An Research On The Physical Properties Of Coal Reservoir Through High Pressure Water Injection

The physical properties of coal can be affected by the drilling process.In this paper,the pore structure,specific surface area,pore volume,pore size distribution,permeability,adsorption and desorption of coal in the Sihe,Changzhi and Anze areas were studied through true density experiment,low temperature nitrogen adsorption experiment,microscopic observation of pore fissure method,nuclear magnetic resonance experiment,wettability experiment,permeability test experiment,and so on.And ability and deformation characteristics of the impact were studied by means of intrusion of coal water desorption experiment and gas-liquid coupling triaxial servo strain dynamic experiment.Through the experimental study to obtain the following achievements and awareness:1.Through the wetting angle test,it is found that the water can enter the pore area of coal in the same area under the same water injection pressure after the high pressure water injection in the three areas,followed by Changzhi area and the largest in Anze area.When the water injection pressure increases from 5MPa to 20MPa,the critical pore scale of coal in three areas decreases rapidly.When the water injection pressure increases from 20MPa to 40MPa,the critical pore scale of coal in three areas decreases slowly.2.1t is found that the high pressure water injection measures can increase the pore volume of coal in three areas.With the increase of water injection time and the increase of water injection pressure,the effect of high pressure water injection on coal pore volume is greater.Under the same high pressure water injection measures,the effect of high pressure water on the pore volume of coal in the three regions is the largest in the Sihe area,followed by the Changzhi area and the minimum in the Anze area.3.Through low temperature nitrogen adsorption experiment,it is found that high pressure water has the most sensitive effect on micropore of coal in three areas after high pressure water injection,and high pressure water can increase the opening degree of parallel plate hole in three areas and expand the neck end of lagena or ink bottle in Changzhi,Anze area.High pressure water injection can increase the specific surface area and pore volume of coal,the higher the metamorphic degree of coal,the smaller the effect of high pressure water on the specific surface area of coal;The greater the critical pore size of coal,the greater the effect of high pressure water on the micropore volume of coal.Fractal analysis shows that high pressure water injection measures increase the irregularity of coal pore surface and improve coal adsorption capacity.4.Through the observation of fissure method by microscope,it is found that high pressure water injection can fill the coal fissure with high pressure water,and expand the fracture width.when the fluid pressure is greater than the fracture pressure of coal matrix,the new fissure or connected fissure direction can be produced.Therefore,the influence of high pressure water injection on the structure of coal pore has three ways:connected fractures,resulting new fractures and increase the width of fractures,so that coal has better opening and connectivity.5.Through permeability test,it is found that the permeability of coal increases with the increase of water injection time and water injection pressure.The micropore and pore of coal in three areas mainly played a role of adsorption and desorption,which has no contribution to coal permeability,and the largest contribution to the big hole on the permeability of coal,is the main channel,coal flow and migration in the hole.6.Through the gas-liquid coupling of the three-axis servo seepage dynamic experiments found that:when the gas through the saturated water coal pores,cracks,can break through the water film to carry part of the water discharge coal,making the water on the methane blocking effect,Coal permeability,but when the coal,cracks in the water is discharged to a certain extent,the gas will not affect the water in the coal,resulting in the permeability remains unchanged.7.The isothermal adsorption experiments show that high pressure water injection can increase the specific surface area and pore volume of coal.And the amount of methane of high pressure water injection coal in the inefficient desorption stage,slow desorption stage and rapid desorption stage are less than the Desorption of natural coal,only the amount of methane of the sensitive desorption stage exceeds the natural coal.8.Through the hydrolysis of methane coal after coal injection,it is found that high pressure water injection plays a depressant role in the early stage,and promotes action in the later stage,makes the desorption of coal after water injection basically the same as natural coal.9.Through the Coupling triaxial servo strain test,it is found that when coal adsorption methane,the coal can expand deformation,so that the coal volume expansion.When the coal pillar methane desorption,the coal pillar shrinkage deformation,the coal volume shrinkage of 0.18,can not recover to the volume of adsorption.After the adsorption of methane coal into high pressure water,the beginning of the slow deformation of coal,coal volume shrinkage.Then the rapid expansion deformation of coal causes the volume expansion of coal.When coal began to water gas,the coal pillar contracted deformation,and the coal volume contracted 0.44.