Impact of divalent ions on dynamics of pressure field in water films influenced by salinity modification

Research output: Contribution to journalArticle

Abstract

It is known that wettability is thermodynamically related to disjoining pressure
in thin films, which is itself determined by short-range and long-range
surface forces. Disjoining pressure is referred to as the net difference between
the pressure in a thin film and that of the bulk fluid. By changing the ionic strength and composition in the fluid in thin films, the electrostatic/ electrokinetic forces are modified, which results in the variation of disjoining pressure. This has been of particular interest in industrial applications such as enhanced oil recovery technology (e.g. low salinity water flooding). In low salinity water flooding, the variation of disjoining pressure has been linked to alteration of wettability, however, there are still many unanswered questions in this regard, such as the role of ion valency in dynamics of the disjoining pressure.
In this work, we simulate the variation of ionic composition and disjoining
pressure in a thin film, induced by the reduction of the ionic strength
in the bulk fluid. The results are compared for different electrolytes, including
asymmetric and divalent ion pairs. We simulate the initial equilibrium
conditions under high ionic strength (high salinity) by solving the Poisson-
Boltzmann equation. Then, the boundary ionic strength is reduced (low
salinity) to induce transient transport of ions, which is simulated using the
Poisson-Nernst-Planck equations. To investigate the impact of ionic composition
on the ionic transport and pressure dynamics, all simulations are
implemented at the same ionic strength, but different ion pairs (1:1, 1:2 and
2:1), and different finite film thicknesses. We discuss the impact of system
scaling factors in the total disjoining pressure, such as the ratio between lmthickness and Debye length, and the relation between the electrostatic and
osmotic pressure effects.

Bibliographical metadata

Original languageEnglish
JournalJournal of Molecular Liquids
Publication statusAccepted/In press - 1 Jul 2019