Immiscible WAG injection: a core-scale investigation of operational parameters impacts

Water Alternating Gas (WAG) injection, commonly used in light to medium crude oil reservoirs, is a well-established technique for enhanced oil recovery combining the effects of two conventional oil recovery processes - water injection and gas injection. Immiscible water alternating gas (IWAG) injection is considered as an appropriate injection type dependent on economical and productive aspects. During the IWAG process, injected gas and oil are always in separate phases due to low-pressure maintenance, and it takes advantages in improving the stability displacement front in the macroscopic sweep as well as enhancing microscopic sweep in narrow pores. In order to check the optimum operational condition in which to apply IWAG injection at the field-scale, this injection process is usually tested as a core-flooding experiment, which is time-consuming and expensive. In this research, a model of core-scale IWAG injection is introduced with validation by Double Displacement Process (DDP) experimental data from previous research. Response Surface Methodology (RSM) with CCD design is used to investigate the impact of five operational parameters on the volume of oil recovery. Particle Swarm Optimization (PSO) is employed to determine the optimum combination of operational parameters to achieve the highest oil recovery factor for each operation scenario. The results indicate that all the main operational parameters, including timing, ratio, flow rate, slug size, and sequence, are significant for the response surface model. The PSO models reach good convergent results, with the volume of oil recovery for each case as 0.613, 0.650, and 0.666 pore volume. The performance of optimum IWAG injection is significantly better than only water-flooding or gas injection, with results approximately 5% higher than water-flooding, similar to double displacement process (DDP), and approximately 20% better than gas injection for the same operational conditions. These optimization tools are recommended for further research of WAG injection, both the experimental and simulation processes