BACKGROUND
Technical Field
[0001] The present invention relates generally to applying torque and thrust to a shaft,
and more specifically to drilling a hole having a varying diameter.
Background
[0002] Various arts require a hole having different diameters at different depths. One portion
of a hole may have a diameter larger than that of another portion. Often (e.g., when
the lengths of the respective portions are not known) drilling such a hole requires
the use of multiple drill bits and sequential steps. Typically, a first portion is
drilled with a first bit having a first diameter, and then the next portion is drilled
with a second bit having the second diameter. Such a multi-step process may add cost,
particularly when the boundary between the two portions is very deep relative to the
diameter of the hole (e.g., as in an oil or gas well in the earth). Maintaining concentricity
and tolerances using long, narrow tools designed for such holes may be challenging.
[0003] In some applications, a hole may have a first depth (e.g., through soft soil) having
a width that is wide enough to accept a casing (e.g. to hinder soft soil from entering
into the drill hole). A deeper (and possibly smaller diameter) hole may be drilled
through bedrock below the soil. Maintaining concentricity of such a sequentially drilled
hole having coaxial and different diameters may be challenging and time consuming.
[0004] From
WO9700371 and
WO9618798 there are known drilling methods according to the latter principle, wherein by means
of reverse rotation an inner drill bit may be disengaged from the drill assembly to
continue drilling of a hole with smaller diameter. However, these methods make use
of down the hole hammers, which may be undesired, as such. Furthermore, it implies
a cumbersome retraction of the drill string to regain the hammer.
SUMMARY OF THE INVENTION
[0005] A drill bit assembly may be configured for use with a drive tube and optionally a
casing. The drill bit assembly may include an inner bit and an outer bit. The inner
bit may be sized to be bonded to the drive tube, which applies torque and thrust to
the inner bit, and thrust applied from a top hammer arrangement. The inner and outer
bits may be removably coupled with a drill coupling. The drill coupling may be configured
to transmit torque and thrust from the inner bit to the outer bit, to enable drilling
with both inner and outer bits. The drill coupling may be configured to disengage
the inner bit from the outer bit, such that torque and thrust may be applied to the
inner bit alone, thereby allowing subsequent continued drilling without the need to
engage new equipment or to restart the drilling operation from the ground level.
[0006] The outer bit may be coupled to a casing ring. The outer bit and casing ring may
be coupled using a thrust ring that provides for the transmission of thrust between
the outer bit and the casing ring. In some configurations, the thrust ring is configured
to allow rotation of the outer bit while the casing ring does not rotate. The casing
ring may be bonded to a casing, and drilling using the inner and outer bits may include
rotating the bits while the casing ring and casing do not rotate. In some implementations
the casing ring may rotate.
[0007] A method may comprise drilling a hole having different diameters at different depths.
A first portion may be drilled using both an inner and outer bit of a drill bit assembly.
The bits may be pulled in reverse a small amount, after which a frictional force on
the casing, casing ring, and/or outer bit may hold the outer bit as the inner bit
is counter rotated. The inner bit may then be disengaged from the outer bit by counter
rotating it a small amount, then the inner bit may be pushed forward to clear the
outer bit. Subsequent drilling may use only the inner bit, yielding a deeper portion
having a smaller diameter than the first portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008]
FIG. 1 illustrates a cylindrical hole having two different diameters at different
depths, according to some embodiments.
FIG. 2 illustrates exemplary components of a drill bit assembly, according to some
embodiments.
FIG. 3 illustrates a setup for operating a drill bit assembly, according to some embodiments.
FIGS. 4A and 4B illustrate a portion of an exemplary drill coupling, according to
some embodiments.
FIGS. 5A and 5B illustrate a portion of a drill coupling, according to some embodiments.
FIGS. 6A and 6B are cross section illustrations of engaged and disengaged configurations,
according to some embodiments.
FIGS. 7A and 7B illustrate a plan view of a coupling in engaged and disengaged configurations
(respectively), according to some embodiments.
FIGS. 8A and 8B show a schematic view and a description respectively for drilling
a hole having multiple diameters, according to some embodiments.
