Viscosity of shale gas.

Nanofluidics, which analyzes fluid transport through sub 100-nm conduits, has fascinated engineers in different fields and we petroleum engineers are no exception. This field gained a significant interest in petroleum engineering only when hydrocarbon production from shales became economically feasible. The basic transport properties of the fluid change for this range of conduit size. With this in mind, we analyze the effective gas viscosity of a shale at different pore pressures. Our objective is not to derive detailed information about the gas transport at a pore or a sub-pore scale, but rather to discuss the implications of pore-scale simulations on the effective gas viscosity at the core scale. We use an acyclic pore model to account for the effective connectivity of the pore space at the core scale. The acyclic model is physically representative because it can capture capillary pressure measurements of the drainage obtained from mercury intrusion experiments. We present the effective gas viscosity with respect to the nominal value, under unconfined conditions. Our analysis shows that the reported permeability in a pressure-driven flow has to be considered an effective transport property if nominal viscosity and density are used for interpretation. That is, we have to modify viscosity and permeability simultaneously in our reservoir model. Our study has major implications for building a realistic reservoir model for shales based on petrophysical measurements. [ABSTRACT FROM AUTHOR]