Geothermal Power Generation

Abstract

An enhanced oil recovery method in which carbon dioxide is injected into a well to pressure the well or add lift a production flow from the well recaptures the injected carbon dioxide for reinjection into the well for lift or into another well in a group of for pressuring the well or adding lift to the production flow from the well. Geothermal energy in the production stream can be converted to electrical power for use in the recapturing of the carbon dioxide or other operations at the well site.

1 - 23 . (canceled) 
     
     
         24 . A method, comprising:
 positioning a heat exchanger within a bore of an oil and gas well below a well head located at the earth's surface; and   circulating a fluid between the heat exchanger and a low temperature geothermal (LTG) power generator on the surface in a closed loop disposed within the well bore to transfer geothermal energy from within the well bore to the LTG electric power generator.   
     
     
         25 . The method of  claim 24 , wherein the fluid in the closed loop is a working fluid for the LTG power generator, and wherein the geothermal energy heats the working fluid to a supercritical state. 
     
     
         26 . The method of  claim 24 , wherein the fluid in the closed loop is a transfer fluid, the transfer fluid being passed through a boiler of the LTG power generator to heat a working fluid in the LTG power generator to heat it to a supercritical state. 
     
     
         27 . The method of  claim 24 , wherein the heat exchanger comprises tubing wrapped around production tubing within the well bore. 
     
     
         28 . The method of  claim 27 , wherein the fluid in the closed loop is a working fluid for the LTG power generator, and wherein the geothermal energy heats the working fluid to a supercritical state. 
     
     
         29 . The method of  claim 27 , wherein the fluid in the closed loop is a transfer fluid, the transfer fluid being passed through a boiler of the LTG power generator to heat a working fluid in the LTG power generator to heat it to a supercritical state. 
     
     
         30 . The method of  claim 24 , wherein
 the well has at least one horizontal segment extending into a formation containing oil and gas that has been previously fractured to stimulate flow of fluids from within the formation into the horizontal segment;   the heat exchanger comprises double string tubing extending from the surface into the horizontal segment, the double string tubing comprising an inner tubing string with an open end that is disposed within larger diameter outer tubing string concentric with the inner tubing string and having a terminating end that is closed and located within the horizontal segment of the well bore; and   the method further comprises:
 pumping the fluid from the LTG power generator at the surface through the inner tubing string and returning the fluid through the outer tubing string to the LTG power generator, thereby establishing the closed loop; 
 transferring heat from well fluids in the well to the fluid in the outer tubing string as it returns to the LTG power generator. 
   
     
     
         31 . The method of  claim 30 , wherein the well has production tubing extending from the surface to an isolated production casing within the horizontal segment to carry production fluids, and wherein the double string tubing extends through into the isolated production casing and production fluids flow within an annulus formed between the outer tubing string of the double string and the production casing to transfer geothermal energy stored in the production fluids. 
     
     
         32 . The method of  claim 30 , wherein the method further comprises:
 after a period of time, removing the inner tubing string and opening the terminating end of the outer tubing string;   coupling the outer tubing string to a boiler of the LTG power generator;   pumping carbon dioxide down the production tubing to pressurize the wellbore to cause well fluids to be produced through the outer tubing string, the well fluids heating a working fluid in the boiler of the LTG electrical power generator to a supercritical state.   
     
     
         33 . The method of  claim 24 , wherein,
 the well has at least one horizontal segment extending into a formation containing oil and gas that has been previously fractured to allow fluids from within the formation to collect within the horizontal segment of the well;   the heat exchanger comprises a single string of tubing extending from the surface into the wellbore into the horizontal segment of the wellbore to a U-bend and back to the surface, each end of the string of tubing being coupled to the LTG electrical power generator thereby establishing a closed loop; and   the method further comprises pumping the fluid through the closed loop formed by the single string of tubing to be warmed by the well fluids prior to returning to the LTG electrical power generator.   
     
     
         34 . The method of  claim 33 , wherein the wellbore has production tubing extending from the surface to an isolated production casing below the tubing string, and wherein the single tubing string with a U-bend extends into the isolated production casing and the well fluids from the horizontal section flow between the single tubing string with a U-Bend formed between the outer tubing string of the double string and the production casing. 
     
     
         35 . The method of  claim 24 , wherein,
 the heat exchanger comprises an isolated section of production casing within the well, through which production tubing passes to carry production fluids from below the isolated section of production casing to the well head at the surface; and   wherein the closed loop is formed by circulating the fluid from a boiler of the LTG electrical power generator to the isolated section of production casing, where it is warmed by the production fluids flowing through the production tubing and returning the warmed fluid to the boiler through a length of tubing running from the isolated section of production casing to the boiler of the LTG electrical power generator.   
     
     
         36 . The method of  claim 24 , further comprising converting geothermal energy stored the production flow to electrical power by heating a working fluid of a low temperature geothermal (LTG) electric generator with geothermal heat transferred from a production flow received from production tubing at the surface. 
     
     
         37 . A method, comprising:
 hydraulically fracturing a hydrocarbon containing formation through which a well bore has been drilled to stimulate flow of hydrocarbons into the well bore;   coupling production tubing at a wellhead to a boiler of a low temperature geothermal (LTG) generator;   carrying to the surface through production tubing an initial flow back of production fluids from the hydraulically fractured well bore, the production fluids containing oil, gas, and water; and   transferring heat from the initial flow back of production fluids to a working fluid in the boiler of the LTG generator.   
     
     
         38 . The method of  claim 37 , wherein, after a flow of rate of the initial flow back production fluid subsides, combining with it production fluid from one or more other well bores before transferring heat from the production fluid to the working fluid in the boiler of the LTG generator. 
     
     
         39 . The method of  claim 37 , wherein, after a flow of rate of the initial flow back production fluid subsides, the working fluid in the boiler is further heated by circulating the working fluid downhole, below the wellhead, to a heat exchanger located downhole that heats the working fluid with geothermal energy from production fluids from the well bore. 
     
     
         40 . The method of  claim 37 , wherein, after a flow of rate of the initial flow back production fluid subsides, the working fluid in the boiler is further heated by heat transferred by circulating a transfer fluid downhole to a heat exchanger that is located below the well head and heats the transfer fluid with geothermal energy from production fluids from the well bore.