Electrically Conductive Methods For In Situ Pyrolysis of Organic-Rich Rock Formations

Abstract

A method and system for heating a subsurface formation using electrical resistance heating includes providing a wellbore which has a production portion that penetrates an interval of organic-rich rock within the subsurface formation. The method includes forming a fracture in the organic-rich rock along a plane that is generally parallel with the production portion of the wellbore. A first electrically conductive proppant is placed into the fracture. Second and third electrically conductive proppants are placed within the wellbore and in electrical communication with the first electrically conductive proppant. The second and third proppants are spaced apart, and have a bulk resistivity that is less than the bulk resistivity of the first proppant. The method then includes passing an electric current through the fracture such that heat is generated by electrical resistivity within the first proppant sufficient to pyrolyze at least a portion of the organic-rich rock into hydrocarbon fluids.

1 . A method for heating a subsurface formation using electrical resistance heating, comprising:
 providing a wellbore having a production portion that penetrates an interval of organic-rich rock within the subsurface formation;   forming a fracture in the organic-rich rock along a plane that is generally parallel with the production portion of the wellbore;   placing a first electrically conductive proppant into the fracture, the first electrically conductive proppant having a first bulk resistivity;   placing a second electrically conductive proppant at a first location within the wellbore, the second electrically conductive proppant having a second bulk resistivity that is lower than the first bulk resistivity;   placing a third electrically conductive proppant at a second location within the wellbore spaced apart from the first location, the third electrically conductive proppant having a third bulk resistivity that also is lower than the first bulk resistivity; and   passing electric current through the fracture between the first and second locations such that heat is generated by electrical resistivity primarily within the first electrically conductive proppant.   
     
     
         2 . The method of  claim 1 , wherein:
 the subsurface formation comprises bitumen; and   the step of passing electric current heats the subsurface formation to at least partially mobilize the bitumen within the formation.   
     
     
         3 . The method of  claim 1 , wherein:
 the subsurface formation comprises oil shale; and   the step of passing electric current heats the subsurface formation to pyrolyze at least a portion of the oil shale into hydrocarbon fluids.   
     
     
         4 . The method of  claim 3 , further comprising:
 providing an electrical source at a surface;   providing a first electrical connection from the electrical source to the second electrically conductive proppant at the first location; and   providing a separate second electrical connection from the electrical source to the third electrically conductive proppant at the second location;   wherein the electrical source, the first electrical connection, the second electrically conductive proppant, the first electrically conductive proppant, the third electrically conductive proppant, and the second electrical connection form an electrical circuit.   
     
     
         5 . The method of  claim 4 , wherein the heat generated within the fracture from the first electrically conductive proppant is at least 25° C. greater than heat generated within the first and second locations from the second and third electrically conductive proppants. 
     
     
         6 . The method of  claim 1 , wherein:
 the production portion of the wellbore is completed vertically; and   the fracture plane of the fracture is substantially vertical   
     
     
         7 . The method of  claim 6 , wherein (i) the first location is proximate a lower portion of the subsurface formation; (ii) the second location is proximate an upper boundary of the subsurface formation; or (iii) both. 
     
     
         8 . The method of  claim 1 , wherein:
 the production portion of the wellbore is a single bore completed substantially horizontally, thereby providing a heel and a single toe; and   the fracture plane of the fracture is substantially horizontal or substantially vertical.   
     
     
         9 . The method of  claim 8 , wherein:
 the first location is proximate the toe;   the second location is proximate the heel; and   the first location and the second location each form a local region of relatively high electrical conductivity in comparison to the first electrically conductive proppant in the fracture of the horizontal production portion.   
     
     
         10 . The method of  claim 1 , wherein placing the first electrically conductive proppant into the fracture comprises.
 perforating the production portion of the wellbore; and   injecting the first electrically conductive proppant through the perforations and into the fracture as part of forming the fracture.   
     
     
         11 . The method of  claim 1 , wherein:
 the wellbore comprises a primary portion;   the production portion of the wellbore comprises at least two lateral wellbores having substantially horizontally production portions extending from the primary portion, thereby forming a multi-lateral wellbore; and   each horizontal production portion has a heel adjacent the primary portion, and a toe distal from the primary portion.   
     
