Note: Descriptions are shown in the official language in which they were submitted.
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PCT PATENT APPLICATION
FORCE STACKING ASSEMBLY FOR USE WITH A SUBTERRANEAN
EXCAVATING SYSTEM
BACKGROUND
1. Field of the Disclosure
[0001] The present disclosure relates to a system for use with a borehole
excavating system
that employs reactive materials that selectively generate impulse forces in
the excavating
system.
2. Description of Prior Art
[0002] Hydrocarbon producing wellbores extend below the Earth's surface where
they
intersect subterranean formations in which hydrocarbons are trapped. The
wellbores
generally are created by drill bits that are on the end of a drill string,
where typically a drive
system above the opening to the wellbore rotates the drill string and bit.
Cutting elements on
the drill bit scrape or otherwise impact the bottom of the wellbore as the bit
is rotated and
excavate material from the formation thereby deepening the wellbore. Drilling
fluid is
typically pumped down the drill string and discharged from the drill bit into
the wellbore.
The drilling fluid flows back up the wellbore in an annulus between the drill
string and walls
of the wellbore. Cuttings produced while excavating are carried up the
wellbore with the
circulating drilling fluid.
[0003] During drilling, cutters or teeth formed on the cutting surfaces of the
drilling bits
impart forces onto the subterranean formation. The forces include shear forces
generated by
rotation of the drill bit with respect to the bottom of the borehole.
Compressional forces are
also transferred between the bit and formation, where the compressional forces
are from a
combination of the weight of a drill string on which the bit is attached and a
column of
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drilling fluid flowing within an axial bore in the drill string. Except when
changing bits due
to wear or failure, the bit remains in contact with the formation during
drilling of the
wellbore.
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SUMMARY OF THE INVENTION
[0004] Disclosed herein is an example of a system for excavating within a
wellbore and that
includes a drill string, a housing having an end that couples to the drill
string, actuators in the
housing that are selectively extendable and that each have an end coupled with
the housing,
and a ram assembly having an end coupled to a drill bit, and that couples to
ends of the
actuators opposite from the ends of the actuators that couple with the
housing, so that when
the actuators are selectively extended, the drill bit selectively extends a
distance from the drill
string.
[0005] In an example, each of the actuators exerts a force onto the ram
assembly when
selectively extended, and wherein the actuators are arranged in series in the
housing such that
a sum of the forces is transmitted to the ram assembly. In an example when the
actuators are
selectively extended, the drill bit is axially displaced an amount
substantially equal to the
axial elongation of a one of the actuators. The members can optionally be made
from an
activatable material that elongates in response to applied electricity.
Examples of activatable
material include piezoelectric material, a magnetorestrictive material, and
combinations
thereof.
[0006] In one embodiment, the bit is made up of an outer bit having an axial
bore, and an
inner bit that reciprocates within the axial bore in response to the actuators
being changed
into the activated state. The actuators can be axially elongated when
selectively activated.
Optionally, the housing can hollow with bulkheads formed in the housing at
axially spaced
apart locations, and wherein outer peripheries of each of the bulkheads couple
with an inner
surface of sidewalls of the housing. In this example, the ends of the
actuators that couple
with the housing are in abutting contact with the bulkheads. In an embodiment,
planar radial
walls are provided inside of ram assembly, and that extend in a direction
transverse to an axis
of the ram assembly, and wherein ends of the actuators that couple with the
ram assembly
abut the radial walls. In an alternative, the ram member coaxially moves
within the housing
when the actuators are selectively extended.
[0007] Also disclosed herein is a method of excavating within a wellbore and
that includes
rotating a drill string in the wellbore that includes drill pipe, a drill bit
coupled to the drill
pipe, and actuators disposed between the drill pipe and drill bit, generating
actuating forces
with the actuators by selectively elongating each of the actuators a
designated distance, and
imparting a summation of the actuating forces against the drill bit to urge at
least a portion of
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the drill bit away from the drill pipe an urged distance that is substantially
the same as the
designated distance.
[0008] The actuators can be elongated at a resonant frequency, such as a
resonant frequency
of the drill string, or a resonant frequency of a formation that surrounds the
wellbore.
Selectively elongating each of the actuators a designated distance can involve
directing
electricity to a magnetorestrictive member disposed in the actuator that
axially expands and
generates a one of the axial forces. The portion of the drill bit urged away
from the drill pipe
can be an inner bit that is proximate an axis of the drill bit. In one
embodiment, at least a
portion of the drill bit is all of the drill bit, and when at least a portion
of the drill bit is urged
away from the drill pipe the urged distance, the drill bit is urged into
excavating contact with
a bottom of the wellbore.
