Polymers for EOR in Offshore Reservoirs: Recommended Practices for Laboratory Screening

Abstract

Most EOR methods, and hence most EOR screening criteria, traditionally focus on onshore applications due to lower cost and complexity in the implementation. Despite the challenges associated to offshore environments, EOR application in offshore fields is receiving increasing attention since the size of the prize is significantly large to overcome the high costs associated to the development. The oil and gas community is evaluating and testing potential applications of chemical EOR to offshore assets based on the need to develop increasingly deeper reservoirs. Some of these reservoirs are characterized by having relative high temperature and high salinity, conditions where most available chemicals for EOR have limited applicability. Recent efforts to develop high temperature polymers have been reported, however, there is no clear understanding of what would work best in those harsh environments. In this work, we propose an integrated workflow for laboratory screening of polymers for application in offshore reservoirs with high temperature and high salinity. We provide an overview of the main steps of the workflow and recommended protocols for the different laboratory measurements. The proposed workflow has been derived from best practices reported in the literature and our experimental work over the last two decades. We also provide a summary of the latest polymers developed for application in high temperature and high salinity reservoirs and point out the required testing that we recommend for an appropriate screening of chemicals for offshore EOR applications. Each of the steps of the recommended workflow is described showing with actual data the limitations used in some prior screening work. We emphasize the need to move away from ‘ideal’ lab conditions by using representative rock and fluid samples and doing the experiments at reservoir conditions of pressure, temperature and representative saturation, and to consider a variety of scenarios for the testing that describe the expected changes that the polymer solutions will experience during their lifetime in the application, and give a list of the minimal testing needed to get a proper understanding of the potential polymer performance. We provide recommendations on the best available polymers for EOR application in offshore assets to date. In summary, for temperatures greater than 95°C and salinity above 90,000 ppm standard polymers like acrylamide, polyacrylamide and partially hydrolyzed polyacrylamide (HPAM) cannot be used, and the promising newly developed polymers include modifications of acrylamide, thermal associated polymers and HPAM functionalized with AMPS monomers. In this study, it has been developed an integrated workflow for laboratory screening of polymers for EOR applications in offshore assets and provide recommendations for the selection of polymers for use in high temperature and high salinity assets.