Laboratory Investigation of CO2 Flooding

Abstract

Abstract Carbon dioxide (CO2) flooding is an efficacious method of EOR and it is a very complicated process, involving phase behavior. To master the performance of CO2 flooding and provide accurate data for designing oil development, a comprehensive investigation of CO2 flooding phase behavior and mechanism based on laboratory study was conducted. In order to get representative fluid samples of a reservoir, it was necessary that the right operation of mixing the separator oil and gas samples to match the bubble point pressure be carried out. The result from PVT experiments shows that for a certain reservoir, through a slight manipulation of the measured PVT properties including bubble point pressure, volume factor, swelling factor, solubility of CO2 and viscosity, it is possible to obtain regression curves, which can be used to estimated the PVT behavior for any hydrocarbon fluid-CO2 mixture of this reservoir. The result of slim tubule tests indicates that it is more appropriate to determine the minimum miscibility pressure of the reservoir fluid-CO2 mixture by the position of inflexion on the curve of oil recovery with flooding pressure than by reaching a special oil recovery point. Introduction Carbon dioxide flooding is an effective enhanced oil recovery process. It appeared in 1930's and had a great development in 1970's. Over 30 years' production practice, CO2 flooding has become the leading enhanced oil recovery technique for light and medium oils1–4. It can prolong the production lives of light or medium oil fields nearing depletion under waterflood by 15 to 20 years, and may recover 15% to 25% of the original oil in place1. CO2 flooding process involves very complicated phase behavior, which depends on the temperature, pressure and fluids properties of a certain reservoir. Many factors have been found contributing to the oil recovery in CO2 flooding. These mainly include5–11:low interface tensions;viscosity reduction;oil swelling;formation permeability improvement;solution gas flooding;density change of oil and water. R.K Srivastava et al6 took a laboratory study of Weyburn CO2 miscible flooding. From the PVT data generated from the three Weyburn reservoir fluid-CO2 mixtures it was showed that viscosity reduction and oil swelling by CO2 contributed to oil recovery. The viscosity showed an almost linear decrease with CO2 concentration. A slight manipulation of the measured PVT properties of the mixtures made it possible to obtain single property curves for the three Weyburn oils. This feature can be used to estimate the PVT behaviour for any Weyburn oil from the reservoir.