| Coal and gas outburst is a complex geological dynamic phenomenon.Geological structure is the main controlling factor of coal and gas outburst.However,the geological control mechanism of coal and gas outburst is very complicated,and the structural factors influencing coal and gas outburst are also more.The shape,structure,scale,cause,mechanical properties,composition and segmentation of the structure compeletly impact the risk,distribution,strength and type characteristics of the coal and gas outburst.The purpose of this study is to reveal the structural deformation characteristics of coal and rock strata by using the theory of structural geology,tectonic physics and rock dynamicsand from the perspective of stuctural deformation of the geological structure.It can explore the kinematics,dynamic mechanism of the the geological structure,and analysis the evolution of geological structure of coal clearly;and then combined with the theory of gas geology,it can reveal the effects of the evolution of geological structure on coal and gas outburst.It is an effective way to study the relationship between the geological structure and the coal and gas outburst in the formation and evolution of structure.In this paper,Xin'an coalfield is used as the research area,and the control effect of structural deformation on coal and gas outburst is studied by field investigation,theoretical analysis,indoor experiment and field test.The main study contents of this paper include the following five aspects.(1)The gas geology law.Based on a large number of relevant gas geological data and measured parameters,the variation law of coal gas content in Xin'an coalfield and the laws of coal and gas outburst risk,type,intensity,distribution and dynamic characteristics are studied,and according to the relevant gas geological law,the key research content and area identified,the relevance of the content of this study improved.The results show that the gas content of coal seam in Xin'an coalfield is closely related to the thickness of coal seam.The gas content of coal seam in Xin'an coalfield is not simple and linearly increases with the increase of coal thickness.When coal thickness reaches about 5m,the coal content has rapid exponential.The results show that the coal content has a peak when the coal thickness is about 12.5 m and 5 m,which is called "Double peak phenomenon".The area where the coal content of the coal seam reaches the peak value at the coal thickness is about 5 m mainly located in the middle of the coal mine where coal and gas outburst often occur.At the same time,the coal and gas outbursts in Xin'an coal field are characterized by concentrated distribution.The 15 outstanding concentrations occur in four regions,and the type of the coal and gas outburst is different in the four regions,and the outburst area is rightly when the "Double peak phenomenon" located.The phenomenon of concentration distribution of outburst and the "Double peak phenomenon" of the coal seam gas content is closely related.(2)Sructural deformation characteristics of coal field.In the different coal and gas outburst areas,the structural deformation characteristics of 24 coal lanes in the coal mine are studied.Based on the differences of the geometric types of tectonic deformation in the study area,the tectonic deformation characteristics are systematically summarized.The results show that the tectonic deformation of Xin'an coalfield has the characteristics of zoning,classification,belting and superposition.The thickness of the thick and thin coal belts in the middle and western areas of Xin'an coal field is large in amount and small in size,the degree of closure is high,the degree of damage is higher than that of the eastern region significantly;at the same time,the structural deformation of Xin'an coalfield can be divided into three types: press-out,press-in and sliding type,and each type has its own different geometric characteristics in deformed coal distribution and structural fissures.The structures deformation of the Xin'an coalfield is dominated by the belting distribution in the region,and the secondary stucrtural deformation of the same type is often arranged in the structral deformation belt,and the distribution direction of the secondary structral deformation is consistent with the structural deformation belt.In the central Yi'an mine,the coal thickness changes drastically,and the coal seam is continuous convex and concave structure,the coal thickness contour line is mostly island-like closed,and the superposition of the deformation of the geometric characteristics is similar with the press-out type structural deformation,but the mylonitic coal of full thickness appears in a large area,and its thickness and extension length is much than larger than that in the deformation area of press-out type.(3)The mechanism of structural deformation in coalfield.Based on the analysis of regional geological background,combined with the geological characteristics of Xin'an coal field,the tectonic stress field of the study area was reconstructed by conjugate "x" shear joint,and the tectonic evolution characteristics of Xin'an coalfield were studied.The results show that the Xin'an coalfield has experienced a strong tectonic deformation movement in the Indosinian and Yanshanian periods.The main compressive stress direction of the Indosinian tectonic stress field is near NS 5°.The main stress field of the Yanshanian tectonic stress field is near NWW 119°.The results show that the structural deformation of the Indosinian period is more significant in the Xin'an coal field as a whole,which causes the thickness of the coal seam in the northern part of Xin'an coalfield to change along the NS direction,and form a group of coal thickness change zones in EW-trending.The direction of the tectonic stress field in Yanshanian has changed significantly compared with the Indosinian period.On the one hand,the coal thickness change zone along the NNE-trending is distributed in the southern part of the coalfield.At the same time,the tectonic extrusion movement in the Yanshanian period has transformed the shape of the coal seam which generated in the early stage,and makes it fault or twisting;as a result,it leads to the change of the coal thickness in the zone with different directions.The change of the coal thickness is fierce,and the effect of structural deformation in the two periods