Gas Transport in Shale Nanopores with Miscible Zone

Abstract

Based on the results of molecular dynamics simulation, in a gas-water miscible zone, the velocity profiles of the flowing water film do not increase monotonously but increase first and then decrease, which is due to the interaction between water and gas molecules. This exhibits a new physical mechanism. In this paper, we firstly propose a gas-water flow model that takes into account the new physical phenomena and describes the distribution of gas-water velocity in the whole pore more accurately. In this model, a decreasing factor for water film in the gas-water miscible zone is used to describe the decrease of water velocity in the gas-water miscible zone, which leads to the gas velocity decrease correspondingly. The new flow model considers the interaction among gas and water molecules in the miscible zone and can provide more accurate velocity profiles compared with the flow models not considering the miscible region. Comparison calculation shows that the previous model overestimates the flow velocity, and the overestimation increases with the decrease of the pore radius. Based on the new gas-water flow model, a new permeability correction factor is deduced to consider the interaction among gas and water molecules.

Exploring Porous Flow Behavior of the Decomposed Gas from CH4 Hydrate in Clayey Sediments by Molecular Dynamics Simulation

“…The effect of pressure on the flow process will be investigated in future work. Therefore, the driving force of gas flow comes from a gas concentration difference between the liq-layer and the vac-layer in our simulations rather than a external force − and a pressure difference …”

“…Molecular dynamics (MD) simulation has been extensively applied to understand the dynamics behaviors of gas molecules on the nanoscale. , MD simulations can provide the information on the gas transport characteristic within nanopores taking into account the radical ambient conditions (e.g., high pressure and low temperature). , In previous studies, the different gas–water two-phase flow models in the hydrophobic nanopore or the hydrophilic nanopore had been constructed by MD simulation. Also, the effects of pore surface properties, water concentration, and the gas–water two-phase velocity on the two-phase flow behaviors were reported. − The flows of these MD simulations were driven by an external force. Zhang et al reported the two-phase flow process of CH 4 –H 2 O in a silica nanopore by a new method “nanomanometer” using MD simulation.…”

Experimental and Theoretical Investigation of the Bound Water Film Thickness in Porous Media

“…As conventional resources worldwide continue to deplete gradually, tight oil, with its significant resource potential, has emerged as a focal point for global development. , During the water displacement process, a thin, bound water film typically develops on the rock surface. , The issue of water films formed by bound water was first raised in the 1950s . It has been demonstrated that the bound water film thickness within the pore space is generally uniform and consistent, typically ranging from 0.01 to 0.1 μm, − and occupies a significant portion of the pore volume . Bound water films are important for shale, tight, and low-permeability reservoirs .…”