In situ oil shale process

#1. Field of the Invention

#This invention relates to the recovery of hydrocarbons from subterrenean oil shale formations. A method is provided for the in situ heating of the subterranean oil shale formation using two horizontal, vertically spaced metallic electrodes formed from cooling molten metal in fractures of the oil shale formation. More particularly, the invention relates to the recovery of hydrocarbons from the formation by drilling a bore hole, fracturing the oil shale formation near the upper and lower boundaries of the formation, injecting molten metal into the relatively horizontal fractures, allowing the metal to cool to form vertically spaced metallic electrodes, providing a radio frequency transmission line or coaxial cable between the electrodes, and inducing unterminated standing waves in the upper and lower metallic electrodes and in the oil shale formation therebetween by means of a radio frequency generator.

#2. Brief Description of the Prior Art

#FIG. 1 is a vertical sectional view of a bore hole entering a subterranean oil shale formation illustrating the formation of a lower metallic electrode.

#FIG. 2 is a vertical sectional view of a bore hole penetrating a subterranean oil shale formation illustrating the production of an upper metallic electrode.

#FIG. 3 illustrates a vertical sectional view of a bore hole penetrating a subterranean oil shale formation in completed condition for recovery of hydrocarbons from the shale.

#Referring now to FIG. 1, a cross-sectional view of an oil shale formation indicated generally at 1 is shown below the surface of the earth 2. The extent of the oil shale formation 1 is defined by boundaries 3 and 4 at the top and bottom of the oil shale formation respectively.

#A bore hole 5 is drilled through the oil shale formation 1 by using conventional rotary drilling techniques to reach a depth in the underburden 7 below the bottom boundary 4. A metallic casing 6 of high temperature and pressure rating is inserted into the bore hole 5 along the entire length of the bore hole. A cement outer coating 8, especially formulated to withstand high temperatures, is injected between the casing 6 and the bore hole along the entire length of the casing. This cementing of the casing may be achieved by conventional oil well cementing techniques. A cement base 9 fills the bottom of the bore hole 5 at a position in the underburden 7 just below the bottom boundary 4 of the oil shale formation 1. A rotatable high pressure tubing 10 is inserted into the casing 6 with an annular space 11 therebetween.

#A lower casing slot 12 of 360.degree. is cut completely through the casing 6 and cement 8 to the oil shale formation 1. A standard technique to effectuate this cutting is a process by which fine sand particles are entrained in water and pumped down the tubing 10. After the casing slot 12 has been cut, the water-sand mixture is returned to the surface 2 through the annulus 11 circumscribing the tubing 10. A lower fracture 20, which is generally horizontal relative to the surface 2, is formed by standard techniques used in the oil industry. To form the fracture 20, pressure is applied down through the casing slot 12 so as to fracture the oil shale formation 2 adjacent to the casing slot 12. Once the formation is parted, a sufficient amount of water is injected into the widening fracture to cause the lower fracture 20 to extend approximately to a 100 foot radius from the casing slot 12. However, various other radius lengths can be achieved depending upon the extent of such deposits. After the fracture 20 is formed, bore hole 5 is opened at the surface 2 to allow some of the injected water to flow back from the fracture 20 to the surface 2.