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A method for lowering the temperature of a portion of a subsurface formation is provided. Preferably, the formation is an oil shale formation. The method includes the step of injecting a cooling fluid under pressure into a wellbore, with the wellbore having been completed at or below a depth of the

A method for lowering the temperature of a portion of a subsurface formation is provided. Preferably, the formation is an oil shale formation. The method includes the step of injecting a cooling fluid under pressure into a wellbore, with the wellbore having been completed at or below a depth of the subsurface formation. In one embodiment the wellbore has an elongated tubular member for receiving the cooling fluid and for conveying it downhole to the subsurface formation. The wellbore also has an expansion valve in fluid communication with the tubular member through which the cooling fluid flows. The method then includes the steps of injecting a cooling fluid under pressure into the wellbore, and expanding the cooling fluid across the first expansion valve. In this way, the temperature of the cooling fluid is reduced. The temperature of the surrounding formation is likewise reduced through thermal conduction and convection. In another embodiment, a partially frozen slurry is used as the cooling fluid.

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What is claimed is: 1. A method for lowering the temperature of a portion of a subsurface formation, the subsurface formation comprising oil shale, and the method comprising: (a) injecting a cooling fluid under pressure into a wellbore, the wellbore being completed at or below a depth of the subsur

What is claimed is: 1. A method for lowering the temperature of a portion of a subsurface formation, the subsurface formation comprising oil shale, and the method comprising: (a) injecting a cooling fluid under pressure into a wellbore, the wellbore being completed at or below a depth of the subsurface formation, and the wellbore having: an elongated tubular member for receiving the cooling fluid and for transporting the cooling fluid to the subsurface formation, wherein the elongated tubular member is a U-tube, and a first expansion valve in fluid communication with the tubular member through which the cooling fluid flows; (b) expanding the cooling fluid across the first expansion valve; (c) circulating the cooling fluid across the formation in order to reduce the temperature of the cooling fluid and to lower the temperature of at least a portion of the formation to a point that is at or below the freezing point of water, wherein circulating the cooling fluid comprises circulating the fluid into the U-tube, down to the subsurface formation, and back up to the surface; (d) repeating steps (a), (b) and (c) for at least ten adjacent wellbores in order to form a flow barrier in the subsurface formation along the at least ten wellbores, and wherein the wellbores are formed at the periphery of an area under shale oil development; and (e) monitoring the integrity of the flow barrier by analyzing compositions of fluid samples taken from wells formed outside of the flow barrier. 2. The method of claim 1, wherein the cooling fluid flows through the first expansion valve upon or before reaching the upper depth of the subsurface formation. 3. The method of claim 1, wherein: the wellbore further comprises an annular region formed between the elongated tubular member and a diameter of the wellbore; and the step (c) of circulating comprises circulating the fluid through the tubular member, to the completion depth, and back up the wellbore through the annular region. 4. The method of claim 1, wherein the first expansion valve is positioned along the tubular member at a depth of about 300 feet or greater. 5. The method of claim 1, wherein the cooling fluid is a vapor at surface injection conditions. 6. The method of claim 1, wherein the cooling fluid is comprised at least of 50 mol. percent of propane, propylene, ethane, ethylene, or a mixture thereof. 7. The method of claim 1, wherein the cooling fluid is comprised at least of 50 mol. percent of a halogenated hydrocarbon. 8. The method of claim 1, wherein the cooling fluid is chilled below ambient air temperature prior to injection into the tubular member. 9. The method of claim 1, wherein the cooling fluid is injected at a controlled rate such that the gas flows through the first expansion valve and adjacent the subsurface formation, and then leaves the subsurface formation with no more than 20 wt.% in a liquid state. 10. The method of claim 1, wherein the subsurface formation comprises in situ water, and the cooling fluid cools the subsurface formation sufficient to freeze at least a portion of the in situ water. 11. The method of claim 1, wherein the cooling fluid is at a temperature after passing through the first expansion valve of about-20° F. to-120° F. 12. The method of claim 1, wherein the cooling fluid is at a pressure of about 200 psia to 8,000 psia before passing through the first expansion valve, and about 40 psia to about 200 psia after passing through the first expansion valve. 13. The method of claim 1, wherein: injecting the cooling fluid creates a downward flow of fluid into the wellbore, and an upward flow of fluid out of the wellbore; and a heat transfer coefficient between the upward and downward flows below the first expansion valve is less than 50 W/m2·C. 14. The method of claim 13, wherein the heat transfer coefficient between the upward and downward flows below the first expansion valve is less than 25 W/m2·C. 15. A method for lowering the temperature of a portion of a subsurface formation, the subsurface formation comprising oil shale, and the method comprising: (a) injecting a cooling fluid under pressure into a wellbore. the wellbore being completed at or below a depth of the subsurface formation, and the wellbore having: an elongated tubular member for receiving the cooling fluid and for transporting the cooling fluid to the subsurface formation, and a first expansion valve in fluid communication with the tubular member through which the cooling fluid flows, wherein the tubular member comprises insulation along at least a portion of the tubular member below the first expansion valve; (b) expanding the cooling fluid across the first expansion valve; (c) circulating the cooling fluid across the formation in order to reduce the temperature of the cooling fluid and to lower the temperature of at least a portion of the formation to a point that is at or below the freezing point of water; (d) repeating steps (a), (b) and (c) for at least ten adjacent wellbores in order to form a flow barrier in the subsurface formation along the at least ten wellbores. and wherein the wellbores are formed at the periphery of an area under shale oil development; and (e) monitoring the integrity of the flow barrier by analyzing compositions of fluid samples taken from wells formed outside of the flow barrier. 