FIG 9 illustrates a perspective illustration of an exemplary drill bit assembly, seen
from above, according to some embodiments, expanded for clarity
FIG. 10 illustrates a view from below of a drill bit assembly, according to fig 9,
expanded for clarity, and,
FIGS 11A-C show the latter embodiment assembled, in perspective from above, from below
and in cross section respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Various aspects provide for a drill bit assembly, which may include at least two
drill bits. An inner bit may be coaxial with and removably coupled to an outer bit
having a larger diameter than that of the inner bit. The outer bit may be coaxial
with and coupled to a casing ring. The casing ring may attach the drill bit assembly
to a casing. A drive tube (hollow or solid) may apply angular and thrust forces to
the inner bit, which may, in an engaged configuration, apply similar forces to the
outer bit. The outer bit may apply thrust forces to the casing ring, and in some embodiments,
the outer bit does not apply substantial torque to (e.g., enough torque to cause rotation
of) the casing ring.
[0010] In a disengaged configuration, the inner bit may rotate and/or move forward or backward
independently of the outer bit. Various apparatus and methods may be used to drill
a hole having two or more different diameters. In some aspects, the inner and outer
bits are first driven together, to drill a hole having the diameter of the outer bit.
The inner bit may then be disengaged from the outer bit, and be driven by the drive
tube to drill a second, deeper portion, having a smaller diameter than that portion
drilled by the outer bit.
[0011] FIG. 1 illustrates a cylindrical hole having two different diameters at different
depths, according to some embodiments. A cylindrical hole 100 may have an upper portion
110 having a first diameter 112 that descends to a first depth 114, and a lower portion
120 having a second diameter 122 (
e.g., 1-90%, including 5-80%, including 10-80%, including 20-70% smaller than first diameter
112) that descends a second depth 124. Hole 100 may be defined by a central axis 130,
and upper portion 110 and lower portion 120 may be coaxial. "Coaxial" may be a relatively
local term (e.g., as in a hole that gradually curves over a distance through the earth).
[0012] Some holes incorporate a casing (e.g., to prevent collapse when the hole is drilled
through soft earth). In FIG. 1, a first casing 116 encases upper portion 110. In some
cases, a second casing 126 may encase lower portion 120. Some holes may include only
one casing; some holes may include multiple casings. Some holes may not have a casing.
[0013] FIG. 2 illustrates exemplary components of a drill bit assembly, according to some
embodiments. Drill bit assembly 200 may include an inner bit 210, coupled to an outer
bit 220, which is coupled to a casing ring 230.
[0014] Drill bit assembly 200 may be designed to work with various other drilling apparatus,
such as casings, drive shafts, impact hammers, collars, drill rigs, and the like.
In some embodiments, inner bit 210 may have a diameter (e.g., inner diameter 212)
sized to attach or bond to a hollow drive tube 214. In an exemplary implementation,
a drive tube 214 is threaded onto inner bit 210 at a drilling site, and then subsequent
drive tubes are sequentially connected, by use of connectors 214A, as the hole is
drilled further and further down with the drill bit 210. In some embodiments, a drive
tube may also be used as a casing. Casing ring 230 may have a diameter (e.g., an inner
diameter 232) sized to bond or attach to a casing 234. In an exemplary implementation,
casing 234 is welded to casing ring 234 at a drilling site, and additional casings
may be added sequentially as drilling proceeds. Outer bit 220 may have an outer diameter
(not shown) that is substantially the same as that (e.g., within 5%, 1 %, or even
0.1%) of casing ring 230. In some cases, outer bit 220 may have a slightly larger
diameter (e.g., 0.1%, 0.5%, 1 %, or even 5% larger) than casing ring 230, which may
provide for a "wide open" hole through which casing ring 230 passes. Outer bit 220
may be slightly smaller (e.g., 0.1%, 0.5%, 1 %, or even 5% smaller) than casing ring
230, which may provide for a "tightly fitting" hole for casing ring 230 (e.g., in
soft or sandy earth). Outer bit 220 may include a contact height 222, that combines
with the outer diameter of outer bit 220 to define a circumferential contact area
between outer bit 220 and a material through which outer bit 220 drills.
[0015] FIG. 3 illustrates a setup for operating a drill bit assembly, according to some
embodiments. Drilling may be described as a combination of thrust force 310 and torque
320 applied to a drill bit. A forward thrust force applied to inner bit 210 via drive
tube 214 may push inner bit 210 in a "downward" direction, and a reverse thrust force
may pull inner bit 210 in an "upward" direction. A torque may spin drive tube 214
and inner bit 210 about axis 130 (e.g., clockwise or counterclockwise, per the design
of the drill bit assembly). The thrust 310 and torque is preferably applied by means
of a top hammer assembly 99 (known per se, see FIG. 8A).
[0016] Inner bit 210 and outer bit 220 may be removably coupled. In an engaged configuration
(not shown), a torque applied to inner bit 210 may be transmitted to outer bit 220,
and a thrust force applied to inner bit 210 may be transmitted to outer bit 220. When
disengaged from outer bit 220, inner bit 210 may rotate, move forward, or move in
reverse independently of outer bit 220.
