Numerical Experiments of Gas Injection Pressurization for CBM Open Hole Cavity Completion

The stimulation of CBM cavity wells are remarkably successful in the San Juan Basin of the United States while it is not encouraging in improving CBM production in China.Considering its application prospect in the low rank coal seam,the mechanism of openhole cavity completion should be studied further.A discrete element numerical model simulating the process of gas injection for coalbed methane openhole cavity completion was built based on UDEC software.Analysis showed that: anisotropic coal reservoirs are more prone to rupture and collapse than those isotropic ones.In the vertical fracture system,the discrepancy in the fluid velocity would lead to differences in effective stress gradient and help to generate shear fractures.Tensile fractures’ generation and growing trend could be reflected by nodal displacement vector distribution.Combined with Shouyang cavity well field test,preliminary forecast showed that the tensile fracture would extend about 25 meters around the wellbore,the average permeability of this tensile fracture influenced area wa seven times lager than the initial permeability.