Experimental Study And Application Of Measuring Technology Of Coal Seam Gas Pressure Without Sealing Hole

The accuracy of the measurement results of coal seam gas pressure is very important.In view of the current situation of coal seam gas pressure measurement that the direct pressure measurement method has strict requirements on the selection of test location and sealing quality,which leads to low success rate of pressure measurement,high test cost and long test cycle,while the indirect pressure measurement method has some shortcomings in accuracy and experimental operation,this paper puts forward a gas pressure measurement technology based on the principle of"state recovery"in unsealed coal seam.Relying on the self-developed non-sealing coal seam gas pressure measuring instrument,the experimental research and application of non-sealing hole pressure measuring technology are carried out.Firstly,the feasibility of the non-sealing pressure measurement technology was verified through the state restoration simulation experiment;Secondly,the experimental results of different coal core volume restoration methods are emphatically studied.The coal core volume restoration methods include:loading axial compression coal core volume restoration,contact injection（water/silicone oil）coal core volume restoration and pressure and liquid injection combined coal core volume restoration.The experimental results of different restoration methods were compared.Determine the coal core volume restoration method combining pressurization and liquid injection;.Finally,combined with the field measurement method and indirect inversion method,the unsealed hole pressure measurement technology was applied in the field.In order to test the application effect of gas pressure measurement technology in coal seam without sealing hole.The results show that:（1）In the feasibility experiment study of the non-sealing pressure measurement technology,the 6 gas pressure recovery values（P_s）based on quantitative compensation of escaped gas,coal core volume restoration and reservoir temperature simulation,they are compared with the initial adsorption equilibrium pressure（P₀）,and the error range is:-10.00%～7.33%,thus verifying the feasibility of the sealing-free pressure measurement technology.（2）The volume recovery of coal core is very important in the pressure measurement technology without sealing hole.When the coal core volume is restored by loading axial pressure,due to the mutual support and resistance between the coal particles,the new pores and fissures caused by the broken coal can not be completely"healed".Therefore,it is difficult to recover coal core volume by simply pressurizing,either from the technical point of view or from the perspective of theoretical analysis.（3）Contact water injection coal core volume restoration method.Gas pressure reco very value（P_S）deviates from the initial adsorption equilibrium pressure（P₀）,the error is40.67%～116.13%.The main reason is that water displaces the absorbed gas in coal and l iquid submerges the coal sample to block the path of the free gas into the coal sample pa rticles.The final result is that the amount of free gas increases and the gas pressure incre ases;（4）The effect of coal core volume recovery by contact oil injection is similar to th at by contact water injection experiment.The error between gas pressure recovery value（P_S）and initial adsorption equilibrium pressure（P₀）is 29.33%～87.10%.Also,because th e oil forms a liquid level of a certain thickness above the coal sample,the coal sample is isolated from the adsorption of free gas on the top.The final performance is the increase of gas pressure,but oil can not replace gas,so the error is relatively small compared wit h contact water injection;（5）The combination of pressure and liquid injection has a better experimental effe ct on the coal core volume restoration.The error ranges from 2.67%to 9.68%.By compa ring the experimental results of three kinds of coal core volume restoration methods,the coal core volume was finally restored by the combination of upper chamber pressure an d lower chamber liquid injection;（6）Through field application test,for the selected 1#to 4#original gas pressure measuring holes,the error range between the pressure measurement results of non sealed holes and the field measurement results is 5.00%～9.52%,and the error range between the pressure measurement results of non sealed holes and the indirect inversion results is-6.25%～1.45%;for the four residual gas pressure measuring points,the error range between the pressure measurement results of non sealed holes and the indirect inversion results is-4.49%～2.74%.（7）The feasibility verification and field application of non sealing hole pressure measurement technology show that the method is reliable,not limited by the pressure measurement location and sealing technology,shortens the pressure measurement cycle,greatly reduces the pressure measurement cost,and provides a fast and reliable new way for the determination of the original gas pressure in coal mine,especially the residual gas pressure in coal seam after taking gas control measures.There are 39 figures,26 tables and 81 references in this paper.