[0017] Outer bit 220 and casing ring 230 may be coupled in a manner that transmits certain
forces while minimizing the transmission of other forces. Outer bit 220 and casing
ring 230 may be coupled by a thrust bearing (e.g., a journal bearing), such that outer
bit 220 does not apply torque (or only applies a small amount of torque) to casing
ring 230. In an exemplary embodiment, a thrust force applied by inner bit 210 to outer
bit 220 is transmitted to casing ring 230 by outer bit 220, which may result in outer
bit 220 "pulling" a casing 234 down the hole (and/or outer bit 220 may be "pushed"
downward by an apparatus, e.g. top hammer assembly, pushing on casing 234 at the surface).
A torque may be minimally transmitted between outer bit 220 and casing ring 230, such
that friction between the casing 234 and the ground does not impede the rotation of
the drill bits. In such cases, outer bit 220 may rotate while casing ring 230 (and
casing 234, if bonded to casing ring 230) does not rotate, and casing ring 230 and
outer bit 220 move together in forward and reverse. A lubricant (e.g., graphite, MoS
2) may reduce friction (e.g., in a thrust bearing) and may ease disengagement of an
inner bit from an outer bit. In some cases, outer bit 220 may be bonded to casing
ring 230.
[0018] FIGS. 4A and 4B illustrate a portion of an exemplary drill coupling, according to
some embodiments. A drill coupling may removably couple an inner bit to an outer bit.
In exemplary FIGS. 4A and 4B, drill coupling 400 may removably couple inner bit 210
to outer bit 220 via one or more male teeth on one bit (in this case, the outer bit)
that engage with corresponding female teeth on the other bit (in this case, the inner
bit). FIG. 4A illustrates drill coupling 400 in a disengaged configuration, in which
inner bit 210 may move vertically independent of outer bit 220. FIG. 4B illustrates
drill coupling 400 in an engaged configuration, in which thrust and a torque (in this
case, counterclockwise as viewed from above) may be transmitted from inner bit 210
to outer bit 220. When inner bit 210 and outer bit 220 are engaged, drilling forces
may be transmitted from a drive tube to outer bit 210 via inner bit 210, causing both
inner bit 210 and outer bit 220 to rotate and drill downward. In the configuration
shown in FIG. 4B, forward, reverse, and counterclockwise rotation forces may be transmitted
from inner bit 210 to outer bit 220.
[0019] A drill coupling may include one or more male teeth 410 and a corresponding number
of female teeth 422. A drill coupling may include 1, 2, 3, 4, 6, 8, 10, or even more
pairs of teeth. In some applications, a drill coupling includes at least 3 pairs of
teeth and at most 12, including 8, and preferably 6 pairs of teeth. Male teeth 410
may be sized to fit within corresponding cavities 420 in female teeth 422. Male teeth
410 and female teeth 422 may be disposed periodically around the facing circumferences
of outer bit 220 and inner bit 210. In some cases, a first pair of male and female
teeth is sized differently than another pair (e.g., the other pairs) to control of
rotational alignment between the inner and outer bits. In some cases, the pairs of
male and female teeth are interchangeable.
[0020] An inner bit may include male teeth that engage with the corresponding female teeth
of an outer bit. An inner bit may include female teeth that engage with the corresponding
male teeth of an outer bit. In exemplary drill coupling 400, male teeth 410 extend
radially inward from an inside circumference of outer bit 220, and inner bit 210 includes
corresponding female teeth 422 extending radially outward. Each cavity 420 and its
corresponding male tooth 410 is sized such that the male tooth 410 may move into or
out of its corresponding cavity 420 as inner bit 210 rotates with respect to outer
bit 220. A tooth need not be explicitly defined. For example, a male tooth may move
into a cavity within a corresponding bit in which the cavity is not disposed in a
female "tooth"
per se.
[0021] Male tooth 410 may have a male tooth width 412 (e.g., an angular width) that is smaller
than a gap 460 between adjacent female teeth 422 (of which only one is shown in FIGS.
4A and 4B). Similarly, a female tooth 422 may have a female tooth width 424 that is
smaller than the gap between two adjacent male teeth 410 (only one of which is shown).
