Study On Activation Effect And Application Of Upper Protective Layer Mining On Coal Seam With Gangue

With the mine of coal resources gradually moving towards the deep environment,the occurrence geological environment of coal seams is becoming more and more complex,and the occurrence frequency of high gas and low permeability coal seams and unconventional coal reservoirs is becoming higher and higher.When two geological conditions occur in the same coal seam at the same time,it will be a very severe challenge to the gas control during the exploitation of coal seam resources.For high gas and low permeability coal seams,one of the most effective measures to improve coal reservoir permeability and reduce gas pressure is protective layer mining.Under the disturbance of protective layer mining,different areas of the protected coal seam will show different stress characteristics.When the protected coal seam belongs to unconventional coal reservoir,which contains non-breathable gangue layer inside,the pressure relief disturbance will have different activation effects on the coal seam and gangue layer.The dual activation differences make the migration path of coal seam gas more complex.Therefore,it is of great significance to study on activation effect and application of upper protective layer mining on coal seam with gangue for the gas control of unconventional coal reservoirs with high gas and low permeability.Focusing on the research theme of “study on activation effect and application of upper protective layer mining on coal seam with gangue”,with the help of numerical simulation,theoretical analysis,indoor test and field application,this thesis analyzes the stress evolution law of protected coal in different areas under the disturbance of upper protective layer mining,obtains the differential activation effect of the protected coal seam with gangue and the evolution law of the permeability characteristics of the coal in different activation areas,reveals the macro-meso damage mechanism of coal seam under the mining disturbance,establishes the two cavity emission model of the gas in the coal seam with non-breathable gangue,and put forward the key technology of gas drainage in the protected coal seam with gangue in close distance.The main conclusions of this thesis are as follows:(1)Based on the mechanical model of simply supported beam,the stress characteristics of coal bodies in different areas above and below the protected coal seam after the mining of the upper protective layer are obtained,which are verified by 3DEC numerical simulation method.Based on this,the stress evolution path of coal and rock mass in different areas of the protected coal seam and the stress path of indoor similar simulation test are put forward.(2)Using the coal rock deformation acoustic emission synchronous test system and taking the raw coal sample and gangue sample as the research object,the differential activation effect of the protected coal seam with gangue under the mining effect is systematically studied,and the mining dynamic behavior and damage characteristics of the raw coal sample and gangue sample under different stress disturbance conditions are compared and analyzed.The results show that the resistance to deformation and damage of gangue sample is higher than that of raw coal sample under the same conditions,the deformation and activation effect of the coal body in the upper and lower areas of the protected coal seam is compared and analyzed.It is concluded that the activation effect of the upper coal body is more obvious than that of the lower coal body of the protected coal seam,and the difference of the activation effect of the upper and lower parts of the protected coal seam will decrease with the increase of loading and unloading rate.(3)Using the coal reservoir fracturing simulation and physical property test system,and taking the raw coal sample as the research object,the permeability characteristics of coal in different activation zones are systematically studied.The evolution law and corresponding quantitative evolution relationship of raw coal sample permeability with volume stress and gas adsorption equilibrium pressure in in-situ stress recovery stage,mining disturbance stage and post mining pressure relief stage are analyzed and obtained;The quantitative evolution relationship of raw coal sample permeability under the coupling action of volume stress and gas adsorption equilibrium pressure is obtained,and it is analyzed that the two have different dominant positions in the influence of different stress stages on raw coal sample permeability;The increase of loading and unloading rate has different effects on the permeability of raw coal samples under different stress paths.This difference is mainly reflected in the post mining pressure relief stage of the stress path of the lower coal body of the protected coal seam.(4)The loading and unloading of complex stress path corresponding to the test scheme in this thesis is realized by using PFC discrete element numerical simulation software,and the acoustic emission monitoring program for damage measurement of meso scale sample model is established based on moment tensor theory.The macro meso characteristics of coal damage under mining effect are systematically studied.By comparing the results of numerical simulation and experimental research,It verifies the scientificity and reliability of the above experimental research conclusions in this thesis.At the same time,the characteristics of numerical simulation research methods are used to make up for the shortcomings of experimental research methods,and the macro failure mode of the sample model under fixed confining pressure triaxial compression and the evolution characteristics of damage visual parameters,porosity and crack number of the sample model under uniaxial compression,fixed confining pressure triaxial compression and complex loading and unloading of specific stress path are obtained,The evolution characteristics of coal damage and gas migration channel are expounded from the meso point of view.(5)Through the construction of composite samples with different porosity containing gangue under laboratory conditions to simulate the protected coal seam with gangue after mining,and using “a gas test device based on constant pressure in the sealed cavity”,the gas emission law of samples with different gangue area and different gangue position is systematically studied.It is concluded that the larger the area of gangue and the closer the position of gangue is to the emission surface,the greater the inhibitory effect of gangue layer on gas emission.The “two chamber” dispersion model of gas in unconventional coal reservoir with non-breathable gangue can be analyzed by traditional dispersion theory for mechanism analysis and mathematical representation of the model.The mathematical expression and dispersion velocity intensity factor of the“two chamber” dispersion model proposed in this thesis can better describe the dispersion characteristics of the “two chamber” dispersion model.(6)Based on the north 1103 working face of Weijiadi coal mine,which is the source of the research problem in this thesis,combined with the above research results of test,numerical simulation and theoretical research results,this thesis puts forward the key technology of " low directional interception borehole + high directional borehole +ground drainage borehole " spatiotemporal coordination trinity pressure relief gas drainage in protected coal seams with gangue in close distance.The actual effect of the technology is verified,the results show that the implementation of the technology effectively reduces the impact of pressure relief gas on the safe mining of the working face,and alleviates the pressure of air and gas drainage of the working face to a certain extent.