Dead oil is generally used in most of the chemical EOR studies. However, the oil in an actual reservoir has dissolved gas. It has been observed that the performance of a surfactant-based (foam) EOR was affected when the oil used in the study was a live oil. How would the presence of dissolved gas in a crude oil affect the performance of foam EOR?
In chemical EOR, like surfactant or ASP, the surfactant cocktail forms a microemulsion together with the crude oil. The type of microemulsion (Winsor type) depends on the crude composition, and other parameters like salinity. When the crude composition changes e.g. Because of dissolved gas, the phase behavior can change as well. Depending on how much gas is dissolved, the optimum salinity condition may change. THe performance of chemcial EOR depends very much on the phase behavior, because the ultralow interfacial tensions that mobilize oil are primarily found for the optimum conditions, so if the phase behavior changes away from optimumum conditions, that can affect the performance of the EOR process.
Absolutely agree with your comment Steffen. That's what we observed that the presence of dissolved gas (mainly methane) in the oil affected the process of oil recovery. What I wonder about is the reasons or mechanisms behind this observation. How did the presence of methane in the oil cause the change in the phase behaviour of the oil and the surfactant solution?
What would happen if the dissolved gas in the oil was mainly CO2 instead of methane?
Thanks Ashkan. Very useful comment indeed. Many factors can affect the performance of chemical EOR and that needs careful investigation of the processes as you mentioned.
Thanks for the book suggestion as well.
A given surfactant can be said to be tailored for a particular system only when the physical parameters of that system remains fairly the same . One of such parameters is the HLB- hydrophile/ lipophile balance. Surfactants work at a particular range of HLB of both the surfactant against that of the emulsion (crude oil).
The presence of dissolved gas in the crude oil will alter this range and will demand an adjustment or change in the surfactant that is applied.
That could possibly due the fact that dissolve gas has the ability to enter inbetween and separate foam bubbles thereby predispose them to decay, these affects the overall sweep and EOR rate.
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