Study of Permeability of Coal Samples Subjected to Confining Pressures

Permeability is assessment of the ability of rock to transmit fluid flow through the rock body. It can be affected by rock structure due to the grain size, formation and the pressure or concentration gradient existing within and across it. Past studies focused on the relationship between permeability and axial stress on rock, and there has been limited research on the impact of circumferential stress and volumetric deformation on permeability. A programme of laboratory tests was conducted on coal samples to evaluate the permeability of coal under different confining pressures. A specialised permeability apparatus known as Multi-Functional Outburst Research Rig (MFORR), was used to study rock permeability under various confining pressures. Methane permeability tests on cylindrical coal samples were conducted at varying axial stress up to 3 MPa and confining CH4 gas pressures between 0.2 MPa and 3 MPa. It was found that by increasing the confining gas pressure the permeability value decreased in elastic phase and maintained an almost constant value at gas pressures greater than 2 MPa. The results show that the permeability of coal sample under triaxial compression tend to decrease with the increase in stress.