Patent Publication Number: US-9416594-B2

Title: System and method for drilling a borehole

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/344,535 filed Jan. 5, 2012; which is a divisional of U.S. patent application Ser. No. 11/667,231 filed Nov. 19, 2007, now U.S. Pat. No. 8,109,345 issued Feb. 7, 2012, which is a U.S. National Stage Application under 35 U.S.C. §371 and claims priority to Patent Cooperation Treaty Application No. PCT/GB2005/004424 filed Nov. 16, 2005; which claims priority to British Application No. GB0425312.6 filed Nov. 17, 2004. All of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     In a variety of subterranean environments, desirable production fluids exist. The fluids can be accessed and produced by drilling boreholes, i.e., wellbores, into the subterranean formation holding such fluids. For example, in the production of oil, one or more wellbores are drilled into or through an oil holding formation. The oil flows into the wellbore from which it is produced to a desired collection location. Wellbores can be used for a variety of related procedures, such as injection procedures. Sometimes wellbores are drilled generally vertically, but other applications utilize lateral or deviated wellbores. 
     Wellbores generally are drilled with a drill bit having a cutter rotated against the formation material to cut the borehole. Deviated sections of wellbore can be formed by “pushing the bit” in which the bit is pushed against a borehole wall as it is rotated to change the direction of drilling. In other applications, the deviated wellbore can be formed by “pointing the bit” in a desired direction and employing weight on the bit too move it in the desired direction. Another alternative is to use an asymmetric bit and pulse weight applied to the bit so that it tends to drill in a desired direction. However, each of these techniques presents problems in various applications. For example, problems can arise when the borehole size is over-gauge or the borehole rock is too soft. Other problems can occur when trying to drill at a relatively high angle through hard layers. In this latter environment, the drill bit often tends to follow softer rock and does not adequately penetrate the harder layers of rock. 
     In the international patent application WO 2005/054620, filed before, but published after the original filing date of this invention, there are described various electro-pulse drill bits including examples where the removal of cuttings are supported by mechanical cutters or scrapers and examples of non-rotary examples where the electro-pulses are given a desired direction. 
     SUMMARY 
     In general, the present invention provides a system and method for drilling wellbores in a variety of environments. A drill bit assembly incorporates a directed energy system to facilitate cutting of boreholes. Although the overall system and method can be used in many types of environments for forming various wellbores, the system is particularly useful as a steerable assembly used to form deviated wellbores. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1A  illustrates a drilling system for operation at a wellsite to drill a borehole through an earth formation; 
         FIG. 1B  is a front elevation view of a drilling assembly forming a wellbore, according to an embodiment of the present invention; 
         FIG. 2  is a schematic illustration of an embodiment of a drilling assembly that may be used with the system illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an embodiment of a drill bit incorporating a directed energy mechanism that may be used with the system illustrated in  FIG. 1 ; 
         FIG. 4  is a schematic illustration of an alternate embodiment of a drill bit incorporating a directed energy mechanism that may be used with the system illustrated in  FIG. 1 ; 
         FIG. 5  is a schematic illustration of another alternate embodiment of a drill bit incorporating a directed energy mechanism that may be used with the system illustrated in  FIG. 1 ; 
         FIG. 6  is an elevation view of a drilling assembly disposed in a lateral wellbore, according to an embodiment of the present invention; 
         FIG. 7  is a front elevation view of another embodiment of a drilling assembly, according to an embodiment of the present invention; 
         FIG. 8  is a front elevation view of another embodiment of a drilling assembly disposed in a well, according to an embodiment of the present invention; 
         FIG. 9A  illustrates a system for delivering laser energy to an earth formation being drilled by a combined mechanical-laser drilling system, in accordance with one embodiment of the present invention; 
         FIG. 9B  illustrates a system for delivering laser energy to an earth formation being drilled by a combined mechanical-laser drilling system, in accordance with one embodiment of the present invention; and 
         FIG. 10  illustrates a laser assisted, mechanical drilling system in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to the drilling of wellbores. A drilling assembly is used to form generally vertical and/or deviated wellbores. A directed energy mechanism is utilized to fracture, spall or weaken formation material as the drilling assembly moves through a subterranean environment. The directed energy mechanism facilitates the drilling process and also can be used in a steerable drilling assembly to aid in steering the assembly to drill, for example, deviated wellbores. However, the devices and methods of the present invention are not limited to use in the specific applications that are described herein. 
