Experimental Investigation of Foamy Oil Solution Gas Drive

Abstract

Abstract A five-year laboratory and simulation investigation on heavy-oil solution-gas drive processes is reported. It is shown how the interpretation of these processes has changed over the years. Initially, it was attempted to take into account the "bubbly" character of the oil by changing the oil thermodynamical properties. Non-conventional PVT properties accounted for supersaturation and trapped gas bubbles. Later, in agreement with work in other research groups, the low produced gas-oil ratio and high recovery factors were modeled by introducing low gas-oil relative permeability. This allowed for history matching of laboratory and field data, but doubts remain about the predictive capacity of reservoir simulation models. This doubt is motivated by the observed flow geometry of the (dispersed flow), which is not physically taken into account in the reservoir simulation equations. It is concluded that more work is necessary on the determination of the mechanisms that govern the flow, and on the development ofm odels that more correctly represent the physics of dispersed gas-liquid flow in porous media. Further experiments in cores and micromodels, together with microscopic modeling of flow in pore spaces, should be part this work. Introduction The term foamy oil describes dispersed gas-liquid two-phase flow that occurs in heavy oil reservoirs during primary production1. This heavy oil production process for is often characterized by a behavior that differs from what would have been expected using traditional reservoir engineering and simulation. Typical observations are high production rates, high primary production recovery, and good pressure maintenance. Many of the heavy oil reservoirs where those observations have been made are situated in the Venezuelan Orinoco Belt2,3 and in Canada4,5 (e.g. Lloydminster). An extensive amount of papers has been published on these phenomena, in which possible explanations were offered, often with the premise of developing better models. Good review papers have appeared1 in which the different phenomenological models that have been developed are discussed. In this article, we do not present a complete review of the available work. Instead, we discuss some specific research that has been carried out in Venezuela over the last few years, focussing on some specific issues and viewpoints with regard to foamy oil. The review starts with work carried out five years ago. The main focus of that initial work was the investigation of apparent thermodynamical properties of foamy oil during depressurization. This initial work was related to a paper published by Kraus et al.6 on a pseudobubble point model for foamy oils. This model tried to incorporate the trapping of bubbles by the oil through changing the apparent oil properties. We implemented laboratory experiments in a PVT cell that allowed characterizing experimentally the trapping of gas by the oil7. The results were applied to field simulation showing improvement in the history matching of the production process.