Abstracts Category : Other

Pore network modelling for coal seams

by Ali Zamani

Pore Network Modelling (PNM) is a well-established micro-scale numerical method for the prediction of permeability in reservoir rocks. We study the capabilities of this method for coal as a heterogeneous unconventional rock. The fracture structure of coal known as cleats is captured using high resolution micro-Computed Tomography (micro-CT) images at the core-scale. A network model is extracted to idealise the fractured geometry and its interconnectivity. This three-dimensional arrangement of pore nodes and throats replaces the entire complex geometry of coal. Flow simulation is then performed on the extracted network model. The absolute permeability is compared with direct computations on micro-CT images by the Lattice Boltzmann Method (LBM). Obtained relative permeability is also compared against Capillary Drainage Transform (CDT) and microfluidic framework as direct simulation and experimental methods, respectively. Comparison of PNM with LBM, CDT and microfluidic results shows applicability of PNM as a predictive method for permeability in anisotropic geometries such as coal. However, the accuracy of calculations is tied to the connectivity of the fractures in the flooding direction. The effects of flow direction, wettability and pore network geometrical statistics such as coordination number, pore size distribution and shape factor on absolute and relative permeabilities are investigated. Then, a numerical simulation model is developed using a commercial reservoir simulator to estimate the average relative permeability at the core-scale. The effect of different wettability conditions on gas production from coal is investigated by moving the cross point in the obtained gas-water relative permeability. Our results quantified the effects of aperture size, wettability and porosity of coal on its permeability. However, to improve the accuracy of the results, it is recommended to combine PNM with stochastic methods to simulate flow on more representative samples in terms of size. In addition, effect of micropores is ignored in this work. Dual networks are recommended to be developed to take them into account.Advisors/Committee Members: Mostaghimi, Peyman, Petroleum Engineering, Faculty of Engineering, UNSW.