Note: Descriptions are shown in the official language in which they were submitted.
CA 02401917 2002-09-06
EXPANDABLE BIT
Field of the Invention
This invention is directed to a drill bit for use in drilling a borehole
through an earthen
formation and, in particular, a drill bit that is expandable from a tripping
position to a
position for use.
Background of the Invention
A drill bit is used when drilling a borehole through an earthen formation. In
some
applications, such as casing drilling or extending a borehole below a cased
section,
the drill bit must be sized to fit through the casing drift diameter, but
capable of
drilling a borehole to a gauge larger than the outer diameter of the casing.
To
achieve this, an under reamer is often used with a pilot bit.
The under reamer is spaced back from the pilot bit and is generally pivotally
attached
such that it can be stored for tripping and expanded radially outwardly for
use.
Summary of the Invention
A bit has been invented that is expandable from a collapsed position, useful
for
tripping, to an radially expanded position for use. The bit is useful to form
a borehole
through an earthen formation. In one embodiment, the bit can be used alone,
without a separate under reamer, to expand a well bore below a casing string,
either
during casing drilling or when extending a well bore below an installed casing
string.
In accordance with one broad aspect of the present invention there is provided
a drill
bit for forming a borehole through an earthen formation, the drill bit
comprising: an
upper end formed to be connectable to a drilling drive means, a lower end
opposite
the upper end; a center axis extending between the upper end and the lower
end; a
center cutter face on the lower end, the center cutter face selected to be
useful to
drill through an earthen formation; and an arm positioned between the center
cutter
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face and the upper end, the arm selected to be radially moveable relative to
the
center axis between a stored position defining a stored bit diameter and an
expanded position defining an expanded bit diameter, greater than the stored
bit
diameter; and an outer cutter face disposed on the arm and exposable for use
to drill
through an earthen formation when the arm is in the expanded position.
The drilling drive means to which the upper end is connectable can vary
depending
on the type of drilling in which the bit is to be used. For example, the
drilling drive
means can be: a drill string formed of, for example, drill pipe or casing.; a
sub
connectable to a drill string; a downhole motor, such as for example, a mud
motor,
for driving the bit; or a sub connected to a downhole motor.
The bit can include one or more arms, with consideration as to size and
complexity
of the bit. In the stored position, the bit is generally selected to be a size
suitable for
passing though the drift diameter of a tube string, such as a casing string
and in the
expanded position, the bit is generally selected to be capable of use to drill
a bore
hole of a gauge greater than the outer diameter of the tube string.
The outer cutter face and the center cutter face include cutters selected to
be useful
in forming a borehole through an earthen formation. In one embodiment, the
center
cutter face and the outer cutter face form a substantially continuous bit
surface when
the arm is in its expanded position.
The arm can be moveable between the expanded position and the stored position
in
any desired way, as by use of a slidable wedge arrangement or by use of a
pivotal
connection.
The bit can include jetting ports through which fluid can be passed, for
example, for
cleaning and lubricating the bit.
The bit can include a housing including an upper end, a lower end, an axis
defined
as extending through the upper end and the lower end and a bore extending
parallel
to the axis into the lower end; and the center cutter face is disposed on a
mandrel
slidingly disposed in the bore, the mandrel having a lower end and an upper
end;
and the arm being drivable into the expanded position by the mandrel bearing
thereagainst to drive the arm out. The mandrel can be formed to support the
arm,
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when it is in the expanded position. For example, the arm can be formed to
bear
against the mandrel when it is in the expanded position. The mandrel and the
arm
can be formed such that they substantially conform to one another along a
portion of
their contacting surfaces once the arm is in its expanded position so that
forces
affecting the arm can be reacted through the mandrel. In its stored position,
the arm
can be positioned below the bore, adjacent the bore or can extend into the
bore.
Generally, it is desirable to form the arms such that they extend into the
bore, when
in the stored position, to reduce the stored size of the bit as much as
possible.
Thus, in accordance with another broad aspect of the present invention there
is
provided a drill bit for forming a borehole through an earthen formation, the
drill bit
comprising: a housing including an upper end, a lower end, an axis defined as
extending through the upper end and the lower end and a bore extending
parallel to
the axis into the lower end; a mandrel slidingly disposed in the bore, the
mandrel
having a lower end and an upper end; a centre cutter face on the mandrel lower
end;
an arm having a lower end and connected to the housing adjacent the bore, the
arm
being radially moveable about between a stored position and an expanded
position,
the arm being drivable into the expanded position by the mandrel bearing
thereagainst to drive the arm out; and a outer cutter face on the arm lower
end.
In one embodiment, the arm is positioned in a slot in the housing. The slot
can be
formed to conform about the arm side and upper surfaces to support the arm and
provide for transfer of stress into the housing.
