Anisotropic pore structure of shale and gas injection-induced nanopore alteration: A small-angle neutron scattering study

Gas transport in the shale matrix is controlled by pore structure, which can ultimately influence natural gas production potential and carbon sequestration in shale gas reservoirs. In this study, in situ small-angle neutron scattering (SANS) measurements under methane and CO₂ injections were employed to investigate two Marcellus Shale thin section samples cut parallel and perpendicular to the bedding. Marcellus Shale nanopores show intrinsic anisotropy over the detected length scale of 5–2000 Å. Microscopic gas transport could be inhibited due to the decrease of accessible porosity with increasing gas pressure. The degree of inhibition may be higher for CO₂ than for methane, and for the direction normal to the bedding than in the bedding direction. In addition, under the condition of liquid CO₂, higher porosity reduction for the direction normal to the bedding may insight into nanoscale anisotropic wettability in the shale matrix.