Simulation Study of the Effect of Smart Water on Relative Permeability During WAG-CO₂ Injection for Light Oil Reservoir

Abstract

Water alternating gas (WAG) injection with its first successful field pilot application on the North Pembina field in Alberta, Canada, in 1957, is one of the most prominent EOR methods that substantially prolong the lives of the otherwise depleted and uneconomical oil fields. This technique is well established, but the practical challenges are often of the occurrence of viscous fingering, gravity segregation, and gas channeling or override, and consequently lower oil recovery rates. Previous researches have focused almost exclusively on modifying the salinity and the ionic composition of the injected water, also termed as smart waterflooding which proved to further enhance the oil recovery obtained from waterflooding. However, obscurity exists on whether the deployment of smart water during WAG-CO₂ injection will be successful. This paper addresses the impacts of the implementation of a technique which combines smart waterflooding and WAG-CO₂ injection on the oil/water relative permeability curves for a light oil reservoir. An analysis on the two-phase relative permeability functions is essential as to predict the effectiveness of the displacement process or the performance of smart water injection applied during WAG-CO₂ injection. CMG STARS was used to simulate the effects of fine-tuning the salinity as well as varying the composition of Ca²⁺ and Mg²⁺ ions in brine on the oil recovery factor. The optimum brine salinity for maximum oil recovery was also determined. The slight shifting of the relative permeability curves to the right which can be observed proves the capability of the smart water to modify the rock wettability toward a more water-wet system. Yet the findings from the simulation study suggest that the use of smart waterflooding is not ideal or has low potential in increasing the oil recovery during WAG-CO₂ injection.