16. A method for lowering the temperature of a portion of a subsurface formation, the subsurface formation comprising oil shale, and the method comprising: (a) injecting a cooling fluid under pressure into a wellbore, the wellbore being completed at or below a depth of the subsurface formation, and the wellbore having: an elongated tubular member for receiving the cooling fluid and for transporting the cooling fluid to the subsurface formation, and a first expansion valve in fluid communication with the tubular member through which the cooling fluid flows. (b) expanding the cooling fluid across the first expansion valve; (c) circulating the cooling fluid across the formation in order to reduce the temperature of the cooling fluid and to lower the temperature of at least a portion of the formation to a point that is at or below the freezing point of water; (d) repeating steps (a), (b) and (c) for at least ten adjacent wellbores in order to form a flow barrier in the subsurface formation along the at least ten wellbores, and wherein the wellbores are formed at the periphery of an area under shale oil development; (e) monitoring the integrity of the flow barrier by analyzing compositions of fluid samples taken from wells formed outside of the flow barrier; and (f) wherein the subsurface formation comprises in situ water, injecting low salinity water into at least a portion of the subsurface formation to reduce the natural salinity of the in situ water and to raise the freezing temperature of the in situ water, and the cooling fluid cools the subsurface formation sufficient to freeze at least a portion of the in situ water. 17. A method for lowering the temperature of a portion of a subsurface formation, the subsurface formation comprising oil shale, and the method comprising: (a) injecting a cooling fluid under pressure into a wellbore, the wellbore being completed at or below a depth of the subsurface formation, and the wellbore having: an elongated tubular member for receiving the cooling fluid and for transporting the cooling fluid to the subsurface formation, wherein the elongated tubular member is a U-tube comprising a downward portion through which the cooling fluid flows to the subsurface formation, and an upward portion through which the cooling fluid flows back to the surface; and the downward portion is insulated above the subsurface formation, and a first expansion valve in fluid communication with the tubular member through which the cooling fluid flows; (b) expanding the cooling fluid across the first expansion valve; (c) circulating the cooling fluid across the formation in order to reduce the temperature of the cooling fluid and to lower the temperature of at least a portion of the formation to a point that is at or below the freezing point of water; (d) repeating steps (a), (b) and (c) for at least ten adjacent wellbores in order to form a flow barrier in the subsurface formation along the at least ten wellbores. and wherein the wellbores are formed at the periphery of an area under shale oil development; and (e) monitoring the integrity of the flow barrier by analyzing compositions of fluid samples taken from wells formed outside of the flow barrier. 18. A method for lowering the temperature of a portion of a subsurface formation, the subsurface formation comprising oil shale, and the method comprising: The method of claim 1, wherein: (a) injecting a cooling fluid under pressure into a wellbore, the wellbore being completed at or below a depth of the subsurface formation, and the wellbore having: an elongated tubular member for receiving the cooling fluid and for transporting the cooling fluid to the subsurface formation, a first expansion valve in fluid communication with the tubular member through which the cooling fluid flows, and a second expansion valve in fluid communication with the tubular member through which the cooling fluid further flows to cool the subsurface formation, such that a first pressure drop takes place through the first expansion valve, and a second pressure drop takes place through the second expansion valve; (b) expanding the cooling fluid across the first expansion valve and expanding the cooling fluid across the second expansion valve, thereby reducing the temperature of the cooling fluid; (c) circulating the cooling fluid across the formation in order to reduce the temperature of the cooling fluid and to lower the temperature of at least a portion of the formation to a point that is at or below the freezing point of water; (d) repeating steps (a), (b) and (c) for at least ten adjacent wellbores in order to form a flow barrier in the subsurface formation along the at least ten wellbores, and wherein the wellbores are formed at the periphery of an area under shale oil development; and (e) monitoring the integrity of the flow barrier by analyzing compositions of fluid samples taken from wells formed outside of the flow barrier. 19. The method of claim 18, wherein: the elongated tubular member is a U-tube; the cooling fluid flows through the first expansion valve upon or before reaching the depth of the subsurface formation; and the cooling fluid further flows through the second expansion valve at or after reaching the depth of the subsurface formation. 20. The method of claim 18, wherein: the cooling fluid is at a pressure of about 800 psia to 4,000 psia before passing through the first expansion valve, and about 100 psia to about 800 psia after passing through the first expansion valve; and the cooling fluid is at a pressure of about 100 psia to 800 psia before passing through the second expansion valve, and about 25 psia to about 100 psia after passing through the second expansion valve. 21. The method of claim 18, wherein the ratio of entry pressure-to-exit pressure across the first expansion valve and the ratio of entry pressure-to-exit pressure across the second expansion value are equal to within a factor of about 3.