US 20060278442 A1
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.
1. A drill bit, comprising:
a drill bit body having a cutting end and a central flow passage;
plural blades extending out from the cutting end of the drill bit body;
cutters in each one of the plural blades;
nozzles in the drill bit body passing through the cutting end, and providing a flow path between the central flow passage and the cutting end;
plural junk slots in the drill bit body, each blade of the plural blades separating adjacent junk slots;
the junk slots alternating in pairs around the cutting end, each pair of junk slots including a junk slot with a higher resistance to fluid flow and a junk slot with a lower resistance to fluid flow, with an intervening blade between the pair of junk slots, such that, in operation, the junk slot of each pair of junk slots with higher resistance to fluid flow forces drilling fluid from the junk slot with higher resistance into the junk slot with lower resistance, the drilling fluid being forced across the intervening blade and between the cutters of the intervening blade.
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24. A drill bit, comprising:
a drill bit body having a cutting end, a central flow passage and a rotational axis;
plural blades extending out from the cutting end of the drill bit body, the blades being made of material having a first heat conductivity;
cutters in each one of the plural blades;
nozzles in the drill bit body passing through the cutting end, and providing a flow path between the central flow passage and the cutting end, the nozzles being directed to force drilling fluid between the blades;
heat conducting conduits in each blade, each heat conducting conduit terminating in heat conducting proximity to a cutter on the respective blade, the heat conducting conduits leading into the blade away from the cutters, and the heat conducting conduits being made of a material having a second heat conductivity, the second heat conductivity being higher than the first heat conductivity; and
plural junk slots in the drill bit body, each blade of the plural blades separating adjacent junk slots.
25. A method of making a drill bit, the method comprising the steps of:
separately machining a shank and lid for the shank;
forming slots in the lid for blades;
welding the lid to the shank; and
welding blades into the slots in the lid.
A challenge in underground drilling is to provide a drill bit with extended life, that cuts quickly through earth formations of various types and that avoids balling up of cuttings in the vicinity of the drill bit. The balling up of cuttings in the vicinity of the drill bit may cause the drill bit to cease cutting as the cutting elements no longer contact the earth formation.
Modern drilling bits typically are formed of a body, blades extending from the body, mostly forwardly but also extending somewhat radially outward of the body, and polycrystalline diamond cutters (PDCs) embedded in the cutting faces of the blades. Two main types of PDC drill bits on the market are the matrix body and steel body. Matrix body bits are one piece construction and are made in a mould as for example disclosed in U.S. Pat. No. 6,823,952. The material is a mixture of steel and tungsten carbide. Steel body bits are also one piece construction but are cut on a lathe and made from 4140 steel, 4145 steel or a similar material. The blades on PDC bits are typically set in a vertical plane, or may be canted forward slightly towards the cutting surface. Some bits have forward sweeping cutting elements, as for example disclosed in U.S. Pat. No. 5,443,565. The PDC cutting elements provide hard wearing surfaces that cut the formation. Junk slots between the blades provide pathways for the removal of cuttings away from the bit face into the annular space of the wellbore. Most PDC bits make the junk slot area as wide and as obstruction free as possible for the pathway to remove cuttings. To further assist in removal of cuttings, drill bits are provided with openings or nozzles in the forward end of the drill bit that direct fluid jets between the blade surfaces. The drilling fluid, which is also typically used in a mud motor to power the drill bit, passes through the inside of the drill bit, through the nozzles and the junk slots, and draws cuttings away from the drill bit towards the surface.
In a further problem with PDC type drill bits, cutter surfaces often fail as a result of high temperatures created from friction between the cutter and the rock it is cutting. When a PDC cutter reaches a critical temperature known as the thermal degradation temperature, the diamond surface will separate from the tungsten carbide substrate. The thermal degradation temperature ranges from 300° C. to 700° C. Heat is removed from the bit face and the cutters by the drilling fluid as it removes the cuttings from the surface of the drill bit. Heat is also transferred through the tungsten carbide cutter into the blade and bit body. Tungsten carbide is a much better conductor of heat than steel. Therefore the transfer of heat away from the cutters into the blades and bit body is not very efficient.
According to an aspect of this invention, there is provided a drill bit, and a method of manufacturing a drill bit, that uses the design of junk slots between the blades of the drill bit to enhance removal of cuttings from the drill bit. In a method of construction of a drill bit, according to an aspect of the invention, a drill bit is made of a shank, lid welded to the shank and blades welded in slots in the lid.
According to further aspects of the invention, junk slot impingement is used to increase cuttings removal through alternating junk slots. Provision of high angle nozzles in the forward end of the drill bit, which is facilitated by the method of construction, also assists in cuttings removal. According to a further aspect of the invention, a drill bit with PDC cutters is provided with a cooling feature to remove heat from the PDC cutters more efficiently. A high conductivity conduit leading from the cutters guides heat away from the cutters into the blade and hence into the bit body.
These and other aspects of the invention are set out in the claims, which are incorporated here by reference.
Preferred embodiments of the invention will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:
In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite article “a” before a claim feature does not exclude more than one of the feature being present.
As shown in
Referring again to
The higher resistance of the junk slots 38 may be caused by a variety of means. For example, the resistance may be caused by a restriction in the junk slot 38, such as an enlargement or extension 40 of a secondary blade 18 rearward. The extension 40 may sweep circumferentially under the intervening or primary blade 16 as shown in
As seen in
As the cutters 34 rotate around the central axis A, and cut into an earth formation, they leave gouges in the formation. Cutters 34 on succeeding blades deepen the gouge. It is conventional for cutters 34 on succeeding blades to overlap, and typically the gouges created by cutters of succeeding blades lie midway between the gouges of the preceding blades. In a preferred embodiment shown in
The cutters, which are cylindrical or conical objects having an axis of rotation, are oriented on the respective blades with their axes of rotation tangential to a circle centered on the central axis A of the drill bit. The cutters 34 are also preferably oriented on the respective blades with their cutting faces parallel to the forward faces of the blades, or may be canted outward from the center of rotation by a side rake of 4°-11°. Inner cutters may have a side rake of 6-11°, while cutters at the gauge may have a side rake of 6°. With the blades behind center and canted rearward, and the cutters on circle, vibration of the blades during use tends to sweep particles away from the cutting face and help prevent balling. It is preferred to keep the number of cutters 34 on the periphery or gauge of the drill bit to a minimum required to make a good gauge in the hole, with the cutters 34 concentrated on the forward cutting end 14A. For example, for given gauge there need only be a single cutter set at the outside edge of each of the primary blades to produce that gauge. There need not be multiple cutters 34 running axially rearward along the outer periphery of the blades.
Once the components are manufactured they are assembled. The lid 14 is welded to the shank 12 and the weld is ground smooth. The blades 16, 18 are set in the rectangular slots 26, 28 in the top of the lid and welded in place as shown in
With the design of the drill bit shown in
As shown in
The flow restrictor 40, which also acts as a stabilizer, creates pressure between the primary and secondary blades 16, 18 for more efficient cuttings removal. The flow restrictor actually forces cross flow across the blades 16 between the cutters 34. That is, the cuttings are forced between the spaces in the cutters 34. This actually works better than trying to get all the cuttings to leave the bit face via the junk slot area. The higher resistance may be achieved by other means such as putting the secondary blades closer to the primary blades. This will create a higher pressure in the narrow passage between the primary and secondary blades. More generally, the concept is to force the cuttings to crossflow between the cutters 34 on every second blade.
As shown in
Immaterial modifications may be made to the embodiments of the invention described here without departing from the invention.