Slippage in shale based on acyclic pore model

Abstract

A significant fraction of the pore-throat size in the matrix of a shale formation is smaller than 100 nm. Nanofluidics, a field that deals with the transport properties of sub-100-nm conduits, indicates that the fluid flow is enhanced for this range of pore-throat size. However, it is unclear how the slippage at the pore scale (single conduit) controls the effective slippage at the core scale (∼1 in.). The present study reviews the slippage models for the gas and liquid flows inside a single conduit based on the experimental and theoretical studies in the literature. It then investigates the effective enhancement in shale formations using an acyclic pore model, which represents the effective connectivity of the shale pore space at the core scale as it captures the mercury injection capillary pressure measurements (drainage). The effective slippage is presented in terms of governing parameters such as pore pressure and wettability. This study presents the effective pore-throat size, whose corresponding slippage is equal to the effective gas slippage at the core scale, for three shale samples. The numerical simulations indicate that the effective pore-throat size for the gas flow depends on the pore pressure. In addition, the measured permeability with liquid is higher than the nominal permeability, often referred to as the Hagen–Poiseuille model, with no slippage. The presented results have major implications for reservoir characterization based on standard petrophysical measurements.