Environmental Consequences of Polymer Flooding

Summary Worldwide polymer flooding (PF) is being introduced as a viable option for increasing recovery rates. In PF projects, back-produced polymer are ideally disposed of by reinjection or injection to a deposit well. However, significant challenges with offshore produced polymer water management creates possibilities for intermittent overboard discharge. If polymers are released to the sea, then how does structure of the polymers change over time and is it important for the marine ecosystem? In spite of the polymers having very low toxicity, the sheer volume of polymer applied in a PF constitutes a major hazard. In addition, the impact and fate of these polymers are largely unknown beyond standardized acute toxicity and biodegradability data. Very few studies on toxicological mechanisms and long-term environmental fate exist, likely because of lacking analytical tools and incentives for in-depth studies. Currently, biodegradability is decisive for chemical classification within the Norwegian offshore environmental regulations. Biopolymers satisfy the criteria, while the non-biodegradable synthetics do not and are as such prohibited from use. Nonetheless, modern PF favor synthetic polymers due to a variety of factors, including concurrent use of biocide. This together with harsh reservoir conditions favors development of physio-chemically stable polymers, impeding environmental performance and complicating risk management. Moreover, the regulations does not take into account that these polymers are especially sensitive to physical and chemical degradation. To begin solving this puzzle we have set up 80-days inherent and ready biodegradability studies on a variety of partially hydrolyzed polyacrylamide derivatives. Respirometry allows for continuous monitoring of biotic degradation. After the end of the experiment, size exclusion chromatography with multi-angle laser light scattering (MALLS) will examine shifts in molecular weight (Mw) distribution. Regarding MALLS limitation on low concentrations and “dirty” samples, we aim to overcome those by applying ultrafiltration techniques capable of isolating and concentrating the Mw-range of interest. The results will yield structure-activity relationships for both aerobe and anaerobe, biotic and abiotic degradation pathways. Preliminary results show that the presence of synthetic polymer does not affect metabolic rates. Which means that if any degradation is observed, it must be through abiotic mechanisms. This study is a part of a larger effort to generate data forming a basis for a mechanistic model that can predict environmental performance based on polymer chain-length and structure. We believe such a model can be made through mentioned long-term degradation studies, mechanistic eco-toxicological studies and state of the art analytical techniques.