Numerical Simulation of Gas Injection for CBM Openhole Cavity Completion Considering the Coal Vertical Fracture System

Abstract

A discrete element numerical model simulating the process of gas pressurization in coalbed methane wells is built based on UDEC software. The model considers the unique vertical fracture system of the coal. Simulates the distribution of effective stress, pore pressure and the node displacement vector around the wellbore in the process of pressurization under different terrestrial stress conditions. The analysis shows that, reservoir fluid flow and matrix deformation in the pressurization of cavity completion can be better represented by taking coal's unique fracture system into consideration. Coal reservoir with anisotropic stress is more prone to rupture and collapse than that under isotropic condition. In the vertical fracture system, the discrepancy of the fluid velocity will lead to differences in formation stress gradient and help generate shearing fracture. Tensile fractures’ formation and growing trend can be reflected by nodal displacement vector distribution.