       FIG. 1A  illustrates a drilling system for operation at a wellsite to drill a borehole through an earth formation. The wellsite can be located onshore or offshore. In this exemplary system, a borehole  311  is formed in subsurface formations by rotary drilling in a manner that is well known. Embodiments of the invention can also use be used in directional drilling systems, pilot hole drilling systems, casing drilling systems and/or the like. 
     A drillstring  312  is suspended within the borehole  311  and has a bottomhole assembly  300 , which includes a drill bit  305  at its lower end. The surface system includes a platform and derrick assembly  310  positioned over the borehole  311 , the assembly  310  including a rotary table  316 , kelly  317 , hook  318  and rotary swivel  319 . The drillstring  312  is rotated by the rotary table  316 , energized by means not shown, which engages the kelly  317  at the upper end of the drillstring. The drillstring  312  is suspended from a hook  318 , attached to a traveling block (also not shown), through the kelly  317  and the rotary swivel  319  which permits rotation of the drillstring relative to the hook. As is well known, a top drive system  366  could alternatively be used to rotate the drillstring  312  in the borehole and, thus rotate the drill bit  305  against a face of the earth formation at the bottom of the borehole. 
     In the depicted system, the surface system may further include drilling fluid or mud  326  stored in a pit  327  formed at the well site. A pump  329  delivers the drilling fluid  326  to the interior of the drillstring  312  via a port in the swivel  319 , causing the drilling fluid to flow downwardly through the drillstring  312  as indicated by the directional arrow  308 . The drilling fluid exits the drillstring  312  via ports in the drill bit  305 , and then circulates upwardly through the annulus region between the outside of the drillstring and the wall of the borehole, as indicated by the directional arrows  309 . In this well-known manner, the drilling fluid lubricates the drill bit  305  and carries formation cuttings up to the surface as it is returned to the pit  327  for recirculation. 
     The bottomhole assembly  300  of the illustrated system may include a logging-while-drilling (LWD) module  320 , a measuring-while-drilling (MWD) module  330 , a rotary-steerable system  363  and motor  360 , and drill bit  305 . 
     The LWD module  320  may be housed in a special type of drill collar, as is known in the art, and can contain one or a plurality of known types of logging tools. It will also be understood that more than one LWD and/or MWD module can be employed, e.g., as represented at  320 A. The LWD module may include capabilities for measuring, processing and storing information, as well as for communicating with the surface equipment. In one embodiment, the LWD module may include a fluid sampling device. 
     The MWD module  330  may also be housed in a special type of drill collar, as is known in the art, and can contain one or more devices for measuring characteristics of the drillstring and drill bit. The MWD tool may further includes an apparatus (not shown) for generating electrical power to the downhole system. This may typically include a mud turbine generator powered by the flow of the drilling fluid, it being understood that other power and/or battery systems may be employed. In one embodiment, the MWD module may include one or more of the following types of measuring devices: a weight-on-bit measuring device, a torque measuring device, a vibration measuring device, a shock measuring device, a stick slip measuring device, a direction measuring device, a rotation speed measuring device, and an inclination measuring device. 
     Drilling an oil and/or gas well using the drilling system depicted in the figure may involve drilling a borehole of considerable length. Boreholes are often up to several kilometers vertically and/or horizontally in length. As depicted, the drillstring comprises a drill bit at its lower end and lengths of drill pipe that are screwed/coupled together. A drive mechanism at the surface rotates the drill bit against a face of the earth formation to drill the borehole through the earth formation. The drilling mechanism may be a top drive, a rotary table or the like. 
     The drillstring may undergo complicated dynamic behavior in the borehole during the drilling procedure, which complicated behavior may include axial, lateral and torsional vibrations as well as frictional and vibrational interactions with the borehole. Simultaneous measurements of drilling rotation at the surface and at the bit have revealed that while the top of the drill string rotates with a constant angular velocity, the drill bit may rotate with varying angular velocities. In extreme cases, known as stick-slip, the drill bit or another portion of the drillstring may stop rotating in the borehole, as a result, the drill string continues to be twisted/rotated until the bit rotates again, after which it accelerates to an angular velocity that is much higher than the angular velocity of the top of the drillstring. 
