Dynamic Change Of Physical Property Of Coal Reservoir During Drainage In West Fukang Area

Taking the Jurassic steep inclined coal reservoir in the western area of Fukang,Xinjiang as the research object,through the vitrinite reflectance of coal,microscopic composition,industrial analysis,mercury intrusion,cryogenic liquid nitrogen,nuclear magnetic resonance and other experimental tests,the coal rank,microscopic composition,coal quality and coal reservoir pore structure characteristics of the coal reservoir in the study area are analyzed.The physical simulation study shows that the permeability of coal samples decreases with the increase of effective stress in the negative exponential form,and increases with the increase of the shrinkage of coal matrix in the form of positive exponential,and increases obviously with the effect of slippage at low pore pressure.It is found that there is obvious directionality in the shrinkage deformation of coal matrix,the strain of coal samples conforms to Langmuir relation with pore pressure during desorption process,there is residual deformation after coal sample desorption.The physical simulation of the elastic modulus and Poisson's ratio of coal pillars saturated adsorption of gas under different pressures shows that the elastic modulus of coal gradually increases and the Poisson's ratio decreases gradually during the coal reservoir drainage process.Based on the physical characteristics of CS18 well reservoir in Fukang west area,using CBM module of Eclipse numerical simulation software to construct geological model,the simulation results show that the drainage in the updip direction and the downdip direction of the steeply inclined coal reservoir is non-synchronous.The downdip direction of coal reservoir drainage firstly,With the drainage proceeding,the upward direction gradually drainage and the speed of depressurization gradually accelerates and exceeds the downdip direction,after the speed of depressurization reaches the peak value,it gradually decreases and tends to a certain stable value,finally,the reservoir pressure drop in the updip direction is larger.Non-synchronization of drainage leads to asynchronous methane desorption,which leads to the preferential decrease of gas content in the downdip direction of coal reservoir,with the development of drainage and production,the gas content in the updip direction decreases gradually and the decline rate is greater than that in the downdip direction.In the stage of stable gas production,the decline rate of gas content in the uppid and downpid directions of coal reservoirs gradually slows down and tends to a certain stable value,and ultimately the gas content in the uppid direction decreases more than that in the downpid direction.The gas/water output characteristics of the steeply inclined coal reservoir during drainage stage,gas/water production stage and gas production stage are discussed,which has guiding significance for the development of coalbed methane in steeply inclined coal reservoirs.