Pressure-Dependent Natural-Fracture Permeability in Shale and its Effect on Shale-Gas Well Production

Abstract

Abstract This paper presents the results of an experimental study of pressure-dependent natural-fracture permeability in tight, unconventional reservoirs. Bakken cores are used in the experiments. For the purpose of this paper, pressure-related permeability losses in hydraulic fractures and matrix system are not considered. Experimental data are used to screen the stress-dependent matrix-permeability correlations available in the literature for application to shale fractures. Selected correlations are matched with the data to delineate the reasonable ranges of the correlation coefficients for shale fractures. The applications of the correlations over practical ranges of pressure drop in shale reservoirs indicate over 80% reduction in fracture permeability, with most of the permeability loss occurring during the initial pressure drop. To appraise the effect of pressure-dependent natural-fracture permeability on shale-gas production, experimentally developed correlations are incorporated in an analytical model of a fractured horizontal well surrounded by a stimulated reservoir volume. The model is used to history match the performances of two wells in the Barnett and Haynesville formations. It is shown that the effect of pressure-dependent natural-fracture permeability on shale-gas-well production is a function of the permeability of the matrix system. If the matrix system is too tight, then the retained permeability of the natural fractures may still be sufficient for the available volume of the fluid when the system pressure drops.