Study on polymer mechanical degradation in core plugs versus in capillary tubes

Abstract

Polymer flooding has been recognized as an effective technology to improve oil recovery. While synthetic polymers have been widely used in this process, mechanical degradation tends to occur at near-wellbore regions where flow rate is high. In this paper, we evaluated the polymer mechanical degradation in both core samples and capillary tubes. Results showed that the degradation tended to be severer when the polymer solution flowing through tighter core samples or through capillary tubes with smaller diameter. After mechanical degradation, the polymer average molecular weight was lower and its distribution became wider, indicating the irreversible fragmentation of polymer molecules. The critical shear rate, beyond which evident polymer degradation occurred, tended to be lower for sandstone cores than that for carbonate cores in the same permeability range. On the other hand, the critical shear rates obtained from capillary tubes were significantly higher than those from the core samples. Correlations between the polymer degradation in core samples and in capillary tubes were established, which can be used to estimate the polymer mechanical degradation in reservoir rocks from the more convenient measurement using capillary tubes. This study provides a robust technique for polymer evaluation, and the results are also helpful for better understanding of the polymer flow in porous media.