Drill bit

Abstract

A drill bit is made from a shank, lid and blades. Junk slots with higher resistance to flow are provided to force drilling fluid between cutters on adjacent blades to improve cleaning. Blades are canted back, and openings at a high angle are provided to further enhance cleaning. The use of a lid facilitates high angle openings. The cutters may be made of sintered powder metal, and may include polycrystalline inserts. The blades may include a preferential conductive cooling material. The drill bit may include an enlarged hollow chamber and a relatively thin and long peripheral drill bit wall.

1 . A drill bit having a central axis of rotation, and a direction of rotation, said drill bit comprising: 
 a body having a driven end for connection to a drive train operable to rotate said bit, and a cutting end axially distant from said driven end;    said cutting end having an array of cutting members mounted thereto;    said array including members defining at least first and second junk slots therebetween;    said first junk slot being at least part of a first flow path for cutting fluid;    said second junk slot being at least part of a second flow path for cutting fluid;    a first of said cutting members of said array defining a partition between said first and second flow paths;    each of said first and second paths for cutting fluid having an entrance at which to introduce cutting fluid, and an exit at which to discharge cutting fluid; and    at least a portion of said second flow path being constricted as compared to said first flow path.    
   
   
       2 . A drill bit as claimed in  claim 1  wherein said second flow path includes a constriction having a hydraulic diameter that is less than ¾ of a hydraulic diameter of a corresponding portion of said first flow path.  
   
   
       3 . A drill bit as claimed in  claim 1  wherein said second flow path includes a first, predominantly radial portion, and a second, predominantly axial portion, and said portion of said flow path that is constricted forms at least part of said predominantly axial portion of said second flow path.  
   
   
       4 . A drill bit as claimed in  claim 1  wherein: 
 said first flow path has a first, predominantly radial portion having a first resistance to flow R 1 , and said a second, predominantly axial portion having a second resistance to flow R 2 ;    said second flow path has a first, predominantly radial portion having a third resistance to flow R 3 , and said a second, predominantly axial portion having a fourth resistance to flow R 4 ; and    R 1 /R 2  is greater than R 3 /R 4 .    
   
   
       5 . A drill bit as claimed in  claim 1  wherein said first of said cutting members of said array defines a leaky partition between said first and second flow paths.  
   
   
       6 . A drill bit as claimed in  claim 1  wherein said first of said cutting members extends predominantly radially and has a toothed profile.  
   
   
       7 . A drill bit as claimed in  claim 1  wherein said first of said cutting members extends predominantly radially and has a first toothed profile, a second of said cutting members extends predominantly radially, and has a second tooth profile, at least one of said first and second toothed profiles including at least one axially protruding asperity radially offset from any asperity of the other of said toothed profiles.  
   
   
       8 . A drill bit as claimed in  claim 7  wherein said first and second tooth profiles are radially phase shifted.  
   
   
       9 . A drill bit as claimed in  claim 1  where said array of cutting members includes at least one member formed of sintered powder metal.  
   
   
       10 . The drill bit of  claim 9  wherein said sintered powder metal cutting member included a polycrystalline diamond insert.  
   
   
       11 . The drill bit of  claim 1  wherein said second junk slot has a flow restriction mounted therewithin.  
   
   
       12 . The drill bit of  claim 11  in which the restrictions include a blade extension.  
   
   
       13 . The drill bit of  claim 11  in which each restriction comprises an extension of a secondary blade.  
   
   
       14 . The drill bit of  claim 11  in which each restriction of a pair of junk slots sweeps circumferentially under the intervening blade.  
   
   
       15 . A drill bit as claimed in  claim 1  wherein said drill bit has a hollow head through which cutting fluid may be supplied.  
   
   
       16 . The drill bit of  claim 15  wherein said hollow end of said drill bit has a lid.  
   
   
       17 . The drill bit of  claim 16  wherein said lid has porting to permit the transport of cutting fluid therethrough.  
   
   
       18 . The drill bit of  claim 17  wherein said porting includes ports angled in an orientation having a radial component of direction.  
   
   
       19 . The drill bit of  claim 1  in which the drill bit body has a rotational axis, and nozzles oriented at an angle greater than 15° to the rotational axis and directed to feed drilling fluid between the members of the array.  
   
   
       20 . The drill bit of  claim 1  wherein the drill bit body includes a cylindrical sidewall capped by an end lid welded thereto, said end lid being multiply ported whereby said end lid defined a drill fluid delivery manifold.  
   
   
       21 . A drill bit for drilling well bores in geological formations, said drill bit comprising a drill bit body, the drill bit body having a first end and a second end, the first end of the drill bit body having a cutting face and cutting members mounted thereto, the second end facing away from the first end and providing a member to which a shank for engagement to a drill string can be mounted, the drill bit body having a peripheral wall extending between the first and second ends, the peripheral wall having a thickness of less than 1 inch, and a chamber defined within said bit body, said chamber having a diameter of at least 3 inches, the chamber having an inlet of a diameter less than 3 inches through which drilling mud may flow into the bit body, and the bit body having ports by which drilling fluid may exit the bit body.  
   
