Transient of flow regimes and slip boundary analysis of water and gas in nano clay pores

Abstract

ABSTRACT Nanoscale two-phase flow is important during shale gas production. In this work, molecular dynamics simulations are employed to investigate fluid flow regimes of water and methane under different pressure gradients inside the nanoscale slit pores. The illite mineral is selected to model the clay pores based on the Small-Angle X-ray Diffraction (SAXD) experiment. The different flow regimes of gas-water two-phase are visualised and the structures are analysed. As the driving pressure gradient increases, it is observed that the two-phase flow in the slit undergoes transitions from intermittent flow to a transition stage between intermittent flow and annular flow, and finally fully converts to annular flow. The slip conditions during the two-phase flow on the hydrophilic illite surface are investigated. We found that the negative slip length stays around 0.25 nm within the range of practical production pressure gradients, which can be used for accurate production prediction. This work provides detailed insights into the nanoscale water and gas two-flow inside the clay nanopores during shale gas exploration.