Experimental Studies of Polymer Degradation in Carbonates Under Challenging Conditions

Abstract

Abstract The primary objective of this study is to investigate the effects of flow rate, salinity, and rock permeability on the degradation of an ATBS-based polymer during polymer flooding (PF). Experiments were conducted using polymer solutions in both moderate (57,670 ppm) and low (5,767 ppm) salinity environments at 80°C. The experiments were carried out on Indiana limestone core plugs with permeabilities of 195 mD and 419 mD. Two distinct flow rates, 0.5 cc/min and 2 cc/min, were employed to assess the degradation behavior. Key findings include a direct correlation between polymer degradation and increasing flow rate. At the high flow rate of 2 cc/min, degradation reached 12% and 21% in low and moderate salinity environments, respectively. In contrast, the low flow rate of 0.5 cc/min resulted in considerably lower degradation levels of 1% and 4% for low and moderate salinity conditions. Furthermore, the study reveals that salinity significantly impacts polymer mechanical stability. In the higher salinity setting (57,670 ppm), degradation was notably higher at both flow rates (4% at 0.5 cc/min and 21% at 2 cc/min) compared to the lower salinity environment (5,767 ppm), which showed degradation rates of 1% and 12% for the respective flow rates of 0.5 and 2 cc/min. In this study, the role of rock permeability was also investigated. The lower permeability rock (195 mD) exhibited higher degradation rates (4% at 0.5 cc/min and 21% at 2 cc/min), whereas the higher permeability core (419 mD) demonstrated lower degradation (1% at 0.5 cc/min and 12% at 2 cc/min). These findings suggest that significant attention must be provided to the selection of reservoir rock permeability, polymer type as well as injection water rate and salinity for successful polymer flooding in harsh conditioned carbonate reservoirs. By proper selection of these parameters, their negative impact on polymer stability can be decreased, resulting in an improvement in the efficacy of polymer-based enhanced oil recovery (EOR) operations.