Electrically Conductive Methods For Heating A Subsurface Formation To Convert Organic Matter Into Hydrocarbon Fluids

Abstract

A method and system for heating a subsurface formation using electrical resistance heating is provided. In one aspect, two or more wellbores are provided that penetrate an interval of solid organic-rich rock within the subsurface formation. At least one fracture is established in the organic-rich rock from at least one of the wellbores, and electrically conductive material is provided in the fracture. In this way electrical communication is provided between the two or more wellbores. The electrically conductive material may include a first portion placed in contact with each of the two or more wellbores, and a second portion intermediate the two or more wellbores. The first portion has a first bulk resistivity while the second portion has a second bulk resistivity. The method also includes passing electric current through the fracture such that heat is generated by electrical resistivity within the electrically conductive material sufficient to pyrolyze at least a portion of the organic-rich rock into hydrocarbon fluids. The resistive heat generated within the first portion of the electrically conductive material is less than the heat generated within the second portion of the electrically conductive material.

1 . A method for heating a subsurface formation using electrical resistance heating, comprising:
 providing two or more wellbores that penetrate an interval of solid organic-rich rock within the subsurface formation;   establishing at least one fracture in the organic-rich rock from at least one of the two or more wellbores;   providing electrically conductive material in the at least one fracture so as to provide electrical communication between the two or more wellbores, the electrically conductive material comprising (i) first portions placed in contact with each of the two or more wellbores and having a first bulk resistivity, and (ii) a second electrically conductive portion intermediate the two or more wellbores and having a second bulk resistivity; and   passing electric current through the at least one fracture such that resistive heat is generated within the electrically conductive material sufficient to pyrolyze at least a portion of the organic-rich rock into hydrocarbon fluids, wherein the generated heat is lower within the first portions of the electrically conductive material than in the second portion of the electrically conductive material.   
   
   
       2 . The method of  claim 1 , wherein the organic-rich rock comprises oil shale. 
   
   
       3 . The method of  claim 2 , wherein:
 each of the two or more wellbores is completed substantially vertically; and   the at least one fracture is substantially horizontal.   
   
   
       4 . The method of  claim 2 , wherein:
 each of the two or more wellbores is completed substantially horizontally; and   the at least one fracture is substantially vertical.   
   
   
       5 . The method of  claim 2 , wherein the electrically conductive material is a granular material that serves as a proppant. 
   
   
       6 . The method of  claim 2 , wherein the first portions of the electrically conductive material comprise granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       7 . The method of  claim 2 , wherein the second portion of the electrically conductive material comprises granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       8 . The method of  claim 2 , wherein the resistivity of the material comprising the second portion of the electrically conductive material is about 10 to 100 times greater than the resistivity of the material comprising the first portions of the electrically conductive material. 
   
   
       9 . The method of  claim 2 , wherein:
 the first portions of the electrically conductive material are substantially non-conductive; and   the second portion of the electrically conductive material contacts at least a portion of each of the two or more wellbores.   
   
   
       10 . The method of  claim 9 , wherein the first portions of the electrically conductive material comprise silica, quartz, cement chips, sandstone, or combinations thereof. 
   
   
       11 . The method of  claim 2 , wherein the resistivity of the first portions of the electrically conductive material is about 0.005 Ohm-Meters. 
   
   
       12 . The method of  claim 2 , wherein the resistivity of the first portions of the electrically conductive material is between about 0.00001 Ohm-Meters and 0.00005 Ohm-Meters. 
   
   
       13 . The method of  claim 2 , wherein the resistivity of the first portions of the electrically conductive material approaches infinity. 
   
   
       14 . The method of  claim 2 , wherein the at least one fracture is formed hydraulically. 
   
   
       15 . The method of  claim 2 , further comprising:
 continuing to pass electrical current through the first and second portions of electrically conductive material so as to cause pyrolysis of oil shale into hydrocarbon fluids; and   producing hydrocarbon fluids from the subsurface formation to a surface processing facility.   
   