As a result, inner bit 210 may be rotated with respect to outer bit 220 (or
vice versa) to a point at which male teeth 410 exit the cavities 420 of female teeth 422, allowing
inner bit 210 to move forward or reverse (e.g., up or down) with respect to outer
bit 220 (e.g., as in FIG. 4A). Subsequently, inner bit 410 may be moved forward or
reverse, to a distance at which male teeth 410 and female teeth 422 do not engage
with each other, and inner bit 210 may rotate independently of outer bit 220.
[0022] Male teeth 410 may engage with female teeth 422 when the male teeth are positioned
within their corresponding cavities. FIG. 4B illustrates drill coupling 400 configured
to engage inner bit 210 with outer bit 220, and to transmit thrust and torque between
inner bit 210 and outer bit 220. Torque may be transmitted from inner bit 210 to outer
bit 220 via an application of angular force from torque face 450 (of cavity 420 in
female tooth 422, FIG. 4A) to corresponding torque face 452 of male tooth 410 (FIG.
4A). As shown in FIG. 4B, an overlap between the matching torque faces may define
a torque area 454, through which inner bit 210 (when rotated counterclockwise as viewed
from above) may apply a torque to outer bit 220.
[0023] As shown in FIG. 4A, cavity 420 in female tooth 422 includes a forward face 430,
which transmits a forward thrust force to a corresponding forward face 432 of tooth
410 when tooth 410 is within cavity 420 (e.g., as in FIG. 4B). An overlap between
these faces may define a thrust area 434 (FIG. 4B), which describes a surface through
which (in this case, forward) thrust is transmitted from inner bit 210 to outer bit
220. A reverse face 440 in cavity 420 (FIG. 4A) may transmit a reverse thrust from
inner bit 210 to outer bit 220 via a corresponding reverse face 442 on tooth 410,
and an overlap between these faces may define a thrust area (not shown) associated
with reverse thrust.
[0024] In some embodiments, forces may be transmitted between inner bit 210 and outer bit
220 (via engaged teeth) using substantially (e.g., greater than 95%, 99%, or even
99.9%) normal forces across matching faces, without appreciable shear forces across
these faces. A vector that defines a thrust face may be within 5%, 1 % or even 0.1
% of an expected drilling direction (e.g., downward). A torque face may be within
5%, 1 % or even 0.1% of coplanar with the expected drilling direction. A vector that
defines a torque face may be orthogonal to an axis 130 that defines an expected drilling
direction. Shear forces may be additionally reduced using a lubricant. By transmitting
force from inner bit 210 to outer bit 220 using normal forces, residual deformations
that tend to attach the bits to each other (when unloaded) may be minimized. As a
result, large forces may be applied during drilling, yet the inner and outer bits
do not "wedge together," and removal of these forces may yield easy disengagement
of the inner and outer bits. In some embodiments, the engagement of inner bit 210
and outer bit 220 by normal forces (e.g., without shear stresses across the interfaces
between the bits) results in an engagement that is easily loosened (e.g., inner bit
210 may be angularly reversed while outer bit 220 remains stationary) even when frictional
forces holding outer bit 220 are small. In some embodiments, a lifting force is applied
to the inner bit 210, which may transmit the lifting force to the casing 234 via casing
ring 230 to create a counter acting frictional force, facilitating loosening of the
inner bit 210. A contact height 222 of outer bit 220 (FIG. 2) may be chosen according
to an expected friction between the outside surface of outer bit 220 and the material
through which outer bit 220 drills. For lower friction or a weak material (e.g., soil),
and/or if a short casing is expected, contact height 222 may be increased enough to
ensure that friction between the material and outer bit 220 is sufficient to hold
outer bit 220 as inner bit 210 is rotated to disengage from outer bit 220. In an application
in which a wider hole is drilled through a weak material (e.g., soil), followed by
a more narrow hole drilled through a stronger (or more tightly gripping) material
(e.g., rock), outer bit 220 may be operated to drill a short distance into the stronger
material. Drilling outer bit 220 into the rock may make it easier to disengage inner
bit 210 from outer bit 220, and may improve sealing between a casing and the weak
material.
[0025] A hole having a diameter defined by the diameter of outer bit 220 may be drilled
using both inner bit 210 and outer bit 220. By disengaging inner bit 210 from outer
bit 220, the hole may be extended deeper to create a lower portion having a diameter
defined by the diameter of inner bit 210.