     
         12 . The method of  claim 11 , wherein placing the first electrically conductive proppant into the fracture comprises:
 perforating each of the horizontal production portions of the wellbore;   forming a fracture comprises forming a fracture along each of the substantially horizontal production portions, and linking the fractures so that the fractures are in fluid communication; and   injecting the first electrically conductive proppant through the perforations and into each of the formed fractures along the horizontal production portions as part of forming the fractures.   
     
     
         13 . The method of  claim 12 , wherein:
 placing a second electrically conductive proppant at a first location within the wellbore comprises placing the second electrically conductive proppant substantially along a length of a first of the substantially horizontally production portions;   placing a third electrically conductive proppant at a second location within the wellbore comprises placing the third electrically conductive proppant substantially along a length of a second of the substantially horizontally production portions; and   the second and third electrically conductive proppants are in electrical communication by means of the first granular proppant residing within the fractures.   
     
     
         14 . The method of  claim 12 , wherein:
 placing a second electrically conductive proppant at a first location within the wellbore comprises placing the second electrically conductive proppant proximate the heel of a first of the substantially horizontal production portions; and   placing a third electrically conductive proppant at a second location within the wellbore comprises placing the third electrically conductive proppant proximate the toe of a second of the substantially horizontal production portions; and   the second and third electrically conductive proppants are in electrical communication by means of the first granular proppant residing within the fractures.   
     
     
         15 . The method of  claim 12 , further comprising:
 placing a second electrically conductive proppant at a first location within the wellbore comprises placing the second electrically conductive proppant proximate the heel of each horizontal production portion of the wellbore; and   placing a third electrically conductive proppant at a second location within the wellbore comprises placing the third electrically conductive proppant the toe of each horizontal production portion of the wellbore.   
     
     
         16 . The method of  claim 1 , wherein the second and third electrically conductive proppants each comprise metal shot, metal coated particles, calcined petroleum coke, graphite, or combinations thereof. 
     
     
         17 . The method of  claim 16 , wherein the second and third electrically conductive proppants are composed of substantially the same material. 
     
     
         18 . The method of  claim 1 , wherein placing the second and third electrically conductive proppants within the wellbore further comprises injecting each of the second and third electrically conductive proppants partially into the fracture. 
     
     
         19 . The method of  claim 1 , wherein the first electrically conductive proppant comprises metal shot, metal coated particles, coke, graphite, or combinations thereof. 
     
     
         20 . The method of  claim 19 , wherein the first electrically conductive proppant further comprises silica, ceramic, cement, or combinations thereof. 
     
     
         21 . The method of  claim 19 , wherein the resistivity of the first electrically conductive proppant is about 10 to 100 times greater than the resistivity of the second and third electrically conductive proppants. 
     
     
         22 . The method of  claim 1 , wherein the bulk resistivity of the first electrically conductive proppant is about 0.005 to 1.0 Ohm-Meters. 
     
     
         23 . The method of  claim 1 , further comprising:
 placing a substantially non-conductive material within the production portion of the wellbore between the second and third electrically conductive proppants.   
     
     
         24 . The method of  claim 1 , further comprising:
 producing hydrocarbon fluids from the subsurface formation to a surface.   
     
     
         25 . A method for heating a subsurface formation using electrical resistance heating, comprising:
 providing a wellbore having a production portion that penetrates an interval of oil shale within the subsurface formation;   forming a fracture in the oil shale interval along a plane that is generally parallel with the production portion of the wellbore;   injecting a first electrically conductive proppant into the fracture, the first electrically conductive proppant having a first bulk resistivity;   placing a second electrically conductive proppant at first and second spaced-apart locations within the wellbore, the second electrically conductive proppant having a second bulk resistivity that is lower than the first bulk resistivity;   placing a substantially non-conductive material within the wellbore intermediate the first and second locations;   installing a first electrically conductive lead in the wellbore providing electrical communication between an electricity source at the surface and the second electrically conductive proppant at the first location;   installing a second electrically conductive lead in the wellbore providing electrical communication between the electricity source at the surface and the second electrically conductive proppant at the second location; and   passing electric current through the fracture such that:
 an electrical circuit is formed between the electricity source at the surface, the first electrically conductive lead, the second electrically conductive proppant at the first location; the first electrically conductive proppant in the fracture, the second electrically conductive proppant at the second location, and the second electrically conductive lead; 
 heat is generated by electrical resistivity within the first electrically conductive proppant sufficient to pyrolyze at least a portion of the oil shale into hydrocarbon fluids; and 
 the heat generated within the fracture is greater than heat generated within the first and second locations. 
   
