Understanding Foamy Oil Mechanisms for Heavy Oil Reservoirs During Primary Production

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

Foamy-Oil-Viscosity Measurement

“…The total mobility appears to remain nearly constant at lower expansion rates. These observations are similar to those in Huerta et al (1996). Fig.…”

“…In light oils, gas bubbles coalesce quickly, resulting in segregated flow (Taitel 1986;Henriot et al 2002), while, in heavy oils, bubbles tend to remain dispersed in the viscous liquid, giving the produced oil the appearance of chocolate mousse, which is largely referred to as foamy oil (Smith 1988;Maini et al 1993). This foamy-oil phenomenon is believed to be linked to higher production rates or higher oil recoveries than expected from conventional reservoir theories (Smith 1988;Huerta et al 1996). In Canada, such production rates are also linked to sand production, while in Venezuela, foamy-oil flow appears to be the dominant factor, with much lower sand production rates if any .…”

Dynamic Surface Properties of Asphaltenes and Resins at the Oil–Air Interface

“…Anomalous behavior can be observed with rates of recovery better than expected (6,7). To explain this high primary production, two main mechanisms have been proposed.…”

Solution-Gas Drive in Heavy Oil: Field Prediction and Sensitivity Studies with Low Gas Phase Relative Permeability

“…High critical gas saturation has also been postulated as one of the factors responsible for this favourable behaviour of heavy oil reservoirs [10][11][12] . However, one of our recent experimental studies 4 has negated this theory.…”