[0009] Another example of a system for excavating within a wellbore is
described herein and
that includes a bottom hole assembly that selectively couples to a drill
string, actuators in the
bottom hole assembly that are selectively extendable a designated distance and
that each
exert a force when extended, a drill bit coupled with the bottom hole
assembly, and a means
for transferring the combined forces exerted by the actuators to the drill
bit, and urging the
drill bit a distance away from the drill string that is substantially the same
as the designated
distance. The actuators can include members made up of material that is
responsive to an
application of electricity. The bottom hole assembly can further include a
housing that is
coupled with the drill string, and wherein members are arranged in series in
the housing, and
ends of each of the members are coupled with the housing. In one alternate
embodiment, the
bottom hole assembly includes a ram assembly that couples to the drill bit,
and wherein ends
of the members opposite from the ends that couple with the housing couple to
the ram
assembly, so that when the members expand, the ram assembly is urged axially a
distance
that is substantially the same.
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BRIEF DESCRIPTION OF DRAWINGS
[0010] Some of the features and benefits of the present disclosure having been
stated, others
will become apparent as the description proceeds when taken in conjunction
with the
accompanying drawings, in which:
[0011] Figure 1 is a sectional view of an example of a drilling system having
actuators for
delivering an axial force to a drill bit.
[0012] Figure 2 is a sectional view of an alternate example of the drilling
system of Figure 1.
[0013] Figure 3 is an axial view of an example of the drilling system taken
along lines 3-3 of
Figure 1.
[0014] Figures 4A and 4B show an example of the drilling system of Figure 1
respectively in
a retracted and an extended configuration.
[0015] Figures 5A and 5B show an example of the drilling system of Figure 2
respectively in
a retracted and an extended configuration.
[0016] Embodiments described here are not intended to limit the present
disclosure to those
embodiments. On the contrary, the present disclosure is intended to cover all
alternatives,
modifications, and equivalents, as may be included within the spirit and scope
of what is
described.
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DETAILED DESCRIPTION OF THE INVENTION
[0017] The method and system of the present disclosure will now be described
more fully
hereinafter with reference to the accompanying drawings in which embodiments
are shown.
The method and system of the present disclosure may be in many different forms
and should
not be construed as limited to the illustrated embodiments set forth herein;
rather, these
embodiments are provided so that this disclosure will be thorough and
complete, and will
fully convey its scope to those skilled in the art. Like numbers refer to like
elements
throughout. In an embodiment, usage of the term "about" includes +/- 5% of the
cited
magnitude. In an embodiment, usage of the term "substantially" includes +/- 5%
of the cited
magnitude.
[0018] It is to be further understood that the scope of the present disclosure
is not limited to
the exact details of construction, operation, exact materials, or embodiments
shown and
described, as modifications and equivalents will be apparent to one skilled in
the art. In the
drawings and specification, there have been disclosed illustrative embodiments
and, although
specific terms are employed, they are used in a generic and descriptive sense
only and not for
the purpose of limitation.
[0019] Shown in a side sectional view in Figure 1 is one example of a drilling
system 10 for
use in forming a wellbore 12. In this example wellbore 12 intersects formation
14, and a
wellbore wall 15 is defined at the intersection of wellbore 12 and formation
14. A drill string
16 is shown projecting into wellbore 12 and which is rotated by a rotary table
18 on surface.
Sections of drill pipe 20 may be added on top of drill string 16 with use of a
derrick 22 shown
mounted over an opening of wellbore 12. Optionally, a top drive (not shown)
may be
mounted to derrick 22 and used for rotating drill string 16 in lieu of rotary
table 18. A bottom
hole assembly ("BHA") 24 is shown coupled to drill string 16. BHA 24 is made
up of an
elongated housing 26 that is hollow and whose outer periphery is made up of
sidewalls 27
that extend along a length of the housing 26 and curve around an axis Ax of
BHA 24. The
outer surface of sidewalls 27 resembles a cylindrical shape. Inside of housing
26 are elongate
compartments 281-n that are formed in series. The compartments 281-n are
defined between
planar bulkheads 30i_n that project radially between the sidewalls 27 of
housing 26 at axially
spaced apart locations. A ram assembly 32 is shown coaxially disposed within
housing 26,
and which has sidewalls 33 that define an outer lateral periphery of the ram
assembly 32.
Sidewalls 33 of the ram assembly 32 are curved around the axis Ax of the
bottom hole
assembly 24 and extend generally parallel with sidewalls 27 of housing 26.
