Method and System for Electrically Heating an Earth Formation

Abstract

A core of subterranean oil sand formation is delineated by a unit of three wellbores extending horizontally through the formation. The wellbores are spaced apart, parallel and coextensive. They are arranged in a triangular pattern. Multi-phase AC power is applied to electrode assemblies positioned in the wellbores to cause current to flow through the core, thereby heating it with the objective of reducing the viscosity of contained oil to render it mobile.

I claim: 
     
         1 . A system for electrically heating a portion of a subterranean earth formation containing heavy oil, from ground surface, comprising:
 a plurality of substantially parallel and equally spaced apart electrode wells forming a unit, each electrode well comprising a wellbore having an upper leg extending downwardly from ground surface and a lower leg further extending horizontally in the earth formation, said horizontal lower legs being positioned in a pattern so as to delineate a central core of formation;   an elongate electrode assembly located in each lower leg of the unit, said electrode assemblies each having at least one conductive electrode electrically coupled to the formation; and   means for supplying multi-phase alternating current power through the wellbores from a source at ground surface to the electrodes of the electrode assemblies so that different phases of power may be simultaneously applied to the electrodes;   whereby the core may be heated by electric current passing through the core between electrodes.   
     
     
         2 . The system as set forth in  claim 1  wherein the unit consists of three electrode wells whose lower legs are arranged in a triangular pattern. 
     
     
         3 . The system as set forth in  claim 2  wherein each upper leg is cased with electrically insulated casing and each lower leg combines with its contained electrode assembly to form an annulus; and further comprising:
 an annular column of electrically conductive fill in each annulus for enhancing transmission of electric current between the electrode(s) and surrounding formation. 
 
     
     
         4 . The system as set forth in  claim 2  wherein each electrode assembly comprises:
 a plurality of electrically conductive electrodes separated and connected by electrically insulating connectors. 
 
     
     
         5 . The system as set forth in  claim 3  wherein each electrode assembly comprises:
 a pipe having electrically conductive electrodes separated and connected by electrically insulating connectors; and 
 a tubular member positioned within the pipe and containing conductor cable means connected with the power source, extending through the casing and connected to the electrodes. 
 
     
     
         6 . The system as set forth in  claim 2  comprising:
 means, extending horizontally through the formation, for producing heated oil up through the casing. 
 
     
     
         7 . A method for electrically heating a portion of a subterranean earth formation from ground surface, comprising:
 forming a unit of a plurality of substantially parallel and equally spaced apart electrode wells, each well comprising a wellbore having an upper leg extending downwardly from ground surface and a lower leg further extending horizontally in the earth formation, said horizontal lower legs being positioned in a pattern so as to delineate a central core of formation;   providing an elongate electrode assembly in each lower leg, said electrode assemblies each having at least one conductive electrode electrically coupled to the formation; and   supplying multi-phase alternating current power to the electrodes of the electrode assemblies so that different phases of power are simultaneously applied to the electrode wells;   whereby the core may be heated by electric current passing through the core between electrodes.   
     
     
         8 . The method as set forth in  claim 7  wherein the unit consists of three electrode wells whose lower legs are arranged in a triangular pattern. 
     
     
         9 . The method as set forth in  claim 8  comprising multiple units arranged in side by side arrays. 
     
     
         10 . The method as set forth in  claim 8  wherein each upper leg is cased with electrically insulated casing and each lower leg is uncased and combines with its contained electrode assembly to form an annulus; and further comprising:
 providing an annular column of electrically conductive fill in each annulus for enhancing transmission of electric current between electrode and surrounding formation.