Pulsed-Electric Drilling Systems and Methods with Reverse Circulation

Abstract

In at least some embodiments, a pulsed-electric drilling system includes a bit that extends a borehole by detaching formation material with pulses of electric current, and a drillstring that transports a fluid flow from the bit to convey detached formation material out of the borehole. The use of reverse circulation may enhance the performance of the pulsed-electric drilling system.

1 . A pulsed-electric drilling system that comprises:
 a bit that extends a borehole by detaching formation material with pulses of electric current; and   a drillstring that transports a fluid flow from the bit to convey detached formation material out of the borehole.   
     
     
         2 . The system of  claim 1 , wherein the fluid flow reaches the bit via an annular path around the drillstring. 
     
     
         3 . The system of  claim 1 , wherein the drillstring defines at least two internal paths for fluid flow, including a path for transporting a fluid flow to the bit and a path for transporting a fluid flow from the bit. 
     
     
         4 . The system of  claim 3 , wherein the two internal paths are substantially concentric. 
     
     
         5 . The system of  claim 3 , further comprising a rim that substantially isolates an annular borehole region around the bit. 
     
     
         6 . The system of  claim 5 , wherein the bit causes the fluid flow through said annular borehole region to vary synchronously with said pulses. 
     
     
         7 . The system of  claim 1 , wherein the fluid flow passes over one or more electrodes before entering one or more orifices in the bit. 
     
     
         8 . The system of  claim 7 , wherein the bit causes the fluid flow to vary synchronously with said pulses. 
     
     
         9 . The system of  claim 1 , wherein the bit includes one or more nozzles that create a pressure differential for cooling by gas expansion. 
     
     
         10 . The system of  claim 1 , wherein the bit is substantially non-rotating relative to the borehole. 
     
     
         11 . A pulsed-electric drilling method that comprises:
 extending a borehole with a bit that detaches formation material using pulses of electric current; and   flushing detached formation material from the borehole with a fluid flow returning from the bit through a drillstring.   
     
     
         12 . The method of  claim 11 , wherein said flushing includes supplying the fluid flow to the bit via an annular space around the drillstring. 
     
     
         13 . The method of  claim 11 , wherein said flushing includes supplying the fluid flow to the bit via an internal supply path in the drillstring. 
     
     
         14 . The method of  claim 13 , wherein the internal supply path and return path are substantially concentric. 
     
     
         15 . The method of  claim 13 , further comprising isolating an annular borehole region around the bit from an annular borehole region around the drillstring. 
     
     
         16 . The method of  claim 15 , further comprising varying the fluid flow through said annular borehole region around the bit, said variation occurring synchronously with said pulses. 
     
     
         17 . The method of  claim 11 , wherein said flushing causes the fluid flow to pass over one or more electrodes before entering one or more orifices in the bit. 
     
     
         18 . The method of  claim 17 , further comprising varying the fluid flow over the one or more electrodes synchronously with said pulses.