CO2 Miscible Flooding for Enhanced Oil Recovery

Abstract

Enhanced Oil Recovery (EOR) is a technique applied for the recovery of oil from a petroleum reservoir beyond what is recoverable by primary and secondary approaches. The key aim of all EOR methods is to increase the macroscopic (volumetric) sweep efficiency as well as enhance the microscopic (displacement) efficiency, in comparison to an ordinary water flooding. One mechanism utilized is to reduce the mobility ratio between the displacing and displaced fluids thereby increasing the volumetric sweep. CO2 flooding has remained an effective and widely used technique for enhanced oil recovery (EOR) methods. Compositional simulation is usually required for the evaluation of CO2 flooding in EOR projects, especially when miscibility is of great concern (miscible flooding). The simulation technique proposed is the multi-dimensional, compositional modeling approach, generally applicable to porous reservoirs. This study tends to investigate the injection pressure conditions necessary to achieve miscibility, various injection patterns and how they affect miscibility as well as Well Placements and their effect on Oil Recovery. Six case scenarios were studied. Results from simulations show that the reservoir pressure is below the minimum miscibility pressure (MMP) of the CO2. As such, for miscibility conditions to be established and maintained, the pressure conditions must be kept above the MMP. Injection pressure was also identified as a key parameter that influences oil recovery. Increase in injection pressure of CO2 resulted to an increase in the performance of the flood project. The optimum injection rate was attained at 5000 Mscf/day above which any further increase in rate would not result to increased recovery. The effect of different well placements resulted in different oil productions. The case "F" well arrangement pattern gave the highest recovery.