A common method of enhanced oil recovery is alkaline-surfactant-polymer (ASP) flooding where a solution of alkali, surfactant, and polymer is injected followed by a polymer drive. Many crude oils contain naphthenic acids that react with the alkali to form soap in-situ. With the proper selection of an injected surfactant that mixes with the soap in-situ, a sufficiently low interfacial tension can be achieved to mobilize the residual oil. However, ASP flooding is complex since it involves chemical reactions that depend on the oil composition, water composition, rock mineralogy, temperature, pH, etc.

Mechanistic simulations of ASP flooding typically involve a large number of reactions to calculate the consumption of alkali due to ion exchange reactions with the clay and micelles as well as other reactions with the minerals and brines. This approach is computationally intensive. After a full mechanistic model of ASP flooding was developed and validated, a simplified ASP model was implemented in a 3D chemical flooding reservoir simulator. In the simplified ASP model, the amount of soap is calculated using the total acid number of the crude oil. A phase behavior mixing rule model was developed to calculate the optimum salinity and solubilization ratio of the soap and surfactant mixtures. Other key mechanisms modeled are alkali consumption and surfactant adsorption as a function of alkali concentration.

Several ASP corefloods were successfully modeled using the simplified ASP model. Based on these results, 3D simulations of an ASP field pilot were performed. In this particular case, the results were comparable to those obtained from ASP flooding simulations using a more complete set of geochemical reactions. The simplified ASP flooding model is a more practical and convenient way to simulate field applications of ASP flooding for such cases.

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