Core-scale modelling and numerical simulation of zwitterionic surfactant flooding: Designing of chemical slug for enhanced oil recovery
Abstract
Surfactant flooding is a proven enhanced oil recovery method for the recovery of trapped crude oil from the pores of the reservoir. In the present study, the applicability of a synthesized zwitterionic surfactant as an efficient EOR agent was tested, in terms of its interfacial tension reduction capability, emulsification behavior, and wettability modification behavior. Core flooding experiments conducted in sandstone core with the injection of 0.3 pore volume of chemical slug after water flooding showed 20% of additional oil recovery. The core flooding experiment was simulated using CMG-STARS simulator and history matching of relative permeability curve and its interpolation parameters were done. The validated model closely represented the experimental core flooding with very low error of 6%. The validated model helps in understanding the movement of crude oil and its interaction with the injected surfactant slug in the porous media. The validated model was further used for optimization of injected chemical slug by varying the parameters such as the surfactant concentration in the injected slug, the volume of injected chemical slug, and the injection rate of chemical slug. Each parameter had different effects on the oil recovery efficiency and cumulative oil recovery of more than 90% OOIP was obtained using model with injection of 1 PV of chemical slug containing 100 ppm of surfactant with the injection rate of 0.3 mL/min. The simulation of core flooding helped in optimization of crude oil production by zwitterionic surfactant and its implementation on field scale production by zwitterionic surfactant flooding.
2. Theory: Governing equations
STARS (Steam, Thermal, and Advanced Processes Reservoir Simulator) is a commercial simulator by CMG (Computer Modelling Group), which has the capabilities for modelling and simulation of complex and advanced recovery processes involving injection of steam, solvents, air, and chemicals. CMG STARS is a finite difference numerical simulator that solves a set of conservation equations, consisting of material balance equations, flow equations, chemical reactions, heat exchange equations, and phase equilibrium equations.
5. Conclusions
A core flooding experiment with injection of zwitterionic surfactant slug was simulated using CMG-STARS simulator. The history matching of relative permeability curve and its interpolation parameters were done to validate the model which most closely represents the experimental core flooding. The production profile of the validated model, determined after the history matching, had a very low error of 6% with the experimental production profile. The history matched model was further used for optimization of injected chemical slug. The optimized chemical slug was obtained by varying the parameters such as the surfactant concentration in the injected slug, volume of injected chemical slug, and injection rate of chemical slug. Each tested parameter had different effect on the oil recovery efficiency of the chemical slug and cumulative oil production of more than 90% OOIP was obtained for model with injection of 1 PV of chemical slug containing 100 ppm of surfactant concentration with injection rate of 0.3 mL/min. However, these values of parameters can change on the basis of required OPEX and crude oil prices during the injection operation.
