Experimental Study On Coal Deformation Influence Gas Pressure Build-up

In view of the problem that the coal deformation gas pressure build-up permeability evaluation method is difficult to be accurately divided in the flow stage,the coal deformation and gas pressure build-up characteristics are studied.The influence and characteristics of coal stress deformation and gas pressure deformation on the process of coal seam gas pressure build-up are analyzed.A model for gas pressure build-up in coal seam is established,and the pressure build-up flow stage is divided.(1)The simulation experiment of homemade device reveals the gas pressure build-up process of coal body,and accurately diagnoses and divides the gas flow stage.Using the theory of pressure build-up,a self-made device is used to simulate the gas pressure build-up process of coal seam drilling,combining the characteristic curve of gas pressure build-up with gas pressure derivative curve,using the double logarithm pressure derivative chart to analyze the pressure build-up process,which solves the deficiencies in the model diagnosis and the flow pattern division.(2)The mathematical model of gas pressure build-up curve of coal body is established theoretically.Using the theory of pressure build-up curve in oil and gas well,by summarizing the current law of gas flow,combining the relationship between the gas parameters of borehole and the transformation of the dimension,the seepage model and interpretation method for coal seam pressure measurement are established based on the most essential equation of gas flow,and the stress build-up formula is used,By using the method of semi logarithmic linear segment analysis,the permeability of coal seam is calculated quickly and accurately.(3)Combining the characteristic curve and the pressure chart derivative curve to accurately divide the pressure build-up flow stage.The pressure build-up flow process is divided into four stages,such as gas storage section,Transition section,Radial flow section and steady flow segment.Based on the comparison between the calculated permeability and the experimental data,it is found that the relative error between the calculated result and the measured result is between 7.89%-17.39%,the average error is 11.05%,and the error is within acceptable range,and the feasibility of the phase dividing method of the pressure build-up characteristic curve is confirmed.(4)Under the action of gas pressure deformation,with the increase of gas pressure,the strain value of coal is changed with "V",and the volume strain value is inversely proportional to the pressure build-up speed.In the initial stage of gas injection coal sample,the strain of coal sample is contracted,and the rebound phenomenon is shown in a short time,the coal sample is expanded and deformed,the coal sample strain growth rate is smaller,the deformation is bigger,the pressure Derivative Curve Radial Flow section appears more late.(5)The deformation of stress plays an important role in the pressure build-up of coal,and the rate of strain change increases gradually with the axial pressure gradient loading.In the process of applying stress,the gas flow velocity in the coal body decreases with the gradual deterioration of the seepage channel.The higher the stress derivative curve,the more slowly the pressure build-up speed,the lower the flow coefficient of gas in the coal body,the higher the pressure derivative curve is in the horizontal segment,The effect of deformation of gas pressure on the process of pressure build-up is more obvious than that of stress.To sum up,the paper studies the gas pressure build-up characteristics of coal-loaded coals in Jiaozuo Guhanshan mine,and provides some experimental and theoretical basis for understanding the internal characteristics and parameter determination of coal seam through the pressure build-up curve later.