Abstract:
A system and method are disclosed for drilling a well and obtaining a downhole core sample. A drilling rig includes a pivotal mast. The mast supports an injector thereon with an injector axis offset with respect to the central axis of the mast when the drilling rig is handling threaded tubular. The mast also supports a drive unit. A drilling assembly includes coil tubing, the injector, and a bottomhole assembly including a percussion tool suspended in the well from the coil tubing. A coring assembly includes a threaded tubular string and the drive unit supported on the mast for rotating the threaded string and the coring bottomhole assembly while the injector is spaced from the axis of the mast.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of U.S. Provisional Application No. 61/301,116 filed on Feb. 3, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a coil tubing system including a rig and, more particularly, to using coil tubing and a drilling bottom-hole assembly (BHA) during mining exploration applications, and to using threaded tubulars and a coring bottomhole assembly during coring operations with the same rig. 
       BACKGROUND OF THE INVENTION 
       [0003]    In typical mining operations, an earth borehole apparatus is used to drill a borehole and then obtain a core sample from a desired subsurface locations. Analysis of a core sample provides information as to the composition of the subsurface formation and helps geologists determine whether further mining activity is warranted. Apparatus for conducting coring operations, as well as core sampling tools, e.g., core barrels, are well known to those skilled in the art. 
         [0004]    In the drilling of a conventional earth and/or hard rock borehole prior to coring, successive lengths of the casing are connected to a suitable bottom-hole assembly, such as a reverse circulation air hammer or a drill bit. In a typical coring operation, the apparatus comprises a mast, a powered drill head or drive unit with a chuck mounted on the mast for longitudinal movement therealong, and threaded tubular pipe similar to surface casing used in oil and gas well drilling, or a rod string. 
         [0005]    Typically, a borehole used in the mining exploration coring operations will be up to about 3,000 meters deep, and can be vertical or at an angle up to about 45°. Drilling below a cased surface borehole may be conducted with various types of drilling methods, such as diamond bits or percussion reverse circulation air hammer bits. The cuttings are commonly returned to the surface using an aqueous medium. The fluid is pumped down the drill string and returned up the annulus between the borehole and the drill string. The cuttings and chip samples may be analyzed to determine the general composition of the subsurface formation at any given depth. In the past, coring activities have been conducted after drilling with a string of rods, or with casing pipes extending to the desired depth to determine the precise composition of the cored sample. 
         [0006]    One of the drawbacks of these conventional methods of drilling is that it requires the making and breaking of successive length of threaded drill pipe, which is jointed. This operation is time consuming and labor intensive, as well as posing safety concerns. The use of so-called down the hole (DTH) percussive drilling assemblies, particularly so-called water hammers, has found wide-spread acceptance in the mining field for percussive drilling of a bore hole in hard rock condition. 
         [0007]    Relevant patents include U.S. Pat. Nos. 4,694,911, 5,476,421, 5,647,445, 5,803,118, 6,125,952, 7,073,610, 7,240,744, 7,617,886, and 7,748,478. Other publications of interest include a description of products and services of Coil Tubing Technology Holding Inc., Products &amp; Services, Operational Strategy by Scientific Prospectus: Integrated Ocean Drilling Program Expedition 313, Steerable Percussion Air Drilling System by Huy Bui, et al., Percussion Drilling in Oil Industry: Review and Rock Failure Modelling by Gang Han, et al., Water Driven Down-the-Hole Well Drilling Equipment for Hard Rock by Bo Nordell, et al., U.S. Publications 2004/0140131 and WO 2008/068546. 
         [0008]    The disadvantages of the prior art are overcome by the present invention, an improved system for drilling and coring a mining exploration well is hereinafter disclosed. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore the logic of the present invention to provide a system for drilling earth and/or hard rock boreholes, then for coring during mining exploration activities. 
         [0010]    Another object of the present invention is to provide a method for drilling an earth and/or hard rock type borehole, and then core sampling in mining exploration applications. 
