Abstract:
A magnetic bit sub for collecting ferrous metal particles from oil wells, gas wells, and water wells during well drilling operations, well completion operations, and well maintenance operations provides tubular member with a threaded male connector on the upper end, for attachment to a drill string, and a threaded female connector on the lower end, for attachment to a drill bit, another portion of drill string, or another magnetic bit sub. Permanent magnets removably secured within recesses spaced along the outer surface of the tubular member collect ferrous metal particles coming into the proximity of the recessed permanent magnets for removal when the drill string is removed from the well.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a well tool, and, more particularly, but not by way of limitation, to a magnetic bit sub for collecting ferrous metal particles from oil wells, gas wells, and water wells during well drilling operations, well completion operations, and well maintenance operations. The magnetic bit sub according to the present invention is also suitable for use alone to collect ferrous metal particles and objects from a well. 
         [0003]    2. Discussion 
         [0004]    Ferrous metal bearing particles, sometimes referred to herein as ferrous particles, iron filings, steel filings, iron cuttings, steel cuttings, iron shavings, or steel shavings, can derive from a number of operations. Any operation which involves cutting a hole into a steel well casing will produce iron cuttings. Frac plugs, often made of steel or iron, are removed by drilling. Collapsed steel casings may be drilled out. From time to time, nuts, bolts, screws, and small tools may end up in the well, where drilling produces iron or steel cuttings. Although the description which follows focuses on oil and gas well operations, it will be understood by one skilled in the art that the magnetic bit sub of applicant&#39;s invention is suitable for recovery of ferrous metal particles and objects from any type of well. 
         [0005]    Iron filings are not easily removed from drilling fluids using shakers and centrifuges common to oil and gas well drilling operations. The presence of iron filings leads to accelerated bit wear and other problems both in the hole and at the surface. 
         [0006]    What is needed is a device which can be incorporated into the drill string at one or more locations to collect and retain ferrous metal particles until the drill string is pulled from the hole. The device should exhibit good strength and wear resistance, toughness, and the ability to resist stress at elevated temperatures. 
       SUMMARY OF THE INVENTION 
       [0007]    A magnetic bit sub for collecting ferrous metal particles from oil wells, gas wells, and water wells during well drilling operations, well completion operations, and well maintenance operations provides a tubular member with a threaded male connector on the upper end, for attachment to a drill string pipe section, and a threaded female connector on the lower end, for attachment to another drill string pipe section or a drill bit. Permanent magnets removably secured within recesses spaced along the outer surface of the tubular member collect ferrous metal particles which are removed after the drill string is pulled from the well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a view of a magnetic bit sub according to the present invention shown in a partially completed hole beneath a derrick. 
           [0009]      FIG. 2  is a greatly enlarged view of a portion of the magnetic bit sub shown in  FIG. 1 . 
           [0010]      FIG. 3  is another view of the magnetic bit sub shown in  FIGS. 1 and 2 . 
           [0011]      FIG. 4  is a cross-sectional view of the magnetic bit sub shown in  FIGS. 1-3 . 
           [0012]      FIG. 5  is an exploded view of one of the permanent magnets of the magnetic bit sub invention shown in  FIGS. 1-4 . 
           [0013]      FIG. 6  is a cross-sectional view of another magnetic bit sub according to the present invention. 
           [0014]      FIG. 7  is an exploded view of another magnet which is part of the magnetic bit sub invention shown in  FIG. 6 . 
           [0015]      FIG. 8  is a view of another magnetic bit sub according to the present invention. 
           [0016]      FIG. 9  is a view of another magnetic bit sub according to the present invention. 
           [0017]      FIG. 10  is a view of another magnetic bit sub according to the present invention. 
           [0018]      FIG. 11  is a view of another magnetic bit sub according to the present invention. 
           [0019]      FIG. 12  is a view of another magnetic bit sub according to the present invention. 
           [0020]      FIG. 13  is a cross-sectional view of another magnetic bit sub according to the present invention. 
           [0021]      FIG. 14  is a view of another magnetic bit sub according to the present invention. 
           [0022]      FIG. 15  is a cross-sectional view of another magnetic bit sub according to the present invention. 
           [0023]      FIG. 16  is a cross-sectional view of another magnetic bit sub according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    In the following description of the invention, like numerals and characters designate like elements throughout the figures of the drawings. 
         [0025]    Referring now to  FIGS. 1-5 , and more specifically to  FIGS. 1-2 , a magnetic bit sub  20  according to the present invention is attached to a drill string S above a drill bit B. The drill string S, supported by a swivel (not shown) suspended from a derrick D, is disposed within a hole H having a wall W surrounded by earth E. Drilling fluid F flows down the drill string S, as shown by arrow  22 , out through the drill bit B, and back up the outside of the drill string S along arrows  24  to the surface. The magnetic bit sub  20 , as illustrated in  FIG. 1 , is located immediately above the drill bit B. As used herein, the term drilling fluid includes drilling muds, foams, hydrocarbons, and water. 
