Reversibility of asphaltene precipitation in porous and non-porous media

Precipitation and deposition of asphaltene particles in the pore spaces of reservoir rocks cause diffusivity reduction and wettability alteration in hydrocarbon reservoir which consequently, reduce the oil recovery considerably. It is of great importance to know the condition at which the asphaltene particles precipitate and also the extension by which precipitated asphaltene particles can be re-dissolved. In this study, the precipitation and re-dissolution of asphaltene particles in a crude oil have been investigated. Series of experiments, in both porous and non-porous media, have been designed and carried out to quantitatively evaluate the reversibility of asphaltene precipitation upon the change in pressure, temperature, and liquid composition. Experiments were conducted in both porous and non-porous media. For non-porous medium, it was observed that the asphaltene precipitation is a partially reversible process upon temperature change with hysteresis, while the precipitation of asphaltene as a function of mixture composition and pressure is nearly reversible with little hysteresis. In the case of porous medium, a slim tube apparatus was used as a one-dimensional reservoir model. After injection of several pore volumes of fresh oil, the oil was allowed to soak enough; then, all deposited asphaltene particles were re-dissolved completely in the crude oil. (C) 2011 Elsevier B.V. All rights reserved.