Intensification of displacement of heavy oil by supercritical carbon dioxide

The regularities of the volumetric and phase behavior of heavy oil during interaction with supercritical carbon dioxide (SC-CO2) at reservoir temperatures and pressures have been studied. In the “heavy oil–SC-CO2” system, thermobaric conditions for pressure changes during fluid injection into the system are determined. The aim of this work is to determine the patterns of change in volumetric and phase behavior, as well as to increase oil recovery of high-viscosity oil when interacting with SC-CO2.The main properties of the processed reservoir oil were on average as follows: reservoir oil density at reservoir pressure 963 kg/m3, viscosity at reservoir pressure 795–802 mPas, concentration (weight %) of paraffins 1.9, resins 49.3, asphaltenes 9.3, water 2.8, mechanical impurities 0.007. The composition of the reservoir oil mainly consisted of C9+ residue (95 %) and lighter hydrocarbons. Laboratory studies of the interaction of SC-CO2 with high-viscosity oil were conducted taking into account the reservoir pressure (7–15 MPa) and reservoir temperature (300–303 K). PVT analysis of oil samples was carried out using the PVT 3000-L unit. The solubility of SC-CO2 in heavy oil was studied in the pressure range of 7.2–7.5 MPa and temperatures of 313–333 K. The error in determining the solubility was 1.5 %. The physicochemical data we obtained allowed us to evaluate new properties on the critical lines of the phase diagram in the heavy oil-SC-CO2 model system. New aspects and thermobaric conditions of heavy oil displacement and the recovery factor over time were determined. With a single effect of SC-CO2 (20 wt. %) on the oil system at 7.2 MPa and 303 K for 200–250 min, the recovery factor is about 23 %. The limiting concentration of SC-CO2 was determined to obtain maximum swelling of oil. It has been shown that the volume of the heavy phase relative to the volume of the system decreases linearly with increasing concentration of SC-CO2 in contact with it. The influence of thermobaric factors on the degree of recovery of heavy oil components was assessed using a reservoir model reflecting the process of oil displacement. The results obtained are important for the transition to new methods and promising technologies for the complex processing of hard-to-recover oils and the safe disposal of valuable oil products. These results will contribute to the intensification of oil production and the expansion of the raw material base of processing plants.