Abstract:
A plurality of cutting faces is attached sequentially at a distal end of a drill string. The forward most cutting face that is distal to the top of the hole is exposed and used for drilling until worn to a point of inefficiency. The forward most or distal cutting face is then detached, exposing the next cutting face in the sequence. Detachment of the forward most cutting face is performed by remote actuation at the top of the drill string and/or outside the hole. A new cutting face is provided without the necessity of removing the drill string. The detachment process is repeated as long as drilling is continued and cutting faces remain.

Description:
[0001]    This application is a continuation-in-part of Application No. 13/918,414 filed June 14, 2013, which claims the benefit of PCT Application No.: PCT/US13/45943, filed June 14, 2013 and U.S. Provisional Application No. 61/659,677 filed June 14, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to drilling of holes in the earth and is more specifically related to a device and method for changing drill cutting faces of drill strings for use while the drill string is in situ in the hole. 
       BACKGROUND OF THE INVENTION 
       [0003]    Drilling for oil and gas involves a drill bit at the end of hundreds of lengths of pipe, collectively referred to as the drill string. The drill bit is attached to the lowest section of pipe of the drill string and is rotated by the drill string to cut or drill into the earth. Each time the drill bit has drilled the length of the pipe, the drilling stops and another pipe section is attached to the pipe so that drilling can continue. Each pipe section is conventionally about thirty feet in length and drilled holes are usually greater than 5,000 feet deep, sometimes greater than 40,000 feet deep. Hence, a drill string for one oil well may consist of hundreds of lengths of pipe. 
         [0004]    During the drilling process, water, chemicals and solids mixtures, called “drilling mud,” are forced through the pipe and ejected at high pressure through ports built into the drill bit. Drilling mud cools the bit, lubricates the cutting action, and washes the drilled earthen material out from the bottom of the hole, and up and around the exterior of the drill pipe. The drilling mud eventually washes the material to the top of the hole where it is filtered out of the drilling mud which is then reused. 
         [0005]    A common drill bit has a cast metal or machined housing which is studded with multiple protrusions. The protrusions comprise a hard surfaced material which may be a ceramic type material that is fortified with multiple industrial diamonds  20 . The resulting cutting discs are known in the industry as polycrystalline diamond (PDC) cutters. 
         [0006]    Drill bits are subject to wear, and wear out during the drilling process. The rate of wear depends on the particular drill bit and the hardness and abrasion characteristics of the drilled earthen material, but once the drill bit becomes dull, it must be replaced with a new, sharp bit. Unfortunately, changing bits requires removing the entire drill string from the hole to access the old bit so that it can be replaced. Removal of the drill string requires pulling the top section of pipe up, unscrewing it, placing it aside, and repeating this sequence until the entire drill string has been removed. A 9000 foot drill string, using common pipe lengths of 30 feet, requires retraction and removal of 300 pipe sections. Once the dull bit is above ground it is removed, and a new bit is attached. The entire drill string is then reconstructed, one pipe section at a time, and lowered into the hole to reach the point where the drilling stopped. The bit replacement process can take 36 hours or more. Drilling platforms operate on a continuous basis at a cost of several hundred thousand dollars per day in some cases. A lost day of drilling to replace bits once or twice a week is very expensive. 
         [0007]    There is a need for a system and process that will allow a useful drill bit to be placed in position for use without removing the drill string from the hole. Accordingly, the present invention provides a system and process employing a novel drill bit which allows provision of a new cutting surface on a drill bit during the drilling process in situ in the drilled hole so that the drill string can remain in place, this saving time and expense. The steps involved in changing drill bits are improved by providing a drill bit having a mandrel which accommodates several drill cutting faces each studded with multiple diamonds or other hardened material that acts as a material cutter. The drill cutting faces are nested within each other and held in a stack with a bolt, which may be an exploding bolt. In one embodiment of the present invention, each drill cutting face has an exploding charge embedded into lt. The discs may contain internal cavities where explosives are strategically placed. After the worn cutting face is expelled from the mandrel or drill string, the cutting face explodes, leaving only small fragments. The small fragments are flushed from the bore bottom with drilling mud through drilling mud ejected from the cutting face&#39;s built in ports. 
         [0008]    Further understanding of the present invention will be had from the following specification and claims taken in conjunction with the accompanying drawings. 
