Apparatus for heating hydrocarbons with RF antenna assembly having segmented dipole elements and related methods

Abstract

The apparatus includes an RF antenna assembly to be positioned within a wellbore and coupled to an RF source. The RF antenna assembly includes a first tubular dipole element having opposing proximal and distal ends, an RF transmission line extending through the proximal end of the first tubular dipole element and including an inner conductor, an outer conductor, and a dielectric therebetween. The inner conductor extends outwardly beyond the distal end of the first tubular dipole element. The outer conductor is coupled to the distal end of the first tubular dipole element. The RF antenna assembly includes a second tubular dipole element having opposing proximal and distal ends, with the proximal end being adjacent the distal end of the first tubular dipole element and being coupled to the inner conductor, and a tubular balun.

That which is claimed is: 
     
       1. An apparatus for heating a hydrocarbon resource in a subterranean formation having a wellbore extending therein, the apparatus comprising:
 a radio frequency (RF) source; and 
 an RF antenna assembly configured to be positioned within the wellbore and coupled to said RF source; 
 said RF antenna assembly comprising
 a first tubular dipole element having opposing proximal and distal ends, 
 an RF transmission line extending through the proximal end of said first tubular dipole element and comprising an inner conductor, an outer conductor, and a dielectric therebetween, said inner conductor extending outwardly beyond the distal end of said first tubular dipole element, said outer conductor coupled to the distal end of said first tubular dipole element, 
 a second tubular dipole element having opposing proximal and distal ends, with the proximal end of the second tubular dipole element being adjacent the distal end of said first tubular dipole element and being coupled to said inner conductor, and 
 a tubular balun having said RF transmission line extending therethrough and opposing proximal and distal ends, with the distal end of the tubular balun being adjacent the proximal end of said first tubular dipole element and the proximal end of the tubular balun being coupled to said outer conductor. 
 
 
     
     
       2. The apparatus of  claim 1  wherein said RF antenna assembly comprises a tubular isolator having said RF transmission line extending therethrough and configured to couple together said tubular balun and said first tubular dipole antenna element. 
     
     
       3. The apparatus of  claim 2  wherein said tubular isolator comprises a cyanate ester composite material. 
     
     
       4. The apparatus of  claim 1  wherein said RF antenna assembly further comprises a feed structure comprising:
 a dielectric tube between said first and second tubular dipole antenna elements; 
 a first connector coupling said outer conductor to said first tubular dipole element; and 
 a second connector coupling said inner conductor to said second tubular dipole element. 
 
     
     
       5. The apparatus of  claim 4  wherein said first and second tubular dipole elements each comprises a threaded end; and wherein said first and second connectors each comprises a threaded end engaging a respective threaded end of said first and second tubular dipole elements for defining overlapping mechanical threaded joints. 
     
     
       6. The apparatus of  claim 4  wherein said first and second connectors each comprises a recess for receiving adjacent portions of said dielectric tube. 
     
     
       7. The apparatus of  claim 4  wherein said dielectric tube comprises a cyanate ester composite material. 
     
     
       8. The apparatus of  claim 1  wherein said inner conductor comprises a tube defining a first fluid passageway therein; and wherein said outer conductor is spaced from said inner conductor to define a second fluid passageway. 
     
     
       9. The apparatus of  claim 1  further comprising a tubular ferrite choke surrounding said RF transmission line and spaced apart from the proximal end of said tubular balun. 
     
     
       10. The apparatus according to  claim 1  wherein said first and second tubular dipole elements have a desired operating frequency; and wherein each of said first tubular dipole element, said second tubular dipole element, and said tubular balun has a length corresponding to +/−10% of a quarter of a wavelength of the desired operating frequency. 
     
