Sweep-Volume Enlargement by a Polymer under High-Temperature and High-Salinity Conditions: Visual Research Using Computed Tomography

The thickening capacity of a polymer in a high-temperature and high-salinity environment is restricted, damaging its performance in expanding the sweep volume and enhancing oil recovery. A special temperature- and salt-resistant polymer (TSRP) was used for viscosity evaluation, more importantly, the joint polymer flooding tests and computed tomography (CT) scans of oil distribution in cores. Thus, the stability of such a polymer under harsh conditions and sweep-volume enlargement by the polymer in heterogeneous cores could be observed visually. The results show that TSRP can be stable at 85 °C and a high salinity of 58,002 mg/L, but its viscosity is significantly reduced when increasing the salinity from 3356.0 to 58,002 mg/L, which hinders oil flooding. However, when the heterogeneity of cores is relatively weak with a permeability contrast (PC) of 1.0-5.0, TSRP can effectively sweep the low-permeability layer, reaching a greater incremental oil recovery of 24.1-28.8%. As the heterogeneity increases significantly to a PC value of 7, TSRP fails to activate the low-permeability layer, and oil recovery can only be enhanced by 18.2%. The surfactant-polymer (SP) system can indeed achieve greater incremental oil recovery of 22.9-34.1%, but it does not significantly outperform a single polymer in sweep-volume enlargement at a PC of 7. Increases in the core size and corresponding thickness of the low-permeability layer do not significantly affect the performance of the polymer in sweep-volume enlargement and oil recovery.