   
       16 . A method for heating a subsurface formation using electrical resistance heating, comprising:
 creating at least one passage in the subsurface formation between a first wellbore located at least partially within the subsurface formation and a second wellbore also located at least partially within the subsurface formation;   providing an electrically conductive material into the at least one passage to form an electrical connection, the electrical connection providing electrical communication between the first wellbore and the second wellbore;   providing a first electrically conductive member in the first wellbore so that the first electrically conductive member is in electrical communication with the electrical connection;   providing a second electrically conductive member in the second wellbore, so that the second electrically conductive member is in electrical communication with the electrical connection, thereby forming an electrically conductive flow path comprised at least of the first electrically conductive member, the electrical connection and the second electrically conductive member; and   establishing an electrical current through the electrically conductive flow path, thereby generating heat within the electrically conductive flow path due to electrical resistive heating, with at least a portion of the generated heat thermally conducting into the subsurface formation, and wherein the generated heat is comprised of first heat generated in proximity to the first electrically conductive member and the second electrically conductive member, and second heat generated from the electrically conductive granular material intermediate the first electrically conductive member and the second electrically conductive member, with the first heat being less than the second heat.   
   
   
       17 . The method of  claim 16 , wherein the subsurface formation is an organic-rich rock formation. 
   
   
       18 . The method of  claim 17 , wherein the subsurface formation contains heavy hydrocarbons. 
   
   
       19 . The method of  claim 17 , wherein the subsurface formation is an oil shale formation. 
   
   
       20 . The method of  claim 17 , wherein:
 the electrically conductive material is a granular material; and   the electrical connection is a granular electrical connection.   
   
   
       21 . The method of  claim 20 , wherein the generated heat causes pyrolysis of solid hydrocarbons within at least a portion of the subsurface formation. 
   
   
       22 . The method of  claim 21 , wherein:
 the electrically conductive granular material comprises (i) first portions in immediate proximity to the first electrically conductive member and the second electrically conductive member, respectively, and (ii) a second portion intermediate the first portions around the first and second electrically conductive members; and   a resistivity of the first portions is different than a resistivity of the second portion.   
   
   
       23 . The method of  claim 22 , wherein the first portions of the electrically conductive granular material have a sufficiently low electrical resistivity so as to provide electrical conduction without substantial heat generation. 
   
   
       24 . The method of  claim 22 , wherein the first portions of the electrically conductive granular material comprises granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       25 . The method of  claim 22 , wherein the second portion of the electrically conductive granular material comprises granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       26 . The method of  claim 22 , wherein the resistivity of the material comprising the second portion of the electrically conductive granular material is about 10 to 100 times greater than the resistivity of the material comprising the first portions of the electrically conductive granular material. 
   
   
       27 . The method of  claim 22 , wherein the first portions of the electrically conductive granular material comprises less than or equal to 50 percent by dry weight of cement and 50 percent or more by dry weight of graphite. 
   
   
       28 . The method of  claim 22 , wherein the first portions of the electrically conductive granular material comprises between 50 to 75 percent of granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       29 . The method of  claim 22 , wherein:
 the first portions of the electrically conductive granular material are substantially non-conductive; and   the second portion of the electrically conductive granular material contacts at least a portion of each of the first and second electrically conductive members.   
   
   
       30 . The method of  claim 29 , wherein the first portions of the electrically conductive granular material comprise silica, quartz, cement chips, sandstone, or combinations thereof. 
   
   
       31 . The method of  claim 26 , wherein the resistivity of the first portions of the electrically conductive granular material is about 0.005 Ohm-meters. 
   
   
       32 . The method of  claim 26 , wherein the resistivity of the first portions of the electrically conductive material approaches infinity. 
   
   
       33 . The method of  claim 22 , wherein:
 the first wellbore and the second wellbore is each completed substantially vertically; and   the passage in the subsurface formation comprises a substantially vertically fracture.   
   