     
       11. An apparatus for heating a hydrocarbon resource in a subterranean formation having a wellbore extending therein, the apparatus comprising:
 a radio frequency (RF) source; 
 an RF antenna assembly configured to be positioned within the wellbore and coupled to said RF source; 
 said RF antenna assembly comprising
 a first tubular dipole element having opposing proximal and distal ends, 
 an RF transmission line extending through the proximal end of said first tubular dipole element and comprising an inner conductor, an outer conductor, and a dielectric therebetween, said inner conductor extending outwardly beyond the distal end of said first tubular dipole element, said outer conductor coupled to the distal end of said first tubular dipole element, 
 a second tubular dipole element having opposing proximal and distal ends, with the proximal end of the second tubular dipole element being adjacent the distal end of said first tubular dipole element and being coupled to said inner conductor, 
 a tubular balun having said RF transmission line extending therethrough and opposing proximal and distal ends, with the distal end of the tubular balun being adjacent the proximal end of said first tubular dipole element and the proximal end of the tubular balun being coupled to said outer conductor, 
 a tubular isolator having said RF transmission line extending therethrough and configured to couple together said tubular balun and said first tubular dipole antenna element, and 
 a feed structure comprising
 a dielectric tube between said first and second tubular dipole antenna elements, 
 a first connector having a first circumferential slot for receiving said dielectric tube, and 
 a second connector having a second circumferential slot for receiving said dielectric tube; and 
 
 
 a tubular ferrite choke surrounding said RF transmission line and spaced apart from the proximal end of said tubular balun. 
 
     
     
       12. The apparatus of  claim 11  wherein said tubular isolator comprises a cyanate ester composite material. 
     
     
       13. The apparatus of  claim 11  wherein said first and second tubular dipole elements each comprises a threaded end; and wherein said first and second connectors each comprises a threaded end engaging a respective threaded end of said first and second tubular dipole elements for defining overlapping mechanical threaded joints. 
     
     
       14. The apparatus of  claim 11  wherein said dielectric tube comprises a cyanate ester composite material. 
     
     
       15. The apparatus of  claim 11  wherein said inner conductor comprises a tube defining a first fluid passageway therein; and wherein said outer conductor is spaced from said inner conductor to define a second fluid passageway. 
     
     
       16. A method for making a radio frequency (RF) antenna assembly for heating a hydrocarbon resource in a subterranean formation having a wellbore extending therein, the method comprising:
 providing a first tubular dipole element having opposing proximal and distal ends; 
 positioning an RF transmission line to extend through the proximal end of the first tubular dipole element, the RF transmission line comprising an inner conductor, an outer conductor, and a dielectric therebetween, the inner conductor extending outwardly beyond the distal end of the first tubular dipole element, the outer conductor to be coupled to the distal end of the first tubular dipole element; 
 providing a second tubular dipole element having opposing proximal and distal ends, with the proximal end of the second tubular dipole element being adjacent the distal end of the first tubular dipole element and coupled to the inner conductor; and 
 positioning a tubular balun to have the RF transmission line extending therethrough, the tubular balun having opposing proximal and distal ends, with the distal end of the tubular balun being adjacent the proximal end of the first tubular dipole element and the proximal end of the tubular balun to be coupled to the outer conductor. 
 
     
     
       17. The method of  claim 16  further comprising coupling together the tubular balun and the first tubular dipole antenna element with a tubular isolator having the RF transmission line extending therethrough. 
     
     
       18. The method of  claim 16  further comprising forming a feed structure by at least:
 coupling a dielectric tube between the first and second tubular dipole antenna elements; 
 coupling the outer conductor to the first tubular dipole element using a first connector; and 
 coupling the inner conductor to the second tubular dipole element using a second connector. 
 
     
     
       19. The method of  claim 16  further comprising:
 forming the inner conductor to comprise a tube defining a first fluid passageway therein; and 
 forming the outer conductor to be spaced from the inner conductor to define a second fluid passageway. 
 
     
     
       20. The method of  claim 16  further comprising positioning a tubular ferrite choke to surround the RF transmission line and to be spaced apart from the proximal end of the tubular balun.