Oxidative degradation of polymers is caused by combination of Fe2+ and O2 resulting in viscosity loss. During lab tests, synthetic brine without Fe2+ is commonly used. However, most lab and field set-ups are made of stainless steel (SS) which is a possible source of Fe. Therefore, this study investigates the impact of Fe2+ and O2 contents on polymer stability with/without contact of SS in presence/absence of protective packages (ITW and oxygen scavenger).

Polymer stability tests were conducted for 1 week at ambient temperature under different O2 concentrations. Four polymer systems were evaluated (without additives, with ITW, with oxygen scavenger and with ITW+oxygen scavenger). Samples were stored in SS and glass bottles. Different Fe2+ concentrations were added to the solutions in the glass bottles. The viscosity of the polymer solutions was measured at anaerobic conditions at different intervals.

Viscosity results for polymer samples aged in glass bottles showed that ITW alone or in combination with oxygen scavenger is able to maintain polymer stability up to Fe2+ and O2 levels of 2.5 ppm and 1500 ppb, respectively. At atmospheric condition, these systems were found efficient as the maximum obtained viscosity loss was < 14%. While samples containing only oxygen scavenger maintained polymer stability up to Fe2+ and O2 levels of 2.5 ppm and 500 ppb, respectively, but experienced severe degradation when exposed to atmosphere. Similarly, blank samples experienced severe degradation after exposure to atmosphere and the stability was maintained up to Fe2+ and O2 levels of 0.5 ppm and 500 ppb, respectively.

Polymer solutions stored in SS cells experienced noticeable viscosity loss indicating that Fe is released from the SS and contribute to polymer degradation. The blank samples and samples containing oxygen scavenger were stable up to O2 level of 500 ppb. Addition of ITW into these polymer solutions boosted its viscosity stability up to O2 level of 1500 ppb. Exposing polymer samples containing either ITW or oxygen scavenger to atmosphere resulted in severe degradation of around 42% which is higher than the viscosity loss of the blank sample (28%). However, when both ITW and oxygen scavenger were added to the polymer solution and exposed to atmosphere, the viscosity loss was reduced to 26%.

This study showed that polymer stability in presence/absence of protective packages can be maintained at initial O2 level of 500 ppb. These findings are directly related to polymer stability during polymer preparation which needs to be considered in any polymer flood design. As protective packages might come handy for maintaining polymer stability in the reservoir, this study can aid in selection of the most feasible protective packages and water treatment requirements.

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