         [0011]    In one aspect, the present invention provides a drilling system comprising a rig with a mast, a coil tubing injector attached to the mast for selective movement into an out of alignment with the mast, and a drilling BHA comprising a percussive drilling component, e.g., water hammer, a shock sub assembly and a down-hole fluid motor. The same drilling rig may be used for coring conducted with threaded tubulars, with a drilling head chuck or drive unit carried by the mast for longitudinal movement along the mast while rotating the tubular string, and a coring BHA including a core sampler. 
         [0012]    These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an elevational, side view of one drilling rig in accordance with the present invention. 
           [0014]      FIG. 2  is an end view of the assembly shown in  FIG. 1 . 
           [0015]      FIG. 3  is an elevational view of a BHA for use in the drilling. 
           [0016]      FIG. 4  is an elevational, side view of the drilling rig shown in  FIG. 1  with the coil tubing injector aligned with the mast. 
           [0017]      FIG. 5  is an elevational view of a BHA for use in coring. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    Referring first to  FIG. 1 , there is shown a carrier comprised of a truck T having a cab  10 , a bed  12 , and a frame  14  on which is mounted a reel  16  of coil tubing (not shown). Carried on bed  12  is usual equipment such as pumps, generators, hydraulics, etc. Pivotally attached to the bed of the truck T is a mast  16  having a core recovery winch  18  at the top thereof. A drilling head chuck or drive unit  20  as shown in  FIG. 2  is connected to mast  16  for longitudinal movement therealong by hydraulic piston/cylinder assemblies. Although shown in a vertical position, it will also be appreciated that mast  16  can be angled at any selected angle up to about 45° to drill off-vertical holes as desired. The drilling head chuck or drive unit  20  is positioned below the injector  22  when the injector is aligned with the mast, and rotates and preferably moves along the mast as threaded tubulars are lowered into or pulled out of the well. Disposed below drill head/chuck  20  is a make-break wrench assembly  23 , so that successive joints of the casing or drill pipe can be made up or broken out as drilling of a borehole proceeds or withdrawal of the casing or drill pipe occurs. A coil tubing injector  22  is pivotally attached to mast  16 , and has a first position shown in  FIG. 1 , wherein it is out of line with the central axis of mast  16 , but can be moved to a second position as shown in  FIG. 4  wherein coil tubing injector  22  is in line with a central axis of the mast  16 . 
         [0019]    Extending from the top and attached to coil tubing injector  22  is a segmented guide arch shown generally as  24 , having a first section  26  and a second section  28 . The guide arch  24  may be moved from its substantially horizontal transportation position, wherein injector  22  and guide arch  24  rest on a suitable support or bed  24  for transit, to the vertical position, as shown in  FIG. 1 , by pivoting the mast  8  to the upright position. 
         [0020]    Sections  26  and  28  of guide arch  24  are connected by a hydraulic/piston cylinder arrangement  25 , so that when injector  22  is in its operative position, i.e., pivoted so as to be in line with mast  16 , section  26  is pivoted by means of hydraulic piston cylinder  25 , so that a smooth curve is formed whereupon coil tubing from reel  16  can be passed through guide arch  24  and into injector  22 . 
         [0021]    The drilling BHA of the present invention is generally comprised of drill collars, one or more stabilizers, a shock absorber sub, a downhole fluid motor or mud motor, a water hammer and a connection to connect to the coil tubing. One such assembly is shown in  FIG. 3  which shows a water hammer  30  connected to a shock sub  32 , which in turn is connected to a mud fluid motor  34 , which is comprised of a drive shaft section  35  and a specialized fluid motor section  36  for this specific application. Such mud motors, commonly known as Moineau motors, are widely used in the drilling of oil and gas well and other boreholes and are well known to those skilled in the art. A suitable connector  38  connects the drilling BHA to the end of the coil tubing  40 . Although not shown, but as noted above, the BHA would also include drill collars and drill hole stabilizers to add weight and maintain a straight hole, and could also include various crossover subs as needed. In the present invention, the shock absorber sub  32  minimizes damage that could occur to the coil tubing  40  or upper components of the BHA from forces generated by the water hammer  30  when drilling the borehole. This is particularly important in the case of coil tubing because of its relatively lower strength compared to conventional drill pipe typically used in prior art drilling methods. In any event, once the drilling BHA is assembled and at least partially in the hole, the injector may be moved to the in line position, as shown in  FIG. 4 , and the drilling BHA connected to the coil tubing  40  which extends through the drilling head/chuck  20  and the coil tubing is powered by the injector during drilling operations. 