     Referring generally to  FIG. 1B , a system  20  is illustrated according to an embodiment of the present invention. In the particular embodiment illustrated, system  20  comprises a drilling assembly  22  used to form a borehole  24 , e.g., a wellbore. Drilling assembly  22  is moved into the subterranean environment via an appropriate drill string  26  or other deployment system. Often, the wellbore  24  is drilled from a surface  28  of the earth downwardly into a desired formation  30 . In the embodiment illustrated, the wellbore  24  has a generally vertical section  32  which transitions towards a deviated section  34  as drilling assembly  22  is steered to form the lateral wellbore. 
     In this example, drilling assembly  22  is a rotary, steerable drilling assembly having one or more fixed cutters  36  that are rotated against formation  30  to cut away formation material as the wellbore is formed. Drilling assembly  22  also comprises a directed energy mechanism  38  utilized to crack, break or weaken formation material proximate drilling assembly  22  as wellbore  24  is formed. The directed energy mechanism  38  directs energy, such as electromagnetic energy, against the formation to fracture or otherwise damage formation material. This non-cutting technique supplements the action of cutters  36  to facilitate formation of wellbore  24 . Additionally, the non-cutting energy can be directed at specific regions of formation  30  to enable the steering of drilling assembly  22  even through hard or otherwise difficult to cut formation materials. 
     Referring to  FIG. 2 , a schematic illustration is provided to show elements of one embodiment of drilling assembly  22 . In this embodiment, drilling assembly  22  utilizes a drill bit  40  having a bit body  41  and one or more of the mechanical cutters  36  for cutting formation material. Mechanical cutters  36  are mounted on bit body  41 . Drill bit  40  is rotated by a mechanical power source  42 , such as an electric motor which may rotate the drillstring  26  either at the surface or downhole, and may also be rotated by a downhole electric motor or other means such as a hydraulic motor, examples of which are positive displacement motors and turbines. Additionally, electrical power is supplied by an electric power supply  44 . The electrical power can be used to power directed energy mechanism  38  for providing a controlled fracturing of formation material proximate drill bit  40 . Additionally, a directed energy controller  46  can be used to control the application of directed energy to the surrounding formation material. 
     The use of directed energy in conjunction with the mechanical bit enhances the cutting of formation materials, particularly materials such as hard rock. The directed energy can be delivered to formation  30  by, for example, directed energy members  48  that are distributed around the circumference of drill bit  40 . As discussed more fully below, such directed energy members  48  can be used for side-cutting, i.e., causing drilling assembly  22  to turn in a desired direction by supplying energy to members on the side of the bit that coincides with the desired change in direction. If the rate of turn becomes excessive, the energy selectively sent to specific elements  48  can be interrupted for a proportion of the time, or more energy can be distributed to other sides of the drill bit to increase rock removal in other locations about drill bit  40 . An example of directed energy is electromagnetic energy that may be supplied in a variety of forms. 
     Examples of drill bits  40  combined with directed energy mechanisms  38  are further illustrated in  FIGS. 3-5 . The figures illustrate several embodiments able to utilize electromagnetic energy in fracturing subterranean materials to form boreholes. In  FIG. 3 , for example, directed energy members comprise a plurality of waveguides  50 , such as fiber optics or gas/fluid filled members. In this embodiment, electrical power provided by electric power supply  44  is pulsed and converted by a laser  52  into pulsed optical power. The laser energy is directed at the formation material surrounding drill bit  40  via waveguides  50 . The laser energy heats the rock and any fluid contained within the rock to a level that breaks the rock either through thermally induced cracking, pore fluid expansion or material melting. The target or formation material at which the laser energy is directed can be controlled by directed energy control  46 . For example, a switching system can be used to direct the pulsed optical power to specific waveguides  50  when they are disposed along one side of drill bit  40 . This, of course, facilitates directional turning of the drill bit to create, for example, a lateral wellbore. 
