Attenuation characteristics of coal fissure induced by gas-water two-phase drive

Finding out the variation characteristics of fracture diversion capacity in coal caused by different particle sizes pulverized coal driven by gas and water is of significance for the formulation of pulverized coal control measures during gaswater twophase flow in coalbed methane wells.Using the selfmade gasliquidsolid threephase displace pulverized coal simulation device,the experiments on the migration of different particle sizes pulverized coal (40-60 mesh,60-80 mesh,80-100 mesh,100-150 mesh,150-200 mesh,greater than 200 mesh) drived by gaswater twophase flow was carried out.By comparing with the blank experiment of no pulverized coal gaswater twophase displace,the difference of gas and water seepage law when the different particle sizes pulverized coal was driven by gaswater twophase flow was analyzed.Based on the gas and water percolation model under different particle sizes pulverized coal driven by gaswater twophase flow,combining the theory of plate,the fitting formula of the gas permeability and crack width to quantitatively describe the gas flow and liquid flow and pulverized coal block occupying crack width changing with the displace time in the displace process,the fracture diversion capacity attenuation characteristics of resincoal core sample were characterized by the variation of the crack width occupied by gas and water.The results show that under almost the same initial displace pressure,the gas and water compete with each other for the crack space in the resincoal core sample,and the gas permeability and liquid permeability change with time in a trigonometric distribution.In the early stage of pulverized coal displacement with different particle sizes,the gas permeability and liquid permeability would still show the characteristic of trigonometric distribution,after a certain degree of pulverized coal blockage,both of them start to decrease.When different particle sizes pulverized coal driven by gaswater twophase flow,the mass concentration of pulverized coal in the produced liquid and the time of crack complete plugging increase with the decrease of pulverized coal particle size.When different particle sizes pulverized coal driven by gaswater twophase flow,the change of fracture conductivity can be divided into four stages:rapid sealing of fracture before liquid production,small increase of fracture width of gas and water carrying pulverized coal out,rapid closing of fracture with sharp decrease of liquid flow capacity,and complete sealing of fracture with slow decrease of gas flow capacity