   
       22 . The drill bit of  claim 21  wherein said chamber is a resonating chamber.  
   
   
       23 . The drill bit of  claim 21  wherein said bit body has a wall thickness of less than 15% of the diameter of the chamber.  
   
   
       24 . The drill bit of  claim 21  wherein said wall thickness is up to ½″.  
   
   
       25 . The drill bit of  claim 24  wherein said wall thickness is at least 5/16″.  
   
   
       26 . The drill bit of  claim 21  wherein said chamber has an internal cross sectional area A f , said wall has a cross sectional area Aw, and a ratio of Af:Aw lies in the range of greater than 4:1  
   
   
       27 . The drill bit of  claim 21  wherein said chamber has a length, that length being in the range of at least ⅔ as great as the chamber diameter.  
   
   
       28 . The drill bit of  claim 21  wherein said chamber has a length, that length being in the range of ¾ to 2 times the diameter of the chamber.  
   
   
       29 . The drill bit of  claim 21  wherein said drill bit has vane members extending predominantly axially externally of said peripheral wall, and at least one of said vane members is relieved to accommodate radial flexing of said peripheral wall.  
   
   
       30 . The combination of the drill bit of  claim 21  and the shank, said shank being mounted to the drill bit body, the combination having at least one of the following features: 
 (a) the shank having a re-entrant nose; and    (b) said ports have nozzles mounted therein, and at least one of said nozzles has a re-entrant end extending into said chamber.    
   
   
       31 . A drill string combination comprising: 
 a pulsating source of drilling fluid;    drill pipe sections for connection together and for connection to said source of drilling fluid;    drill collars for connection to said drill pipe sections;    a drill bit for mounting below said drill collars;    said drill bit having a first end for cutting the well bore, and a second end having a shank for connecting the drill bit to the drill string below the drill collars;    a tensioning device for holding back a portion of the weight of the drill collars;    said drill pipe section having an internal diameter;    said drill bit having a chamber therein between said first and second ends, said chamber having a diameter greater than said drill pipe section;    said chamber being surrounded by a peripheral wall, said peripheral wall having a wall thickness of less than 1″, and said chamber having a length at least ⅔ as great as the diameter of the chamber; and    said chamber having an inlet through which drilling mud can enter said chamber, and an outlet through which drilling mud may be directed to remove cuttings.    
   
   
       32 . The drill string combination of  claim 31  wherein said combination includes between 30,000 lbs and 50,000 lbs of drill collars.  
   
   
       33 . The drill string combination of  claim 31  wherein said drill bit includes at least one of the following features: 
 (a) said wall thickness is in the range of ¼ to ½ inches;    (b) said wall thickness is in the range of 5/16″. to 7/16″;    (c) said wall thickness is in the range of 5% to 15% of said diameter;    (d) said wall thickness is in the range of 6% to 10% of said diameter    (e) said wall has a cross sectional area A w , and said chamber has a cross-sectional area A f , and A w  lies in the range of less than 25% of A f ;    (f) said chamber has a length, and said thickness is less than ⅕ of said length;    (g) said chamber has a length and said thickness is less than 1/10 of said length;    (h) said chamber has a length, and said length is at least ⅔ of said diameter of said chamber; and    (i) said chamber has a length, and said length lies in the range of ¾ to 2 times the diameter of said chamber.    
   
   
       34 . The combination of  claim 33  wherein said drill bit includes items (b), (d), (g) and (i).  
   
   
       35 . A well boring process employing the drill string combination of  claim 31 , said process including providing a pulsating flow of drilling fluid to said bit while said bit is boring a well.  
   
   
       36 . A well boring process employing the drill string combination of  claim 31 , said process including inducing torsional stress in said bit body and at the same time imposing a time varying stress field in said body that in addition to said torsional stress includes at least one of 
 (a) a fluctuating hoop stress in said peripheral wall;    (b) a fluctuating axial stress in said peripheral wall; and    (c) a fluctuating bending stress in said peripheral wall.    
   
   
       37 . The process of  claim 36  wherein said process includes inducing a reversing axial stress in said peripheral wall.  
   
   
       38 . The process of  claim 36  wherein the chamber has a face area, A f , the drill string includes a weight of drill collars W and the drill string is partially tensioned to impose a hold down force on the drill bit, the hold down force being a portion of W, said process includes pumping the drilling fluid at a pressure P, and the force obtained by multiplying the pressure P by Af is greater than the hold down force.  
   
   
       39 . The process of  claim 36  wherein said process includes providing pulsatingjets of drilling fluid to urge cuttings away from said drill bit.  
   
   
       40 . The process of  claim 36  wherein the process includes at least one of the following: 
 (a) operating pumping equipment to supply drilling fluid at a pressure in the range of 500 to 1500 psi;    (b) operating pumping equipment to produce pulsations in the range of 150 to 300 pulses per minute in the drilling fluid; and    (c) operating rotating equipment to cause said bit to rotate at a rotational speed in the range of 60 to 150 r.p.m.