Critical properties (Tc, Pc) of shale gas at the core scale

Abstract

The transport properties of gas deviate from the nominal values, reported without confinements, when it is confined inside a nano-size conduit. This is because the interactions between the gas molecules and the conduit become more important than do those of the gas molecules with each other. The deviation is relevant to shale gas because of the ultra-narrow pore size in the matrix. With this in mind, we determine the critical temperature (Tc) and critical pressure (Pc) for shale formations in North America at the core scale. The shale formations are the Bakken, Barnett, Eagle Ford, Haynesville, Marcellus, Monterey, New Albany, Niobrara, Utica, Wolfcamp, and Woodford. The present study uses the acyclic pore model to account for the effective connectivity of shale samples at the core scale. It also differentiates between the pore-throat and pore-body size distributions. The former is used to derive the critical properties relevant to the fluid flow (displacement), and the latter is used to determine the effective properties relevant to the storage. Our study shows that the displacement-critical properties change significantly, whereas the storage-critical properties do not require modifications. Quantitative corrections of the critical properties for various formations are presented. The results have major applications in developing a realistic reservoir model for shale formations.