The Impact of Copolymers and Sulfonated Polymers on the Adsorption of Phosphonate Scale Inhibitors

Abstract

Abstract Enhanced oil recovery (EOR) is critical to optimally producing existing reserves with a minimized carbon footprint. However, it is essential that the EOR process does not impact negatively on ongoing production chemistry treatments. The focus of this work is on the interactions between polymers and scale inhibitor in terms of adsorption. The adsorption of both is assessed using static adsorption tests to understand and analyze for any evidence of competitive adsorption between these species. The study also elucidates some features of the adsorption kinetics of the polymers used in this study. Copolymers of acrylamide (AM) and acrylic acid (AA) have been the most prominent chemicals to be applied in polymer EOR, whereas sulfonated polymers containing acrylamide tertiary butyl sulfonic acid (ATBS) have been used for higher temperature and/or salinity conditions. This work was carried out in a field brine at a temperature of 31°C. The polymers consisted of AA-AM co-polymers (20-33 % AA) and AM-AA-ATBS ter-polymers (up to 15 mol% ATBS) and DETPMP as a common scale inhibitor. The adsorption levels of the polymers and DETPMP were measured both separately and in sequential addition experiments (at t = t1). The adsorption results in the open laboratory were compared with anaerobic results as they may better represent the field conditions – these experiments were conducted on North Sea water at 70°C as this is a common mid-range temperature at which DETPMP would be used. While polymer adsorption levels of ~20 µg/g were measured after 24 hours, this increased continuously over 20-30 days for the AA-AM co polymers. The same trend was observed for the AM-AA-ATBS terpolymers – with adsorption at 24 hours of ~15 µg/g which again increased significantly over time. However, DETPMP adsorption when added into a pre-adsorbed layer of polymer showed a surprising behavior not reaching the equilibrium after ~ 72 hours regardless of the concentration tested, continuously increasing over time. To the author's knowledge, the DETPMP equilibrium has been reported to be around 24 hours or less. These results are amongst the first observations of this type in the literature, and they highlight the need for the industry to develop a better understanding of the competitive interactions between scale inhibitor treatments and EOR polymers.