Improving the Oil Recovery from High-Temperature and High-Salinity Heavy-Oil Reservoirs with Temperature-Resistant and Calcium–Magnesium Resistant Polymer and Surfactant

It is a challenging process to recover oil from high-temperature and high-salinity (HTHS) heavy oil reservoirs because the viscosity of conventional polymers will be greatly reduced under HTHS conditions, and precipitation will easily occur. Temperature-resistant and calcium–magnesium-resistant (TR & CMR) polymers and TR & CMR surfactant–polymer (SP) flooding systems are being employed for oil recovery. To elucidate the mechanisms behind the enhanced oil recovery performance of these systems in such challenging environments and to investigate viable strategies for further improvement in oil recovery, this study examined the effectiveness of polymer flooding and SP flooding using a large three-dimensional (3D) flat-plate model. Following an evaluation of the properties of the polymer and surfactant employed in the experiment, large 3D flat-plate displacement oil experiments were conducted. Subsequently, the mechanism underlying the enhanced oil recovery from HTHS heavy-oil reservoirs achieved through the application of the TR & CMR polymer and TR & CMR SP flooding system was elucidated. The results showed that (1) The TR & CMR polymer exhibited a smaller molecular coil size, coupled with robust intermolecular association and cross-linking, significantly augmenting its capacity for viscosity enhancement. Furthermore, the incorporation of AMPS into the polymer enhanced its rigidity, thereby imparting it with excellent salt tolerance and high-temperature stability. The incorporation of the surfactant did not compromise the viscosity of the polymer, and the polymer and surfactant exhibited excellent compatibility. (2) In the process of TR & CMR polymer displacement, the water cut of the produced fluid was significantly reduced, the swept volume was effectively increased, and the recovery degree could be improved. Compared with water flooding, the water cut during polymer flooding decreased by 34.08%, the swept area increased by 28%, and the oil recovery increased by 11.67%. (3) Compared with water flooding, the water cut of the SP flooding system decreased by 46.28% during flooding, the swept area increased by 30%, and the recovery rate increased by 17.91%. Compared with polymer flooding, the oil recovery was further increased by 6.24%. SP flooding improved the oil washing efficiency, the remaining oil production degree was higher, and the remaining oil saturation was lower. The study can serve as an important basis for improving oil recovery from HTHS heavy-oil reservoirs.