Abstract:
A method of severing a drill string or other tubular string that includes lowering a torch into the drill string, positioning the torch at a joint in the drill string, such that the joint may have a pin component engaged with a box component, igniting the torch to produce cutting fluids, and directing the cutting fluids into the joint in a direction that is along a length of the drill string to cut the joint.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/055,428, filed on Mar. 26, 2008. 
     
    
     BACKGROUND OF THE DISCLOSURE 
       [0002]    1. Field of the Disclosure 
         [0003]    The present disclosure relates to methods for removing drill collars from well bores. 
         [0004]    2. Description of the Related Art 
         [0005]    In oil and gas wells, a drill string that is used to drill a well bore into the earth. The drill string is typically a length of drill pipe extending from the surface into the well bore. The bottom end of the drill string has a drill bit. 
         [0006]    In order to increase the effectiveness of drilling, weight in the form of one or more drill collars is included in the drill string. A string of drill collars is typically located just above the drill bit and its sub. The string of drill collars contains a number of drill collars. A drill collar is similar to drill pipe in that it has a passage extending from one end to the other for the flow of drilling mud. The drill collar has a wall thickness around the passage; the wall of a drill collar is typically much thicker than the wall of comparable drill pipe. This increased wall thickness enables the drill collar to have a higher weight per foot of length than comparable drill pipe. 
         [0007]    During drilling operations, the drill string may become stuck in the hole. If the string cannot be removed, then the drill string is cut. Cutting involves lowering a torch into the drill string and physically severing the drill string in two, wherein the upper part can be removed for reuse in another well bore. The part of the drill string located below the cut is left in the well bore and typically cannot be retrieved or reused. Cutting is a salvage operation. A particularly effective cutting tool may be a radial cutting torch as disclosed by U.S. Pat. No. 6,598,679. 
         [0008]    The radial cutting torch produces combustion fluids that are directed radially out to the pipe. The combustion fluids are directed out in a complete circumference so as to cut the pipe all around the pipe circumference. 
         [0009]    It is desired to cut the drill string as close as possible to the stuck point, in order to salvage as much of the drill string as possible. Cutting the drill string far above the stuck point leaves a section of retrievable pipe in the hole. 
         [0010]    If, for example, the drill bit or its sub is stuck, then in theory one of the drill collars can be cut to retrieve at least part of the drill collar string. Unfortunately, cutting a drill collar, with its thick wall, is difficult. It is much easier to cut the thinner wall drill pipe located above the drill collars. Consequently, the drill collar string may be left in the hole, as the drill string is cut above the drill collar. 
         [0011]    It is desired to cut a drill collar for retrieval purposes. 
       SUMMARY OF THE DISCLOSURE 
       [0012]    Embodiments of the present disclosure provide a method of severing a drill string or other tubular string that may include the steps of lowering a torch into the drill string, positioning the torch at a joint in the drill string, such that the joint may have a pin component engaged with a box component, igniting the torch to produce cutting fluids, and directing the cutting fluids into the joint in a direction that is along a length of the drill string to cut the joint. 
         [0013]    The present disclosure provides a method of severing a drill collar string, which drill collar string forms part of a stuck drill string in a borehole. A torch is lowered into the drill string. The torch is positioned at a joint in the drill collar string. The torch is ignited so as to produce cutting fluids. The cutting fluids are directed into the joint in a direction that is along the length of the drill collar string so as to cut the joint and allow the joint to unwind. 
         [0014]    In accordance with one aspect of the present disclosure, the step of positioning the torch at a joint in the drill collar string further comprises the step of positioning cutting fluid openings of the torch at the joint. 
         [0015]    In accordance with still another aspect of the present disclosure, the step of directing the cutting fluids into the joint further comprises producing a pattern of cutting fluids, the pattern having a length at least as long as the joint. 
         [0016]    In accordance with still another aspect of the present disclosure, the joint further comprises a pin component on an inside diameter and a box component on an outside diameter. The pin component is severed while leaving the box component unsevered. 
         [0017]    In accordance with still another aspect of the present disclosure, the portion of the drill collar string that is above the cut joint is removed from the borehole. 
         [0018]    In accordance with still another aspect of the present disclosure, the cut end of the drill collar with the cut joint is redressed so as to make a new, uncut joint. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a cross-sectional view of a borehole with an uncut drill collar and a torch, in accordance with an embodiment of the present disclosure. 
           [0020]      FIG. 2  is the same as  FIG. 1 , but the torch has been ignited, in accordance with an embodiment of the present disclosure. 
           [0021]      FIG. 3  shows the drill collar of  FIG. 1 , having been cut and separated, in accordance with an embodiment of the present disclosure. 
           [0022]      FIG. 4  is a cross-sectional view of  FIG. 1 , taken along lines IV-IV, in accordance with an embodiment of the present disclosure. 
           [0023]      FIG. 5  is a cross-sectional view of  FIG. 3 , taken along lines V-V, in accordance with an embodiment of the present disclosure. 
           [0024]      FIG. 6  is a longitudinal cross-sectional view of the torch, in accordance with an embodiment of the present disclosure. 
