Anisotropy and Stress Dependence of Permeability in the Barnett Shale

We document vertical permeability of $$2.3 \times 10^{-21}\, \hbox {m}^{2}$$2.3×10-21m2 (2.3 nd) and horizontal permeability of $$9.5 \times 10^{-20}\, \hbox {m}^{2}$$9.5×10-20m2 (96.3 nd) in two Barnett Shale samples. The samples are composed predominantly of quartz, calcite, and clay; have a porosity and a total organic content of $$\sim $$∼4 % each; and have a thermal maturity of 1.9 % vitrinite reflectance. Both samples exhibit stress-dependent permeability when the confining pressure is increased from 10.3 to 41.4 MPa. We measure a permeability anisotropy, the ratio of the horizontal to the vertical permeability, of $$\sim $$∼40. We find that the permeability anisotropy does not vary with effective stress. Multiscale permeability, as demonstrated by pressure dissipation, is related to millimeter-scale stratigraphic variation. We attribute the permeability anisotropy to preferential flow along more permeable layers and attribute the stress dependence to pore closure. A determination of permeability anisotropy allows us to understand flow properties in horizontal and vertical directions and assists our understanding of upscaling. Characterization of stress dependency allows us to predict permeability evolution during production.