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CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. provisional application 60/874,121, filed Dec. 11, 2006. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to earth boring bits and in particular to a drag bit having a diamond impregnated crown having replaceable nozzles for drilling fluid flow. 
       BACKGROUND OF THE INVENTION 
       [0003]    One type of earth boring bit, called “impregnated bit” is used for drilling relatively hard, abrasive, or hard and abrasive rock formations, such as sandstones. An impregnated bit has a crown or cutting face composed of diamond impregnated matrix. The matrix may comprise super abrasive cutting particles, such as natural or synthetic diamond grit, dispersed within a matrix of wear resistant material. The wear resistant matrix typically comprises a tungsten carbide powder infiltrated with a copper-based binder. 
         [0004]    The crown is molded to define blades having a variety of shapes. Flow channels, also called “junk slots”, are located between the blades. Ports are located in some of the channels. Each port extends through the shell of the crown to an interior cavity for discharging drilling fluid pumped down the drill string. 
         [0005]    The ports are fixed in diameter and they tend to wear or wash out during use. Using replaceable nozzles is known for some types of earth boring bits, particularly rolling cone bits. However, the widths of the flow channels are not sufficient for these types of nozzles. 
       SUMMARY 
       [0006]    The bit of this invention has a crown mounted on a body. The crown is formed of a carbide matrix material and has a plurality of impregnated blades formed thereon, at least portions of the blades being separated from each other, defining channels. At least some of the channels has a nozzle port formed therein. A nozzle is releasably fastened to each of the nozzle ports. Each of the nozzles is in fluid communication with a cavity in the body for discharging drilling fluid. 
         [0007]    Preferably, each of the nozzle ports is located within an enlarged portion of one of the channels. Each of the enlarged width portions joins a tapered width portion on it outer side. The inner portion of the tapered width portion is smaller in width than the maximum width of the enlarged portion, and it diverges outward to the gage area. 
         [0008]    Preferably at least some of the channels have a fixed port, which does not have a replaceable nozzle but leads from the cavity for discharging drilling fluid. Each of the fixed ports is smaller in diameter than any of the nozzle ports. In the preferred embodiment, the nozzle ports are evenly spaced apart from each other and spaced the same distance from an axis of the crown. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a plan view of the bit face of a drag bit constructed in accordance with the invention. 
           [0010]      FIG. 2  is a perspective view of the drag bit of  FIG. 1 . 
           [0011]      FIG. 3  is an enlarged sectional view of one of the nozzles of the drag bit of  FIG. 1 , taken along the line  3 - 3  of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to  FIG. 1 , a crown  11  of a drag bit is illustrated. Crown  11  is a casting formed of a matrix containing hard metal particles, such as tungsten carbide. Crown  11  has a bit face  13 , which is the portion that will engage the bottom of the wellbore. Crown  11  is rotated about its central axis  14  during drilling. Crown  11  has a generally cylindrical gage area  15  surrounding bit face  13  for engaging the sidewall of the wellbore. Normally, crown  11  will have a central region  16  or throat in the center of bit face  13 . Central region  16  extends upward into crown  11  from bit face  13  a short distance and has a closed or partially closed base. Central region  16  may have various configurations, such as an inverted cone. 
         [0013]    A blade pattern  17  made up of a plurality of blades is formed on bit face  13 . Blade pattern  17  is integrally formed as a part of crown  11  during the casting process and contains diamond or other super abrasive particles mixed in with the carbide particles. The relatively fine tungsten carbide material is intended to wear away from the diamond particles interspersed therein, exposing unworn diamonds therein. In this embodiment, the exterior surface of blade pattern  17  is a smooth abrasive surface. Blade pattern  17  may be formed by known processes, such as a pressure infiltration process. 
         [0014]    Blade pattern  17  defines a plurality of channels or junk slots that are located between and recessed from the various blades. In the example shown, the channels include a plurality of long channels  19 , which extend axially along gage area  15  and generally radially across bit face  13  into central region  16 . In this example, seven long channels  19  are shown, but the number could differ. Three of the six long channels  19  extend completely to axis  14 , while the other four terminate short of axis  14 , but within central region  16 . Three of the long channels  19  intersect each other at axis  14 . Two of the long channels  19  (shown on the lower right side of the drawing) intersect each other within central region  16 , but radially outward from axis  14 . The last two long channels  19  do not intersect each other, but terminate within central region  14  radially outward from axis  14 . 
         [0015]    In this example, each of the seven long channels  19  has a central region portion  21  that forms its radially innermost portion and is located within central region  16 . Each long channel  19  has an enlarged width portion  23  joining its central region portion  21  and located a short distance outward from central region  16 . Enlarged width portion  23  has a generally circular or rounded contour. In the preferred embodiment, enlarged width portion  23  leads to a reduced width portion  25 . A diverging width portion  27  extends radially outward from reduced width portion  25  to gage area  15 . The width increases in an outward direction in the diverging width portion  27  to a width somewhat larger than the width of enlarged width portion  23 . 
         [0016]    A replaceable nozzle  29  is mounted to bit crown  11  within the enlarged width portion  23  of each long channel  19 . All of nozzles  29  are located the same radial distance from bit axis  14  in this embodiment. Nozzles  29  are uniformly spaced apart from each other the same circumferential distance in this embodiment. Each nozzle  29  is a short tubular member made of hard, wear resistant material, such as tungsten carbide. 
