U.S. patent application number 11/150907 was filed with the patent office on 2006-12-14 for drill bit.
Invention is credited to Henry L. Kristensen.
Application Number | 20060278442 11/150907 |
Document ID | / |
Family ID | 37523107 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060278442 |
Kind Code |
A1 |
Kristensen; Henry L. |
December 14, 2006 |
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.
Inventors: |
Kristensen; Henry L.;
(Edmonton, CA) |
Correspondence
Address: |
LAW OFFICE OF MARC D. MACHTINGER, LTD.
750 W. LAKE COOK ROAD
SUITE 350
BUFFALO GROVE
IL
60089
US
|
Family ID: |
37523107 |
Appl. No.: |
11/150907 |
Filed: |
June 13, 2005 |
Current U.S.
Class: |
175/393 ;
76/108.2 |
Current CPC
Class: |
E21B 10/42 20130101;
E21B 10/46 20130101; E21B 10/62 20130101; E21B 10/602 20130101 |
Class at
Publication: |
175/393 ;
076/108.2 |
International
Class: |
E21B 10/60 20060101
E21B010/60 |
Claims
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.
2. The drill bit of claim 1 in which the blades alternate between
primary blades and secondary blades, and the primary blades are the
intervening blades.
3. The drill bit of claim 2 in which each junk slot with higher
resistance incorporates a restriction in the junk slot.
4. The drill bit of claim 3 in which the restrictions comprise an
extension of a blade.
5. The drill bit of claim 4 in which each restriction comprises an
extension of a secondary blade.
6. The drill bit of claim 5 in which each restriction of a pair of
junk slots sweeps circumferentially under the intervening
blade.
7. The drill bit of claim 1 in which each blade is canted
backward.
8. The drill bit of claim 1 in which the drill bit body has a
rotational axis, and the nozzles are oriented at an angle greater
than 15.degree. to the rotational axis and directed to force
drilling fluid between the blades.
9. The drill bit of claim 8 in which the drill bit body includes a
shank, and the cutting end of the drill bit body is formed of a lid
welded to the shank.
10. The drill bit of claim 9 in which the blades are welded into
slots in the lid.
11-23. (canceled)
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.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.degree. C. to 700.degree. 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.
SUMMARY OF THE INVENTION
[0004] 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.
[0005] 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.
[0006] These and other aspects of the invention are set out in the
claims, which are incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES
[0007] 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:
[0008] FIG. 1 is perspective view of a drill bit according to the
invention;
[0009] FIG. 2 is a view of a shank for use with the drill bit of
FIG. 1;
[0010] FIG. 3 is a perspective view of a cutting end of a lid for
use with the drill bit of FIG. 1;
[0011] FIG. 4 is a perspective view of the opposed end to the
cutting end of the lid of FIG. 3;
[0012] FIGS. 5A-5D illustrate method of making a blade for use with
the drill bit of FIG. 1;
[0013] FIG. 6 shows a method of assembling blades into the drill
bit of FIG. 1;
[0014] FIG. 7 is a cross-section through a blade showing a cooling
feature according to an aspect of the invention;
[0015] FIG. 8 is a cross-section through the bit showing a nozzle
aspect of the invention;
[0016] FIG. 9 illustrates offset cutters on succeeding blades;
and
[0017] FIG. 10 is a section through a blade and cutter showing a
soft metal insert behind the cutter.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] 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.
[0019] Referring to FIG. 1, there is shown a drill bit 10 formed of
a threaded shank 12, lid 14 and blades 16, 18 extending out from
the cutting end of the drill bit 10. The shank 12 is threaded in
conventional fashion for threading onto a downhole end of a drill
string. There should be at least four and preferably eight blades
16, 18. The blades 16, 18 alternate between primary blades 16 and
secondary blades 18. The drill bit 10 is intended to be rotated
counterclockwise in use when taking a view of the cutting, bladed,
end or face of the drill bit, which would be clockwise looking in
the downhole direction in use. The operational direction of
rotation defines a forward and rearward direction. The blades 16,
18 are preferably canted rearward at an angle of about 5.degree. to
10.degree. to the vertical (the central axis A of the drill bit 10
is vertical in a desired operating position). The shank 12, lid 14
and blades 16, 18 are manufactured separately from steel using a
machine lathe type of construction and then welded into one unit,
for example using electric arc welding. Not seen in FIG. 1, but
shown in FIG. 2, is a cylindrical central passage 20 in the shank
12 that widens towards the lid 14 and supplies drilling fluid to
the cutting end of the drill bit 10. The shank 12 is made from
circular steel bar stock on a machine lathe. The passage 20 is
drilled through the shank 12. The shank 12 is a cylindrical body
having a central axis indicated by the arrow A about which the
drill bit 10 rotates.
