Understanding Foamy Oil Mechanisms for Heavy Oil Reservoirs During Primary Production

Abstract

Abstract A set of experiments in porous media was performed to determine oil recovery factor during natural depletion for a heavy oil reservoir. Results on "critical or mobile" gas saturation, produced fluid characterization, residual oil saturation, production profile and effective viscosity versus pressure are presented. In order to characterize the ability of the heavy oil to trap the released gas, conventional and non conventional PVT tests were carried out. By comparing the experimental results during differential liberation tests, a gas trapping factor for the oil was obtained. It accounts for the amount of solution gas that has been thermodynamically released but does not form instantaneously a free gas cap. The so called pseudo-bubble pressure was obtained. In this work the hypothesis involved in the "Low Viscosity Model" was also tested. Introduction During the last years it has been a very large discussion about different production mechanisms to explain the production behavior observed in some heavy crude oil reservoirs specially in the Orinoco Belt in Venezuela and Lloydminster in Canada. It has been characterized by high production rates and/or high primary oil recovery, besides a good pressure maintenance. In the past, we have evaluated other drive mechanisms such as compaction, water drive and thermal process. A considerable amount of laboratory and field work has been done to evaluate compaction effects in the area of our interest. The results obtained from that study showed no evidence of subsidence or compaction, therefore it is not likely to be a major production mechanism. On the other hand, no active aquifer has been found either. According to field (well head samples) and laboratory evidence, the heavy and extra heavy Hamaca oil exhibits "foaminess" when produced under solution gas drive. P. 671