Simulation of polymer alternating gas (PAG) flooding in a synthetic highly permeable reservoir model

Abstract

Water alternating gas (WAG) or miscible CO2-WAG injection has been a prevalent method to control mobility and enhance volumetric sweep efficiency for CO2 flooding. Recent studies however show that most fields were unable to achieve the expected recovery factor from the WAG process, especially for high-permeability reservoirs. The effect of using polymer in water alternating gas injection (PAG) method as an enhanced oil recovery method in a synthetic sandstone reservoir model is investigated. The model of under investigation is a high permeable reservoir, so injected flood front would be breakthrough early times of injection periods. Hence, in the present work, a simulation study using reservoir simulator called STARS® commercialized by Computer Modelling Group Ltd. (CMG) was done to evaluate the potential benefit of adding polymer to the water during CO2 WAG. The studies have shown that PAG flooding has recorded the lowest residual oil saturation (ROS) of 0.04 and the highest recovery factor (RF) of 56% compared to the water, CO2 flooding, CO2-WAG flooding and polymer flooding, implying PAG flooding have improved the sweep efficiency due to reduced the mobility ratio. The simulation results also showed a remarkable GOR reduction (at production well), a noticeable delay in the gas breakthrough, and an improvement in the areal sweep efficiencies during the PAG processes. Therefore, the synergy of polymer and CO2-WAG flooding by taking advantage of polymer conformance control during water cycle and CO2 miscibility with oil is said to have improved the microscopic displacement efficiency which is the paramount importance in the measurement of field’s expected recovery, especially in a highly permeable reservoir.