Tapered WAG Ratio Optimization in an Egg Model With Brazilian Pre-Salt Fluid Using PSO Algorithm

Abstract

Abstract The Water Alternating Gas (WAG) is a well-established enhanced oil recovery method, which overpasses as waterflooding or gas injection. A particular type of WAG is the Tapered WAG which consists of varying the injection WAG ratio during the reservoir life instead of maintaining this parameter unchanged. In general, injection optimization may increase the cost function value, as the more complex and more parameters the technique has, the optimization becomes more time and computationally expensive. This is the case of the Tapered WAG, which makes its optimization unfeasible to be applied for real reservoirs. For this reason, to decrease the complexity of the problem, a Particle Swarm Optimization (PSO) is employed to optimize the Net Present Value (NPV) with only three variables of optimization, the water injection time equal for all injectors in three different pre-established periods. To explore other options, a PSO with twenty-four variables was also studied with different water injection times for injectors in the three periods. The PSO algorithm was applied in a modified version of the reservoir benchmark Egg model. The fluid compositions were replaced to mimic the Brazilian Pre-salt reservoirs, and some WAG and Tapered WAG of typical literature parameters were also tested. As a result, the NPV was improved by 10.44% in comparison to the waterflooding case, and it was the highest among the evaluated techniques.