Adsorption of Asphaltenes in Porous Media under Flow Conditions

Abstract

Asphaltene adsorption on minerals induces wettability alteration in porous media, which, in turn, affects capillary pressure, relative permeability, and residual oil saturations. The majority of existing work addresses the adsorption of asphaltenes on minerals under static conditions, where adsorption isotherms are measured and modeled. Very little work currently exists on the adsorption kinetics of asphaltenes under dynamic conditions, which are more relevant to laboratory-scale experiments, specifically those involving dynamic wettability alteration of minerals. In this study, we propose to investigate the dynamic adsorption of different asphaltenes on various minerals using UV−vis spectroscopy. The experimental setup consists of a core holder containing crushed minerals with comparable mesh size. Asphaltene solutions in toluene are then flown though the mineral pack with a constant flow rate, and their concentrations are recorded with time at the outlet. Preliminary results indicate that adsorption is largely controlled by the type of mineral rather than the asphaltene itself. The highest adsorption amounts per unit area are found on calcite. Furthermore, the effect of several parameters, such as concentration, asphaltene composition, and flow rate, are considered. The theory of activated adsorption/desorption (TAAD) approach (Rudzinski, W.; Plazinski, W. J. Phys. Chem. C 2007, 111, 15100−15110) is incorporated into the convection-dispersion transport equation to model the flow of asphaltenes inside the porous medium. The resulting equation is then solved numerically using Barakat−Clark finite difference technique (Satter, A.; Shum, Y.; Adams, W.; Davis, L. SPE J. 1980, 20, 129−138). We find that kinetics and not equilibrium governs asphaltene adsorption in porous media. Levenberg−Marquardt’s optimization algorithm is used to derive kinetic parameters, such as Γm, ka, and kd. Once these concentration-independent parameters are found, the model is able to predict with reasonable accuracy the effect of concentration on asphaltene adsorption in porous media.