Surfactant Optimization for EOR using Advanced Chemical Computational Methods
- Marten Adriaan Buijse (Shell Exploration & Production) | Kunj Tandon (Shell) | Shekhar Jain (Shell) | Jan-Willem Handgraaf (Culgi B.V.) | Johannes Fraaije (Culgi BV / Leiden University)
- Document ID
- Society of Petroleum Engineers
- SPE Improved Oil Recovery Symposium, 14-18 April, Tulsa, Oklahoma, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements, 4.3.4 Scale, 4.1.5 Processing Equipment, 5.4.1 Waterflooding, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.2.3 Rock properties
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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.
Surfactant EOR is a method to mobilize and produce capillary trapped oil, which is the oil remaining in the reservoir after water flooding 1,2. The purpose of the surfactant is to lower the interfacial tension (IFT) between water and oil. For effective oil mobilization, the IFT must be reduced by three to four orders of magnitude, from a value of about 20-50 mN/m to a value below 0.01 mN/m. The surfactant is usually injected as a dilute solution in brine, often in combination with other chemicals such as alkali, polymer and co-solvents to improve over-all oil displacement efficiency. With suitably selected surfactants, and at optimum salinity & temperature conditions, the mixing of the surfactant solution with the oil will create a so-called microemulsion phase, which is a thermodynamically stable mixture of oil, brine and surfactant with ultra-low IFT 3.
The optimum surfactant system, that minimizes the IFT, depends to a large extend on the composition of the crude oil. Every crude oil is unique and requires a tailored solution4. Also, the composition of the brine, used in the field to mix the surfactant, limits the surfactant choice and may complicate surfactant optimization. To satisfy all requirements the surfactant system is usually formulated as a mixture of two or more surfactants plus a co-solvent. The experimental screening study, to identify and optimize the surfactant components, requires testing of many surfactant/solvent combinations and is often quite laborious.
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