     In another embodiment, illustrated in  FIG. 4 , directed energy members  48  comprise a plurality of electrodes  54 . Electrodes  54  can be utilized in delivering electromagnetic energy against the material surrounding drill bit  40  to break down the materials and enhance the wellbore forming capability of the drilling assembly. In this particular embodiment, electrodes  54  are used for electrohydraulic drilling in which drill bit  40  and directed energy mechanism  38  are submerged in fluid. Selected electrodes  54  are separated from a ground conductor and raised to a high-voltage until the voltage is discharged through the fluid. This produces a local fluid expansion and, hence, a pressure pulse. By applying the pressure pulse close to the formation material surrounding drill bit  40 , the material is cracked or broken into pieces. This destruction of material can be enhanced by utilizing a phased electrode array. Again, by supplying the electrical power to selected electrodes  54 , the breakdown of surrounding material can be focused along one side of drill bit  40 , thereby enhancing the ability to steer the drilling assembly  22  in that particular direction. 
     Another embodiment of directed energy mechanism  38  is illustrated in  FIG. 5 . In this embodiment, electric energy is provided by electric power supply  44  and controlled by directed energy control  46  to provide electrical pulses to electrodes  56 . The electric pulses enable electric pulsed drilling in which electrical potential is discharged through surrounding rock, as opposed to through surrounding fluid as with electrohydraulic drilling. As voltage is discharged through rock close to electrodes  56 , the rock or other material is fractured to facilitate formation of the borehole  24 . As with the other embodiments described above, electrical power can be selectively supplied to electrodes  56  along one side of drill bit  40  to enhance the steerability of drilling assembly  22 . 
     In the embodiments discussed above, the directed energy members  48  rotate with drill bit  40 . Thus, there is no need for components to remain mechanically stationary with respect to the surrounding formation. However, other designs and applications can utilize stationary components, such as a stationary directed energy mechanism. 
     Additionally, directed energy members  48  may be arranged in a variety of patterns and locations. As illustrated, each of the directed energy members  48  may be positioned to extend to a bit face  58  of drill bit  40 . This facilitates transfer of directed energy to the closely surrounding formation material, thus enhancing breakdown of the proximate formation material. Drill bit  40  may be constructed in a variety of forms with various arrangements of mechanical cutters  36  connected to bit body  41 . For example, mechanical cutters  36  may be fixed to bit body  41  and/or the drill bit can be formed as a bi-center bit. Additionally, passages  60  can be formed through drill bit  44  to conduct drilling fluid therethrough. Passages  60  can be formed directly in bit body  41 , or they can be incorporated into a replaceable nozzle to conduct drilling fluid through bit face  58 . The drilling fluid conducted through passages  60  aids in washing cuttings away from drill bit  40 . It should be noted that these are just a few examples of the many potential variations of drill bit  40 , and that other types of drill bits can be utilized with directed energy mechanism  38 . 
     Referring to  FIG. 6 , a detailed example of one type of drilling assembly  22  is illustrated in which the drilling assembly comprises a rotary steerable drilling assembly. In this embodiment, drilling assembly  22  comprises drill collars  62  through which extends a flow passage  64  for delivering drilling fluid to outlet passages  60  that extend through bit face  58 . In the embodiment illustrated, flow passage  64  lies generally along the centerline of collars  62 , and other components surround the flow passage. However, in an alternate embodiment, components can lie along the centerline, and the drilling fluid can be routed through an annular passage. 
     As illustrated, directed energy mechanism  38  comprises directed energy members  48  in the form of electrodes  56 , surrounded by an insulation material  66 . Electric power is generated by, for example, a turbine  68  positioned as part of the steerable drilling assembly  22 . However, the power generating turbine  68  also can be located remotely with respect to drilling assembly  22 . Electric power generated by turbine  68  is used to charge a repetitive pulsed power unit  70 . In this embodiment, pulsed power unit  70  is disposed between turbine  68  and drill bit  40 , however, the components can be arranged in other locations. One example of a repetitive pulsed power unit  70  is a Marx generator. 
     The pulses output by pulsed power unit  70  may be compressed by a magnetic pulse compressor  72 . In some applications, for example, the output from pulsed power unit  70  may not have a fast enough rise time for electric pulsed drilling. In such applications, the magnetic pulse compressor  72  may be used to compress the pulses. Between discharges through electrodes  56 , the individual pulses can be switched between different electrodes  56 . As discussed above, the utilization of specific electrodes disposed, for example, along one side of drill bit  40  substantially facilitates the steerability of drilling assembly  22 . 