       SUMMARY OF THE INVENTION 
       [0009]    A preferred embodiment of the present invention is a drill bit comprising a plurality of sequentially nested cutting disks or faces. Each cutting face is removably attached to the drill bit and contains an explosive charge and a control which can selectively activate to disintegrate the cutting face. In accordance with a preferred embodiment of the method of this invention, a drill bit having a plurality of sequentially nested cutting faces is attached to the distal end of a drill string. The forward most cutting face is used for drilling until worn to a point of inefficiency. The forward most cutting face is then detached, exposing the next cutting face in sequence. Detachment of the forward most cutting face is performed by withdrawing the drill string a short distance from the bottom of the wellbore and then separating the most distal cutting face from the mandrel by remote controlled actuation. After the forward-most cutting face is detached, it is disintegrated by activating an internally contained explosive charge from the top of the drill string and/or outside the hole. A new cutting face is exposed without the necessity of removing the drill string. The drill string is then lowered to the bottom of the hole. High pressure drilling mud then flushes the worn cutting face fragments away from the bottom of the bore hole and up and around the pipe of the drill string. After the fragments begin to migrate upwardly and away from the bottom of the bore hole, which generally takes only a few minutes, downward pressure is applied to the drill string, and the attached drill bit system. Rotation of the drill string resumes, which resumes the drilling process. This method allows a new cutting face to be exposed for use without pulling the entire drill string from the hole. The process may be repeated as long as an unused cutting face is available in the sequence. The number of cutting faces that may be sequentially positioned or stacked for use may be from 2 to 6 or even more. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an elevation view, partly in section and broken away, showing a conventional oil drilling rig with a preferred embodiment of a drilling device of the present invention having a drill bit and a remote control station; 
           [0011]      FIG. 2  is a perspective view of the preferred embodiment drill bit of  FIG. 1 ; 
           [0012]      FIG. 3  is a left side elevation view of the drill bit of  FIG. 1 ; 
           [0013]      FIG. 4  is a bottom plan view of the drill bit of  FIG. 1 ; 
           [0014]      FIG. 5  is a top plan view of the drill bit of  FIG. 1 ; 
           [0015]      FIG. 6  is a front elevation view of the drill bit of  FIG. 1 ; 
           [0016]      FIGS. 7 and 8  are exploded views of the drill bit of  FIG. 1 ; 
           [0017]      FIG. 9  is a horizontal cross-sectional view of the mandrel of the drill bit of  FIG. 1 ; 
           [0018]      FIG. 10  is a vertical sectional view of the drill bit of  FIG. 1 ; 
           [0019]      FIGS. 11-18  are elevation views, partly in section and broken away, illustrating the sequence of method steps of a preferred embodiment of the present invention; 
           [0020]      FIG. 11  shows the drill bit of  FIG. 1  in drilling position at the bottom of a bore hole; 
           [0021]      FIG. 12  shows the drill bit of  FIG. 1  partially retracted from the bottom of the bore hole; 
           [0022]      FIG. 13  shows the drill bit of  FIG. 1  with its most distal cutting face being separated from the drill bit and discarded; 
           [0023]      FIG. 14  shows the discarded drill cutting face of the drill bit of  FIG. 1  at the bottom of the bore hole; 
           [0024]      FIG. 15  shows the discarded drill bit cutting face of  FIG. 9  being fragmented into pieces; 
           [0025]      FIG. 16  shows the fragmented pieces of the discarded drill bit cutting face of  FIG. 10  at the bottom of the bore hole; 
           [0026]      FIG. 17  shows the remainder drill bit of  FIG. 1  and with a newly exposed cutting face being advanced to the bottom of the bore hole; and 
           [0027]      FIG. 18  shows the remainder of the drill bit of  FIG. 1  continuing drilling operations with the next drill cutting face at the distal end of the drill string. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Now referring to the Figures, a preferred embodiment of a drilling device of the present invention is indicated generally by the numeral  10 . Drilling device  10  comprises drill bit  12  and remote control  14  and is shown in  FIG. 1  in use in an otherwise typical oil drilling rig  16 . Drill bit  12  is attached to the lowest of the many pipe sections  18  which have been connected end to end to comprise drill string  20 . Additional pipe sections  18  are shown in  FIG. 1  as stored on site for use during the drilling process. As illustrated in  FIG. 1 , drilling rig  16  also includes platform  22  which supports derrick  24  and has traveling block  26  for raising and lowering drill string  20 , rotary table  28  for rotating drill string  20  and kelly  30  which allows drill string  20  to rotate while it is lowered or raised. It will be appreciated by those skilled in the art that drilling device  10  is useful with a wide variety of drilling rigs and that oil drilling rig  16  is shown as illustrative of one of many different drilling rigs which are suitable for use with drilling device  10 . 
