Optimizing Enhanced Oil Recovery: The Benefits of Preceding ASP and SP Floods with Polymer Flooding

Abstract

This study aims to illustrate the benefits of polymer injection before other chemical processes, e.g., ASP, SP, ACP, etc. Data in the literature showcases the benefits of polymer pre-injection, but the information is not organized into a coherent, unambiguous study to enable operators to confidently move forward with polymer projects where other chemical processes will be implemented in the future. Furthermore, a train of thought states it is deleterious to inject polymer in advance of a surfactant-based flood because viscous fluid ahead of surfactant could slow down chemical front propagation, and oil recovery. The benefits of reduced surfactant mass with alkali and polymer pre-flooding have been shown in optimization work (Dean, et al., 2014). The highly successful Mangala ASP project (Pandey, et al., 2016) followed a well-established polymer flood. The Sabriyah Mauddud ASP pilot also used a polymer pre-flood to increase injectivity into low permeability zones. Laboratory studies (Dean, et al., 2014) show polymer pre-injection for the successful ASP pilot in Minas (Masduki, et al., 2020). Aitkulov (2017) showed improved recovery, reduced surfactant retention, and better conformance when a heterogenous 2-D reservoir model in the laboratory was polymer flooded before ASP flooding rather than waterflooding. Commercial simulators do not properly model surfactant phase behavior. Polymer is better modeled with the Jouenne model (Jouenne & Levache, 2020) in UTCHEM with salinity changes such as those seen in chemical floods. This study uses the mechanistic simulator UTCHEM to history match both of the heterogenous 2-D experiments in Aitkulov (2017). The first case shows water injection before ASP, whereas the second case shows polymer injection before ASP. The history-matched parameters were then upscaled to a reservoir model. Due to existing ASP studies in Milne Point, it is also suggested to history match the most favorable ASP coreflood to obtain the proper inputs for the field scale model. The conformance learnings of Milne Point, e.g., the drop in water-cut shortly after polymer injection, indicate that the polymer injection is improving conformance and not allowing water to flow through pre-existing fingers, thus making the field a good example to simulate.