     A greater degree of control over the turning of drilling assembly  22  can be achieved with the aid of directed energy control  46  which, in this embodiment, comprises a directional sensor unit  74 . Sensor unit  74  comprises, for example, accelerometers  76  and magnetometers  78  to determine through which electrode the pulse should be discharged to maintain or change the direction of drilling. In this example, electrodes  56  are arranged in a symmetric pattern around the lead face of drill bit  40 . However, other arrangements of directed energy members  48  may be selected for other applications. Also, directed energy mechanism  38  is used in cooperation with mechanical cutters  36  to more efficiently form cuttings and provide greater steerability of the drilling assembly  22 . 
     Another embodiment of drilling assembly  22  is illustrated in  FIG. 7 . In this embodiment, drilling assembly  22  comprises an acoustic imaging system  80  for downhole formation imaging during drilling. Acoustic imaging system  80  comprises, for example, an acoustic receiver section  82  having an acoustic receiver and typically a plurality of acoustic receivers  84 . By way of example, acoustic receivers  84  may comprise piezoelectric transducers. Acoustic receiver section  82  may be formed as a collar coupled to a damping section  86 . Damping section  86  may be formed of a metal material able to provide damping of the acoustic waves transmitted therethrough to acoustic receivers  84 . In other words, electrodes, such as electrodes  56 , provide an acoustic source during the electric discharges used to break down formation material. Acoustic receivers  84  are used to sense the acoustic waves transmitted through and reflected from the different materials comprising the rock formation, providing the means to image the formation downhole while drilling. 
     It should be noted that the directed energy mechanism  38  can be used in a variety of drilling assemblies and applications. For example, although the use non-cutting directed energy substantially aids in the steerability of a given drilling assembly, the use of directed energy mechanism  38  also facilitates linear drilling. As illustrated in  FIG. 8 , directed energy mechanism  38  can be used with a variety of drill bits  40 , including drill bits without mechanical cutters. Sufficient directed energy can sufficiently destruct formation materials without mechanical cutting. The resultant cuttings can be washed away with drilling fluid as in conventional systems. Additionally, the size, number and arrangement of directed energy members  48  can be changed according to the design of drilling assembly  22 , the size of wellbore  24 , the materials found information  30  and other factors affecting the formation of the borehole. 
     Furthermore, drilling assembly  22  is amenable to use with other or additional components and other styles of drill bits. For example, the directed energy mechanism  38  can be combined with drilling systems having a variety of configurations. Additionally, the directed energy mechanism can be combined with alternate steering assemblies, including “pointing the bit” and “pushing the bit” type steering assemblies. 
     One issue with using electromagnetic energy to assist/enhance mechanical drilling is delivery of the electromagnetic energy to the tool face/earth formation. 
       FIG. 9A  illustrates a system for delivering laser energy to an earth formation being drilled by a combined mechanical-laser drilling system, in accordance with one embodiment of the present invention. 
     In  FIG. 8A  an earth formation  810  is being drilled by a drilling system (mechanical cutters, etc., not shown for clarity) comprising a laser delivery system  800  comprising laser energy  805  delivered through an optical fiber  802 . The laser delivery system  800  includes an annulus  804  through which a fluid  807  can be delivered to the tool face. In embodiments of the present invention an optically clear, with respect to the laser energy being used, fluid may be delivered through the annulus  804  to provide for transmission of the laser energy  805  to the earth formation  810 . 
     In some aspects the laser system  800  may extend beyond the optical fiber  802  or a guard  809  may be positioned on the end of the laser system  800  to help maintain the fluid  807  in front of the optical fiber  802  when the laser energy  805  is being transmitted through the optical fiber  802 . 
     In the laser delivery system  800 , a clear path is provided for the laser energy  805  to reach the earth formation  810 . In aspects of the described system, flow rate of the fluid  807  may be selected/adjusted to be sufficient to provide a substantially clear channel between the end of the optical fiber  802  and the surface of the earth formation  810  being drilled. As the annular jet impinges on the surface it fans outwards ensuring a clear area of surface on which the photons can impinge. 
     In an oil well the wellbore may have fluids in motion. So in some aspects, the annular flow rate is selected to be sufficiently strong to ensure it is not unduly disturbed by any cross currents of opaque fluids. In embodiments of the present disclosure a fixed known distance between the end of the optical fiber and the surface, in which case an additional ‘stand-off’ construction can be made to hold the above device at a known distance from the surface. In some embodiments, the guard  809  may produce the desired stand-off. The guard  809  may include perforations and/or have a cage design to allow for flow of the fluid  807  through the guard  809 . 