         [0022]    Drilling is conveniently carried out using, for example, a DTH water hammer  30  manufactured and marketed by Wassara. Water hammers of the type under consideration are generally powered by high water pressure which in this case is pumped through coil tubing  40  using pumping equipment mounted on the bed  12  of truck T. The high pressure water or other incompressible fluid provides both the driving force for the hammer and rotation of the rotor of the fluid motor  34  for delivering a known revolution range needed for adequate drilling performance, as well as returning the cuttings to the surface for possible analysis. 
         [0023]    Because it is necessary for the efficiency of drilling to rotate the water hammer  30  so as to present a constantly changing face for impact, down-hole fluid motor  34  is employed to rotate the portion of the BHA below motor  34 . Mud motor  34  in conjunction with steering capabilities also ensures that the borehole stays on a desired track. 
         [0024]    Because coil tubing is used, there is no necessity to stop the drilling operation for the purpose of adding additional joints of drill pipe as would be conventionally done. Furthermore, when it is necessary to replace the bit mounted on the water hammer, it is unnecessary to break out successive joints of threaded tubular rods since the coil  40  can simply be reeled back upon the reel  16  to retrieve the drilling BHA and replace the bit. 
         [0025]    In a typical coring operation, the drilling head/chuck  20  and mast  16  in the  FIG. 1  position may be used to obtain a core sample using successive lengths of casing or other threaded tubulars for lowering a core sampler to the desired bore depth, then the tubular string rotated to rotate the sampler and obtain the desired core. In this regard, crown block assembly/winch  18  can be used to move the casing joints in line with mast  16  so they can be connected conventionally, generally manually. The casing may serve as surface casing or a liner for further drilling activities. 
         [0026]    A suitable coring bottomhole assembly  50  as shown in  FIG. 5  is suspended in a drilled well on a threaded tubular string. The coring BHA includes a coring sampler  52 , preferably the sliding sleeve type, for obtaining the downhole sample. The coring sampler  52  includes a drill collar sub  54 , with an inner tube  56  axially movable with respect to the drill collar sub, a stabilizer sub  58 , and a diamond bit  60 . The inner tube stabilizer  62  is provided at the lower end of the stabilizer sub  58 , while head sub  64  connects the threaded tubular string to the drill collar sub  54 . The threaded tubular string is thus rotated by the drive unit movable along the mast, that provides the torque necessary to rotate the diamond bit  62  and obtain a cored sample. While other types of coring tools have been used for obtaining core samples, the drive unit and the threaded tubular string as provided herein provide a highly reliable technique for obtaining a sizable core sample from hard rock formations. 
         [0027]    The present invention is particularly suitable for conducting coring activities for mining operations which require a core sample to return to the surface for analysis. The present invention can also be used for other applications in which a well is drilled and a core sample obtained. 
         [0028]    A drill rig as disclosed herein includes an injector which is movable from a position in line with the mast for conducting coil tubing operations, e.g., when drilling the well, but the injector may be spaced laterally from the mast for conducting coring operations which require threaded tubulars. In a preferred embodiment as disclosed herein, the injector will be tilted into and out of alignment with the mast by one or more hydraulic cylinders in a manner similar to the disclosure in WO 2008/068546. In other applications, the injector may be moved laterally relative to the mast from an in line to an out of line position. In the out of line position, the injector is thus sufficiently spaced from the mast so as not to interfere with the movement of threaded tubulars. Moreover, this feature allows the drive unit which moves along the mast and rotates the threaded tubulars to be positioned below the injector, so that when the rig is moving coil tubing with the injector, the coil tubing passes through the drive unit. 
         [0029]    The present system presents a huge improvement toward a safer environment for the drill workers as well as a cost effective improvement to the mining exploration drilling practice. 
         [0030]    Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.