Robert Kaminsky and William Symington of Houston Texas have invented a high temperature oil shale fracking method. The inventors were granted United States Patent 7,857,056 entitled “Hydrocarbon recovery from impermeable oil shales using sets of fluid-heated fractures.” The invention involves pressure fracturing a formation containing hydrocarbons such that vertical fractures are created. Then a heated fluid is injected into the fractures at less than the original fracturing pressure. The fluid used to further open the oil shale being fractured is between 260 and 370°C. The kerogen in the oil shale is converted into oil and gas at these temperatures allowing both the recovery of that material and the further opening of the oil shale formation for greater production. The patent was assigned to ExxonMobil Upstream Research Company of Houston, TX.
As shown in both the figure above and the figure below the fracturing is done in a way that minimizes the opportunity for the hot drilling fluid to cool off and lose its effectiveness. This is accomplished by controlling the distance through the formation that the hot fluid must traverse.