         [0029]    During the drilling process, drill string  20  is rotated and lowered to lower drill bit  12  into earth formation  32  to form wellbore  34 . Pump  36  circulates drilling mud  38  through feed pipe  40  to kelly  30 , down through the tubular interior passage of the pipe sections  18  of drillstring  20 , through orifices in drill bit  12  and then upwardly between wellbore  34  and drillstring  20  to return pipe  42  and then into retention pit  44 . Drilling mud  38  may be mud, gas, mist, foam or gasified mud or any other material suitable to transport cuttings from the wellbore  34  into retention pit  44 . 
         [0030]    Drill bit  12  is part of drilling device  10  which comprises drill bit  12  and surface (remote) controller  14  which is used to change cutting faces of drill bit  12 . Surface controller  14  is used in accordance with a preferred method of this invention as is described in more detail below. 
         [0031]    It will be appreciated by those skilled in the art that a conventional oil drilling operation involves adding individual lengths of pipe sections to the drill string as the hole is drilled deeper and deeper and that, in a conventional drilling process, when the drill bit at the distal end of the drill string becomes dull and ineffective, the entire drill string must be removed from the wellbore to replace the worn out drill bit with a new drill bit. The removal of the entire drill string requires removing and disassembling the drill string pipe section by pipe section as the drill string is lifted out of the wellbore. Then a new drill bit is installed on the lowest pipe section of the drill string and the entire drill string is reassembled, one pipe section at a time, as the drill string is lowered back down into the wellbore. Drill strings usually comprise hundreds of pipe sections and the process of removing and reinserting the drill string is very time consuming and expensive. This time and expense is greatly reduced or even eliminated by the present invention. The drilling device and method of the present invention provides a drill bit system and a drill bit which has drilling faces which can be replaced in situ in the wellbore without removal of the associated drill string. 
         [0032]    Drill bit  12 , a preferred embodiment of a drill bit of the present invention, is shown in further detail in  FIGS. 2 to 10 . Broadly speaking, drill bit  12  comprises mandrel  46  and a plurality of cutting faces  48 . The drill cutting faces are used to cut away earth, rock, and other geological material. To cut through such hard material, each cutting face has a cutting material such as polycrystalline diamond (PCD) embedded therein. The exact number of cutting faces carried by the mandrel can vary as desired. Ideally, there will be a sufficient number of cutting faces to avoid having to withdraw the drill string during the drilling process. Three, four, five or even more cutting faces can be attached to mandrel if desired. 
         [0033]    Mandrel  46  has a generally cylindrical body  50  having a somewhat crown shaped dome  52  and a threaded conical end  54  for attachment to the end  56  of conventional drill string  20 . Dome  52  has radially outwardly and forwardly extending shoulders or projections  58  which define a plurality of channels  60 . Shoulders  58  carry a multiplicity of PCD or similar abrasive elements  62  for reaming the borehole. Pores are provided in channels  60  to allow drilling mud  38  to pass through channels  60  to aligned pores in cutting faces  48  or to wellbore  34  if there are no cutting faces  48  attached to mandrel  46 . Mandrel  46  has a generally hollow interior  66  which provides a passageway for drilling mud  38  and also has an axially extending threaded central bore  68  for securement of cutting faces  48  as set forth below. Secured within hollow interior  66  of mandrel  46 , for example where indicated by the numeral  70 , is a communication receiver module for selectively sequentially detaching cutting faces  48  as described in more detail hereinafter. 
         [0034]    Two analogous cutting faces  48  are shown in the Figures and are respectively designated by numerals  72  and  74 , although it will be appreciated that additional cutting faces  48  may be used if desired and it is expected that two, three, four, five, six or more cutting faces will be used. 
         [0035]    Cutting face  72  is a somewhat crown-shaped disk with a central bore  76  and has radially outwardly and forwardly extending shoulders or projections  78  which define a plurality of forward facing channels  80  and a plurality of rearward facing recesses  82 . Shoulders  78  carry a multiplicity of PCD or similar abrasive elements  84  for reaming the borehole. Pores  86  are provided in shoulders  78  to allow drilling mud  38  to pass from pores  4  in mandrel  46  through cutting face  72  to aligned pores in cutting face  74  or to wellbore  34  if cutting face  72  has been detached. 
         [0036]    Cutting face  74  is of a construction analogous to cutting face  72 , and has central bore  88  and radially outwardly and forwardly extending shoulders  90  defining a plurality of forward facing channels  92  and having rearward facing recesses  94 . Shoulders  90  carry a multiplicity of abrasive elements  96  and pores  98  are provided in shoulders  90  to allow drilling mud  38  to pass through cutting face  74  to wellbore  34 . 