[0026] Engaged bits may be disengaged via a series of steps. Having drilled a hole to a
first depth with both (engaged) bits, a reverse thrust may be applied to the engaged
inner and outer bits (e.g., disposed as in FIG. 4B). The drill bit assembly (incorporating
drill coupling 400 and casing 234) may then be moved in reverse (
e.g., pulled upward) to a distance that is greater than the sum of height 470 of female
bit 422 above forward face 432 (FIG. 4A) and height 414 of male tooth 410. Subsequently,
inner bit 210 may be rotated in reverse, an angular distance greater than the depth
to which male teeth 410 engage with cavities 420, and less than a distance 460 at
which male teeth 410 would contact adjacent female teeth 422 (
e.g., until male teeth 410 exit their corresponding cavities 420). Rotation may then
be stopped, and inner bit 210 may be thrust forward (while outer bit 220 remains stationary)
a distance greater than the sum of height 414 of male tooth 410 and height 470 of
female tooth 422, so that the female teeth 422 are "below" or "past" male teeth 410.
Inner bit 210 may then be rotated independently of outer bit 220, and drilling may
continue using inner bit 210. In some embodiments the casing 234 (with the casing
ring 230 and outer bit 220) may be subsequently pushed downward (from an apparatus
above) to abut and seal against the bottom of the outer hole.
[0027] FIGS. 5A and 5B illustrate a portion of a drill coupling, according to some embodiments.
Drill coupling 500 illustrates an example in which male teeth 510 extend radially
outward from an outer circumference of inner bit 210 (not shown). Male teeth 510 removably
disengage with corresponding cavities 520 in female teeth 522, that may extend radially
inward from outer bit 220. Inner bit 210 may be rotated to cause engagement between
male teeth 510 and female teeth 520 (clockwise from above as shown in FIG. 5A). Inner
bit 210 may be rotated to disengage male teeth 510 from female teeth 520 (as shown
in FIG. 5B), allowing for upward or downward motion of inner bit 210 with respect
to outer bit 220. When engaged (as in FIG. 5A) drill coupling 500 may transmit thrust
and (in this case, clockwise) torque from inner bit 210 to outer bit 220. After reaching
a desired depth, inner bit 210 may be rotated counterclockwise to disengage male teeth
510 from cavities 520 (
e.g., as in FIG. 5B). Inner bit 210 and teeth 510 may then be thrust forward without
rotation, until male teeth 510 clear female teeth 522 (e.g., by moving inner bit 510
forward a distance greater than the sum of a lower height 570 of female tooth 522
and the height 572 of male tooth 510). Rotation of inner bit 210 may then resume without
causing rotation of outer bit 220.
[0028] FIGS. 6A and 6B are cross section illustrations of engaged and disengaged configurations,
according to some embodiments. In FIG. 6A, drill bit assembly 600 may have drill coupling
400 configured to engage inner bit 210 and outer bit 220. In FIG. 6B, drill bit assembly
600 may have drill coupling 400 configured to disengage inner bit 210 from outer bit
220 (
e.g., to allow inner bit 210 to move downward independent of outer bit 220).
[0029] Outer bit 220 may be coupled to casing ring 230 via a thrust ring 610. Thrust ring
610 may include a ring extending radially from one of outer bit 220 and casing ring
230, sized to fit within an annular groove in the other of outer bit 220 and casing
ring 230. In some embodiments, an outer surface of inner bit 210 and an inner surface
of outer bit 220 may have facing grooves, and a thrust ring may be disposed within
the grooves to transmit thrust between the bits (e.g., as a piston ring is disposed
within a piston).
[0030] Thrust ring 610 may provide for the transmission of a forward and/or reverse thrust
force between outer bit 220 and casing ring 230. Thrust ring 610 may be shaped to
minimized the transmission of torque from outer bit 220 to casing ring 230, such that
outer bit 220 may rotate while casing ring 230 does not rotate. A thrust ring may
include a "male" feature (e.g., a ring extending from a surface) and a corresponding
"female" feature (e.g., a race within which the ring slides). In some implementations,
a thrust ring and/or casing ring may be cut or split longitudinally and stretched
to fit around outer bit 220; it may then be welded along the cut.
[0031] In some implementations, casing ring 230 may be connected to a casing 234 via a bond
620. Drive tube 214 may be connected to inner bit 210 via a bond 622, wherein preferably
the inner bit 210 is arranged with an upwardly protruding annular collar 210A having
an inner diameter adapted to fit the outer diameter of the front end 214A of the drive
tube 214, to enable overlapping introduction of the front end 214A of the drive tube
214 within the annular collar 210A of the inner bit 210. A bond may include a weld,
one or more bolts, an adhesive, a threaded fitting, a rivet, and the like. A bond
may provide for the transmission of angular (e.g., torque), shear and thrust forces
between bound objects. In an exemplary implementation at a drilling site, drive tube
214 may be threaded into inner bit 210, and casing ring 230 may be welded to casing
234.