     It should also be noted that the optical fiber may be shorter, or longer, than the annulus  804 . In aspects where it is shorter, a length of the delivery tube  801  extends beyond the optical fiber  802  in which the annular jet can converge within the delivery tube  801  to provide a cylindrical tube of clear fluid through which the laser energy  805  may pass. A variable focusing mechanism (not shown) may also be provided within the laser system  800  to allow for variety of cutting profiles, shapes and rate. 
     The above arrangement can also be used in a system in which the back-scatter of the laser energy  805  from the earth formation  810  is measured by a measuring system (not shown). In the depicted system, both the path from the end of the optical fiber  802  to the earth formation  810  and the return path for any backscattered energy is within the jet of clear fluid allowing the backscattered laser energy to be detected/measured. 
     In embodiments of the present disclosure, the laser system  800  may be combined with a mechanical drilling system. In some embodiments, the fluid  807  may be provided during a drilling procedure from a tool based reservoir. In some embodiments, the fluid  807  may assist in ‘washing away’ any swarf that is produced by the laser drilling and/or provide a more robust seal with the cut surface to ensure that laser standoff is optimized. 
       FIG. 9B  illustrates a system for delivering laser energy to an earth formation being drilled by a combined mechanical-laser drilling system, in accordance with one embodiment of the present invention. 
     In some aspects of the present invention, a controller, not shown, may control fluid dispersal and laser operation and provide that the laser is fired a certain amount of time after the fluid  807  is pumped out of the drill bit and/or onto the earth formation being drilled. 
     In  FIG. 9B , a second fluid  808  may be provided through a second annulus  806 . The second fluid  808  may provide for washing away debris from the drilling and may also act as a guard flow that surrounds the fluid flow  807  and washes debris and/or drilling fluids away from the fluid flow  807 . An elastomeric sealing element  812  may be used to seal the laser system  800  to the earth surface  810 . 
       FIG. 10  illustrates a laser assisted, mechanical drilling system in accordance with one embodiment of the present invention. The drilling system may comprise a bottomhole assembly  900  and a drill bit  910 . 
     In  FIG. 10 , a laser source  903  may be used to produce a laser energy output. The laser energy output from the laser source  903  may be passed to a tool face of the drill bit  910  via an energy transmission conduit  906 . The energy transmission conduit  906  may comprise a light pipe, an optical fiber and/or the like. 
     As will be appreciated by persons skilled in the art, the laser source  903  could be another type of electromagnetic energy source, such as an electropulse source or the like, and the energy transmission conduit  906  may comprise a corresponding type of electromagnetic energy transmission conduit, such as an electrode. 
     As noted above, steps may be taken, such as use of transmissive fluids or the like, to provide for transmission of electromagnetic energy from the energy source, through the mechanical drill bit to the earth formation. In embodiments of the present invention, an electromagnetic transmission conduit or the like may take the electromagnetic energy to the tool face of the drill bit or even through a one of the mechanical cutters or a protuberance on the drill bit. While directing electromagnetic energy down a longitudinal axis of the drill bit may be quite simple, in some embodiments of the present invention, the electromagnetic energy may be directed to off-center locations on the drill bit face. 
     Applicants have found that directing energy to the drill bit face, especially through the cutters or a protuberance on the drill bit, which may be referred to as an electromagnetic cutter, provides for direct interaction of the electromagnetic energy with the earth formation. In some aspects, the electromagnetic cutter not extend as far as the mechanical cutters from the drill bit face and the electromagnetic energy may be directed at cuttings produced by the mechanical cutters. 
     The laser source  903  may be disposed in the drill bit  910 , in the bottomhole assembly  900 , in drill pipe (not shown) above the bottomhole assembly  900 , at a surface location and/or the like. The energy transmission conduit  906  transmits energy from the laser source  903  to the tool face and into an earth formation  920  being drilled by the drilling system. 