Similar to the
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bulkheads 30iõ in housing 26, are planar radial walls 341, 342 that extend
radially between
the sidewalls of the ram assembly 32 at axially spaced apart locations to form
compartments
361õ within ram assembly 32.
[0020] BHA 24 further includes actuators 371õ that selectively apply a
cumulative force
against the housing 26, and an opposing force against ram assembly 32. More
specifically,
actuators 371õ of Figure 1 are made up of reactive members 381õ, that in the
illustrated
embodiment are disposed in housing 26. Further illustrated is that each of the
reactive
members 381õ have an end that is coupled with the housing 26 via contact with
an associated
bulkhead 301õ. Examples of the reactive members 381õ include things that
change in size or
shape. Embodiments exist where the change in size or shape is in response to
applied energy,
such as electricity or magnetism; or introducing a fluid to the actuators
371õ, such as
hydraulic or pneumatic. Changes in size include becoming longer, shorter,
wider, thinner, or
combinations thereof. Example constituents of the reactive members 381õ
include electro-
active materials, magnetostrictive materials, magneto-active materials, lead-
zirconate-
titanate, lead-magnesium-niobate, terfenol-D, galfenol, and combinations
thereof. An
opposing end of each of the reactive members 381õ couples with the ram
assembly 32 via
resilient members 401õ where each of the resilient members 401õ are in contact
with the ram
assembly 32. In the example of Figure 1, resilient member 401 abuts a drill
chuck 42 shown
formed on a lower end of ram assembly 32. As will be described in more detail
below, ram
assembly 32 and drill chuck 42 are recriprocatable with respect to the housing
26 and drill
pipe 20 portion of the drill string 16. In the illustrated example, resilient
member 402 mounts
on radial wall 341, resilient member 403 mounts on radial wall 342, and
resilient member 40n
mounts on radial wall 34n. Examples of the resilient members 401õ include
springs,
Belleville washers, elastomeric members, combinations thereof, and the like.
In an alternate
embodiment, resilient members 401õ are not included so that the ends of the
reactive
members 381õ directly contact the ram assembly 32.
[0021] A drill bit 44 is shown mounted to drill chuck 42 on an end of drill
chuck 42 that is
opposite from its connection to ram assembly 32. Drill bit 44 is equipped with
cutters 46 on
its cutting face for excavating wellbore 12. Further shown in Figure 1, is a
controller 48
which connects to a communication means 49 for communicating signals and/or
electrical
power to the reactive members 381,. In one example of operation, reactive
members 381,
respond to applied electrical energy (such as that provided from controller 48
via
communication means 49) by elongating, which imparts a force against the
housing 26, and
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another force against ram assembly 32 that is in a direction opposite to the
force applied to
the housing 26. Embodiments exist where controller 48 includes a power supply
(not shown)
from which electricity is selectively provided to reactive members 381-n. In
an alternate
embodiment, a dedicated power supply 50 is shown with an output line
connecting to
communication means 49 and through which electricity is routed downhole. An
interface 51
between the controller 48 and power supply 50 provides communication from
controller 48 to
power supply 50 for providing electricity to communication means 49. It should
be pointed
out that ram assembly 32 is axially movable with respect to housing 26, so
that the oppositely
directed forces applied by the reactive members 381-n to the housing 26 and
ram assembly 32
causes ram assembly 32 to move axially with respect to housing 26. In one
example, the
applied forces of the reactive members 381-n axially urges the ram assembly
32, thereby
axially moving drill chuck 42 and drill bit 44 in a direction away from drill
string 16 and
towards the bottom of the wellbore 12. Further, the axial movement of the
drill bit 44 is with
respect to the rest of the drill string 16, increases the force exerted by the
drill bit 44 against
the bottom of wellbore 12 to above that of the weight on bit.
[0022] Thus selectively generating forces against ram assembly 32 with
reactive members
38i_n can generate a reciprocating motion of bit 44 against the bottom of
wellbore 12, wherein
the resultant force is greater than the standard weight on bit that takes
place during a normal
drilling operation. An advantage of the strategic combination of the reactive
members 381-n
within housing 26 and ram assembly 32 creates a resultant force on the ram
assembly 32, and
thus drill bit 44, which is cumulative of the forces generated by each of the
reactive members
381-n. Moreover, the axial displacement of the ram assembly 32 with respect to
the rest of the
drill string 16 is about that of an axial extension of a single one of the
reactive members 381õ
rather than a sum of all of their elongations. In one example, controller 48
energizes
actuators 371-n at designated intervals of time, and at designated durations
of time, so that the
frequency at which the bit 44 strikes the bottom of the wellbore 12 is at a
designated
frequency. Examples of designated frequencies are a resonant frequency of the
drilling
system 10, a resonant frequency of the rock making up the formation 14, or a
combination
thereof. Resonance is a phenomenon seen by some cyclical systems, whereby
energy from
one cycle is stored by the system and used in the next cycle. In one example
of the drilling
system 10 described herein, recycling of energy between cycles allows for a
greater impact
force of the percussive elements than could be achieved for a non-resonant
percussive system
using the same energy input. It is well within the capabilities of one skilled
in the art to
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operate controller 48 so that the actuators 371-n are energized at the
designated time intervals
and durations so the bit 44 strikes the bottom of the wellbore 12 at the
designated frequency.
