Salinity-Dependent Contact Angle Alteration in Oil/Brine/Silicate Systems: the Critical Role of Divalent Cations

Abstract

The effectiveness of water flooding oil recovery depends to an important extent on the competitive wetting of oil and water on the solid rock matrix. Here, we use macroscopic contact angle goniometry in highly idealized model systems to evaluate how brine salinity affects the balance of wetting forces and to infer the microscopic origin of the resultant contact angle alteration. We focus, in particular, on two competing mechanisms debated in the literature, namely, double-layer expansion and divalent cation bridging. Our experiments involve aqueous droplets with a variable content of chloride salts of Na+, K+, Ca2+, and Mg2+, wetting surfaces of muscovite and amorphous silica, and an environment of ambient decane containing small amounts of fatty acids to represent polar oil components. By diluting the salt content in various manners, we demonstrate that the water contact angle on muscovite, not on silica, decreases by up to 25° as the divalent cation concentration is reduced from typical concentrations in seawater to zero. Decreasing the ionic strength at a constant divalent ion concentration, however, has a negligible effect on the contact angle. We discuss the consequences for the interpretation of core flooding experiments and the identification of a microscopic mechanism of low salinity water flooding, an increasingly popular, inexpensive, and environment-friendly technique for enhanced oil recovery.

Mechanisms of Surface Charge Modification of Carbonates in Aqueous Electrolyte Solutions

“…Previous studies show that the structure and stability of the stearic acid (SA) Langmuir-Blodgett (LB) film undergo changes in the presence of aqueous electrolyte solutions, depending on whether they contain mono or divalent ions, as well as on the pH of the solution [71,72]. At sufficiently high pH, divalent cations compress the monolayer, forming a packed structure, therefore improving crystalline order, while monovalent cations result in a less ordered monolayer [73].…”

Interfacial and Colloidal Forces Governing Oil Droplet Displacement: Implications for Enhanced Oil Recovery

“…While our study only considered dewetting dynamics in Milli-Q water the effect of water chemistry on oil film dewetting has received little attention and is an area for further study. High salinity brine can increase oil-water interfacial tension [40], enhance solvation forces between solid-liquid interfaces [41], bind surfactants to substrate via multicomponent ion exchange [42], and impact the stability of chemical additives used for EOR. and the initial receding rate increased by 107.2%.…”

Preventing crude oil adhesion using fully waterborne coatings

“…The surface reconstruction toward these liquids was eliminated as neither the hydrophilic moieties nor the other components within the coating matrix were compatible with these liquids. In addition, an inverted pendant drop method was used to investigate the underwater contact angles of crude oil in the presence of artificial seawater (ASW) and a series of diluted ASW samples (denoted as DIL) . The brine compositions and the underwater oil contact angles are listed in Supporting Information Table S1, and the images taken during the tests are given in Supporting Information Figure S11.…”