Dynamics of CO2 in coal as a reservoir

Abstract

The mechanisms, by which the coal seams sorb, retain and store gases needs, to be understood. The results presented in this thesis give an insight into the dynamics of CO2 and other flue gas components in coal that are related to operation feasibility of ECBM projects. The main issues relate to the permeability behavior and the flue gas/ CO2 sorption. The cleat network in coal seams provides the principal source of permeability for fluid flow. Understanding and predicting the cleat attributes is necessary for creating a flow model. A methodology for determining the cleat spacing is proposed, which uses a Gaussian point spread function. Using this method, the cleat apertures were measured with the aid of CT images. In addition, a method to determine the cleat orientation and cleat spacing distribution from CT scans of coal samples was developed. Regarding the cleat orientation and relevant cleat spacing, we observe configuration dependent spacing distributions, which can be used for fracture modeling in coal specimens, up to one cubic foot in size. The method combines these two different techniques, and gives a better understanding of the cleat framework. Up-scaling to seam size was not investigated. This combined procedure also proves that it is possible to distinguish the face cleat, the butt cleat and the bedding system. However, no measurement can be exact in the sub-pixel level, including the method described above. At best, choosing the right method can reduce the error in the approximations.