         [0037]    When assembled together, dome  52  of mandrel  46 , cutting face  72  and cutting face  74  are in nesting relationship with shoulders  58  of dome  52  fitting closely into recesses  82  in cutting face  72  and shoulders  78  of cutting face  72  fitting closely into recesses  94  in cutting face  74 . Thus, relative rotational movement between mandrel  46 , cutting face  72  and cutting face  74  is prevented by the geared relationship of their respective shoulders and recesses. 
         [0038]    Mandrel  46  and cutting faces  72  and  74  are axially held together by bolt  100  and respective exploding nuts  102 ,  104 , and  106 . Alternatively, bolt  102  can be a bolt with exploding sections. Thus, each of the drill cutting faces is attached to the mandrel and/or an adjacent cutting face by an exploding fastener. Each cutting face is connected to an adjacent cutting face and/or mandrel by an exploding nut or an exploding bolt, or both. The exploding fastener is remotely controlled to selectively initiate the fastener explosion and subsequent separation of the most forward or distal cutting face. 
         [0039]    Now referring to  FIGS. 11 to 18 , further understanding of the present invention will be had from the following description of a preferred embodiment of a method of the invention.  FIG. 11  shows drill bit  12  in use drilling wellbore  34 . The drawing figures demonstrate only the most forward or distal section of drill string  20 , and depict only the last few feet of a wellbore  34  that may be up to thousands of feet deep.  FIG. 11  represents the situation where drill bit  12  is no longer achieving the desired or expected rate of penetration because the most distal cutting face that has been in use is now dull and in need of replacement.  FIGS. 12 through 18  illustrate the process discarding the used cutting face and replacing it with the next most distal cutting face. 
         [0040]      FIG. 12  illustrates the initial step of retracting drill string  20  a short distance, usually less than the length of one pipe section  18 , which may be  30  feet in length. This step does not necessitate the disassembly of even one section  18  of drill string  20 . Of course, drill string  20  can be retracted further if desired. 
         [0041]      FIGS. 13 and 14  illustrate the next step of removing the most distal cutting face by remote controlled actuation. As demonstrated by  FIG. 13 , the most distal cutting face  74  is separated from the remaining cutting faces, for example by exploding nut  106 , which causes the worn and discarded cutting face  74  to fall away from the remaining cutting faces that remain attached to the mandrel at the distal end of the drill string. Each exploding fastener responds to a different code or command, so that, in normal operation, the most distal drill cutting face is the only separated cutting face discarded by exploding the associated exploding fastener. 
         [0042]    In the preferred embodiment, a wireless code is sent to a small receiver embedded in the mandrel. The code may be sent by RF (radio frequency) or ultrasonic messaging. The receiver, upon receiving the proper code, actuates an electronic circuit to initiate the charge in the exploding fastener, such as an exploding nut or stacking bolt. The bolt explodes, causing the distal end cutting face to separate from the remaining drill cutting faces. This exposes the next cutting face in the sequence. The next disk comprises new cutters, such as sharp PCD material. 
         [0043]    The exploding fastener may be exploded by an igniter that is excited electrically from an internal battery in the drill mandrel. Electrical energy is controlled by an internal micro-processor. The internal micro-processor is controlled by a remote surface control device using coding schemes and security algorithms transmitted to the internal micro-processor via a transceiver, which may be present in both the mandrel and the surface controller, using RE energy and/or ultrasonic energy. The communications link between the surface controller and the drill bit for remote actuation to discard the distal cutting disk is preferred to be wireless. Wireless technology links may include radio electromagnetic energy that is radiated and received, or mechanical ultrasonic energy generated and received by ultrasonic transducers. The use of wireless communications eliminates the extra effort of threading physical wires through the drill string, which would be cumbersome and unreliable. Even though the drill bit may be 3 miles below the earth&#39;s surface (and the earth is an excellent RF attenuator), the drill string, formed of metal pipe sections, is an excellent conduit for RE, and acts as a long antenna. If ultrasonic technology is utilized, the string provides an excellent conduit for the transfer of the ultrasonic energy to the receiver that is associated with the drill bit at the bottom of the drill bore. 
         [0044]    The surface controller for wireless communication and actuation may comprise a physical container, RF transceiver or ultrasonic transceiver, micro-processor, software and/or other appropriate means for a plurality of digital inputs. Embedded into the disposable cutting face may be another RF transceiver powered by a small battery. Lithium battery technology is preferred for its long shelf life and 10w internal resistance for the high amperage output necessary to excite the explosive firing cap. The battery may also power an igniter for the explosive that fragments the cutting face, and in one embodiment, to power a timer that delays ignition for a time after the cutting face is separated from the mandrel 
         [0045]      FIG. 14  shows the discarded cutting face  74  after it has been separated from the mandrel and fallen to the bottom of the well bore. The drill string  20  is pulled further upward toward the surface for several feet to isolate mandrel  46  and newly exposed cutting face  72  from the worn and separated cutting face  74 . 