[0032] FIG. 6A illustrates fittings 630, that may be sized to receive cutting tool inserts
632. An exemplary cutting tool insert may include a tool steel, a carbide, a nitride,
a cemented carbide or carbonitride, a diamond or diamond-like-carbon composite, or
coatings thereof.
[0033] FIG. 6A illustrates a drilling fluid passage 640 in inner bit 210. Passage 640 may
provide for fluid communication between an interior volume (e.g., of inner bit 210
and drive tube 214) and an exterior side (e.g., the drilling face) of inner bit 210.
In some cases, an exterior passage 650 provides for fluid communication between the
exterior side and a volume between drive tube 214 and casing 234, whereby preferably
said exterior passages 650 include outlet openings 650A arranged at the outside of
the collar portion 210A of the inner bit 210.
[0034] The engaged configuration shown in FIG. 6A may be operated to rotate both inner bit
210 and outer bit 220 while casing ring 230 and casing 234 do not rotate (
e.g., if they are held by friction with the earth). FIG. 6B illustrates a disengaged configuration
of drill bit assembly 600, in which inner bit 210 has been disengaged from outer bit
220. Inner bit 210 may continue to drill while outer bit 220 remains stationary. A
difference in diameter between that of inner bit 210 and that of outer bit 220 may
yield a corresponding difference in hole diameter as inner bit 210 descends past outer
bit 220.
[0035] FIGS. 7A and 7B illustrate plan views (from above) of a coupling in engaged and disengaged
configurations (respectively), according to some embodiments. Female teeth 422 (of
which only one is shown) have cavities 420 shaped to engage with male teeth 410. A
total thrust area may describe the sum of the thrust areas 434 between the thrust
surfaces of corresponding male and female teeth. A total torque area may describe
the sum of the torque areas between the torque faces of corresponding male and female
teeth (not shown). Increasing the number of teeth (at constant height) may increase
the torque area. Decreasing the number of teeth (and increasing tooth width) may increase
the thrust area. The relative ratio of thrust area to torque area may be chosen according
to the requirements of the site to be drilled. A configuration having more teeth may
have higher torque area and lower thrust area. A configuration having fewer teeth
may have lower torque area and higher thrust area. Tooth and cavity height may be
increased to increase torque area.
[0036] In FIG. 7A, female teeth 422 are disengaged from male teeth 410, and inner bit 210
may move forward or reverse (in/out of the page) with respect to outer bit 220. In
FIG. 7B, male teeth 410 are disposed within cavities 420 of female teeth 422, and
thrust and (in this case, clockwise) torque may be transmitted from inner bit 210
to outer bit 220.
[0037] An outer passage 650 may provide for fluid communication between inner passage 640
and a gap 710 between adjacent pairs of engaged teeth. Gap 710 may be defined by a
distance 712 between a side of a female tooth 422 and the facing side of an adjacent
male tooth 410 when the drill coupling is engaged, and a distance between the outside
of inner bit 210 and inside of outer bit 220.
[0038] Passage 640 may be in fluid communication with a volume within drive tube 214 (FIG.
3), and passage 650 may provide fluid communication from passage 640 to gap 710. Gap
710 may be in fluid communication with the volume between drive tube 214 and casing
234 (FIG. 6) which may extend to the surface of the material being drilled. Gap 710
may form at least a portion of a passage (e.g., passage 650). In some applications,
a drilling fluid (e.g., air, water, mud, and the like) is pumped down through an interior
of the drive tube, through passage 640 to the drilling face, then up through a passage
650 comprising gap 710 to the volume between the drive tube and the casing (and if
desired, back to the surface). Fluid may be pumped in the opposite direction.
[0039] In certain embodiments, various passages may be filled (
e.g., with cement, concrete, and the like) by pumping a settable fluid. As shown in FIG.
8A concrete 730 may be pumped down drive tube 214 as air escapes up through the volume
between drive tube 214 and casing 234. Concrete may possibly also be pumped down through
the volume between drive tube 214 and casing 234 as air escapes up through drive tube
214 (or
vice versa). Concrete 730 may be pumped until it fills both the interior of drive tube 214 and
the volume between drive tube 214 and casing 234. The concrete may set, to form a
composite pillar having concrete reinforced by (
e.g., steel) drive tube 214 and casing 234. In some embodiments, a surface (e.g., an
exterior of a drive tube and/or an interior of a casing) may have a pattern or texture
(e.g., ridges, grooves, knobs, and the like) that grip or otherwise reinforce the
material filling the volume bounded by that surface. Accordingly the drill bits 210,
230 will then also remain as integrated parts of such a pillar.
