Three-dimensional modeling of nanoconfined multiphase flow in clay nanopores using FIB-SEM images of shale

Abstract

<p>Understanding the flow characteristics within shale nanopores is crucial for enhancing hydrocarbon recovery. However, the flow characteristics of wetting and non-wetting fluids on nanopore surfaces differ significantly, limiting the accurate prediction of hydrocarbon accumulation and migration. This work introduces the Euler-Euler volume of fluid method to establish a multiphase flow numerical model in shale nanopores, considering complex pore topology, slip flow, and capillary effects. Based on natural three-dimensional shale nanoporous systems constructed from FIB-SEM images, single-phase water/oil flow and water-oil forced imbibition simulations are carried out under the complete wetting condition. Results show that the displacement pressure is reduced and the imbibition rate is elevated considering nanoscale slip effects. As imbibition progresses, the pressure and imbibition rate gradually converge toward the values observed in conventional flows. In complete wetting nanoporous systems, water flow experiences high pressure and low velocity, whereas the pressure for oil flow is significantly reduced. Forced imbibition may undergo a transition from capillary force-dominated to viscous force-dominated, with a negative displacement pressure at the initial stage. Furthermore, the fluctuations in water-oil mass flow considering the slip effect are less pronounced than those observed in conventional flows, leading to reduced residual fluid saturation in blind-end pores and pore bodies caused by snap-off events. Pore systems with poor connectivity and narrow throat structures correspond to low displacement efficiency. The findings of this work explain the impact of nanoscale slip effects on flow characteristics in unconventional reservoirs, contributing to the reasonable assessment of fluid flow capacity and facilitating production planning.</p>