Microscopic remaining oil initiation mechanism and formation damage of CO2 injection after waterflooding in deep reservoirs

Abstract

Injecting CO2 into deep reservoirs with high temperature and pressure (HTHP) is a promising method for enhancing oil recovery (EOR) and CO2 utilization and storage (CUS). It is, however, challenging to quantitatively unravel the initiation mechanisms of micro-remaining oil and formation damage using microfluidic technology at 115 °C and 55 MPa. In this study, water/gas flooding experiments in the micromodel has carried out on the HPHT microfluidic experimental platform. The results reveal that 35.41% of the micro-remaining oil is recovered by scCO2 extraction on the funnel-shaped interface, and 11.21% by carbonated water swelling. When water is injected into heterogeneous reservoirs, the oil-water displacement front in the high-permeability zone is less stable than that in the low-permeability zone. Subsequent scCO2 injection resulted in asphaltene deposits (approximately 10.49% of pore volume), including low-velocity deposition, corner deposition and trap deposition, which reduced reservoir permeability. Moreover, compared with continuous CO2 injection, the asphaltene deposition is reduced by 4.25% of CO2 injection after waterflooding, including 2.64% in the high-permeability zone and 1.61% in the low-permeability zone. These observations provide important theoretical support for the application of CO2-EOR technology and carbon storage in deep reservoirs.