Adsorption Kinetics of Copolymers and Sulfonated Polymers for Enhanced Oil Recovery

Abstract

Abstract Polymer flooding is one of the most mature enhanced oil recovery (EOR) techniques, where the injection water viscosity is increased through addition of a high molecular weight polymer. In field operations, one of the most critical parameters for successful polymer flooding is the polymer adsorption. During transport, the polymer will irreversibly adsorb onto the reservoir rock, with the exact extent of adsorption depending on reservoir/polymer properties, such as the polymer composition and molecular weight, mineralogy of the reservoir, brine composition, reservoir temperature etc. For each reservoir, there will be an upper limit of adsorption above which sufficient polymer will be removed from solution to make the process uneconomic. Copolymers of acrylamide (AM) and acrylic acid (AA) have been the most prominent chemicals to be applied, whereas sulfonated polymers containing acrylamide tertiary butyl sulfonic acid (ATBS) have been used for higher temperature and/or salinity conditions. In this work, it is demonstrated that there is a large kinetic component to the adsorption for a range of six polymer species on silica sand. The work was carried out in a field composition 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). While an adsorption of ~20 µg/g was 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 an adsorption at 24 hours of ~15 µg/g increasing over time to 36 ug/g. Two polymer species (33 % AA & 15 % ATBS) were then taken forward to dynamic core flood experiments where a novel shut-in procedure was used to highlight the kinetic behavior. The breakthrough profiles were matched via numerical simulation using a simple isotherm and kinetic constant. These results were then extrapolated to other conditions to highlight the potential for misinterpretation of traditional core flooding approaches. To the authors knowledge, the kinetic adsorption and its impact has not been very extensively discussed in the literature. The ability to accurately plan polymer flooding projects is essential to fully optimise recovery performance as efficiently as possible, minimise the environmental footprint and reliably predict polymer breakthrough for production chemistry requirements. Thus, a complete understanding of the polymer adsorption and adsorption kinetics is critical for the continued development of polymer EOR.