[0040] FIG. 8A describes a method for drilling a hole having multiple diameters, according
to some embodiments, e.g. to make a composite pillar as shown in FIG. 8A. Method 800
includes steps 810, 820, 830, 840, and 850. In step 810, a hole 100 is drilled with
a drill bit assembly 201, 230 configured to drill with both inner and outer bits.
In step 820, the drill bit assembly is pulled upward (reverse) a distance large enough
that the male teeth on one bit will clear the female teeth on the other bit. In step
830, the inner bit is counter-rotated a short distance (e.g., less than gap 460) to
disengage the male teeth from their corresponding female teeth. In step 840, the inner
bit is thrust downward (forward) a distance large enough that the male and female
teeth clear each other. In step 850, drilling continues with only the inner bit to
form a hole 120 of a smaller diameter. A drilling fluid (
e.g., air) may be pumped during various steps. In an optional step (not shown), concrete
730 may be pumped (
e.g., down the drive tube) to fill a casing bonded to the casing coupling of the drill
bit assembly and/or the drive tube driving the inner bit.
[0041] FIG. 9 illustrates a perspective illustration of an exemplary drill bit assembly,
according to some embodiments. Drill bit assembly 900 includes an inner bit 210, an
outer bit 220, and a casing ring 230. In exemplary drill bit assembly 900, outer bit
220 includes four pairs of male teeth 410 that engage with cavities 420 in corresponding
and female teeth 422. FIG. 9 illustrates drill bit assembly 900 as viewed from above,
with the various components "expanded" for clarity. In some implementations, a drill
bit assembly may be assembled by cutting a casing ring (e.g., longitudinally) and
fitting the casing ring around the outer bit (e.g., as a piston ring is fit into a
corresponding race in a piston). A casing ring may be subsequently welded or otherwise
bonded across the cut, typically in a manner that does not impede the performance
of thrust ring 610.
[0042] FIG. 10 illustrates another view of a drill bit assembly, according to some embodiments.
FIG. 10 illustrates a view of drill bit assembly 900 as viewed from below, expanded
for clarity. In some embodiments, a face of a tooth may include a divot 1010. Divot
1010 may be a machining feature that (inter alia) removes portions of a torque face
that would be non-parallel with corresponding portions on a facing tooth or cavity.
Divots 1010 may minimize the creation of shear forces between male and female teeth,
which may reduce undesired binding or wedging during use. FIG. 10 also illustrates
corresponding male and female features of thrust ring 610.
[0043] FIGS. 11A, 11B, and 11C illustrate various views of a drill bit assembly, according
to some embodiments. FIG. 11A illustrates drill bit assembly 900 in an "assembled"
configuration. At a drilling site, a drive tube may be attached to inner bit 210,
and optionally a casing may be attached to casing ring 230. FIG. 11B illustrates a
plan view (from below, facing opposite the drilling direction) of drill bit assembly
900. FIG. 11B provides additional illustration for an exemplary embodiment in which
passages 640 and 650 provide for fluid communication between the volume within a drive
tube and the volume between the drive tube and a casing (see FIG. 3). FIG. 11C illustrates
an assembled drill bit assembly 900 as viewed in cross section, according to the section
"A" shown in FIG. 11B.
[0044] The above description is illustrative and not restrictive. Many variations of the
invention will become apparent to those of skill in the art upon review of this disclosure.
The scope of the invention should, therefore, be determined not with reference to
the above description, but instead should be determined with reference to the appended
claims along with their full scope of equivalents.
1. A drill bit assembly (200, 900) comprising:
an inner bit (210, 210);
an outer bit (220, 220) coupled to the inner bit (210, 210) via a drill coupling (400,
500); and
a casing ring (230, 230) coupled to the outer bit (220, 220) via a thrust ring (610),
wherein the drill coupling (400, 500) may be operable to engage the inner bit (210,210)
with the outer bit (220, 220) or disengage the inner bit (210,210) from the outer
bit (220, 220) and the drill coupling (400, 500) comprises a pair of teeth,
preferably a plurality of pairs, the pair comprising:
a male tooth (410, 510) extending radially from one of the inner and
outer bits (210, 220) toward the other of the inner and outer bits (210, 220), the
male tooth (410, 510) having a male thrust face (432) and a male torque face (452);
a female tooth (422, 522) extending radially from the other of the
inner and outer bits (210, 220) toward the bit (210, 220) having the male tooth (410,
510); and
a cavity (420, 520) in the female tooth (422, 522), the cavity (420, 520) defined
at least in part by a female thrust face (430) and
a female torque face (450), the cavity (420, 520) sized to receive the male tooth
(410, 510) and create a thrust area (434) to transmit a thrust (310) from the inner
bit (210,210) to the outer bit (220, 220), and a torque area (454) to transmit a torque
(320) from the inner bit (210,210) to the outer bit (220, 220), characterized in that the inner bit (210,210) is sized to be bonded to a drive tube (214), and the casing
ring (230, 230) is sized to be bonded to a casing (234), wherein the drive tube (214)
is arranged to transmit torque and thrust to the drill assembly (200,900) by means
of a top hammer.
