,and the development degree of tectonic coal under reverse faulting stress regime and strike-slip faulting stress regime are studied.The window measurement method is used to calculate the fracture occurrence of tectonic coal,and development characteristics of tectonic coal fracture of C and E coal seam are obtained by means of stereographic projection method.The corresponding relationship between the development characteristics of tectonic coal fracture and the evolution characteristics of tectonic stress environment is studied,and the influence of tectonic communities on the development of tectonic coal fracture is investigated by fracture density of tectonic coal.Using geological record results and laboratory tests,the physical characteristics of tectonic coal are summarized from structural features,macroscopic features and fracture properties.The relationship between the distribution characteristics of damage degree of tectonic coal and lateral pressure coefficient and damage degree division and transformation trend of tectonic coal are studied.Combined with macroscopic characteristics of tectonic coal,it is proposed that deformation mode of tectonic coal under the tectonic stress is divided into friction sliding and solid state flow,and the types of deformation mode of tectonic coal in different fault zones are discussed.(4)Quantitative evaluation of fault zone sealing and gas enrichment lawBased on the study of the mechanism and type of fault zone sealing,a comprehensive quantitative evaluation system for the fault zone of different sealing types was established.The triangular map was used to evaluate the docking sealing,clay smear poential to evaluate the shear sealing,shale smear factor to evaluate the intrusive sealing and shale gouge ratio to evaluate the non-uniform sequence sealing,combining with distribution characteristics of gas.It is found that the mud-sand docking area is sealing well and the sand-sand docking area is sealing weak.Clay smear poential value 15,shale smear factor value 9 and shale gouge ratio value 31 were determined as critical values for the identification of fault zone sealing.Taking the 13140 working face and the Zhangwan normal fault as the research object,the quantitative evaluation of the working face fault,planar fault and vertical fault is carried out and the fault sealing zone and the fault opening zone are depicted.Compare the distribution characteristics of fault sealing zone and gas enrichment area,they are match well in the spatial distribution.It is verified that the fault sealing area is evaluated by shale gouge ratio and the reliability of the gas enrichment area is delineated.(5)Empirical analysis of control mechanism of coal and gas outburst by fault structure and its stress environmentTaking the distribution characteristics of structure as the subject,systematic analysis is conducted to study the folding structure,fault structure,small fault structure and bedding shear structure in the area.The correlative characteristics between coal and gas outburst and burial depth,coal volume of outburst and gas volume of outburst of B and C coal seam are analyzed,and outburst strength of B coal seam is significantly larger than that of C coal seam.The effect of fault structures on coal and gas outburst are discussed from four aspects:fault combination type,distribution of tectonic coal,terrain curvature,coal thickness and dip angle.The spatial position relationship between coal and gas outburst and geological structure shows that coal and gas outburst have obvious zonality.It is mainly concentrated in the fold-fault belt in NWW direction composed of Niuzhuang syncline,Niuzhuang reverse fault,Yuan 11 mine reverse fault and Guozhuang anticline,as well as the intersection of fault belt composed of Xindian normal fault and Zhangwan normal fault.The tectonic pattern belongs to the horst structure,and the cross-section view of the two outburst belts are inverted trapezoidal and trapezoidal,respectively.The outburst belt of inverted trapezoid structure is located in the north of outer block of faults,and the outburst belt of trapezoid structure is located in the block between faults.The development and thickening zone of tectonic coal are frequent zones of coal and gas outburst,and the area with a radius of curvature of(1.0×104?3.0×104)is the danger zone of coal and gas outburst.Coal seam thickening zone and coal thick abrupt zone are favorable zones for coal and gas outburst.Coal and gas outburst are prone to occur in the areas with large dip angle and steep dip.The stress environment of the outburst belt in the study area is reconstructed by slickenside,and the control effect of the stress environment on coal and gas outburst is studied.The outburst belt in the west of coalfield is controlled by the NNE-NE compression.The outburst belt in the middle of coalfield is controlled by the NW-NNW compression.From the perspective of coal and gas outburst energy,the two theoretical calculation models of different energy carriers of elastic energy and gas expansion energy are established.The coal and gas outburst energy of different characteristic areas in the study area are analyzed.Control of different energy carriers on coal and gas outburst are discussed.