In one embodiment, the outer cutter face, when the arms are expanded, are
substantially co-planar with the center cutter face. Thus in accordance with
another
broad aspect of the present invention, there is provided a drill bit for
forming a
borehole through an earthen formation, the drill bit comprising: a center
cutter face;
an arm positioned about the center cutter face and selected to be radially
moveable
relative to the center cutter face between a stored position defining a stored
bit
diameter and an expanded position defining an expanded bit diameter, greater
than
the stored bit diameter; and an outer cutter face disposed on the arm and
selected
such that when the arm is in the expanded position, the outer cutter face and
the
center cutter face are substantially co-planar.
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Brief Description of the Drawings
A further, detailed, description of the invention, briefly described above,
will follow by
reference to the following drawings of specific embodiments of the invention.
These
drawings depict only typical embodiments of the invention and are therefore
not to
be considered limiting of its scope. In the drawings:
Figure 1 is an axial sectional view through a bit in accordance with the
present
invention, in an expanded position for use. Reference can be made to Figure 3
line
1-1 for understanding of the section which is illustrated in Figure 1;
Figure 1A is an axial sectional view of the bit of Figure 1 in a stored
position;
Figure 2 is a transverse sectional view through the bit of Figure 1 taken
along line 2-
2;
Figure 3 is a transverse sectional view through the bit of Figure 1 taken
along line 3-
3;
Figure 4 is an end elevation of the bit of Figure 1;
Figure 5 is an end elevation of the bit of Figure 1 A;
Figure 6 is a side view of an arm and slot of Figure 1;
Figure 6A is a side elevation of an arm useful in the bit of Figure 1;
Figure 6B is an axial sectional of the lower portion a bit housing useful in
the bit of
Figure 1;
Figure 7 is an axial sectional view through another bit in accordance with the
present
invention, in an expanded position for use. Reference is made to the sectional
line
7-7 in Figure 10;
Figure 7A is an axial sectional view of the bit of Figure 7 in a collapsed,
stored
position;
Figure 8 is a transverse sectional view through the bit of Figure 7 taken
along line 8-
8;
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Figure 9 is a side view of an arm and slot of Figure 7;
Figure 10 is an end elevation of the bit of Figure 7;
Figure 11 is an end elevation of the bit of Figure 7A;
Figure 12 is a side elevation of the lower portion of the bit of Figure 7;
Figure 13 is an axial sectional view through another bit in accordance with
the
present invention, in an expanded position for use. Reference is made to
Figure 14,
wherein the section of Figure 13 is shown along line 13-13;
Figure 13A is an axial sectional view of the bit of Figure 7 in a collapsed,
stored
position; and
Figure 14 is an end elevation of the bit of Figure 13.
Detailed Description of the Present Invention
Referring to Figures 1 to 6, there is shown one embodiment of a bit according
to the
present invention. As will be appreciated. the bit is useful to form or extend
a
borehole. The bit is engageable at the lower end of a drill string. If the bit
is used
when drilling with casing, the drill string is a string of casing and the bit
is releasably
locked to the string of casing by, for example, a drilling lock assembly. The
bit is
rotated either by rotation of the casing string from surface or by use of a
mud motor.
The bit includes a cutter face 10 formed of a center cutter face and an outer
cutter
face, a mandrel 12 and a housing 14.
Mandrel 12 includes a lower end 12a and an upper end 12b. In the illustrated
embodiment, upper end 12b is formed as a blank. However, this blank will be
milled
or otherwise treated to a form suitable for connection to the drilling drive
means. In
one embodiment, the blank will be formed as a threaded pin end for connection
to
the drilling lock assembly or another component for eventual connection to the
drill
string. Mandrel further includes an inner borE: 13.
Housing 14 includes an upper end 14a and a lower end 14b. Housing 14 further
includes an upper inner bore 14c defined between a return 14d at the upper end
of
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the housing and a shoulder 14e. Housing 14 further includes a lower inner bore
14f
extending below shoulder 14e.
The housing carries three, or any desired number of, bit arms 15. The bit arms
are
moveable between a stored position (Figure 1A), wherein they are retracted
against
or, as shown, into the housing and its inner bore and an expanded position
(Figure
1 ) wherein they are supported for use to extend the well bore. The bit arms
are
moveable between the stored position and the expanded position by relative
axial
movement of the mandrel and the housing. In particular, when housing 14 is in
a
lower position relative to the mandrel wherein the mandrel is retracted into
the bore
of the housing bit arms 15 are in or can be driven into the stored position
and when
housing 14 is moved upwardly over mandrel 12, the bit arms are driven out to
the
expanded position. In the expanded position, lower end 12a of the mandrel is
flush
with or extends from lower end 14b of the housing. Bit arms 15 each retain
cutters
16a, 16b over a portion of their outer surfaces. Bit arms 15, when in the
expanded
position, form the outer cutter face of the bit, as will be discussed in
greater detail
herein below.