         [0046]      FIG. 15  shows the next step of fragmenting the discarded cutting face so that it will not interfere with further drilling. Thus, after the worn cutting face is expelled from the mandrel, the explosive charge is remotely actuated so that it explodes, leaving only small fragments  108 , i.e., the explosive in the cutting face is activated to fragment the cutting face. In one embodiment, separation of the worn cutting face invokes an internal electronic timer embedded within the core of the cutting face. The timer counts down several seconds before initiating a second explosion from within the worn cutting face. The explosion of the worn cutting face core fragments the core body. The cutting faces may be machined or cast to possess certain thicknesses and/or score marks to weaken the cutting face at strategic points to facilitate fragmentation. The cutting faces may be formed of thicker and/or stronger materials where necessary to insure structural integrity while cutting, but may be formed of less material and/or weaker material at other points to facilitate fragmentation when discarded. 
         [0047]      FIG. 16  illustrates the fragments of cutting face  74  at the bottom of the wellbore. 
         [0048]      FIG. 17  illustrates the next step of lowering the drill string to place drill bit  12  in position for further drilling and  FIG. 18  illustrates the further drilling process, with drilling fluid  34  removing fragments. The small fragments of the cutting face are flushed from the bore bottom with drilling mud through drilling mud ejected from the cutting face&#39;s built in ports. The high pressure drilling mud is then allowed to flow and wash up the fragmented old cutting face without the drill string rotating for a few minutes. In this way, the discarded, worn cutting face does not interfere with drilling operations, and can be removed from the bore hole. 
         [0049]    While a preferred embodiment of the present invention is disclosed above, it will be appreciated by those skilled in the art that the present invention is subject to modification and variations. For example, the plurality of drill cutting faces attached to the mandrel may be two, three, four, five, or six or more drill cutting faces. Such modifications and variations are intended to be included within the broad scope of this invention which is intended to be limited only by the following claims. 
         [0050]    The invention may be used with cone roller bit designs. Roller bits are bits that possess a plurality of rollers, such as two or three rollers, opposing the other. Stacking may require additional bit structure, such as a base, roller support arms, bearings and rollers. Explosive material may be integrated into the body and associated components. Larger detonation strength is likely to be required to sufficiently fragment the mass, and possibly a longer “flush” time may be required because of additional fragments. 
         [0051]    The mandrel may comprise an internal cavity that is accessible, but sufficiently sealed against the environment to prevent dirt, water and other solids and liquids from entering the cavity. The cavity may accommodate a variety of devices, including electronic components. A replaceable battery pack may be used to supply the electrical energy to power electrical components. A micro-processor with a plurality of inputs and outputs and having support circuitry, power conditioners, buffers, and associated integrated circuits may function as a control or computer for the system to perform and provide monitoring functions, communications to and from surface controllers, and to initiate and control actions at the drill bit. 
         [0052]    A variety and plurality of sensors may be part of the well drilling device and may be positioned in proximity to the drilling environment may interface with the control/computer to measure, monitor and record the operating environment, such as temperature, material density, drill bit pressure, and drill string and bit vibration. Additional sensors may include solid state gyroscopes for directional control and accelerometers for shock monitoring. Also, various sensors may monitor wear gradients and patterns of the cutting faces to facilitate the timing of cutting face replacement. All functions, monitoring and recording is preferred to be communicated to the surface controllers by either RF energy of ultrasonic energy generated and modulated by the control/computer. The communications link is preferred to be duplex, and the surface controllers can send instruction sets to the control/computer internal to the mandrel. 
         [0053]    Various firing algorithms, coding and built in self tests may be utilized to promote safety. Examples include: 
         [0054]    1. A prominent “wear point” with a signal conductor embedded below the wear point surface. When sufficient wear of the wear point&#39;s surface is experienced, the exposed signal conductor wire sends a signal to the processor that in turn relays the status to the surface control panel and invokes an annunciator. 
         [0055]    2. Actuation codes for each exploding device are different. Pseudorandom number assignments may be used to ensure that no two explosive devices are assigned the same identifier or code. 
         [0056]    3. Algorithmic schemes employ plural checks of each unique identifier, and check schemes over several interrogations and iterations. Sufficient time is available for even thousands of checks before detonation, which may take only a few seconds.