Ultrarefined model of a coal bed methane reservoir: Connectivity and implications for production

Abstract

The Western Canadian Sedimentary Basin contains large quantities of deep coal which can be produced as coal bed methane (CBM) reservoirs. The Mannville Formation of Alberta is an attractive CBM play because of its high gas-in-place potential of 4–10 BCF per section depending on coal seam thickness and gas content. One requirement for enhanced reservoir access and gas production is detailed geological models that highlight the heterogeneity of the coal seams – this provides more insightful understanding of the architecture of the system enabling improved well planning. Here, we describe an ultrarefined Mannville Formation coal bed geological model which was constructed with input data derived from logs, core, core photos, adsorption isotherms, and gas composition analysis. This model reveals the structure of the underground coal beds and shows that they are laterally discontinuous and interbedded between sandstone and shale layers. Since they are subjected to high in-situ stress, low porosity and permeability is observed in these coal seams. The heterogeneity of the coal seams in the Mannville Formation is clear with ‘lenses’ of coal within the domain. These lenses are not fully connected and thus accessing the coal beds to produce gas presents difficulties unless complex trajectory wells and multilateral wells are used.