Combined multiple solvent and thermal heavy oil recovery

Abstract

Petroleum may be recovered from viscous petroleum-containing formations including tar sand deposits by a process involving injecting into the formation a multiple-component solvent for the petroleum and a thermal fluid. At least one solvent component is gaseous at the temperature and pressure of the petroleum reservoir such as carbon dioxide, methane, ethane, propane, butane or pentane, and at least one component is liquid at the reservoir conditions, such as hexane and higher molecular weight aliphatic hydrocarbons or aromatic hydrocarbons such as benzene. The multiple solvent injection is continued with no production until the pressure is from 50 to 250% above the vapor pressure of the solvent, at which pressure the solvent mixture is substantially all in the liquid phase. Recovery of petroleum and solvent is from a remotely located well by reducing the pressure in the portion of the formation contacted by the solvents to a value from 5 to 100% above the vapor pressure of the gaseous solvent. A fluid heated to a temperature above the boiling point of the solvent, such as steam, is then injected into the same well as was used for solvent injection. The heated fluid raises the temperaure of the solvent on contact therewith, causing vaporization of the gaseous component, which gaseous solvent expands to force viscous petroleum with liquid solvent dissolved therein toward the production well. In formations having oil saturation greater than 50%, this oil saturation should first be reduced to a value below 50% to prevent plugging.