The roles of foamy oil flow in cold production of heavy oils under solution gas-drive have been extensively studied in recent years. However, the mechanisms of foamy oil flow in porous media are still not fully understood. The viscosities of heavy oils and bitumen are often so high that the solution gas drive should yield very little oil production. However, several heavy oil reservoirs in Canada and Venezuela have displayed very high solution gas drive recovery factors and foamy oil flow is believed to be the cause. The recovery factor projected for steam stimulation operation in Cold Lake is also very high, up to 30% of OOIP. Since the primary drive energy in Cold Lake comes from solution gas drive, it has been suggested that foamy oil flow may be responsible for this high recovery factor.
The objective of this work was to examine the effects of temperature on foamy oil flow in a clean sand with Cold Lake oil and methane gas. Solution gas drive experiments were carried out in a sand-pack at several different temperatures and depletion rates. The results show that in isothermal depletion tests, the highest recovery factor does not occur at the highest temperature used. Instead, a much lower optimum temperature exists which provides the highest recovery. The reasons for this appear to be the diminished gas solubility and reduced foamy behaviour at higher temperatures, which counteract the positive influence of reduced viscosity
It has been found that an oil continuous foam is produced during primary production of heavy oil in several heavy oil reservoirs. Essentially the foam is formed by release of solution gas in the continuous oil phase. These foamy oils, because of their very complex structure, exhibit complicated and unusual flow behaviour. They exhibit not only remarkable rheological properties, but also very marked trapped gas effects, which in turn, may be responsible for the high primary oil recovery factor.
In solution gas-drive process, the primary drive energy comes from the dissolved gas in the oil phase. The role of the dispersed gas bubbles in the oil displacement process has been studied for a long time by a number of investigators. The formation of dispersed gas bubbles in the heavy oil has been suggested to be an important factor contributing to the success in primary production of several heavy oil reservoirs. [1,2,3]
Several investigators have reported the results of pressure depletion experiments. These results indicate that the beneficial effects of foamy oil diminish as the rate of pressure change becomes small. However, most previous work on foamy oil flow has been aimed at cold production, so that the temperature factor is not considered. Although some useful insights into the foamy oil flow mechanisms were developed, foamy oil flow in conjunction with thermal recovery methods has not been adequately studied.
Maini and Nicola[4] have carried out laboratory scale solution gas-drive experiments to examine the effect of the rate of pressure change. Their results indicated that the solution gas-drive recovery factor increased dramatically as the rate of pressure decline was increased.
