Simulation Studies on Determination of Displacement and Areal Sweep Efficiencies for Hot CO<sub>2</sub> Flooding in Niger Delta Heavy Oilfield

Abstract

Recovery efficiency is very important in enhanced oil recovery (EOR) processes as it helps in the planning, design and selection of EOR methods that will be technically and economically feasible. In this study, Simulation on hot CO2 flooding is conducted using data from Niger Delta heavy oil reservoir. The compositional simulation process was carried out in ECLIPSE 300 compositional oil simulator. The recovery efficiency and injection calculations were modeled and simulated in Matlab. Numerical equations enabled the determination of the residual oil saturation and the consequent calculation of the injection and recovery before and after solvent breakthroughs. CO2 of 0.095cp viscosity was injected at pressure of 3500 psia and 200°F to heat up the reservoir at payzone and reduce the viscosity of the reservoir oil at in-situ reservoir condition. The reservoir oil initially at 14.23cp at initial reservoir temperature and pressure was heated and reduced to a viscosity of 2cP making the oil mobile and amenable to flow. Results show recovery of the process before and after breakthroughs. CO2 breakthrough was realized after 221 days of the flooding process. Of the 2461.2 ft distance from the injection wells to the producer well, CO2 reached only a distance of 100 ft at breakthrough. Out of the 2.77 PV total volume of CO2 injected in the flooding process, 0.1222 PV of CO2 was injected as at breakthrough. The recovery efficiency result show that the displacement efficiency at CO2 breakthrough and at the end of the flooding process are 15.17% and 78.63% respectively while the areal sweep efficiency at CO2 breakthrough and at the end of the flooding process are 44.02% and 93.32% respectively. The low displacement and areal sweep efficiency at breakthrough were due to early breakthrough of CO2 which did not allow sufficient period of time for the CO2 to contact considerable portions of the reservoir given its viscous nature. Furthermore, at CO2 breakthrough time, the injected hot CO2 had no sufficient time to soak the reservoir and reduce the viscosity of the oil; as such only a small fraction of the in-situ oil became mobile. An overall recovery efficiency of 73.33% realized in the flooding process signifies favourable flooding design hence is recommended for the development and recovery of Niger Delta heavy oilfield.