Production of low permeability geothermal resources

Abstract

A system for recovering thermal energy from a fractured subterranean formation can include a fluid removal system configured to remove a fluid comprising a liquid phase from the fractured subterranean formation through a wellbore that is in fluidic communication with a low permeability rock matrix through fractures in the fractured subterranean formation. The system can also include a heated fluid collection system configured to recover, through the wellbore, a heated fluid comprising a vapor phase that is expelled from the low permeability rock matrix of the fractured subterranean formation as a result of a reservoir pressure of the fractured subterranean formation falling below a saturation pressure of the fluid, where the fluid removal system is configured to be shut down while the heated fluid collection system operates, and where the heated fluid collection system is configured to be shut down while the fluid removal system operates.

What is claimed is: 
     
         1 . A system for recovering thermal energy from a fractured subterranean formation, the system comprising:
 a fluid removal system configured to remove a fluid comprising a liquid phase from the fractured subterranean formation through a wellbore that is in fluidic communication with the fractured subterranean formation, wherein fractures within the fractured subterranean formation are in fluidic communication with a low permeability rock matrix, and wherein the fluid removal system is configured to be shut down when a reservoir pressure is less than a saturation pressure of the fluid; and   a heated fluid collection system configured to recover, through the wellbore, a heated fluid comprising a vapor phase that is expelled from the low permeability rock matrix of the fractured subterranean formation as a result of a reservoir pressure of the fractured subterranean formation falling below a saturation pressure of the fluid, wherein the fluid removal system is configured to be shut down while the heated fluid collection system is collecting the heated fluid comprising the vapor phase, and wherein the heated fluid collection system is configured to be shut down while the fluid removal system is removing the fluid comprising the liquid phase.   
     
     
         2 . The system of  claim 1 , wherein the heated fluid collection system collects the heated fluid comprising the vapor phase at a surface facility. 
     
     
         3 . The system of  claim 1 , further comprising:
 a heated fluid delivery system configured to obtain the heated fluid comprising the vapor phase from the heated-fluid collection system and deliver the heated fluid comprising the vapor phase to a heated fluid consumption source.   
     
     
         4 . The system of  claim 3 , wherein the heated fluid consumption source comprises an electric generator. 
     
     
         5 . The system of  claim 1 , wherein the fluid comprising the liquid phase comprises a native reservoir fluid, an injection fluid, a hydraulic fracturing fluid, or any combination thereof. 
     
     
         6 . The system of  claim 1 , wherein the fluid comprising the liquid phase comprises water, and wherein the heated fluid comprising the vapor phase comprises steam. 
     
     
         7 . The system of  claim 1 , wherein the heated fluid comprising the vapor phase is expelled from the low permeability rock matrix of the fractured subterranean formation until the heated fluid comprising the vapor phase becomes superheated. 
     
     
         8 . The system of  claim 1 , wherein the low permeability rock matrix within the fractured subterranean formation has an average permeability that is no greater than about 0.1 millidarcy. 
     
     
         9 . The system of  claim 1 , wherein the low permeability rock matrix within the fractured subterranean formation has an average porosity that is greater than about 2%. 
     
     
         10 . The system of  claim 1 , further comprising:
 a fluid injection system that is configured to inject an injection fluid comprising the liquid phase into the low permeability rock matrix of the fractured subterranean formation through the wellbore when a parameter falls outside a range of acceptable values, wherein the fluid removal system and the heated fluid collection system are configured to be shut down while the fluid injection system is injecting the injection fluid comprising the liquid phase, wherein the fluid injection system is configured to be shut down while the fluid removal system is removing the fluid comprising the liquid phase, and wherein the fluid injection system is configured to be shut down while the heated fluid collection system is collecting the heated fluid comprising the vapor phase.   
     
     
         11 . The system of  claim 10 , wherein the injection fluid comprising the liquid phase that is injected into the wellbore is imbibed into the low permeability rock matrix by capillary pressure effects. 
     
     
         12 . The system of  claim 10 , wherein the parameter comprises a pressure within the wellbore, a temperature within the wellbore, or any combination thereof. 
     
     
         13 . The system of  claim 10 , wherein the fluid injection system injects the injection fluid comprising the liquid phase through the wellbore to resaturate the low permeability rock matrix of the fractured subterranean formation. 
     
     
         14 . The system of  claim 10 , wherein the fluid comprising the liquid phase that is removed through the wellbore by the fluid removal system is transferred to the fluid injection system to be used as the injection fluid comprising the liquid phase when the fluid injection system operates. 
     
     
         15 . The system of  claim 1 , wherein the low permeability rock matrix within the fractured subterranean formation has an average fracture spacing that is between 1 meter and 100 meters on average. 
     
     
         16 . The system of  claim 1 , wherein the wellbore is drilled from a pad among a plurality of pads, and wherein the wellbore has essentially no underground fluidic communication with other wellbores from a remainder of the plurality of pads. 
     
     
         17 . The system of  claim 1 , wherein an average spacing between fractures in the fractured subterranean formation is designed to maximize an amount of the heated fluid comprising the vapor phase that is expelled from the low permeability rock matrix of the fractured subterranean formation. 
     
     
         18 . The system of  claim 1 , wherein the fluid comprising the liquid phase within a porous space of the low permeability rock matrix transitions to the heated fluid comprising the vapor phase that is expelled from the low permeability rock matrix. 
     
     
         19 . The system of  claim 1 , further comprising:
 a wellbore pressure testing system that performs pressure tests to confirm that there is essentially no underground fluidic communication between the wellbore and at least one other wellbore.   
     
     
         20 . The system of  claim 1 , wherein the fluid removal system and the heated fluid collection system are used for a plurality of wellbores on one or more pads.