Stochastic Optimization of a Water-Alternating-Gas Injection Scheme

Summary Water-alternating-gas(WAG) injection is known to lead to higher reservoirs’ recovery factors than their isolated injections. In this production scheme, the gas injection improves the microscopic displacement efficiency while the water injection improves the macroscopic sweep efficiency of oil displacement while maintaining the reservoir pressure. However, poorly designed WAG-parameters can result in sub-optimal performance, increasing costs and decreasing productivity. In this work, we apply a stochastic-based-optimization technique to estimate the optimal well-controls and WAG-cycles that maximize oil production and its life-cycle in two different scenarios considering a 5-spot wells-pattern. In the first-scenario, a simultaneous-water-alternating-gas(SWAG) injection scheme was implemented on a sectorial synthetic-reservoir, where injection and production parameters were optimized for increased field production. The second-scenario comprises a sectorial real-reservoir, where the experience from the first-scenario was used as starting point to optimize a water-alternating-gas injection scheme. In this application example, the injection rates were optimized, and compared to optimized isolated water and gas injections. Two different permeability-models were also tested and compared in order to assess the impact of the geological-model in results. Results from both scenarios shows that optimization studies can help improve the EOR techniques efficiencies. These examples show a 2% to more than 10% increase in recovery factor.