[0020] Referring to FIGS. 3 and 4, the lid 14 is shown separately
from the shank 12 and blades 16, 18. The lid 14 has openings 22
passing from the shank end 14A to the cutting end 14B of the lid
14. Nozzles 24 are inserted in the openings 22. The nozzles 24 are
hardened tubes, made for example of tungsten carbide, that protect
the steel of the lid 14 from excessive wear from drilling fluid.
Typically, there are as many openings 22 as there are blades 16, 18
and the exit of each opening in the cutting end 14B is located at
an inward end of a corresponding blade 16, 18, adjacent the forward
face of the blade 16, 18. The openings 22 are oriented at an angle
to the central axis A preferably greater than 15.degree., and for
openings closer to the central axis of the drill bit, greater than
30.degree., and directed so that fluid exiting the nozzles 24 flows
between adjacent blades 16, 18. The greater the angle of an opening
22, the more the fluid is directed between the corresponding
blades. The nearer the opening 22 is to the central axis A of the
drill bit, the greater the angle of the opening to the central
axis. The openings 22 may be drilled through the lid 14 after it
has been machined into the general shape shown in FIGS. 3 and 4.
Use of a lid 14 facilitates a high angle of the nozzles 24 as
opposed to a one piece design, which makes high angle nozzles
difficult to achieve. The nozzles 24 provide a flow path for
drilling fluid pumped through the central passage 20 of the shank
12. The nozzles 24 may be provided for example in different sizes,
such as 10 mm for the primary blades 16 and 7.5 mm for the
secondary blades 18.
[0021] As shown in FIGS. 1, 3 and 6, rectangular slots 26, 28 are
provided in the cutting end 14B of the lid 14 for the blades 16,
18. The blades 16, 18 are secured in the slots for example by
welding. The blades 16, 18 and the corresponding slots 26, 28 may
have a front edge 27 that is parallel to but offset rearward from a
radius extending outward from the central axis A. The amount of
offset may be in the order of 2-4 mm. The blades 16, 18 may be
provided with laminated steel backings welded to the lid 14 to
strengthen the blades 16, 18 and dampen vibrations of the blades
16, 18. The underside 30 of the lid 14 (FIG. 4) in the area around
the nozzles 24 is coated with a tungsten carbide material to
protect the area from erosion as the drilling fluid is pumped
through the nozzles 24. The lid 14 is also made from circular steel
bar stock on a machine lathe. The under side of the lid 14 is
milled to a diameter suitable for the intended use and the openings
22 are drilled through the lid for the nozzle inserts 24.
[0022] Referring to FIGS. 5A-5D, a blade 16 (or 18) is made from
steel flat bar stock of a suitable width, thickness and length for
the intended application. Multiple holes 32, depending on the
required number of cutters, are drilled in the blade 16, and the
blade 16 is then cut along the line B in FIG. 5C to yield cutter
holes. Polycrystalline diamond cutters 34 are inserted in the holes
32 and soldered in place. The blade 16 is coated with a tungsten
carbide hard metal to protect the blade from erosion. The cutters
34 are shown in FIGS. 1, 5A-5C and 6 as fully penetrating the
blades, but in practice there will be a small amount of steel left
behind the cutters 34, as shown in FIG. 5D.
[0023] Referring again to FIG. 1, junk slots 36, 38 are formed by
each pair of adjacent blades. Each blade 16, 18 separates adjacent
junk slots 36, 38. The junk slots alternate in pairs 36, 38 around
the cutting end 14B. Each pair of junk slots 36, 38 includes an
impeded junk slot 38 with a higher resistance to fluid flow and an
unimpeded junk slot 36 with a lower resistance to fluid flow, with
an intervening blade 16 between the pair of junk slots 36, 38. In
operation, the junk slot 38 of each pair of junk slots with higher
resistance to fluid flow forces drilling fluid from the junk slot
38 with higher resistance into the junk slot 36 with lower
resistance. Drilling fluid exiting the nozzles 24 is forced by the
resistance of the junk slots 38 across the intervening blade 16 and
between the cutters 34 of the intervening blade 16. The drilling
fluid passes across the intervening blade through openings created
by previous cutters, which may be ensured by radially offsetting
and overlapping the cutters 34 on succeeding blades. The amount of
offset and overlap may be varied. Increasing overlap creates a more
aggressive cutting action, at the expense of decreasing the size of
the flow path between the cutters. Thus, for cutters of radius R,
the cutters on one blade may be spaced by R/2 and the centers of
cutters on succeeding blades offset by 3R/4. When the blades 16, 18
alternate between primary blades 16 and secondary blades 18, the
primary blades 16 are the intervening blades.