         [0026]    Still referring to  FIGS. 1-5 , and especially  FIGS. 1-2 , the drilling fluid F flows (by means of a drilling fluid pump, not shown) down the drill string S according to the arrow  22  through the drill string S, through an elongated internal conduit  26  in the magnetic bit sub  20 , and through the drill bit B. The drilling fluid F then flows back to the surface according to the arrow  24  through an annular space  28  between the drill string S, the magnetic bit sub  20 , and the drill bit B, on the inside, and the wall W of the hole H, on the outside. The magnetic bit sub  20  has an upper portion  30 , an intermediate portion  32 , and a lower portion  34 . The upper portion  30  and the lower portion  34  have an outside diameter  36 , whereas the intermediate portion  32  has a reduced outside diameter  38 . 
         [0027]    Still referring to  FIGS. 1-5 , permanent magnets  40  are secured within recesses  42  (See  FIG. 4 ) spaced along the length of the intermediate portion  32  of the magnetic bit sub  20  to form an array of permanent magnets  40 . As shown in greater detail in  FIGS. 4-5 , the permanent magnets  40  have a center counterbore  44  which aligns with threaded radial bores  46  centered in the recesses  42 . Threaded bolts  48  secure the permanent magnets  40  within the recesses  42 . The upper portion  30  of the magnetic bit sub  20  terminates in a male connector  50 , and the lower portion  34  of the magnetic bit sub  20  terminates in a female connector  52 . 
         [0028]    It will be understood by one skilled in the art that the magnetic bit sub  20  is suitable for placement at any location in the drill string S. Two or more magnetic bit subs  20  can be coupled to increase the number of permanent magnets  40  coming in contact with the drilling fluid F. In the alternative, two or more magnetic bit subs  20  can be placed at separate locations in the drill string S. It will be further understood by one skilled in the art that the outside diameter  36  of the magnetic bit sub  20  and the size of the connectors  50 ,  52  corresponds to the pipe size of the drill string S. Magnetic bit sub prototypes have been constructed from Alloy 4140 Steel wherein the upper and lower portions have an outside diameter of about 3.75 inches and the intermediate portion has an outside diameter of about 2.75 inches. 
         [0029]    Still referring to  FIGS. 1-5 , and more particularly to  FIGS. 2-3 , a transition  56  between the upper portion  30  and the intermediate portion  32  is a radius of a convenient dimension. Likewise, a transition  58  between the intermediate portion  32  and the lower portion  34  is a radius of any convenient dimension. 
         [0030]    Referring now to  FIG. 2 , particles  60  from the drilling fluid F are lodged on the permanent magnets  40  arrayed in the intermediate portion  34  of the magnetic bit sub  20 . For any constant flow rate of the drilling fluid F (as determined by the pumping rate of the drilling fluid pump), the upward velocity of the drilling fluid F along arrows  24  will decrease as the drilling fluid F moves past the lower transition  58  between the lower portion  34  and the intermediate portion  32 . The reduced outside diameter  38  of the intermediate portion  34  results in a larger annular space  28  cross section in vicinity of the intermediate portion  34 . The reduced velocity of the drilling fluid F adjacent the intermediate portion  32  and the permanent magnets  40  arrayed therein is thought to facilitate collection of ferrous metal particles  60  on the permanent magnets  40 . In addition, the reduced diameter  38  of the intermediate portion  32  provides space for accumulation of ferrous particles  60  without restricting the flow of the drilling fluid F. When the drilling fluid F moves upwardly passed the upper transition  56 , the velocity of the drilling fluid F increases. 
         [0031]    Referring now to  FIGS. 6-7 , another magnetic bit sub  70  is like the magnetic bit sub  20  shown in  FIGS. 1-5  except for the dimensions of the permanent magnets. Permanent magnets  90  are secured within recesses  92  spaced along the intermediate portion  82  of the magnetic bit sub  70  (identical to the intermediate portion  32  of the magnetic bit sub  20 ). Although a variety of permanent magnets are capable of functioning at ambient temperatures, Alnico magnets have been found superior in the face of high temperatures encountered in deep well drilling operations—temperatures which cause most permanent magnets to lose their magnetic strength. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico alloys have some of the highest Curie points of any magnetic material, around 800° C. They are also one of the most stable permanent magnets if they are handled properly. Generally, cylindrical Alnico permanent magnets achieve a maximum magnetic strength when the thickness of the magnet approaches its diameter. Thus the magnets  90  shown in  FIGS. 6-7  are relatively thicker than the magnets  40  of  FIGS. 1-5 . 
