Year

2014

Degree Name

Master of Philosophy in Mining Engineering

Department

Faculty of Engineering and Information Sciences

Abstract

Permeability of rock is the ability of transmitting the fluid flow through the rock body. It can be affected mainly by rock structure and it’s matrix due to the grain size, formation and the pressure or concentration gradient existing within and across it. Past studies mainly focused on the relationship of permeability and axial stress of rock, and there was a little research on the impact of circumferential stress and volumetric deformation on the permeability. A programme of laboratory tests was conducted on sandstone and coal samples from two mines (Mines A and B) to evaluate the permeability of different rock formations. Two specialised permeability apparatuses, Multi-Functional Outburst Research Rig (MFORR), and a high pressure triaxial apparatus were used to study rock permeability under various confining pressures. Triaxial tests were conducted on sandstone samples under different confining pressures of 750 kPa to 1582 kPa at different vertical stress of 0.5, 1, 2, 3 and 4 MPa, and for coal samples testes were made, at varying vertical stress of 1, 2 and 3 MPa and gas pressures ranging from 0.2 MPa to 3 MPa. Methods of permeability testing of sandstone and coal samples under different triaxial conditions are discussed. Permeability testing of the sandstone with water and coal samples with CH4 are described. The permeability of coal sample was evaluated using MFORR rigs; in addition, the impact of circumferential stress and volumetric changes on the permeability of coal was evaluated by MFORR. The laboratory test results for coal samples showed that by increasing the confining gas pressure the permeability value decreased in elastic phase and maintained an almost constant value at gas pressures of > 2000 kPa. The results show that the permeability of coal sample under triaxial compression tends to decrease with the increase in stress, which indicates that permeability of the coal is actually controlled by the evolution of cracks in the coals. For sandstone samples, the permeability decreased monotonously with axial compression, mainly due to pore collapse and compressive closure of the preexisting micro-cracks. The permeability first decreased with increasing axial stress, then began to maintain an almost constant value.

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