Patent ID: 7516785

Claim:
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.