           [0025]      FIG. 7  is a side elevational view of the nozzle pattern of the torch, taken along lines VII-VII of  FIG. 6 , in accordance with an embodiment of the present disclosure. 
           [0026]      FIGS. 8A-8C  show the dressing of a cut end of a drill collar to form a new pin joint, in accordance with an embodiment of the present disclosure. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    The present disclosure cuts a drill collar  11  (see  FIGS. 1 and 4 ) in a well  12 , thereby enabling the retrieval and future reuse of some or most of the drill collar string. The present disclosure utilizes a cutting torch  15  lowered down inside of the drill string  17 . A torch is positioned at one of the joints  21  of one of the drill collars. The joints are high torque couplings. 
         [0028]    When the torch  15  is ignited (see  FIG. 2 ), it produces combustion fluids  81 . The combustion fluids form a longitudinal slice or cut  23  through the coupling  21 . This is different than conventional cutting techniques that cut a pipe all around its circumference. The longitudinal cut effectively splits the coupling (see  FIGS. 3 and 5 ). Because the coupling is under high torque before being cut, after being cut it unwinds and decouples. Thus, a relatively small amount of cutting energy can effectively cut a thick walled drill collar  11 . The portion of the drill collar string that is decoupled is retrieved. 
         [0029]    The present disclosure will be discussed now in more detail. First, a drill collar  11  will be discussed, followed by a description of the torch  15  and then the cutting operation will be discussed. 
         [0030]    Referring to  FIG. 1 , the drill collar  11  is part of a drill string  13  that is located in a well  12  or borehole. The drill string  13  typically has a bottom hole assembly made up of a drill bit  25  and its sub and one or more drill collars  11 . There may be other components such as logging while drilling (LWD) tools, measuring while drilling (MWD) tools and mud motors. Drill pipe  27  extends from the bottom hole assembly up to the surface. The drill string may have transition pipe, in the form of heavy weight drill pipe between the drill collars and the drill pipe. The drill string forms a long pipe, through which fluids, such as drilling mud, can flow. 
         [0031]    The various components of the drill string are coupled together by joints. Each component or length of pipe has a coupling or joint at each end. Typically, a pin joint is provided at the bottom end, which has a male component, while a box joint is provided at the upper end, which has a female component. For example, as shown in  FIG. 1 , the lower joint of a drill collar  11  is a pin joint  21 A, while the upper joint  21 B is a box joint. 
         [0032]    As illustrated in  FIG. 1 , the drill collar  11  is a heavy or thick walled pipe. The thickness of the drill collar wall  31  is greater than the thickness of the drill pipe wall  33 . A passage  35  extends along the length of the drill collar, between the two ends. 
         [0033]    The wall thickness of the pin joint  21 A is less than the thickness of the wall  31  of the drill collar portion that is located between the two ends. Typical dimensions of the pin joint are 4 inches in length and ½ to 1 inch in wall thickness. The pin joint is tapered to fit into the similarly tapered box joint  21 B. 
         [0034]    The joints or couplings in the drill string and particularly in the drill collars are tight due to drilling. During drilling, the drill string  13  is rotated. This rotation serves to tighten any loose couplings. Consequently, the joints are under high torque. 
         [0035]    The cutting torch  15  is shown in  FIG. 6 . The torch  15  has an elongated tubular body  41  which body has an ignition section  43 , a nozzle section  45  and a fuel section  47  intermediate the ignition and fuel sections. In the preferred embodiment, the tubular body is made of three components coupled together by threads. Thus, the fuel section  47  is made from an elongated tube or body member, the ignition section  43  is made from a shorter extension member and the nozzle section  45  is made from a shorter head member. 
         [0036]    The ignition section  43  contains an ignition source  49 . In the preferred embodiment, the ignition source  49  is a thermal generator, which may resemble the thermal generator disclosed by U.S. Pat. No. 6,925,937. The thermal generator  49  is a self-contained unit that can be inserted into the extension member. The thermal generator  49  has a body  51 , flammable material  53  and a resistor  55 . The ends of the tubular body  51  are closed with an upper end plug  57 , and a lower end plug  59 . The flammable material  53  is located in the body between the end plugs. The upper end plug  57  has an electrical plug  61  or contact that connects to an electrical cable (not shown). The upper plug  57  is electrically insulated from the body  51 . The resistor  55  is connected between the contact  61  and the body  51 . 
         [0037]    The flammable material  53  is a thermite, or modified thermite, mixture. The mixture includes a powered (or finely divided) metal and a powdered metal oxide. The powdered metal includes aluminum, magnesium, etc. The metal oxide includes cupric oxide, iron oxide, etc. In the preferred embodiment, the thermite mixture is cupric oxide and aluminum. When ignited, the flammable material produces an exothermic reaction. The flammable material has a high ignition point and is thermally conductive. The ignition point of cupric oxide and aluminum is about 1200 degrees Fahrenheit. Thus, to ignite the flammable material, the temperature must be brought up to at least the ignition point and preferably higher. It is believed that the ignition point of some thermite mixtures is as low as 900 degrees Fahrenheit. 
