Enhanced oil recovery applications in carbonate reservoirs present the unique challenges of high salinity and high temperature. For foam applications, foaming agents that have good stability at those harsh conditions are therefore desirable. Crude oil, especially light crude has been known to be a destabilizer for foams and therefore foaming agents need to be designed to handle reservoirs with such oil. In this work, we sought to improve our understanding of the de-foaming behavior of Arabian light crude oil on foams generated using an anionic foaming agent and an amine oxide surfactant. Potential anionic and amphoteric foaming agents dissolved in seawater were screened using the dynamic foam analyzer as well as the high temperature high pressure cell. The stability of foam in the presence and absence of crude oil was studied using both nitrogen and air. Foam decay curves were plotted as a function of time.

Foam decay with time for both types of surfactant fitted a log decay curve confirming the assumption of exponential decay behavior. A semi-log plot of foam decay revealed interesting phenomena along the decay curve. Three regions were shown by the semi-log plot representing liquid drainage, drainage and coalescence and coalescence alone. In general, foam decay was faster in the presence of oil than without oil as shown by the foam half-life calculated for each case. The effect of pressure on foam stability was also investigated at a temperature of 90°C. Generally, foam stability tended to be better at higher pressures in most cases. Foam stability parameters were also evaluated to indicate the relative stabilities of foams generated. The amine oxide, while having excellent solubility in seawater also had a longer liquid drainage section as well as a longer decay time in the presence of oil, than the anionic foaming agent. The harsh conditions of high salinity and high temperature present in carbonate reservoirs therefore favor the amphoterics as better candidates.

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