Lower end 12a of the mandrel forms the center cutting face and retains cutters
18 on
its lower outer surface forming the center cutter face, as will be described
in greater
detail hereinbelow.
Mandrel 12 is positioned in the inner bore of housing 14 and housing 14 is
slidably
mounted to move axially over mandrel 12. Mandrel 12 includes an annular groove
defined by shoulder 19a and annular flange 19b which limit movement of the
housing
over the mandrel by abutment against upper end 14a and return 14d of the
housing.
When the bit is not in operation, housing 14 is normally in a lower position
relative to
the mandrel wherein return abuts against flange 19b. However, for operation of
the
bit, housing 14 is driven to an upper position on mandrel wherein end 14a
abuts
against shoulder 19a.
Housing 14 is driven upwardly by injection of hydraulic fluid into a chamber
26
formed between the housing and the mandrel. In particular, in chamber 26 a
piston
face 28 is formed on the housing against which fluid pressure can act to drive
the
housing along mandrel 12. Piston face 28 is in communication with inner bore
13 of
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the mandrel via ports 30, such that fluid pressure applied from surface, such
as
during pressuring up of the drill string communicated through bore 13 and into
chamber 26. Seals 32, 33 act between the housing and the mandrel to contain
fluid
pressure within the chamber.
To enhance operation of chamber 26 to move housing 14 upwardly over the
mandrel, bore 13 has formed or positioned therein a restriction nozzle 34 to
increase
the pressure in the mandrel inner bore above the nozzle, in ports 30 and in
chamber
26. Restriction nozzle 34 acts as to increase the pressure differential
between the
fluid pressure in these parts and the pressure external to the tool in the
borehole in
which the bit is operated.
While housing 14 and mandrel 12 can move axially with respect to each other,
they
are restricted from relative rotational movement by an interlock arrangement
such as
a splined area 36 on the mandrel that mates with a similarly shaped area 37 on
the
housing or other arrangement. The interlock arrangement ensures that torque
applied to the mandrel is transferred to the housing and thereby to the
plurality of bit
arms 15 mounted in slots 42 on the housing.
Bit arms 15 include cutters 16, 16b at their lower surfaces and are pivotally
connected at their opposite ends by pins 46 to housing 14. The pivotal
connection
permits arms 15 to move between the stored position within slots 42 and the
radially
expanded position wherein cutters 16, 1 Gb extend out from slots 42 past the
outer
surface of the housing. In the radially expanded position, cutters 16, 16b are
exposed for enlarging the well bore. The position of each bit arm in the
radially
expanded position is limited by abutment of surface 50 against upper end 42a
of the
slot in which it is mounted. In addition, each arm includes a hook 53 on each
of its
side edges. The hooks are selected to engage under shoulders 54 formed in the
slots. Together with abutment of surface 50 against upper end 42a of the slot,
the
engagement of hooks 53 under shoulders 54 provide thrust support for the arms
during use.
Bit arms 15 are mounted to extend through slots 42 into lower inner bore 14f
of the
housing when it is in the lower position on the mandrel and the mandrel is
retracted
up into the housing. As such, arms 15 when in the stored position, can abut
against
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one another at or about the center axis of inner bore 14f. To reduce the
effective
outer diameter, d, of the arms 15 in the stored position, a portion of 56a of
the arm
rear surface can be formed, for example as wedges, to fit closely together
(Figures 5
and 6).
Bit arms 15, as noted hereinbefore, are driven radially outwardly when the
housing is
moved upwardly over the mandrel. In particular, the arms are driven outwardly
by
abutment of end 12a of mandrel against the rear surfaces of the arms.
In the expanded position, the arms are held out by the mandrel. The arms can
be
supported about their sides and rear surfaces to enhance their durability and
strength. In particular, slots 42 are formed at their upper ends 42a and sides
42b to
substantially conform to the sides of the arms. In addition, preferably the
arms are
formed with respect to the mandrel such that when they are in the expanded
position, they are supported adjacent their ends by the mandrel. In
particular, the
arms have curved rear surfaces 56b which substantially correspond to the outer
curvature of the mandrel adjacent its lower end. This close positioning
provides that
forces can be effectively transferred from the arms to the housing and the
mandrel.