2. The assembly of claim 1, wherein the female teeth (422, 522) are separated by a gap
(460) that is larger than a width (412) of the male teeth (410, 510).
3. The assembly of claim 2, wherein the gap (460) extends past a height (470) of the
female teeth (422, 522) above the thrust face (432).
4. The assembly of any of the preceding claims, wherein the thrust ring (610) transmits
a thrust (310) between the outer bit (220, 220) and the casing ring (230, 230).
5. The assembly of any of the preceding claims, further comprising a drilling fluid passage
(640) in the inner bit (210,210) that provides for fluid communication with the inner
space of the drive tube (214) through a drilling face of the inner bit (210,210) and
an exterior passage (650) that provides for fluid communication between drilling fluid
passage (640) and a volume between inner bit (210,210) and outer bit (220, 220).
6. The assembly of any of the preceding claims, further comprising a gap (710) between
the inner bit (210,210) and the outer bit (220, 220), the gap (710) defined at least
in part by a first distance (714) between inner bit (210,210) and outer bit (200)
and a second distance (712) between a first side of a female tooth (422, 522)) and
a second side of a male tooth (410, 510) that is facing the first side.
7. The assembly of any of the preceding claims, wherein:
a first volume is defined at least in part by an interior surface of the inner bit
(210,210);
a second volume is defined at least in part by an exterior surface of the inner bit
(210,210) and
an interior surface of the outer bit (220, 220); and the first and second volumes
are in fluid communication via one or more passages and gaps in at least one of the
inner bit (210,210) and outer bit (220, 220).
8. The assembly of any of the preceding claims, further comprising a divot (1010) associated
with at least one of the male or female teeth.
9. A method for producing a composite pillar, using an assembly defined in any preceding
claim, the method comprising:
drilling a hole (100) using a drive tube (214) bonded to a drill bit assembly (210,
220, 230) according to any of the preceding claims;
supplying a set able fluid (730) down into the hole (100), and filling at least one
annular space outside of the drive tube (214) from the drill bit assembly up to the
ground level,
allowing the fluid (730) to settle to form a composite pillar together with the drill
bit assembly (210, 220, 230) and the drive tube (214).
10. A method according to claim 9, wherein further:
prior to supplying a set able fluid (730),
disengaging the inner bit (210,210) from the outer bit (220, 220) using the drive
tube (214); and
drilling a lower hole portion (120) having a smaller diameter (122) than the upper
portion (110) of the hole (100) using the inner bit (210,210).
11. A method according to claim 10, wherein disengaging comprises:
pulling the drill bit assembly (210, 220, 230) a first distance in reverse;
counter-rotating the inner bit (210); and
pushing the inner bit (210) forward a second distance that is greater than the first
distance, wherein the first distance is at least a sum of a first height (414, 572)
and a second height (470, 570), the first height (414, 572) of a male tooth (410,
510) associated with the drill coupling (400, 500) and the second height (470, 570)
between the male tooth (410, 510) and a surface of a corresponding female tooth (422,
522) associated with the drill coupling (400, 500).
12. A method according to any of claims 9- 11, wherein supplying the set able fluid (730)
is achieved first via the inner of the drive tube (214) and then via the drill bit
assembly (210, 220, 230) to thereafter achieve a subsequent filling upwardly of the
volume outside of the drive tube (214).
13. A method according to claim 12, wherein the set able fluid (730) is supplied via a
plurality of outlet holes (640) and passage ways (650) of the inner bit (210), wherein
preferably each outlet hole communicates with two passageways (650).
14. A method according to claim 13, wherein the outlets (650A) of said passage ways (650)
are arranged at the outside of a collar portion (210A) of the inner bit (210).
15. A method according to claim 12 or 13, wherein a casing tube (234) is used whereby
the subsequent filling includes filling a volume between the drive tube (214) and
the casing tube (234).