Field scale coal permeability modeling and sweet-spotting using seismic attributes

Pre-drill estimation of coal bed permeability is a major challenge for Coal-bed Methane (CBM) extraction and CO 2 sequestration in coal beds. Unlike conventional reservoirs, the permeability of coal is solely dependent on fractures, as matrix permeability is negligible. The distribution of primary (face and butt cleats) and secondary fractures (tectonic fractures) imparts significant heterogeneity in coal beds. This remains a challenge for CBM Operators to quantify and map permeability sweet-spots. In this paper, an innovative solution to these is proposed by building permeability models within a sector of the Raniganj coal field, India. Initially, structural realizations are constructed by interpreting thirteen 2D seismic lines over the study area. Thereafter, permeability distribution in these structural models is populated by permeability-depth trends. Separate trends of primary and secondary fractures are derived from literature, field observations, and discrete fracture network (DFN) models of coal samples. The curvature attribute of the interpreted coal beds from seismic reflection surfaces is used as a substitute for the intensity of tectonically controlled fractures. Finally, a workflow of integrating tectonically controlled fracture permeability with cleat-controlled permeability is demonstrated to locate possible permeability sweet-spots. Although the workflow is demonstrated in the Raniganj coalfield, it can be used globally for pre-drill permeability estimation and well-planning during appraisal/development.