Pore-scale analysis of flow resistance in tight sandstones and its relationship with permeability jail

Abstract

In tight sandstones from the Sichuan basin, permeability jail is observed. Because tight sandstones in the Sichuan basin have a high water saturation, gas and water exist as discontinuous phases at the pore scale, which could be the cause of permeability jail. In this paper, flow resistance in tight sandstones was studied, and its relationship with permeability jail was investigated. First, a model to characterize flow resistance in discontinuous phase flow was proposed. The model was based on a bundle of capillary tubes with non-uniform radii, which took the capillary pressure difference induced by the Jamin effect, water viscosity force and gas viscosity force into account. Then, a gas-water relative permeability test and NMR experiment were conducted to verify the model. Finally, the flow resistance at a series of water saturation points was calculated to study the relationship between flow resistance and permeability jail. The results show that discontinuous phase flow is affected by the Jamin effect, which induces permeability jail because the capillary pressure difference reaches the maximum and leads to a very high flow resistance in permeability jail. Capillary pressure difference falls, however, when water saturation is outside of permeability jail, which contributes to the drop of the flow resistance and helps recover the flow capability.