Foam Stability in Presence of Oil
A Simulation and Experimental Study
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Abstract
This thesis investigates bulk foam stability in absence of oil, and in presence of oil (hexadecane). Foam in absence of oil was produced by sparging nitrogen at a fixed flow rate through the surfactant solution. Foam in presence of oil was produced by stirring a mixture of surfactant and oil with an immersion mixer. The behavior of foam in absence of oil did not give any prediction of the behavior of foam in the presence of oil. We show that commonly referred methods for foam stability in presence of oil, the entering, spreading, and bridging coefficients and lamella number, did not give reliable predictions. The surfactants that produced most stable foams in presence of oil had the lowest interfacial tension with oil. We also show that in our experiments, foam in presence of oil does not show a relationship between foam bubble diameter and drainage rate, unlike foam in absence of oil. We illustrate that foam in presence of oil, produced with a mixture of surfactants, can be more stable than the foams in presence of oil, which were produced with the individual surfactants. We observed emulsions forming under foam in presence of oil, and their maximum volumes have not shown any relationship with other parameters. This thesis also investigates foam injection into a water-flooded reservoir by a single cycle surfactant-alternating-gas (SAG) mode. We demonstrate that if not enough surfactant is injected into the reservoir, the oil bank (ahead of the foam front) does not reach the production well. Therefore less oil is produced, since less gas is injected due to foam reducing the injectivity of gas. We show the effect of oil on the foam front stability. In our simulations foam collapses in gridblocks where oil saturation is above a certain threshold value. The liberated gas flows upward in the reservoir, and pushes down oil and water. This can result in the formation of an oil bank at the bottom of the reservoir, and in our simulations this oil bank is not displaced by foam because its oil saturation is high enough to destroy foam. We varied the threshold value of minimum water saturation for stable foam; if the threshold is set at a larger value (reflecting less stable foam), then foam has a less significant impact on oil production and gas injection than if it is set at a lower threshold value (reflecting more-stable foam).