Mechanisms of Oil Displacement By Carbon Dioxide

CO/sub 2/ can enhance the recovery of oil from porous rock by (1) solution gas drive, (2) swelling oil and reducing its viscosity, and (3) miscible effects. The most efficient use of carbon dioxide as an oil recovery agent is obtained at flooding pressures where miscible type displacement is achieved.The extraction of hydrocarbons (C/sub 3/ to C/sub 30/) from the crude oil in place by CO/sub 2/ at these pressures promotes a displacement efficiency which approaches 100%. This high displacement efficiency can be obtained at flooding temperatures below 200/sup 0/F and pressures below 3,000 psi with any crude oil containing appreciable hydrocarbons in the gasoline-light gas-oil range. Also, the process is applicable to waterflooded reservoirs which have been depleted of their gas and LPG components. The presence of methane in the injected CO/sub 2/ or in the reservoir oil reduces the overall recovery efficiency of the displacement process. A simple correlation is presented to determine the optimum displacement pressure for CO/sub 2/ floods.