The cutter face of the bit is formed by the center cutter face including
cutters 18 on
mandrel 12 and the outer cutter face formed by cutters i 6a on arms 15, when
the
arms are expanded out and mandrel 12 is positioned between them. The relative
sliding movement of the mandrel and the housing is selected such that, the
mandrel
is positioned with center cutter face substantially co-planar with the outer
cutter face
when the bit is expanded for use. In the illustrated embodiment, the cutter
face also
includes cutters 59 positioned on the lower end of the housing to facilitate
the
formation of a borehole using the bit. Cutters 16b, positioned on the
outwardly
facing front surfaces of the bit arms are useful for reducing failure due to
wear of the
arms and clean out the hole behind the cutter face of the bit. While
percussive type
cutters have been shown, it is to be understood that other cutter types can be
used.
Ports 57, in communication with bore 13.. are provided, as in a standard bit,
to
lubricate and clean the cutting face, Ports 57 open in the center cutter face.
However, due to the nature of bit operation, fluids jetted through the ports
will also
pass over, clean and lubricate cutters 16a, 16b and 59. Expansion of the arms
is
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also facilitated by jetting of fluid though ports 57 during pressuring - up of
the drill
string.
In operation, it is advantageous that the housing not move over the mandrel
every
time there is a pressure drop. Thus, in one embodiment, there is provided a
releasable lock assembly to lock mandrel 12 and housing 14 in the operating
position. In the illustrated embodiment of Figures 1 and 1A, the releasable
lock
assembly is a spring-biased detent arrangernent including a plurality of
spring-biased
detents 66 in the housing which engage in a groove 68 in the mandrel. The
spring
force of detents 66 is selected to be greater than the force generated by the
weight
of housing 14 and arms 15, which would tend to pull the housing down over the
mandrel. However, the spring force of the detents 66 can be overcome to move
the
housing down and allow retraction of bit arms 15 when a selected force is
applied,
such as the force generated by pulling the arms against the end of the casing
to trip
the bit to surface. Upper surfaces 15a of the arms are ramped to facilitate
folding
down of the arms when they are butted against the end of the casing. Detents
66
can be replaced with other lock means, as desired.
To facilitate manufacture, mandrel 12 and housing 14 can be formed in sections
as
shown and threaded together or secured in some other way. Pins 46 are
conveniently installed through bores in the housing and secured between
shoulders
70 and bolts 72. Detents 66 are installed in ports 74 by threaded caps 76.
Referring to Figures 7 to 12, there is shown another expandable bit according
to the
present invention. The bit includes a mandrel 112, a housing 114 and a pair of
bit
arms 115 supported on the housing. Mandrel 112 includes a lower end 112a and
an
inner bore 13 with a venturi nozzle 34 formed therein.
Housing 114 includes a lower end 114b and an inner bore 114c in which mandrel
112 is telescopically disposed. A hydraulic chamber 26 is formed between the
housing and the mandrel and includes a piston face 28 formed on housing 114.
The
hydraulic chamber reacts to fluid injection though bore 13 to drive the
housing axially
over the mandrel.
An interlock arrangement 36, 37 is provided between the mandrel and the
housing to
prevent relative rotational movement therebetween. The under reamer includes a
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releasable operational lock assembly including a plurality of spring-biased
detents 66
and a groove 68.
Bit arms 115 have mounted thereon cutters 116, The bit arms 115 are pivotally
mounted by pins 146 in slots 142 in a region of the housing from which mandrel
112
is retracted when the housing is in the lower position on the mandrel. In this
position, arms 115 extend into bore 114c when the mandrel is retracted, but
are
pushed out into an expanded position by the center cutter face 118a of the
mandrel
when the housing is driven axially up over the mandrel by injection of fluid
into
chamber 26.
In the illustrated embodiment, slots 142, and thereby arms 115, are spaced
from end
114b of the housing such that arms 115 are spaced from the center cutter face
118a
on the mandrel when the bit is expanded for use. However, cutters 159 are
disposed on the housing between end 114b and the slots 142 such that a
substantially continuous cutter face is provided including cutters 116 on the
bit arms,
cutters 159 on the housing and the center cutter face 118a. This cutter face
provides extended cutter engagement with the borehole wall during formation of
a
borehole.
By use of only two bit arms 115, the arms can be elongated and positioned to
overlap in bore 114c in side-by-side configuration when in the stored
position. Slots
142 are formed to closely surround the bit arms to support them in the
expanded
position. Each bit arm includes a shoulder 153 which engages under a shoulder
154
formed in the slot. In addition, the lower end of each bit arm is selected to
engage
under the lower end of its slot when in the expanded position. This limits
outward
expansion and stabilizes the arms by being secured both at their top and
bottom
ends.
Ports 157 extend from bore 13 and open into center cutter face 118a. Channels
180
are formed in the center cutter face and channels 182, which substantially
align with
channels 180 when the cutter face 118a is exposed for use at the end of the
housing, are provided to facilitate flow of fluid, as shown by the arrows in
Figure 10,
from ports 157 along the cutter face to the clean and lubricate cutters 116 on
the
arms.
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