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

This paper presents an investigation of the effect of pressure-dependent natural-fracture permeability on production from shale-gas wells. The motivation of the study is to provide data for the discussion of whether it is crucial to pump proppant into natural fractures in shale plays. Experiments have been conducted on Bakken-shale core samples to select appropriate correlations to represent fracture conductivity as a function of pressure (the actual characterization of fracture conductivity under stress for a specific formation is not an objective of the study). Correlations have been used in a flow model to demonstrate the potential impact of natural-fracture closure as pressure drops during production. Although the correlations indicate up to an 80% reduction in fracture permeability over practical ranges of pressure, the results of the flow model do not warrant the claims that fracture closing plays a significant role in the productivity losses of shale-gas wells. A history match of the performances of two wells in the Barnett and Haynesville formations also indicates 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.