System for rotary drilling by electrical discharge

Abstract

The invention relates to a downhole device for rotary drilling, including a power generator installed at the end of a series of rods; a pulse generator which is mechanically and electrically connected to said electricity generator; an electric drilling tool; and an electrical sliding switch system. The invention is useful in the field of drilling by electrical discharge.

1 . Downhole device for rotary drilling comprising:
 an electricity generator installed at the end of a string of drill pipes and/or drill collars and converting the hydraulic drilling fluid into electrical energy;   a pulse generator mechanically and electrically connected to the said electricity generator, and powering a system of electrodes carried by the drilling tool;   an electric drilling tool, mechanically and electrically connected to the said pulse generator, driven in rotation by the string of drill pipes and/or drill collars and comprising a system of active and passive electrodes; and   an electrical slide switch system.   
     
     
         2 . Device according to  claim 1 , in which the sliding switch system is incorporated (i) with the said electric drilling tool or (ii) at the interface between the said electrical drilling tool and the said pulse generator or (iii) with the said pulse generator or (iv) between the said pulse generator and the said electricity generator or (v) with the said electricity generator or (vi) above the said electricity generator. 
     
     
         3 . Device according to  claim 1 , comprising two slide switches:
 a first electrical slide switch between the part of the electricity generator which converts the hydraulic energy into mechanical energy and the part of the electricity generator which converts the mechanical energy into electrical energy, such that when in the “open” position, this switch prevents production of electricity, even if drilling fluid is circulating in the said hydraulic compartment; and   a second electrical slide switch at the electric drilling tool such that when in the “open” position this switch forces discharge of the capacitors of the said pulse generator and prevents their charging even when the electrical compartment is producing an electrical current.   
     
     
         4 . Device according to  claim 1 , in which rotation of the said electric drilling tool combines the mechanical effect of the said passive electrodes with the effect of electrical discharges. 
     
     
         5 . Device according to  claim 1 , in which rotation of the said electric drilling tool sweeps the entire surface of the hole with radial electric arcs which are produced between the said passive and active electrodes. 
     
     
         6 . Device according to  claim 1 , in which the said slide, playing the role of an electric switch, is normally open by means of a mechanical spring holding the said slide open and the open state of the power circuit of the said pulse generator and the “short-circuited” state of the capacitors through a circuit which connects the two terminals of the said capacitors to a discharge resistor. 
     
     
         7 . Device according to  claim 6 , in which the “normally open” position of the said slide is reinforced by a positive action triggered from the surface by injection of drilling fluid in the casing. 
     
     
         8 . Device according to  claim 1 , in which switching from the open position to the closed position of the said switch is enabled by a positive action triggered from the surface consisting of applying a weight on the said electric drilling tool. 
     
     
         9 . Device according to  claim 1 , in which
 the electricity generator comprises a turbine or positive displacement motor, whose rotor, driven in rotation by the flow of drilling fluid, in turn drives the alternator rotor,   the interface between the said rotor of the said turbine or the said motor and the said rotor of the said alternator comprises an electrical slide switch permitting mechanical clutching.   
     
     
         10 . Device according to  claim 1 , in which
 the said system of active and passive electrodes comprises two groups of electrodes electrically insulated from one another but mechanically joined to one another both from an axial point of view and from an angular point of view, the said group comprising (i) a group of passive electrodes, grounding electrodes, and (ii) a group of active electrodes, high voltage electrodes; or   the said system of active and passive electrodes comprises two groups of electrodes electrically insulated from one another but mechanically uncoupled from one another from an angular point of view but not uncoupled from an axial point of view, the said group comprising (i) a group of passive electrodes, grounding electrodes, located in the periphery of the said electric drilling tool, and a group of active electrodes, high voltage electrodes, located centrally in the said electrical drilling tool, and not mechanically joined to the group of passive electrodes such that it is not driven in rotation by it; or   the said system of active and passive electrodes comprises two groups of electrodes electrically insulated from one another but mechanically uncoupled from one another both from an angular point of view and from an axial point of view, said group comprising (i) a group of passive electrodes, grounding electrodes, located in the periphery, and (ii) a group of active electrodes, high voltage electrodes, located centrally in the said electric drilling tool, equipped with an axial track preferably of several centimetres and subjected to the force of a bellows spring enabling the electrodes to be in continuous contact with the rock; or
 the said system of active and passive electrodes comprises two groups of electrodes electrically insulated from one another but mechanically attached to one another from an angular point of view and but not mechanically attached to one another from an axial point of view, said group comprising (i) a group of passive electrodes, grounding electrodes, and (ii) a group of active electrodes, high voltage electrodes, located off-centre relative to the axis of the said electric drilling tool, equipped with an axial track of preferably several centimetres and subjected to the force of a bellows spring allowing the electrodes to be in continuous contact with the rock. 
   
     
     
         11 . Device according to  claim 1 , in which the terminal part of the electric drilling tool comprises an internal chamber free of any solid materials other than electrodes. 
     
     
         12 . Device according to  claim 1 , in which the said pulse generator is crossed in its axis by a hollow axial tube in insulating material connected mechanically at the lower part of the said pulse generator with a metal tube such that the continuum of the said tubes provides for transmission of the drilling fluid and that the said lower metal tube, and preferably only this tube, receives the electrical discharges from the said pulse generator. 
     
     
         13 . Device according to  claim 1 , in which the said pulse generator is a LTD Linear Transformer Driver type generator or a Marx generator or a TESLA transformer. 
     
     
         14 . Device according to  claim 12 , in which several modules composed of energy storage devices, preferably capacitors, and power switches, preferably gas discharge tubes, are stacked on one another in the annular space located between the said hollow tube and the exterior metal envelope. 
     
     
         15 . Device according to  claim 14 , in which the said power switches consist of annular electrodes having the form of a ring. 
     
     
         16 . Device according to  claim 1 , in which the device also includes an insulating connector consisting of two metal parts, an upper part and a lower part, separated by an insulating material and nested between them to transmit the axial stresses as well as the torque stresses between the said upper part and the said lower part. 
     
     
         17 . Device according to  claim 1 , in which the electrodes comprise inserts of hard and abrasive material, preferably of Polycrystalline Diamond Compact (PDC) type or tungsten carbide and/or metal matrix comprising a powder or microparticles of hard material, preferably diamond. 
     
     
         18 . Device for rotary drilling, comprising the downhole device according to  claim 1 , which is incorporated at the end of a drill string comprising an assembly of drill pipes and possibly drill collars for transmission of the electrical energy and a drilling rig comprising a system for rotary driving of a string of drill pipes and/or drill collars, and drilling pumps for injection of drilling fluid inside the string of drill pipes and/or drill collars. 
     
     
         19 . Drilling process, through rotation of the rotary drilling device according to  claim 18 .