superimposed in the area.Based on the study of structural deformation geometrical characteristics of Xin'an coalfield,the formation and evolution of geological structure are analyzed by using the theory of structural geology,tectonic physics,rock dynamics and other related disciplines,and its kinematics and dynamics genetic mechanism were analyzed.The results show that the hard layer in the coal-bearing rock series and the tectonic stress field are the main factors to control the structural deformation characteristics of the coalfield.The difference of the thickness of the hard layer leads to the change of the wavelength,scale and degree of closure of the coal strata,and resulting in the zoning structural deformation of the coalfield.The difference of the deformation type of the hard layer leads to the characteristics of the passive deformation of the coal seam and the different rheological behavior of the coal body,and it can be accordingly divided into three types: press-in,sliding and press-out type.Tectonic stress field has important influence on the structural deformation characteristics of the coalfield,and the compassion action of the tectonic stress field leads to the formation of the structural deformation zone and controls its direction along the vertical direction of the compassion action.The combined effect of the two-stage tectonic stress field caused the superposition of the main stress direction and the superposition of the structural deformation type,resulting in the drastic change of coal thickness and the generation of superposition structural deformation.(4)Influences of the structural deformation on tectonic stress,deformed coal distribution and coal seam gas.Based on the study of the kinematics and dynamic mechanism of the structural deformation in Xin'an coalfield,and combined with relevant gas geological theory and a large number of measured parameters of gas geological experiment,the effects of structural deformation and evolution process on stress and strain of the coal-rock layers,coal structure and coal seam gas occurrence were researched.The results show that there are significant differences in the stress and strain,the distribution law of deformed coal and the occurrence characteristics of coal seam gas in different types of structural deformation.In the tectonic stress concentration aspect,the rock structure of the hard roof in the press-out and superimposed sturcural deformation areas are high,and the elasticity of the rock formation is increased.Under the same pressing stress,the elastic deformation is more likely to occur,and the tectonic stress concentration occurs.In the structure of coal body aspect,the type and thickness of deformed coal in different types of structural deformation are different.In the deformation area of thepress-out type,the granular coal appeared in full thickness,but the thickness of the coal seam and deformed coal is thicker.The superposition type deformation is dominated by the whole layer of mylonitic coal,and the thickness of which is gradually thickened from the tilting end to the raised end.In the case of coal seam occurrence,the two-tectonic dynamic metamorphism in the superposition deformation area leads to an increase in the degree of metamorphism of the coal.It mainly cased the increase of coal gas production,and adsorption capacity of the fullthickness mylonitic coal is especially strong,which is beneficial to the preservation of the coal seam gas.The combination of the two processes cacsed the coal seam gas content in the superposition area is highest in the coal field.(5)The control effect of structural deformation on coal and gas outburst.Based on the study of the stress and strain,the coal structure and the coal gas occurrence in the Xin'an coal field,the comprehensive effect of the tectonic stress,deformed coal and coal seam gas on the coal and gas outburst was studied.And a experimental mining face was selected to predicted the coal and gas outbursts,and the predicted results were validated.The results show that the control effect of structural deformation on coal and gas outburst in Xin'an coalfield is mainly due to the different risk and type of coal and gas outburst in different types of structural deformation control area.In the superposition type deformation control area,the two-stage tectonic compression movement leads to the increase of coal metamorphism and the increase of coal gas production.At the same time,the existence of the full thickness mylonitic coal has obstructed the dissipation of gas on the other hand,and it leads to the increase of gas adsorption capacity in the coal seam,finally it causes the gas content and pressure of coal seam in this area rised sharply,and he risk of coal and gas outburst is serious and the prominent coal and gas are prominent,and it prone to occur outburst.In the deformationcontrol area of press-out type,the full thickness of granular coal is developed and the thickness of the coal seam is thin,which reduces the outstanding resistance of the coal and gas out burst,and the the elasticity of the rock is increased,so it easy to occur elastic deformation and press the coal seam,finally resulting in coal seam movement,and it prone to occur extrusion,but the risk of this area is much lower than that it in superposition area.In the deformation control area of the press-in type,the slide action of the coal seam enhanced,and the coal thickness thickened,it resulting in the increase of the gravity of the coal seam.At the same time,the development of the scaled coal leads to the existence of a large number of structural fractures in the coal seam,and the coal is soft and easy to fall off,meanwhile,the dip angle of the granular coal layer is large,it provided the main slip surface for the coal dump,the combination of the three causes finally make the coal dump tends to occur in the deformation zone of press-in type.According to control effect of structural deformation on coal and gas outburst,the prediction method of coal and gas outburst based on structural deformation was studied,and the coal and gas outburst risk prediction model was established and calculated.At the same time,the experimental face was selected to predict the coal and gas outburst risk,and the rationality of coal and gas outburst prediction based on structural deformation was verified finally. |
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