Preliminary numerical modelling of CO₂ gas foaming in heavy oil and simulations of oil production from heavy oil reservoirs

Basic understanding of numerical modelling for the effects of CO₂ foaming on heavy oil production behaviour using the huff-and-puff process is relevant for CO₂-EOR performance. The numerical model was constructed based on laboratory measurements: CO₂ solubility, foam swelling, and apparent viscosity. The model for unsaturated solubility in porous media, such as sandstone cores and oil reservoirs, was proposed by defining CO₂ solubility in heavy oil for generating foamy oil. The foaming process was modelled with four kinds of foamy oils at discrete depressurizations below each equilibrium pressure. A numerical model of apparent foam viscosity with discrete depressurization was set up based on experimental measurements as a function of pressures and temperatures of 0.1-10MPa and 20-50°C. The matching between the numerical simulations of heavy oil drainage and experimental measurements of foaming in Berea sandstone cores (P_sat=10MPa at 50°C) shows 31% oil recovery after depressurization to atmospheric pressure. The numerical simulation results of heavy oil production at field-scale showed that CO₂ gas production quickly increases after depressurization and then the foamy oil production increases following the peak gas production rate. In the first cycle of the huff-and-puff process, the maximum oil production rate ranged from 4-68m³/day. From the sensitivity study it can be concluded that the initial oil saturation and the CO₂ dissolution zone as compared with reservoir size play a main function in heavy oil production by CO₂ gas foaming in the huff-and-puff process.