     In some embodiments, the laser energy from the laser source  903  passes through an optical delivery system  930  and onto/into the earth formation  920 . The optical delivery system  930  may comprise optical elements lenses, beam shaping optics and/or the like and may be encased in a protective optical head made of, for example, steel, chrome-moly steel, steel cladded with hard-face materials such as an alloy of chromium-nickel-cobalt, titanium, tungsten carbide, diamond, sapphire, and/or other materials and may comprise a transmissive window  933  to emit the laser energy. The transmissive window  933  may comprise sapphire, diamond, boron doped diamond and/or the like. In some aspects the optical delivery system  930  may comprise only the transmissive window  933  and the transmissive window  933  may be shaped to focus the laser energy. 
     The optical delivery system  930  may be disposed in/integrated into the drill bit  910  so that the optical delivery system  930  is appurtenant to or in contact with the earth formation  920 . In some embodiments, the optical delivery system  930  may be disposed in/integrated with one of the mechanical cutters  912 . In other embodiments the optical delivery system  930  may be disposed appurtenant to the mechanical cutters  912 . In some aspects, the optical delivery system  930  may not extend as far from a body of the drill bit  910  as the mechanical cutters  912 . In aspects of the present invention, by positioning the optical delivery system  930  millimeters or tens of millimeters behind the reach of the mechanical cutters  912 , the laser energy may be effectively transmitted into the earth formation  920  and the transmissive window  933  of the optical delivery system  930  may be protected from adverse contact effects with the earth formation  920 . 
     In one embodiment, the electromagnetic energy may be directed through the drill bit  910  to an off-center location on the tool face of the drill bit  910 . Off-center delivery of the electromagnetic energy can increase the effectiveness of the mechanical cutters  912  and/or provide for control of a direction of cutting of the drill bit  910 . 
     In some embodiments, a protective element  932  may be disposed next to the optical delivery system  930 . The protective element may comprise a protuberance, a lip, a cylinder or the like, that may extend the same distance out from the body of the drill bit  910  to the same extent or slightly further than the optical delivery system  930  so as to provide protection for the transmissive window  933 . 
     As illustrated in  FIG. 10  laser light may be ported directly through the mechanical cutter  912  and/or the drill bit  910  onto the earth formation  920 . This direct path to the target negates non-transmissive properties of fluids in the wellbore. As shown in  FIG. 1 , the laser energy may heat/interact with the rock in a laser interaction zone  915 . The laser energy and/or the mechanical cutters may cause damage, such as small fractures  917 , to the earth formation  920  and remove cuttings  916  from the earth formation  920 . In some embodiments of the present invention, the rock may be damaged by the laser energy then removed by the mechanical cutter  912 . 
     The optical path through the mechanical cutter  912  and/or the drill bit  910  may be provided by a fixed light path that may be eroded back as the mechanical cutter  912  and/or the tool face of the drill bit  910 . The optical path may comprise a high temperature optically transparent material such as chemically vapor deposited (CVD) diamond or the like. 
     In some embodiments, the mechanical cutter  912  may comprise shaped cutters, such as stinger cutters that extend almost along a longitudinal axis of the drill bit  910 . In such configurations, the light path within the cutter may not have to be deviated much if at all as the cutters axis of symmetry is nearly perpendicular to the rock. In some embodiments, the laser energy may be ported through the side of the mechanical cutter  912  and/or the drill bit  910  so that it weakens the rock in the path of adjacent cutters—effectively side exiting the mechanical cutter  912  and/or the drill bit  910 . 
     On some embodiments, the laser energy delivery system shown in  FIG. 10  may be used with hole openers, under reamers, milling systems, concentric reamers, bi-centered drill bits and/or the like. 
     In some embodiments of the present invention, the laser energy needs to provide thermal energy to the rock in order to weaken (but not melt it) without producing thermal degradation of the mechanical cutter  912  and/or the drill bit  910 . In embodiments of the present invention, thermal degradation may be mitigated by cooling from the fluid, use of hard wearing reflective coatings; blocking of reflected light energy by control/adjustment of the opacity of the drilling fluid; modulation of the light energy into pulse streams, i.e., reducing the average energy whilst maintaining the energy peaks to cause disruption; modulation of light energy level in response to the specific rock formation being drilled; modulation of the light energy within one rotation of the bit to adjust to the heterogeneity of the rock (different rock require different levels of disruption); modulation of the light energy to cut specific patterns of weakness into the rock face to strategically weaken the rock (no need to weaken the whole surface volume just produce patterns/designs); modulating the speed of drilling to maintain thermal limits within acceptable bounds (this may involve significant speed modulation within one revolution of the bit—requiring a relatively high speed bit local control of RPM—preferably servoed electrical or hydraulic motor); modulating the flow of coolant and/or the like. 
