Transforming Ongoing Field Scale Polymer Flood in Oman to a Lean and Competitive Polymer Development Using Insights from Detailed Simulations Based Study

Abstract Polymer flood (PF) applications have increasingly been extended to medium-to-heavy oil reservoirs for enhanced displacement, sweep efficiency and improving the ultimate recovery. The relatively low carbon footprint and gas-light nature has made PF as an attractive way-forward EOR technique. This study, a follow-up of SPE-200207-MS, intends to develop theoretical based considerations, utilizing detailed high-resolution simulations, for optimizing an ongoing large-scale polymer flood application in Oman. The study intends to propose transformation of the ongoing polymer flood to a cost competitive polymer development strategy with minimal trade-off on recovery, while reducing the operational challenges. To these effects, this research uses the advanced simulation capabilities to investigate the subjects of 1) optimal polymer slug-size for multitude of geological scenarios and scales, 2) phenomenon of viscous fingering/instabilities and how does it scale from core- plug to field, and 3) concepts of polymer grading/tapering and related cost savings. The study builds on the foundation laid for holistic simulations study presented in preceding paper SPE- 200207-MS, capturing the details of polymer flow-physics. It starts with understanding the nature of polymer/polymer and polymer/water type displacements and stabilities. It encompasses modelling viscous fingering/instabilities in a range of model set-ups, starting from high resolution core-scale 2D models to 3D sector models incorporating varying degrees of geological heterogeneities. The understanding of unstable displacement gained with different high-resolution models is then extended to investigate the phenomena of polymer/water mixing, Water-Alternating-Polymer (WAP) recovery and polymer grading (tapering). Different prevailing concepts of polymer grading on the likes of those proposed by Claridge, Ligthelm-Schulte and Stegemeier in combination with various mixing rules are investigated and potential polymer savings for development strategies are evaluated. Research outcomes are integrated to formulate the optimal polymer slug size and viscosity requirements, demonstrated with creaming curve analyses for a variety of reservoir systems. Improved recovery performance and lower cost are achieved, underpinned by eliminating Water-Alternating-Polymer type of flooding. This was achieved with better design of polymer injection schemes encapsulating grading philosophies. This results not only in significant polymer savings (and hence, cost) but also reduces constraints/load-factor on injection facilities. The study highlights significant scope for optimizing polymer flood in fields both in terms of long-term improved recovery performance at reduced cost as well as tackling the short-term operational challenges, potentially influencing the business bottom-line. It reveals that adequate polymer grading design can potentially yield polymer saving of 26%-36% with minimal trade-off on recovery. Moreover, such initiatives and optimization of development strategy not only ensures smoother operations but also significantly improves the energy efficiency/utilization per barrel of oil produced and reduces the GHG intensity of such EOR projects.