A Comparative Study on the Performance of Different Secondary Recovery Techniques for Effective Production from Oil Rim Reservoirs

Early water and gas breakthrough is a challenge for developing thin oil rim reservoirs. Secondary recovery methods such as water, gas, simultaneous water and gas (SWAG) and gravity-assisted simultaneous water and gas injection (GASWAG) methods are proven methods for developing thin oil rim reservoirs. Knowledge about a preferred technique is important to minimize cost and enhance performance. In this study, various water and gas injection scenarios applied to thin oil rim reservoirs were evaluated using reservoir simulation studies such that horizontal and vertical wells were used for production and injection respectively. The performance indicators considered include cumulative oil produced, oil production rate, and the onset of water and gas coning. Simulation results showed that injecting gas at the gas-oil contact (case 1) and at the water-oil contact (case 2) were the least favorable in improving oil recovery and in delaying gas coning and gas-cap surface production. SWAG and GASWAG resulted to an increase in production rate by 18.5% and 37.9% respectively in comparison to gas injection. Water injection at water-oil contact (case 3), SWAG and GASWAG augmented reservoir pressure with GASWAG sustaining the force balance within the reservoir much more than other methods during the simulation period. GASWAG technique also resulted to a 28% increase in cumulative oil produced in comparison to SWAG. This is because the GASWAG technique improved sweep efficiency with the downward movement of water and the upward movement of injected gas. Results from this study shows that GASWAG is a preferred method for developing thin oil rim reservoirs and should be adopted. It is however recommended to carry out an optimization study which determines the optimal input parameters for a GASWAG process that maximizes cumulative oil produced and delays water and gas breakthrough. © 2023 School of Science, IHU. All rights reserved