Closed loop energy production from geothermal reservoirs
Apparatus and methods for recovering and using geothermal energy. Such methods include at least partially vaporizing a working fluid by passing it through a flow loop that at least partially extends into a heated subterranean zone and employing the vaporized working fluid to power a turbine. At least a portion of the flow loop can comprise a depleted or partially depleted hydrocarbon well.
1. A system for extracting geothermal energy from a heated subterranean zone, said system comprising:
(a) a turbine assembly defining a turbine inlet and a turbine outlet;
(b) a depleted hydrocarbon well comprising a wellbore having casing and a tubing string within the casing defining an annulus space between the tubing string and the casing and where the casing and tubing string at least in part define a closed flow loop coupled in fluid flow communication with said turbine inlet and said turbine outlet, wherein at least a portion of said closed flow loop extends downwardly into said heated subterranean zone where said closed flow loop includes flow in one direction through said tubing string and in the opposite direction through said annulus space and wherein the tubing string comprises an inner tube disposed with an outer tube and defining an annular space therebetween and wherein one or more insulating materials fill the annular space between the inner and outer tubes;
(c) a hydrocarbon working fluid operable to flow through said closed flow loop where the working fluid is transported to the heated subterranean zone through said annular space, where the working fluid undergoes an indirect heat transfer from the heated subterranean zone, where the indirect heat transfer heat exchange causes at least a portion of the working fluid to vaporize thereby forming a predominately vapor phase working fluid, where the predominately vapor phase working fluid flows into a bottom opening of the tubing string, into the tubing string and flows substantially counter current to the flow of the working fluid in the annular space thereby forming an expanded working fluid;
(d) a heat exchanger defining a first pass and a second pass, where the expanded working fluid is discharged from the turbine assembly via the turbine outlet and routed to the first pass thereby forming a pre-cooled working fluid;
(e) a condenser interposed in said closed flow loop and operable to cool at least a portion of said expanded working fluid downstream of said turbine outlet and upstream of the portion of said flow loop contacting said heated subterranean zone thereby producing a cooled working fluid;
(f) a pump interposed in said closed flow loop between said condenser and the portion of said closed flow loop contacting said heated subterranean zone wherein the pump is operable to pressurize the cooled working fluid thereby producing a pressurized working fluid; and
where the pressurized working fluid is discharged from the pump into the heat exchanger second pass thereby forming a pre-heated working fluid, where the pre-heated working fluid is directed down into the wellbore through said annulus space so that the pre-heated working fluid, when heated and vaporized, returns up through said tubing string and further wherein the depleted hydrocarbon well previously operated to produce a hydrocarbon-containing material and has produced hydrocarbon-containing material in an amount of at least 50 percent of the initial estimated hydrocarbon capacity.