An experimental study of oil recovery from tarmat reservoirs using hot water and solvent flooding

Abstract

The existence of tar deposits beneath the oil zone in tarmat reservoirs creates problems of productivity restriction during the primary recovery stage. This affects the performance of water injection projects and natural aquifers and hence, results in poor hydrocarbon recovery. The principal objective of this study was to investigate and evaluate the combined use of solvent and hot water to improve the hydrocarbon recovery from tarmat reservoirs by displacing and dispersing the tar. Most of the displacements were conducted in one-foot long Berea sandstone composite cores, simulating a tar zone and an oil zone in series, at injection rates of 1 cc/min and higher. The results show that although the oil recovery from hot water displacement is lower than cold water displacement in the absence of tar, the gain in recovery for hot water is substantial in the presence of tarmat. Driving a slug of solvent with hot water to displace tar increases the hydrocarbon recovery. For the different types of solvents studied, there is an optimum slug size which maximizes the hydrocarbon recovery. It was found that both large and small solvent slugs are less effective than an "optimal" slug. The effect of injection rate has been investigated applying different displacement schemes. The results showed consistently that the recovery is higher at lower injection rates. Moreover, the effect of injection mode on recovery was examined. The results showed that alternating injection the solvent slugs of solvent and hot water leads to higher recovery than injecting the solvent slug as one portion followed by hot water flooding. Additionally, the combined use of solvent slug(s) and hot water reduces the injection pressure more than cold or hot water flooding alone.