1. Field of the Invention
This invention pertains to the improved recovery of heavy oil and tars from underground formations containing same by the injection of hot hydrocarbon vapors to heat the formation and extract the oil. It pertains more particularly to the effective recovery of such oils from relatively impermeable formations such as tar sand by hot hydrocarbon solvent vapor injection into the formation to extract and recover the oil using a single well hole.
2. Description of Prior Art
The in situ recovery of oil from underground formations is well known and there are several prior art patents in the area of oil recovery by injecting either aqueous or hydrocarbon solvent vapors into oil formations. Some of these patents use vaporized solvents such as benzene, toluene, carbon disulfide, kerosene, and a variety of other aromatic solvents and mixtures of solvents. These known processes usually depend upon the use of two or more boreholes, one borehole used for injection of the heated solvent vapor into the formation and one or more boreholes used for recovering the oil/solvent liquids. For example, U.S. Pat. No. 3,608,638 to Terwilliger shows injecting hot pressurized vapor into one well at the top of an oil bearing formation to promote oil production from another adjacent well. But these prior art systems require that the oil bearing formations have sufficient permeability to allow lateral fluid communication between the injection and production wells. However, in many oil bearing formations, such as tar sands, the original permeability is too low to permit using a two well production arrangement.
Oil recovery methods using single well systems have been used for producing oil from oil shale formations, which have been previously fractured by explosive means to make them permeable, followed by injecting hot gases and vapors into the formation. For example, U.S. Pat. No. 3,515,213 to Prats and U.S. Pat. No. 3,695,354 to Dilgren et al disclose shale oil recovery from such permeable shale formations by injecting heated fluids to stimulate oil recovery from the same well. However, the prior art apparently does not disclose recovering heavy oils and/or tars from essentially impermeable formations by injecting hot hydrocarbon solvent vapor into an upper portion of the formation and recovering oil along with condensed solvent from a lower portion of the formation using a single well hole. Thus, the present invention is directed to the effective recovery of heavy oils and tars by hot vapor injection using single wells, without regard to or depending on lateral fluid communication between adjacent wells, by directing the hot vapor to desired portions of the formation and recovering the liquids from a lower portion of the well.