[0024] 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 FIG. 1. The extension 40 may be machined from a steel
flat bar stock and welded to the outer periphery of the shank 12
and lid 14. The extension 40 is shaped to be continuous with the
blade 18. The radially outward surface of the extensions 40 may be
fluted in conventional fashion for a stabilizer.
[0025] As seen in FIG. 1, the blades 16, 18 extend axially forward
of the cutting end 14B to engage an earth formation during
drilling. The blades 16, 18 also extend radially outward from the
cutting end 14B and extend axially rearward along the outer
periphery 42 of the drill bit body to form stabilizers. The blades
16, 18 include blades that extend axially rearward for different
distances, and in the preferred embodiment alternate between longer
blades 18 and shorter blades 16. As seen in FIG. 3, the blades 16,
18 and the corresponding slots 26, 28 are also oriented on the
cutting end 14B of the drill bit body such that a linear extension
of the blade passes behind the central axis in the direction of
rotation in operation. The linear extension may be part of the
blade itself or an extrapolation of a blade that terminates
inwardly of the central axis. Such off-center orientation of the
blades, where the blades do not all point towards the same center,
assists in stabilizing the drill bit.
[0026] 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 FIG. 9, the cutters 34 in succeeding blades
preferably differentially overlap cutters in preceding blades in
the direction of rotation such that a cutter on a succeeding blade
overlaps more of one, outer, cutter, on a preceding blade than it
overlaps an adjacent, inner, cutter on a preceding cutter. The
overlap of the outer cutter should be more than 25% but less than
100%, for example 60-75% of the outer cutter. In FIG. 9, cutters
34A are in a leading or preceding blade in the direction of
rotation. Cutters 34B are in the following or succeeding blade. The
cross-hatched areas 37 indicates the areas being cut by the
following blades. The hatched area 35 in the path of the cutters
34A shows where cuttings from the drilling activity of the
following blades may slide sideways away from the cutters and be
cleared from the cutting area. With the overlap system described
here, the cutters of a preceding blade cut a slot in the formation
through which fluids can pass during cutting by the cutters of a
succeeding blade.
[0027] 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.degree.-11.degree..
Inner cutters may have a side rake of 6-11.degree., while cutters
at the gauge may have a side rake of 6.degree.. 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.
[0028] 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 FIG. 6.
[0029] With the design of the drill bit shown in FIGS. 1-5D,
greater angle can be achieved on the nozzle orientation because the
nozzle holes 22 are drilled from the underside of the lid 14 before
it is welded to the shank 12. The nozzle orientation is important
to the cleaning characteristics of PDC bits. If the nozzles 24 can
be oriented at the correct angle, cleaning is enhanced, thus the
bit will drill faster and cutter wear life is extended. In
addition, with the method of manufacture shown in FIG. 6, the
blades 16, 18 can be easily replaced, unlike with a matrix body or
one piece steel body bit. When the blade of a one piece steel or
matrix body bit is damaged, the bit may be un-repairable. To remove
one of the blades 16, 18, the weld is cut using a grinder, the
blade is heated up and pops out or is easily pulled out. Use of a
lid 14 allows more blades to be used.
[0030] As shown in FIG. 1, the blades 16, 18 are canted back away
from the cutting structure. This improves cleaning and cuttings
removal. The faster cuttings can be moved away from the blades the
higher the rate of penetration (ROP) will be. This prevents bit
balling. Moving the cuttings away from the blades quickly also
prevents regrinding of the cuttings, which can increase the
temperature of the cutters. Increased temperature can cause
premature cutter failure.
[0031] 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.
[0032] As shown in FIG. 5D and FIG. 7, during blade construction
small diameter holes (conduits) 46 are drilled from the base of the
blades 16, 18 and terminate in the tops of the blades 16, 18 below
the cutters 34 but in heat conducting proximity to the cutters 34,
for example 1-4 millimeters away. Heat conducting proximity means
sufficiently close to provide a cooling effect to the cutters 34.
The hollow conduits 46 are then filled with a material with high
heat conductivity, at least higher than the heat conductivity of
the blade material, such as copper. This high conductivity conduit
can remove heat quickly form the PDC cutters 34 and dissipate the
heat into the surrounding blade. The ends of the heat conducting
conduits 46 near the cutters 34 may have small holes, not filled
with the high heat conductivity material, drilled through the blade
from the cutter to the metal in the conduit. FIG. 10 also shows a
backing part 48 of the blade 16 behind the cutter 34, and the
hardened cutting surface 50 of the cutter. A softer metal such as
brass 52 may be placed between the cutter 34 and the backing part
48 to help reduce cutter vibration, as shown in FIG. 10.
[0033] Immaterial modifications may be made to the embodiments of
the invention described here without departing from the
invention.
* * * * *