Revisiting Water Injection Post-Polymer Flooding: A Global Perspective on Project Performance

Summary This paper aims to synthesize theoretical insights and field experiences concerning water injection efficiency following polymer flooding. The objective is to summarize fluid and reservoir dynamics during this critical transition to guide the design of cost-effective and technically robust enhanced oil recovery (EOR) projects. Key discussions focus on the integrity of the polymer slug when injection is resumed, the diversion (or lack thereof) of water into previously unswept zones due to polymer-induced resistance, and potential tailing strategies to mitigate premature water breakthrough. Our methodology involves an extensive review of historical and contemporary case studies, complemented by a series of laboratory tests guided by reservoir engineering principles. Initially, we analyze fluid dynamics relevant to this phase of the project, followed by an evaluation of existing laboratory experiments and the investigation of strategies designed to conclude injection while minimizing water breakthrough. Drawing insights from projects across Kazakhstan, China, the Middle East, and the Americas, we develop guidelines and strategies aimed at extending the operational lifespan of existing projects. Analyses of several enhanced oil recovery projects reveal a rapid decline in recovery efficiency upon switching from polymer to water flooding, predominantly driven by unfavorable mobility ratios. Notably, water channels swiftly through higher permeability zones where polymer-induced resistance remains the lowest compared to less permeable areas. The ineffective displacement of the polymer slug by water often signals the premature conclusion of the project. These findings underscore the need to reduce mobility ratios to preserve polymer bank integrity and, consequently, the efficiency of the flood. These statements are substantiated by examining field cases in Kazakhstan, China, the Middle East, and the Americas. The recommendations provide a pragmatic approach to extending the polymer injection phase, significantly deviating from traditional EOR practices. They present a robust strategy for future polymer flooding projects. By emphasizing the importance of maintaining polymer slug integrity and optimizing injection strategies, the guidelines aim to enhance overall recovery efficiency and extend the productive life of oil fields. This comprehensive analysis integrates theoretical principles with practical insights, offering valuable guidance for the successful implementation of polymer flooding and subsequent water injection in diverse reservoir conditions. The findings and recommendations are expected to contribute significantly to the advancement of EOR methodologies, promoting more sustainable and efficient oil recovery practices.