Application of DLVO Theory to Characterize Spreading in Crude oil-Brine-Rock Systems

摘要

The presence of thin aqueous films and their stability has a profound effect on reservoir rock-fluids interactions involving spreading and adhesion. The stability of thin wetting aqueous films on rock surfaces is governed by several variables including pH, brine and crude oil compositions, and capillary pressure. These variables govern the wetting states in the solid- liquid-liquid systems. The wetting states influence the residual oil saturation and the oil-water relative permeabilities and consequently the oil recovery.The objective of this study is to deduce a functional dependence of thin film stability on the above parameters by considering intermolecular and surface interactions in crude oil- brine-rock systems. The surface forces are manifested as disjoining pressure in thin films. The disjoining pressure isotherms for the selected solid-liquid-liquid system have been computed in terms of the bulk properties of the media. The equilibrium contact angles have also been computed from the integration of the Young-Laplace equation, which relates contact angle to the capillary pressure and disjoining pressure isotherms of the system. The contact angle data obtained from sessile drop experiments have been compared with the calculated results as well as with other published results. Adhesion maps, which relate the film stability to brine pH and molarity, have been developed. The rock-fluids system considered for study consisted of smooth Glass, Quartz and Yates reservoir fluids. The DLVOtheory has been used to model the intermolecular forces. The structural forces are incorporated to overcome the limitations of the DLVO theory. A charge regulation model was used to analyze the crude oil-brine and Glass-brine interfaces. The effects of multivalent ions have been incorporated by an equivalent molarity concept. The overall computational model being developed in this study is aimed at providing a-priori prediction capability of rock-fluids interactions in petroleum reservoirs for inclusion in reservoir simulators.