         [0038]    The fuel section  47  contains the fuel. In the preferred embodiment, the fuel is made up of a stack of pellets  63  which are donut or toroidal shaped. The pellets are made of a combustible pyrotechnic material. When stacked, the holes in the center of the pellets are aligned together; these holes are filled with loose combustible material  65 , which may be of the same material as the pellets. When the combustible material combusts, it generates hot combustion fluids that are sufficient to cut through a pipe wall, if properly directed. The combustion fluids comprise gasses and liquids and form cutting fluids. 
         [0039]    The pellets  65  are adjacent to and abut a piston  67  at the lower end of the fuel section  47 . The piston  67  can move into the nozzle section  45 . 
         [0040]    The nozzle section  45  has a hollow interior cavity  69 . An end plug  71  is located opposite of the piston  67 . The end plug  71  has a passage  73  therethrough to the exterior of the tool. The sidewall in the nozzle section  45  has one or more openings  77  that allow communication between the interior and exterior of the nozzle section. The nozzle section  45  has a carbon sleeve liner  79 , which protects the tubular metal body. The liner  75  is perforated at the openings  77 . 
         [0041]    The openings are arranged so as to direct the combustion fluids in a longitudinal manner. In the embodiment shown in  FIG. 7 , the openings  77  are arranged in a vertical alignment. The openings  77  can be rectangular in shape, having a height greater than a width. Alternatively, the openings can be square or circular (as shown). In another embodiment, the nozzle section  45  can have a single, elongated, vertical, slot-type opening. 
         [0042]    The piston  67  initially is located so as to isolate the fuel  63  from the openings  77 . However, under the pressure of combustion fluids generated by the ignited fuel  63 , the piston  67  moves into the nozzle section  45  and exposes the openings  77  to the combustion fluids. This allows the hot combustion fluids to exit the tool through the openings  77 . 
         [0043]    The method will now be described. Referring to  FIG. 1 , the torch  15  is lowered into the drill string  13 , which drill string is stuck. Before the torch is lowered, the decision has been made to cut the drill string and salvage as much of the drill string as possible. Also, the drill string is stuck at a point along the drill collar string or below the drill collar string. 
         [0044]    The torch  15  can be lowered on a wireline, such as an electric wireline. The torch is positioned inside of the drill collar  11  which is to be cut. Specifically, the openings  77  are located at the same depth of the pin coupling  21 A which is to be cut. The length of the arrangement of openings is longer than the pin joint. The longer the arrangement of openings, the less precision is required when positioning the torch relative to the pin joint  2   1 A. Then, the torch is ignited. An electrical signal is provided to the igniter  49  (see  FIG. 6 ), which ignites the fuel  65 ,  63 . The ignited fuel produces hot combustion fluids. The combustion fluids  81  produced by the fuel force the piston  67  down and expose the openings  77 . The combustion fluids  81  are directed out of the openings  77  and into the pin coupling  21 A (see  FIG. 2 ). The combustion fluids are directed in a pattern that is longitudinal, rather than circumferential. The combustion fluid pattern is at least as long as the pin joint, and in practice extends both above and below the pin joint. 
         [0045]    The torch creates a cut  23  along the longitudinal axis in the pin joint  21 A (see  FIGS. 3 and 5 ). The pin  21 A is severed. The portions of drill collar above and below the pin joint have longitudinal cuts therein, but due to the wall thickness, these cuts do not extend all the way to the outside.  FIG. 5  shows the cut extending part way into the corresponding box joint. Thus, the box joint and the portions of the drill collar above and below the pin joint are not cut completely through and are unsevered. Nevertheless, when the pin joint is cut, it unwinds or springs open. The joint decouples and the drill string becomes severed at the joint. Thus, only the pin joint need be cut to sever the drill collar. That portion of the drill string that is unstuck, the upper portion, is retrieved to the surface. 
         [0046]    The drill collar  11  that was cut at its pin joint can be reused. Referring to  FIG. 8A , the pin joint  21 A has a longitudinal cut  23  therein. The pin joint  21 A is cut off of the drill collar, as well as any damaged portions of the collar to form a clean end  83  (see  FIG. 8B ). The end  83  is remachined to form a new pin joint (see  FIG. 8C ). The drill collar can now be reused. 
         [0047]    Each of the torches can be provided with ancillary equipment such as an isolation sub and a pressure balance anchor. The isolation sub typically is located on the upper end of the torch and protects tools located above the torch from the cutting fluids. Certain well conditions can cause the cutting fluids, which can be molten plasma, to move upward in the tubing and damage subs, sinker bars, collar locators and other tools attached to the torch. The isolation sub serves as a check valve to prevent the cutting fluids from entering the tool string above the torch. 
         [0048]    The pressure balance anchor is typically located below the torch and serves to stabilize the torch during cutting operations. The torch has a tendency to move uphole due to the forces of the cutting fluids. The pressure balance anchor prevents such uphole movement and centralizes the torch within the tubing. The pressure balance anchor has either mechanical bow spring type centralizers or rubber finger type centralizers. 
         [0049]    The foregoing disclosure and showings made in the drawings are merely illustrative of the principles of this disclosure and are not to be interpreted in a limiting sense.