Experimental Study on Optimizing Steam Solvent Co-Injection Process in Akan Carbonate Oilfield

Abstract

Steam solvent co-injection processes are generating considerable interest in terms of improving heavy oil upgrading in unconventional reservoirs. The characteristics of the opted solvents in the field have not been dealt with in depth. This paper presents a study on selecting the most optimal solvent for the Akan oilfield enhanced oil recovery (EOR). The first step in this work consisted of determining the Akan oil field viscosity, through an elemental and SARA analyses. Next, a set of physical and chemical methods was used to understand the mechanism of solvents’ effect on oil viscosity dynamics. The compositions of the used solvents were analyzed by a gas chromatography-mass spectrometer system equipped with a mass selective detector ISQ (USA). The evidence from the present study suggests that toluene and o-xylene are the most optimal solvents for enhancing the Akan oil recovery and reducing its viscosity. The obtained data demonstrated a higher efficiency of the used solvents on the oil viscosity reduction where the maximum oil viscosity reduction was observed in the presence of toluene, which led to a value of 178.1 mPa.s. Moreover, the obtained results reported that the solvent co-injection process efficiency increases gradually depending on the chemical composition of the used solvent, as witnessed by the obtained oil recovery factor (RF) values. It has been found that the oil recovery factor values during the capillary soaking in the presence of water was equal to 20%, in the presence of o-xylene it was equal to 61%, and in the presence of toluene, it was equal to 69%. Likewise, a similar efficiency behavior has been demonstrated during filtration experiments where water led to a 26% recovery factor, o-xylene to 69%, and toluene to 78%, meanwhile the solvent slug led to 65%. The results of this study would seem to suggest that the viscosity of the investigated oil decreases in the presence of aromatic solvents, such as toluene and o-xylene, as witnessed by the recovery factors they demonstrated. A consequence of these changes is the possibility that aromatic solvent molecules tend to separate the asphaltene layers and reduce the overlap between large asphaltene macromolecules, which leads to the dissociation of asphaltene aggregates.