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

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.

A Review of Critical Conditions for the Onset of Nonlinear Fluid Flow in Rock Fractures

“…The normal stress applied on a cuboid sample and/or confining pressure applied on a cylindrical sample can decrease the permeability of rock mass, following exponential functions [107][108][109][110][111][112]. With increasing the normal stress , both the fracture closure and the increasing rate increase as shown in Figure 8, where max is the maximum closure and 0 is the initial stiffness [113,114].…”

Estimation of the width of microfractures in shale rocks

“…The base question is: are measured permeability values reflect to intergranular or fracture permeability? Assuming that the 22 nD is the lowest value of rock matrix permeability, and considering that rock matrix permeability (according to the available published materials) [2,3,12] can reach to up to 1.3 μD, it should be assumed that all samples with permeability values greater than 0.0013 mD (1.3 μD) are associated with the system of microfractures.…”

“…The values of shale gas pearmeability, presented in the literature range between several and several hundred nanoDarcy (for the rock matrix) [2,3]. The dispersion of results is associated with the mineral composition and the petrographic type of shale rocks (mudstones, claystones, siltstones).…”

Experimental Study on the Stress Sensitivity and Influence Factors of Shale under Varying Stress

“…The pore characteristics influence the storage capacity, occurrence state, and migration capacity of shale gas within the reservoir. Permeability is a measure of the ability of porous media to allow fluid flow and is the key parameter of shale gas production capacity [11,12]. Experimental research has been an important means to study the permeability of shale gas; some scholars have analysed the permeability characteristics of shale gas accounting for Klinkenberg's effect and the shale gas migration form [13][14][15][16][17][18].…”