Numerical Simulation of Tight Coalbed Methane Reservoir with the Matrix Shrinkage Effect

Coal seams in China are commonly of low permeability,especially those coal seams under one thousand meters which are yet tight porous media.The obvious slippage effect for gas flow has been found due to the low gas permeability,and the effect of coal matrix shrinkage on the permeability is also indispensable.Considering the effects of gas slippage and coal matrix shrinkage in tight coalbed methane reservoirs,a three-dimensional,nonequilibrium sorption,pseudosteady state two-phase flow mathematical model and a fully implicit numerical model were presented.Then,a coalbed methane reservoir simulator was developed.The simulation result indicates that the effects of gas slippage and coal matrix shrinkage on the well production are obvious,and the gas forecast production is higher with these two effects,of which the existence of the matrix shrinkage effect makes the cumulative gas production increased by 12.2%.