Abstract

Surfactant EOR is an attractive method to recover the residual oil left behind in the reservoir after water flooding. The formulation of an effective surfactant system is a relatively complex and often time consuming process because the surfactant activity depends on the crude oil composition and the surfactant system must therefore be tailored to the oil. In practice many surfactant (and solvent) combinations need to be tested in the laboratory to optimize the performance.

An alternative approach, which is the focus in this paper, is to start with the molecular structure of surfactant and oil and apply Molecular Modeling techniques to optimize the surfactant system. The dissipative particle dynamics (DPD) method, used in the simulations discussed in this paper is a relatively new coarse-grained (meso-scale) method especially suited to study phase behavior in multiple phase systems such as surfactant/oil/brine. The paper will discuss the basic DPD features and results of DPD calculations of surfactants at the oil/brine interface.

To simulate the microemulsion structure on molecular level it is necessary to have a physical model of the surfactant interfacial film. The first part of the paper will review the relevant microemulsion physics, in particular the bending properties of the interfacial film that determine the magnitude of the (experimentally observed) interfacial tension.

To efficiently calculate microemulsion properties such as optimum salinity, a new method, called Method of Moments, was developed and implemented on DPD level. In this method a section of the surfactant/oil/brine interface is simulated to calculate the (lateral) stress profile and its moments. Computationally the method is relatively fast and it is flexible and can handle mixtures of surfactants/solvents, complex oils, etc. Results of calculations will be discussed in the paper.

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