     In some embodiments, the drilling system may comprise a drillstring, not shown, that connects the bottomhole assembly  900  to a surface location. The drillstring may comprise a continuous coil tubing or composite pipe with electrical wires implanted in the tube/pipe to deliver electrical energy to the laser source  903 . In some embodiments, the electrical power for the laser source  903  may be generated locally using hydraulic energy extracted from the flow of drilling fluid pumped around the wellbore during drilling, which may drive an alternator. 
     In aspects of the present invention, the conversion of electrical energy to laser light energy may either be done at the surface or down hole. In the former case, the laser source  903  may be disposed at a surface location and a continuous light path may bring the laser energy down the drilling system to the drill bit  912 . In the later case, specially hardened electronic and optical systems may be used downhole to produce the laser energy. 
     In some embodiments of the present invention, where the laser energy is produced downhole, a low shock environment may be provided for the laser source  903  in which the drilling system is self-bracing against the borehole wall to resist linear and rotary vibrations and shocks in all axes. In some embodiments, the laser source  903  may be coupled to the drilling system using polymers/elastomers or the like that may be reactive to applied electrical signals or undergo property changes when a force is applied to them so as to mitigate shock/vibration effects. 
     In one embodiment, the bottomhole assembly  900  may be coupled with a downhole motor, such as a positive displacement motor, a mud motor, a turbine and/or the like that may be used to drive the drill bit  912 . Using the laser source  903  in combination with a downhole motor may reduce the shock/vibration undergone by the laser source  903 . Moreover, the downhole motor may also be used at least in part to generate electrical power for the laser source  903 . 
     In one embodiment of the invention, a controller may control the laser source  903  to generate laser energy when the downhole motor is not rotating the drill bit  912 . Laser energy may then be directed through the non-rotating drill bit to one or more locations on the formation. After application of the laser source  903 , the downhole motor may be activated to rotate the drill bit  912 . 
     In embodiments of the present invention wherein the laser energy is used to make the rock particles break down into a plasma, laser induced breakdown spectroscopy (LIBS) may be applied to identify the rock and fluid constituents downhole in real time by using the back reflection of the laser energy up through the energy transmission conduit  906  or by using a nearby sensor within mechanical cutter  912  and/or the drill bit  910 . The analysis could be done in total or part within the BHA, within the drill string at the surface or at a more remote location. 
     In embodiments in which a cable or a light path is used to transmit power/laser energy from the surface down the wellbore, the cable/light path may also be used for communication with the bottom of the wellbore. In such embodiments, the light path may be used to image the rock directly and construct a formation image and/or the control of rate of penetration and direction of the drilling system may be tied into the LIBS information about the rock being drilled. 
     One issue for any electromagnetic energy assisted drilling system is delivery of power downhole. As such, in some embodiments, one or more downhole sensors (not shown) may be used to sense the performance of the drilling system, components of the drilling system, properties of the earth formation  920  and/or the like and provide data to a downhole controller that may control operation of the electromagnetic source as required. 
     For example, sensors may monitor the operation of the downhole motor driving the drill bit  912  and electromagnetic energy may be supplied to the earth formation  920  when the downhole motor is not operating as desired, i.e., the rate of rotation of the drill bit falls below a threshold and or the like. In other embodiments, rotation speed of the drill bit  912 , rotation speed of the bottomhole assembly  900 , cutter wear, direction of drilling may be sensed and sensed data may be passed to the controller. In other embodiments, properties of the earth formation  920 , such as rock strength or the like, cutting depth, rate of penetration, drilling fluid pressure, amount of cuttings being produced, downhole temperature and/or the like may be sensed and communicated to the controller. 
     The controller may be a processor or the like and may control the operation of the electromagnetic source. For example, it may turn the source on/increase power produced by the source when rock strength increases, rate of penetration declines, cuttings build up around the drill bit, drill bit rotation speed declines, cutter wear increases and/or the like. In embodiments, where the electromagnetic source provides electromagnetic energy to multiple locations on the drill bit  910  or to multiple of the mechanical cutters  912 , the controller may use the incoming data to control power/turn on delivery of electromagnetic energy at the different locations/cutters. 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.