Importance of Fabric on Production Rates of Gas Shales: Experimental and Numerical Analyses

Bustin, Amanda M.M.¹, Xiaojun Cui¹, Venkat Murthy¹, R. Marc Bustin¹ (1) University of British Columbia, Vancouver, BC

Gas production from shales is widely postulated to be controlled principally by Darcy flow through the fracture system and the matrix is considered important principally for gas storage. Gas diffusion/flow for the matrix is generally not considered production limiting. Based on a series of diffusion/flow experiments under triaxial (reservoir) conditions we show that gas released from the matrix is strongly stress dependent and occurs at rates that in many shale reservoirs with wide fracture spacing is production limiting. The stress sensitivity of permeability and pore compressibility of the shales is directly correlatable to the mineralogy and fabric, with clay-rich shales being both more compressible and stress sensitive than most biogenic silica-rich shales. In order to test the relative importance of fracture spacing and matrix diffusion on the permeability and production of gas shales, we have developed a 1D numerical simulation model, which considers both the diffusion in shale matrices and the flow of gas through fractures for varying fabrics utilising experimental data obtained from a variety of important gas shales. Understanding the relationship between shale fabric, composition and effective stress on gas production will assist in exploration and exploitation of potential gas shales.