         [0032]    Still referring to  FIGS. 6-7 , the permanent magnets  90  are secured within recesses  92  spaced along the length of the intermediate portion  82  of the magnetic bit sub  70  to form an array of permanent magnets  90 . The permanent magnets  90  have a center counterbore  94  which aligns with threaded radial bores  96  centered in the recesses  92 . Threaded bolts  98  secure the permanent magnets  90  within the recesses  92 . 
         [0033]    In  FIG. 8 , a magnetic bit sub  120  has an upper portion  130  and a lower portion  132 . An internal conduit  126  permits flow of drilling fluid F through the magnetic bit sub  120 . The upper portion  130  has an outside diameter  136 , whereas the lower portion  132  has a reduced outside diameter  138 . Permanent magnets  140  are secured within recesses  142  spaced along the lower portion  132  of the magnetic bit sub  120  to form an array of permanent magnets  140 . The upper portion  130  of the magnetic bit sub  120  terminates in a male connector  150 . The lower portion  132  of the magnetic bit sub  120  has no connector. A transition  156  between the upper portion  130  and the lower portion  132  is a machined radius. 
         [0034]    Still referring to  FIG. 8 , the magnetic bit sub  120  is suited for insertion into a well for removal of ferrous particles and other undesirable ferrous metal items. The permanent magnets  140  are secured within recesses  142  (not shown) as described with respect to the attachment of the permanent magnets  40  within recesses  42  in the magnetic bit sub  20  of  FIGS. 1-5 . 
         [0035]    In  FIG. 9 , a magnetic bit sub  170  has an upper portion  172 , an intermediate portion  174 , and a lower portion  176 . The upper portion  172 , the intermediate portion  174 , and the lower portion  176  are of a constant diameter  178 . Permanent magnets  180  are secured within recesses  182  (not shown) spaced along the intermediate portion  174 . The upper portion  172  of the magnetic bit sub  170  terminates in a male connector  184 . The lower portion  174  terminates in a female connector  186 . 
         [0036]    In  FIG. 10 , a magnetic bit sub  220  has an upper portion  230 , an intermediate portion  232 , and a lower portion  234 . The upper portion  230  and the lower portion  234  have an outside diameter  236 , whereas the intermediate portion  232  has a reduced outside diameter  238 . 
         [0037]    Still referring to  FIG. 10 , permanent magnets  240  are secured within recesses  242  (not shown) spaced helically along the length of the intermediate portion  232  of the magnetic bit sub  220  to form an array of permanent magnets  240 . The upper portion  230  of the magnetic bit sub  220  terminates in a male connector  250 , and the lower portion  234  of the magnetic bit sub  220  terminates in a female connector  252 . A transition  256  between the upper portion  230  and the intermediate portion  232  is a radius of a convenient dimension. Likewise, a transition  258  between the intermediate portion  232  and the lower portion  234  is a radius of any convenient dimension. 
         [0038]    While the magnets  40 ,  80 ,  140 , and  180  of  FIGS. 1-9  are substantially vertically aligned in offset adjacent quadrants, the magnets  240  of the magnetic bit sub  220  shown in  FIG. 10  are spaced in adjacent helices along the intermediate portion  232 . It will be understood by one skilled in the art that the permanent magnets  40 ,  80 ,  140 ,  180 ,  220  can be arrayed in any convenient configuration. It will be further understood by one skilled in the art that the permanent magnets  40 ,  80 ,  140 ,  180 , and  200  will magnetize any ferrous metal to which they are attached. Thus the intermediate portions  32 ,  82 ,  174 ,  232  of  FIGS. 1-7 ,  9 , and  10 , respectively, and the lower portion  132  of  FIG. 8 , if made from magnetically permeable alloys, will become magnetized and provide an additional area for accumulation of ferrous particles  60  removed from the drilling fluid F. This magnetization may extend to the upper portions  30 ,  80 ,  130 ,  172 , and  230  of the magnetic bit subs shown in  FIGS. 1-10 . 
         [0039]    In  FIG. 11 , a magnetic bit sub  270  has an upper portion  280 , an intermediate portion  282 , and a lower portion  284 . The upper portion  280  and the lower portion  284  have an outside diameter  286 , whereas the intermediate portion  282  has a reduced outside diameter  288 . Permanent magnets  290  are secured within recesses  292  (not shown) spaced along the length of the intermediate portion  282  of the magnetic bit sub  270  to form an array of permanent magnets  290 . The upper portion  280  of the magnetic bit sub  270  terminates in a male connector  300 , and the lower portion  284  of the magnetic bit sub  270  terminates in a female connector  302 . A transition  306  between the upper portion  280  and the intermediate portion  282  is substantially a right angle. Likewise, a transition  308  between the intermediate portion  282  and the lower portion  284  is substantially a right angle. 
