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Abstract

An alkaline/surfactant/polymer (ASP) pilot in the Karamay field was designed using a reservoir simulator with detailed chemical mechanisms modeled. The Karamay field is an onshore oil field in China. Oil recovery was predicted for different processes, designs, and operating parameters of this 13-well pilot. In particular, the benefits of adding sodium carbonate to the injected surfactant/polymer slug were evaluated. Oil recovery predictions were made for continued water, polymer, alkaline, surfactant/polymer, and ASP flooding with the best results, 24% of OOIP incremental oil recovery, obtained for the ASP process. The simulator used in this study has previously been used to simulate ASP corefloods, but this is the first time that three-dimensional reservoir simulations have been done with the detailed chemistry of the UTCHEM simulator. Alkaline agents such as sodium carbonate react with the acid in crude oils to form surfactant in situ. Such agents are inexpensive compared with manufactured surfactants. The pH of such fluids under the conditions that we studied is about 11, and which reduces the surfactant adsorption. However, the alkaline agent is partly consumed by undesirable reactions with calcium and other cations in the brine, cation exchange with the clays, and dissolution reactions with various formation minerals. A total of 26 chemical species were needed to model these reactions.

The phenomena modeled included the reduction of surfactant adsorption with increasing pH, aqueous-phase chemical reactions of the alkaline agent and consequent consumption of alkali, the in-situ generation of surfactant by reaction with the acid in crude oil, surfactant phase behavior, reduction in interfacial tension, and cation exchange with clay and with surfactant micelles. ASP coreflood data were first matched to validate model parameters. The reservoir description was provided by the operator and included the use of stochastic permeability. This study shows that it is feasible to make affordable field-scale mechanistic simulations of ASP flooding in three dimensions. This is a major achievement since such modeling is of great value in selecting the best improved oil recovery process and then optimizing this process.

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