Core Flooding Experimental Study on Enhanced Oil Recovery of Heavy Oil Reservoirs with High Water Cut by Sub- and Supercritical Water

In recent years, the excellent thermochemical properties of supercritical water (SCW) have been exploited in the development of supercritical water flooding (SCWF) technology as an efficient and green enhanced oil recovery (EOR) method for thick oil. The EOR method is frequently employed in the tertiary oil recovery of oilfields. However, the high water cut within the reservoir represents a main challenge to heavy oil recovery. The recovery process and recovery mechanism of SCWF technology under high water cut conditions remain unclear. This study established a novel experimental system (450 degrees C, 30 MPa) to conduct SCWF experiments for heavy oil reservoirs with high water cut. The results showed that SCWF at 400 degrees C and 25 MPa had exhibited the recovery factor efficiency up to 96.27% and the viscosity reduction factor up to 61.6% for Gudao heavy oil, compared to conventional steam flooding and subcritical water flooding. Further, the dynamic process of SCWF was divided into three stages: pressure rising drainage stage, heating and depressurization stage and miscible flooding stage. It is evident that the high diffusivity, solubility and reactivity of supercritical water play a crucial role in thermal fluid breakthrough, miscible flooding and aquathermolysis reactions, which become the key mechanisms for EOR and in situ upgrading of SCWF in heavy oil reservoirs with high water cut. This work provides a theoretical basis and experimental validation for the extraction of heavy oil in oilfields.