Effect of dominated coal pores and fractures on water migration after low-pressure water injection based on CT images

A computational model for water migration in porous media is developed based on the CT images of coal samples to study the effect of dominant pores and fractures on water migration after low-pressure water injection. The pore and fracture structure in this model is regarded as porous media with a porosity ratio close to 1, and the fluid exchange between the pores and fractures and the matrix area is considered. The effect of pore and fracture structure on water migration is determined through numerical solution. Results show that the velocity of the fluid flowing into the matrix from the corner of the fracture increases significantly. Moreover, the efficiency of water migration in the radial fractures is high, and water tends to flow to the radial fractures. The pores mainly play a role in quickly absorbing and efficiently transporting water. The non-connected pores can increase the range of water migration and should not therefore be ignored. The role of pores and fractures in dominating water migration is most obvious at the front edge of water migration. The water migration is divided into three stages: high-velocity, transitional, and low-velocity migration stages. In addition, the distance difference between the saturation contours of water migration has a logarithmic relationship with time, and the macro fractures around the boreholes cause the increase in the distance difference between the two saturation contours.