“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 basiscompared to methane. It is also known that methane desorption is a strong function of the partialpressure 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, andthe productivity of produced methane; both are determined by the bulk coal reservoir permeability andits variance over time.A joint Chemical Engineering & Earth Sciences project at The University of Queensland isinvestigating the absolute, effective and relative permeability of in-situ coals, under realisticconditions of stress and pore pressure, utilising a world-first True Triaxial Stress CoalPermeameter. This paper summarises the 4-D nature of coal permeability and the research program toarrive at the requisite knowledge of the behaviour of in-situ coals to CO2 injection: measuring theeffective and relative permeabilities of the CO2 & CH4 system, and the displacement efficiencies onmethane-saturated samples. Also, comparisons are made between utilising pure CO_2 and a mixture ofCO_2 & nitrogen, on the feasibility economics of utilising such a process in Australia. The kinetics ofcompetitive adsorption and desorption, of Fickian diffusion and the geochemical and geomechanicalinjection-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 theimportance of considering the correspondence principle between directional stresses and cleatorientation.