Assessment of Surfactant Flooding with Variations of Slug Injection Strategies in Waterflooded Reservoir

Abstract

Introduction of surfactant into waterflooded reservoir may cause the reduction in surfactant efficiency by means of surfactant dilution and adsorption. However, it is possible to overcome this issue by utilizing concept of equilibrium shifting between different surfactant concentrations. Therefore, this study aims to evaluate the effects of surfactant flooding with multi-slug grading in waterflooded reservoir on additional oil recovery. Flooding operating conditions are initially evaluated to identify effects of injected surfactant concentration, surfactant injection rate, and time to implement surfactant flooding after water pre-injection for single-slug injection and multi-slug injection. The effects on oil recovery of reservoir parameters related to interaction between surfactant and rock surface including changes of properties related to relative permeability curves, such as irreducible water saturation and endpoint relative permeability, are then evaluated. Performance of surfactant flooding strategy is evaluated based on oil recovery factor. Simulated results indicate that two-slug surfactant injection yields better oil recovery than single-slug surfactant injection due to benefit of sacrificial adsorption or desorption process. Selection of type of two-slug injection strategy would depend on surfactant concentration of single-slug which is chosen to be modified; whereas, the selection of magnitude of concentration contrast between the two slugs would depend on placement of surfactant mass ratio. Modification of two-slug into three-slug injection does not show improvement in oil recovery in this study. However, additional oil recovery is observed to be better than single-slug surfactant injection. Assessment of operating parameters implies impacts on oil recovery performance. Surfactant concentration slightly shows effects on rate of change in oil recovery, but not on final oil recovery. The final oil recovery as well as the rate of recovering is more sensitive to the change in surfactant injection rate. Increase in injection rate results in faster and higher oil recovery. Time to implement surfactant injection does not show much impact on final oil recovery. Implementing at higher watercut would just delay production as a whole. For the effects of reservoir properties, changes in endpoint relative permeability to oil is more sensitive to the performance of surfactant flooding when compared to changes in endpoint water saturation.