   
       34 . The method of  claim 26 , wherein:
 the first wellbore and the second wellbore is each completed substantially horizontally; and   the at least one passage in the subsurface formation comprises a first substantially vertical fracture.   
   
   
       35 . The method of  claim 33 , further comprising:
 providing a third electrically conductive member in a third wellbore, such that the third electrically conductive member is also in electrical communication with the electrical connection and is part of the electrically conductive flow path; wherein   the third wellbore is completed substantially horizontally;   the at least one passage in the subsurface formation comprises a second substantially vertical fracture; and   the second wellbore intersects both the first fracture and the second fracture.   
   
   
       36 . The method of  claim 22 , wherein the material comprising at least a portion of the first electrically conductive member, the second electrically conductive member, or both has an electrical resistivity of less than 0.0005 Ohm-meters. 
   
   
       37 . The method of  claim 22 , further comprising:
 continuing to pass an electrical current through the electrical connection until the subsurface formation immediately adjacent the electrically conductive flow path reaches a selected temperature; and   reducing an amount of current through the electrical connection.   
   
   
       38 . A system for in situ heating of a subsurface formation using electrical resistance heating, comprising:
 a plurality of wellbores that penetrate an interval of solid organic-rich rock within the subsurface formation;   at least one fracture in the organic-rich rock established from at least one of the wellbores, wherein the at least one fracture comprises electrically conductive material to provide electrical communication between at least two of the wellbores, the electrically conductive material including
 (i) first portions placed in contact with at least two wellbores and having a first bulk resistivity, and 
 (ii) a second electrically conductive portion intermediate the at least two wellbores and having a second bulk resistivity; and 
   at least one electrical conductor operatively connected to the first portions of the electrically conductive material in each of the at least two wellbores, the at least one electrical conductor being configured to pass electric current through the at least one fracture such that resistive heat is generated within the electrically conductive material sufficient to pyrolyze at least a portion of the organic-rich rock into hydrocarbon fluids, and wherein the generated heat is lower within the first portions of the electrically conductive material than in the second portion of the electrically conductive material.   
   
   
       39 . The system of  claim 38 , wherein:
 each of the two or more wellbores is completed substantially vertically; and   the at least one fracture is substantially horizontal.   
   
   
       40 . The system of  claim 38 , wherein:
 each of the two or more wellbores is completed substantially horizontally; and   the at least one fracture is substantially vertical.   
   
   
       41 . The system of  claim 38 , wherein the electrically conductive material is a granular material that serves as a proppant. 
   
   
       42 . The system of  claim 38 , wherein the first portions of the electrically conductive material comprise granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       43 . The system of  claim 38 , wherein the second portion of the electrically conductive material comprises granular metal, metal coated particles, coke, graphite, or combinations thereof. 
   
   
       44 . The system of  claim 38 , wherein the resistivity of the material comprising the second portion of the electrically conductive material is about 10 to 100 times greater than the resistivity of the material comprising the first portions of the electrically conductive material. 
   
   
       45 . The system of  claim 38 , wherein:
 the first portions of the electrically conductive material are substantially non-conductive; and   the second portion of the electrically conductive material contacts at least a portion of each of the two or more wellbores.   
   
   
       46 . The system of  claim 45 , wherein the first portions of the electrically conductive material comprise silica, quartz, cement chips, sandstone, or combinations thereof. 
   
   
       47 . The system of  claim 38 , wherein the resistivity of the first portions of the electrically conductive material is about 0.005 Ohm-Meters. 
   
   
       48 . The system of  claim 38 , wherein the resistivity of the first portions of the electrically conductive material is between about 0.00001 Ohm-Meters and 0.00005 Ohm-Meters. 
   
   
       49 . The system of  claim 38 , wherein the resistivity of the first portions of the electrically conductive material approaches infinity. 
   
   
       50 . The system of  claim 38 , wherein the at least one fracture is formed hydraulically. 
   
   
       51 . The system of  claim 38 , further comprising at least one production well for producing hydrocarbon fluids from the subsurface formation.