         [0017]    As shown in  FIG. 3 , each nozzle  29  has a passage  33  extending through it that is in communication with the interior of crown  11  for discharging drilling fluid pumped down the drill string. Passage  33  may have various configurations, and is illustrated as having a converging downstream portion. Nozzles  29  are oriented to spray drilling fluid generally downward for cooling crown  11  and forcing cuttings radially outward along long channels  19 . The downstream end of each nozzle  29  is preferably flush or slightly recessed within the exterior surface of one of the long channels  19 . A fastening means allows each nozzle  29  to be readily removed and replaced. In this example, the fastening means comprises mating threads  31  formed on the outer diameter of nozzle  29  and in the hole or port within crown  11  that receives nozzle  29 . The downstream end of each nozzle  29  has slots (not shown) formed in it for receiving a tool to tighten or loosen threads  31  of nozzle  29 . Alternately, snap rings or threaded retaining rings could be utilized. 
         [0018]    In this embodiment, a plurality of central ports  37  are located within central region  16  near axis  14 . Three central ports  37  are shown, one in each central region portion  21  of one of the long channels  19 . Central ports  37  also discharge drilling fluid pumped down the drill string, however are smaller in diameter than passages  33  of nozzles  29  and do not have replaceable nozzles. 
         [0019]    The channels formed by blade pattern  17  also include a plurality of intermediate length channels  39 , which extend from gage area  15  partially across bit face  13 . The inner end of each intermediate length channel  39  is approximately the same radial distance from axis  14  as each long channel enlarged width portion  23 . Each intermediate length channel  39  is located between two of the long channels  19 , extends generally radially, and has a dog-leg portion near its inner end. An intermediate port  41  is formed in crown  11  at the inner end of each intermediate channel  39 . In this example, there are seven intermediate ports  41 , and each is located the same radial distance from axis  14 . Intermediate ports  41  also discharge drilling fluid pumped down the drill string, however are smaller in diameter than central ports  37  and do not have replaceable nozzles. 
         [0020]    The channels formed by blade pattern  17  also include a plurality of short length channels  43  that extend from gage area  15  partially across bit face  13 . The inner end of each short length channel  43  is a longer radial distance from axis  14  than the inner end of each intermediate channel  39 . Each short length channel  39  is located between two of the long channels  19  and extends generally radially parallel to the outer portion of one of the intermediate channels  39 . An outer port  44  is formed in crown  11  at the inner end of each short channel  43  farther outward from axis  14  than intermediate ports  41 . In this example, there are seven outer ports  44 , and each is located the same radial distance from axis  14 . Outer ports  44  also discharge drilling fluid pumped down the drill string, however are smaller in diameter than central ports  37  and do not have replaceable nozzles. 
         [0021]    The pattern of the various channels  19 ,  39  and  43  results in blade pattern  17  having a plurality of trunks  45  within central region  16  and extending generally radially outward. Six of the trunks  45  intersect another trunk  45 . Each trunk  45  divides into two long branches  47  that spread apart from each other, similar to branches of a tree. Each long branch  47  extends generally radially outward from one of the trunks  45  to gage area  15 . A short branch  49  joins one of the long branches  47  and extends generally radially outward, but terminates short of gage area  15 . Blade pattern  17  may be divided into three generally fan-shaped patterns  17   a ,  17   b  and  17   c , with fan-shaped patterns  17   a  and  17   b  being identical and defined by two intersecting trunks  45 , four long branches  47  and two short branches  49 . The third fan-shaped blade pattern  17   c  in this example spreads over a greater angle than the other two blade patterns  17   a ,  17   b . It, too, has two intersecting trunks  45 , four long branches  47  and two short branches  49 . However, it has a smaller fan-shaped inset  17   d  that is not fully shown but has a single trunk  45  extending partially into central region  16 . Two long branches  47  extend from the trunk  45  of inset  17   d.    
         [0022]    Each long channel  19  starts between two of the trunks  45  and is located between two of the long branches  47 . Each intermediate channel  39  is located between one of the long branches  47  and one of the short branches  49 . Each short channel  43  is located between one of the long branches  47  and one of the short branches  49 . 
         [0023]    Central region  16  may have cutting elements within. In this embodiment, a plurality of polycrystalline diamond (PDC) cutting elements  51  are mounted to trunks  45 . PDC elements  51  have flat faces oriented into the direction of rotation for scraping the earth formation. Other than within central region  16 , bit face  13  does not have any PDC cutting elements. 
         [0024]    Referring to  FIG. 2 , crown  11  is mounted conventionally to a body  53  that is typically formed of steel. Body  53  is a tubular member having a set of threads  55  for connection to a string of drill pipe. 
         [0025]    In operation, body  53  is secured by threads  55  to a drill string and lowered into a wellbore. The operator rotates body  53  and pumps drilling fluid down the drill string. Bit face  13  engages and abrades the bottom of the wellbore. Drilling fluid exits the various nozzles  29  and ports  37 ,  41  and  44 . The fluid flows out the various channels  19 ,  39  and  43  and returns up the annulus of the borehole surrounding the drill string. 
         [0026]    After drilling a particular section of a well, the bit may be retrieved for various reasons. Blade pattern  17  may still have a useful life. However, the drilling fluid tends to erode and wear away nozzles  29 . If damaged too severely, the operator can unscrew one or more of the nozzles  29  and replace them with new ones. The operator may re-use the bit in the same wellbore or another. 
         [0027]    While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.

Summary:
A diamond impregnated bit crown has blades formed thereon. Flow channels are formed between the blades, the flow channels having inner and outer ends and extending outward to a gage surface of the crown. At least some of the flow channels have an enlarged width area that has a greater width than a portion of the channel immediately outward from the enlarged width area. A nozzle is releasably secured in each of the enlarged width areas for discharging drilling fluid.