Mixed CO/N Foam for EOR as a Novel Solution for Supercritical CO Foam Challenges in Sandstone Reservoirs.

Among the various enhanced oil recovery (EOR) processes, CO injection has been widely utilized for oil displacement in EOR. Unfortunately, gas injection suffers from gravity override and high mobility, which reduces the sweep efficiency and oil recovery. Foams can counter these problems by reducing gas mobility, which significantly increases the macroscopic sweep efficiency and results in higher recovery. Nevertheless, CO is unable to generate foam or strong foam above its supercritical conditions (for CO, 1100 psi at 31.1 °C), and most of the reservoirs exist at higher temperatures and pressure than CO supercritical conditions. The formation of strong CO foam becomes more difficult with an increase in pressure and temperature above its supercritical conditions and exacerbated CO-foam properties. These difficulties can be overcome by replacing a portion of CO with N because a mixture of N and CO gases can generate foam or strong foam above CO supercritical conditions. Although many researchers have investigated EOR by using CO or N foam separately, the performance of mixed CO/N foam on EOR has not been investigated. This study provides a solution to generate CO foam above its supercritical conditions by replacing part of CO with N (mixed CO/N foam). The mixed foam not only generates strong foam above CO supercritical conditions but also remarkably increases the oil recovery. This solution overcomes the difficulties associated with the formation of CO foam at HPHT conditions enabling the use of the CO-foam system for effective EOR and other applications of CO foam such as conformance control.