A relative permeability model for CBM reservoir

Abstract

Relative permeability is an effective tool for studying multiphase fluid flow in porous media. For conventional reservoirs, a relatively reliable relative permeability curve can be obtained by laboratory core test. But because of the coalbed gas reservoir permeability is low, the stable steady state method will take a very long time, and the operation is relatively complex. For the non-steady state method, the coalbed gas reservoirs are rich in micro nano pore, which causes the strong heterogeneity and gas is easy to break in through the cracks, it makes non-steady displacement experiment very difficult. Also, the experimental results are greatly affected by human factors and computational methods. Therefore, based on the ideal pore structure and the consideration of different displacement mechanisms, the analytical method not only helps to understand the mechanism of gas water two-phase flow, but also is a convenient and practical method. Coalbed methane reservoirs are rich of nano pores, and the percolation process is more complicated due to the water. Consider of the nano pore of the coal, the capillary force’s effect will be more important. The different pressure will cause different flow channel, which will change the permeability. In this paper, the relative permeability model of coalbed methane reservoir has been built which considers the gas diffusion and slippage effect, pore throat structure parameter, water saturation distribution, and gas water interface pressure drop. It can describe the difference flow channel between different pressure.