Design of Economical Polymer and Surfactant-Polymer Processes in High Temperature Carbonated Um Gudair Kuwaiti Field.

Abstract

Um Gudair Minagish Oolite reservoir (UGMO), in Kuwait, is a high temperature mature carbonate field. It is also naturally water-flooded by a strong bottom active aquifer. Specifics challenges for Polymer (P) or Surfactant-Polymer (SP) chemical enhanced oil recovery (cEOR) are faced in high temperature carbonated reservoirs such as UGMO's field. P and SP process selection prior multiwell evaluation is addressed by a well-crafted laboratory approach. This involves extensive laboratory work including coreflood experiments to select the most effective processes in terms of oil recovery and cost-effectiveness. Softened sea water through nanofiltration two passes was considered as the most appropriate water source to be used in a SP cEOR process. Polymer was selected based on classical workflow relying on bulk measurements such as solubility, stability and viscosity, and on coreflooding experiments to characterize polymer injectivity and in-depth propagation. The selected polymer was also tested for compatibility with surfactant. SP formulation was designed and evaluated following a dedicated workflow in order to achieve low interfacial tension (IFT), high solubility, oil recovery and promising economics in reservoir conditions. The most favorable SP formulation regarding economics, surface facility modifications, operating costs and performances were evaluated through coreflood tests. The best SP formulation was selected based on chemicals in-depth propagation in reservoir core, incremental oil recovery and surfactant adsorption. The process was then optimized through additional corefloods to reduce chemicals dosage while keeping high oil recovery performances. Finally, the robustness towards both, rock and field variation conditions, was tested and confirmed. P and SP process were designed and proved to be both promising for UGMO's field. SP while using more chemicals than P process leads to a far better oil recovery as final oil saturation is decreased from 42% (P process) to 11% (SP process). As surfactant adsorption is a key parameter for both SP process efficiency and cost efficiency, several surfactant adsorption mitigation strategies were tested. Injection of a non-ionic surfactant after the main surfactant flood proved to efficiently manage surfactant adsorption despite of the very challenging conditions, allowing to reach very low adsorption level of 60 μg/g. Reservoir simulations showed afterwards that both P or SP process designed were economical at commercial pilot scale. Applied laboratory study on high temperature carbonate UGMO oil reservoir in Kuwait provides useful insights that can be used on other chemical EOR projects in such challenging conditions. This allows to select the most appropriate P or SP process and injection strategy while having reduced surfactant adsorption to very low levels in highly challenging conditions and enhanced profitability.