     
     
         26 . The method of  claim 25 , wherein:
 the production portion of the wellbore is completed substantially vertically; and   the fracture plane of the fracture is substantially vertical.   
     
     
         27 . The method of  claim 25 , wherein:
 the production portion of the wellbore is completed as a single substantially horizontally bore, thereby forming a heel and a single toe; and   the fracture plane of the fracture is either substantially horizontal or substantially vertical.   
     
     
         28 . The method of  claim 27 , wherein:
 the first location is proximate the toe;   the second location is proximate the heel; and   the first location and the second location each form a local region of relatively high electrical conductivity in comparison to the first electrically conductive proppant in the fracture of the horizontal production portion.   
     
     
         29 . The method of  claim 25 , wherein:
 the wellbore comprises a substantially vertical parent portion;   the production portion of the wellbore comprises at least two lateral bores having substantially horizontal portions;   each lateral wellbore has a heel adjacent a parent wellbore, and a toe distal from the parent wellbore extending from the parent portion, thereby forming a multi-lateral wellbore; and   forming a fracture comprises forming a fracture along each of the substantially horizontal production portions.   
     
     
         30 . The method of  claim 29 , wherein:
 placing a second electrically conductive proppant at a first location within the wellbore comprises placing second electrically conductive proppant substantially along a length of a first of the substantially horizontally production portions; and   placing a second electrically conductive proppant at a second location within the wellbore comprises placing second electrically conductive proppant substantially along a length of a second of the substantially horizontally production portions.   
     
     
         31 . The method of  claim 25 , wherein the resistivity of the first electrically conductive proppant is about 10 to 100 times greater than the resistivity of the second electrically conductive proppant. 
     
     
         32 . The method of  claim 25 , wherein the second electrically conductive proppant comprises metal shot, metal coated particles, coke, graphite, or combinations thereof. 
     
     
         33 . A system for electrically heating an organic-rich rock formation below an earth surface, the system comprising:
 an electricity source at the earth surface;   a wellbore having a production portion that penetrates an interval of solid organic-rich rock within the subsurface formation;   a fracture in the organic-rich rock along a plane that is generally parallel with the production portion of the wellbore;   a first electrically conductive proppant within the fracture, the first electrically conductive proppant having a first bulk resistivity;   a second electrically conductive proppant at a first location within the wellbore, the second electrically conductive proppant having a second bulk resistivity that is lower than the first bulk resistivity and being in electrical communication with the first electrically conductive proppant;   a third electrically conductive proppant at a second location within the wellbore spaced apart from the first location, the third electrically conductive proppant having a third bulk resistivity that also is lower than the first bulk resistivity, and the third electrically conductive proppant being in electrical communication with the first electrically conductive proppant;   a first electrical lead in the wellbore providing electrical communication between the electricity source at the surface and the second electrically conductive proppant at the first location; and   a second electrical lead in the wellbore providing electrical communication between the electricity source and the second electrically conductive proppant at the second location;   wherein:
 the second electrical lead is electrically insulated from the first electrical lead within the wellbore; and 
 the electricity source, the first electrical lead, the second electrically conductive proppant, the first electrically conductive proppant, the third electrically conductive proppant, and the second electrical lead form an electrical circuit. 
   
     
     
         34 . The system of  claim 33 , wherein the organic-rich rock formation comprises oil shale. 
     
     
         35 . The method of  claim 33 , wherein the second and third electrically conductive proppants are composed of the same material. 
     
     
         36 . The system of  claim 33 , further comprising:
 a substantially non-conductive material within the wellbore between the second and third electrically conductive proppants.   
     
     
         37 . The system of  claim 36 , wherein the substantially non-conductive material comprises mica, silica, quartz, cement chips, or combinations thereof. 
     
     
         38 . The system of  claim 33 , wherein the bulk resistivity of the first electrically conductive proppant is less than about 0.005 to 1.0 Ohm-meters. 
     
     
         39 . The system of  claim 33 , wherein the bulk resistivities of the second and third electrically conductive proppants is at least 10 times less than that of the first electrically conductive proppant. 
     
     
         40 . The system of  claim 33 , wherein the wellbore comprises one or more strings of casing, with at least a portion of the casing being non-conductive.