         [0040]    In  FIG. 12 , a magnetic bit sub  320  has an upper portion  330 , an intermediate portion  332 , and a lower portion  334 . The upper portion  330  and the lower portion  334  have an outside diameter  336 , whereas the intermediate portion  332  has a reduced outside diameter  338 . Permanent magnets  340  are secured within recesses  342  (not shown) spaced along the length of the intermediate portion  332  of the magnetic bit sub  320  to form an array of permanent magnets  340 . The upper portion  330  of the magnetic bit sub  320  terminates in a male connector  350 , and the lower portion  334  of the magnetic bit sub  320  terminates in a female connector  352 . A transition  356  between the upper portion  330  and the intermediate portion  332  is a curved ramp. Likewise, a transition  358  between the intermediate portion  332  and the lower portion  334  is a curved ramp. 
         [0041]    In  FIG. 13 , another magnetic bit sub  370  has permanent magnets  390  secured within recesses  392  by an adhesive  394 . 
         [0042]    In  FIG. 14 , a magnetic bit sub  420  has an upper portion  430  and a lower portion  432 . The upper portion  430  has an outside diameter  436 , whereas the lower portion  432  has a reduced outside diameter  438 . Permanent magnets  440  are secured within recesses  442  (not shown) spaced along the lower portion  432  of the magnetic bit sub  420  to form an array of permanent magnets  440 . The upper portion  430  of the magnetic bit sub  420  terminates in a male connector  450 . The lower portion  432  of the magnetic bit sub  420  has no connector. A transition  456  between the upper portion  430  and the lower portion  432  is a machined radius. Unlike the magnetic bit sub  120  shown in  FIG. 8 , the magnetic bit sub  420  has no internal conduit to facilitate flow of the drilling fluid F. 
         [0043]    In  FIG. 15 , a magnetic bit sub  470  has permanent magnets  490  secured within threaded recesses  492  by threaded retainers  494 . 
         [0044]    In  FIG. 16 , a magnetic bit sub  520  has permanent magnets  540  secured within recesses  542  by snap rings  544 . 
         [0045]    In view of the foregoing detailed descriptions, it will be understood by one skilled in the art that the magnetic bit subs  20 ,  120 ,  170 ,  220 ,  270 ,  320 ,  370 ,  470 , and  520  are, essentially, tubular members with one or more connectors for attachment to drill pipe or well pipe. In each instance, the tubular member supports an array of permanent magnets secured in spaced recesses along the outside of the tubular member. The recessed permanent magnets attract and hold iron particles from the fluid moving past the recessed permanent magnets for removal when the drill pipe or well pipe is removed from the well. The magnetic bit sub  120  shown in  FIG. 8  has only an upper connector, so the magnetic bit sub  120  is suitable for use only at the bottom of the drill string. The magnetic bit sub  420  shown in  FIG. 14  has no internal conduit to accommodate flow of drilling fluid and is also suitable for use only at the bottom of the drill string. 
         [0046]    It will be further understood by one skilled in the art that locations of the permanent magnets within recesses provides protection from side impact of drilling chips carried win the drilling fluid. Moreover, the attachment of the permanent magnets to the tubular member by threaded bolts (See  FIGS. 1-5 ), retaining rings (See  FIG. 15 ), and snap rings (See  FIG. 16 ) facilitates replacement of the permanent magnets when the permanent magnets eventually wear out. Further, the recessed permanent magnets do not interfere with flow of the drilling fluid. 
         [0047]    The tubular member which supports the permanent magnets can be made from any alloy (either permeable or non-permeable magnetically) having suitable strength, wear resistance, toughness, ductility, and an ability to resist stress at elevated temperatures. Prototypes have been made from Alloy C4140 (steel), chosen because of its use in drill collars, bolts, and rotary table shafting in the oil and gas well drilling industry. Alloy 4140 will become magnetized due to the presence of the permanent magnets. When the magnetic bit sub is positioned just above the drill bit (See  FIG. 1 ), the magnetic bit sub supports only the weight of the drill bit. When the magnet bit sub is placed higher in the drill string, the magnetic bit sub may be required to support the weight of a substantial portion of the drill string. Placement of the magnetic bit sub at the very bottom of the drill string (See  FIGS. 8 and 14 ) relieves the magnetic bit sub of any weight-bearing requirements. 
         [0048]    The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.