Simulation optimization of water-alternating-gas process under operational constraints: A case study in the Persian Gulf

Abstract

The optimization of the efficiency of Water Alternating Gas (WAG) flooding projects can guarantee the success of these projects. Many operational constraints can indirectly affect flooding efficiency. Their effects are not normally considered during routine optimizations. The main aim of this study is to determine the influence of these constraints (e.g., maximum water-cut, maximum Gas-Oil Ratio (GOR), and minimum Bottom Hole Pressure (BHP) during the WAG process). Implementing a reservoir simulator coupled with Simulating-Annealing (SA) enables us to discover the effects of these constraints during simulation optimization. The developed optimizer is applied to a case study from an Iranian formation located in the Persian Gulf. The recovery factor of WAG flooding is compared with that of the conventional waterflooding and gas injection. Moreover, the optimization of individual and simultaneous WAG parameters is analyzed. Results indicate that: (a) Operational constraints can not only alter the production mechanism but also directly affect the ultimate recovery factor; (b) The recovery factor of simultaneous optimization of all WAG parameters is higher than that of individual parameter optimization; (c) Irrespective of the approach to parameter optimization, WAG ratio (or the volume fraction of injected water to gas) remains almost constant during all optimizations, showing the influence of this parameter during WAG flooding scenarios.