“4-D Coal Permeability for Geological Sequestration of CO_2”

摘要

It is well known that CO_2 adsorbs unto coal’s internal microstructure on a preferential +2:1 basis compared to methane. It is also known that methane desorption is a strong function of the partial pressure to methane, so that carbon dioxide and even nitrogen can be used to coax the methane out. Key technical parameters affecting the economic viability are the injectivity of CO_2 and flue gases, and the productivity of produced methane; both are determined by the bulk coal reservoir permeability and its variance over time. A joint Chemical Engineering & Earth Sciences project at The University of Queensland is investigating the absolute, effective and relative permeability of in-situ coals, under realistic conditions of stress and pore pressure, utilising a world-first True Triaxial Stress Coal Permeameter. This paper summarises the 4-D nature of coal permeability and the research program to arrive at the requisite knowledge of the behaviour of in-situ coals to CO2 injection: measuring the effective and relative permeabilities of the CO2 & CH4 system, and the displacement efficiencies on methane-saturated samples. Also, comparisons are made between utilising pure CO_2 and a mixture of CO_2 & nitrogen, on the feasibility economics of utilising such a process in Australia. The kinetics of competitive adsorption and desorption, of Fickian diffusion and the geochemical and geomechanical injection-induced alterations, are investigated as to effect on the main Darcy flow of the cleat system. Added insight is provided by petrological characterisation of potential coal sequestering reservoirs. Some preliminary results are presented on the anisotropic behaviour of permeability and the importance of considering the correspondence principle between directional stresses and cleat orientation.