Apparatus and Process For Drilling A Borehole In A Subterranean Formation

Abstract

An apparatus and process is disclosed for drilling a borehole into a subterranean formation with reverse circulation of drilling fluid. A tubular drill pipe extends into a subterranean formation. A bottom hole assembly connected to the drill pipe includes a drill bit for excavating the subterranean formation. A downhole motor is adapted for receiving electrical power from a cable extending into the subterranean formation. A downhole pump is powered by the motor and is configured for reverse circulating drilling fluid from the annular space surrounding the drill pipe to the interior space of the drill pipe. The drilling fluid is pumped upwards in the drill pipe by the downhole pump to carry excavated cuttings upwards through the interior space of the drill pipe.

What we claim is: 
     
         1 . An apparatus for drilling a borehole into a subterranean formation with reverse circulation of drilling fluid, the apparatus comprising:
 (a) a tubular drill pipe extending into the subterranean formation, the drill pipe having an interior space and an annular space on the exterior of the drill pipe;   (b) a bottom hole assembly connected to the drill pipe, the bottom hole assembly comprising a bit to excavate the subterranean formation to form cuttings;   (c) a downhole motor, the downhole motor being adapted for receiving electrical power from a cable extending into the subterranean formation; and   (d) a downhole pump powered by the motor, the downhole pump being configured for reverse circulating drilling fluid and cuttings upwards through the interior space of the drill pipe.   
     
     
         2 . The apparatus of  claim 1  further comprising a mechanism for removing the excavated cuttings from the drilling fluid and recirculating the drilling fluid downwards through the annular space on the exterior of the drill pipe. 
     
     
         3 . The apparatus of  claim 1  wherein the bit comprises a rotary rock bit. 
     
     
         4 . The apparatus of  claim 1  wherein the bit comprises one or more electrodes configured for applying a pulsed voltage to excavate the formation with applied pulsed power. 
     
     
         5 . The apparatus of  claim 1  wherein the downhole pump is a positive displacement pump. 
     
     
         6 . The apparatus of  claim 1  wherein the bit does not rotate. 
     
     
         7 . The apparatus of  claim 1  wherein the cross sectional area of the interior space of the drill pipe is less than the cross sectional area of the annular space, thereby minimizing the drilling fluid flow rate that is required to carry excavated cuttings upwards through the interior space of the drill pipe. 
     
     
         8 . The apparatus of  claim 1  further comprising a downhole generator for applying pulsed power to the bit. 
     
     
         9 . The apparatus of  claim 1  wherein the drilling fluid comprises an electrically insulating formulation having a low level of electrical conductivity. 
     
     
         10 . The apparatus of  claim 9  wherein the drilling fluid comprises a carbon-based material. 
     
     
         11 . A process for drilling a borehole into a subterranean formation with reverse circulation of drilling fluid, the process comprising the steps of:
 (a) extending a tubular drill pipe into the subterranean formation, the drill pipe having an interior space and an annular space on the exterior of the drill pipe, the drill pipe having a proximal end near the top of the wellbore and a distal end with an attached bottom hole assembly, the bottom hole assembly comprising a bit;   (b) excavating the formation with the bit to form cuttings;   (c) providing a pump and a motor in the borehole, the pump being powered by the motor, the pump being in fluid communication with the interior of the drill pipe;   (d) circulating drilling fluid from the annular space to the interior space of the drill pipe; and   (e) pumping drilling fluid with cuttings upwards through the interior space of the drill pipe.   
     
     
         12 . The process of  claim 11  further comprising the step of:
 (f) removing excavated cuttings from the drilling fluid near the top of the wellbore; and 
 (g) recirculating the drilling fluid downward through the annular space. 
 
     
     
         13 . The process of  claim 11  wherein the bit comprises one or more electrodes, further wherein the excavating step (b) comprises applying a pulsed voltage to one or more electrodes to excavate the subterranean formation. 
     
     
         14 . The process of  claim 11  wherein the pump is a positive displacement pump. 
     
     
         15 . The process of  claim 11  wherein the bit is a rotary rock bit, the process comprising the additional step of rotating the rotary rock bit to excavate the formation. 
     
     
         16 . The process of  claim 11  wherein the cross sectional area of the interior space of the drill pipe is less than the cross sectional area of the annular space, thereby minimizing the drilling fluid flow rate required to carry excavated cuttings upwards through the interior space of the drill pipe. 
     
     
         17 . The process of  claim 13  further comprising a downhole generator for applying pulsed voltage to the bit. 
     
     
         18 . The process of  claim 13  wherein the drilling fluid comprises an electrically insulating formulation having a low level of electrical conductivity. 
     
     
         19 . The process of  claim 18  wherein the drilling fluid comprises a carbon-based material. 
     
     
         20 . The process of  claim 13  wherein a control system is employed to regulate the pulse repetition rate of the electrodes.