[0023] The high frequency vibration imparted against the formation 14 creates
a series of
impacts that cause compressive failure of the formation 14 under load, which
is in addition to
the shear failure caused by rotating the bit 44 while in contact with the
formation 14. Tuning
the frequency of vibration of the drilling system 10 to a resonance mode
increases drilling
efficiency above that of operating at a range of different frequencies, or by
rotating the drill
string 16 alone. An advantage of the arrangement shown is that although the
actuators 371-n
are arranged in series, the resulting force is as though the actuators 371-n
were in parallel, that
is, the resulting force is substantially equal to the sum of force exerted by
each of the
actuators 371-n. Moreover, in an example the axial displacement of the bit 44,
due to the
cumulative axial displacement of the actuators 371-n, is substantially the
same as if the
actuators 371-n are in parallel. In an embodiment, the Young's modulus of the
rock making
up the formation 14 can be inferred from the frequency of vibration of the BHA
24, as the
stiffness of the rock will have an effect on the resonant frequency of the
system 10.
[0024] The velocity of the mass m of the bottom hole assembly 24 changes by Av
during
impacts of the oscillator of period T, due to the contact harmonic force F =
Pd sin(gt/t) which
is governed by Eauation 1. for the changing momentum of the system.
mAv = sin(L) dr = Pd ) Equation
1.
,
In one example, hie umaxial compressive strength of a rock is defined as the
value of the
peak stress sustained by a rock specimen subjected to failure by uniaxial
compression. It is
the maximum load supported by the specimen during the test divided by the
effective contact
area subjected to the compression. Thus the compressive strength of the rock;
Us = Pd/Ae, Equation
2;
where A, is the effective area, which in an example is assumed to be about 5%
of the area of
the hole drilled.
mAv = (by substituting Eqn. 2 into Eqn. 1) Equation
3.
I
c 0.05D 2T,
[0025] /6o , = 2 performs
a harmonic motion between impacts, in this
example the maximum velocity of the drill bit is Vm=Aw, where A is the
amplitude of the
vibration and 0.)=27rf is its oscillation frequency in rad/s. Assuming further
that the impact
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occurs when the drill bit 44 has maximum velocity Vm and that the drill bit 44
stops during
the impact, then Av=Vm=2Anf. Accordingly in this example, the vibrating mass
is expressed
as:
0.05D2tis T
= _____________________________________________________________ Equation 4.
[0026] The period of the impact, T, in the above expression can be determined
by many
factors including the material properties of the formation 14 and the bottom
hole assembly
24, other factors include the frequency of impacts. In one example of
operation, is
estimated to be about 1.0 percent of the period of oscillation, that is, =
0.01/f. By
substituting into Equation 4 a lower bound estimation of the resonant
frequency that can
----ilse for the impacts is given by Equation 5 as follows.
n2IT
f = __________________________________________________________ Equation 5.
q00074),1
'
[0027] In an example, Equation 5 provides a lower bound estimate for the
stable frequency of
the oscillator. The use of a frequency too much greater than this lower bound
frequency can
generate a crack propagation zone in the formation 14 that is in front of the
drill bit 44 during
operation, which could lead to compromise borehole stability and reduced
borehole quality.
Moreover, if the oscillation frequency is too large then accelerated tool wear
and failure may
occur. A scaling/safety factor, Sf, with appropriate value less than 1.0 can
be applied to the
frequency as a precautionary measure.
[0028] The dynamic force, Pd, applied to the oscillation system can be
calculated by
rearranging Equation 2 and can be expressed as follows:
Pd= AeUs = 7t/4(De2Us) Equation 6;
where in this example De is an effective diameter associated with effective
area (Ae) of the
rotary drill bit 44 which is the diameter, D, of the drill bit 44 scaled
according to the fraction
of the drill bit 44 which contacts the material being drilled. Thus in this
example, the
effective diameter, De, can be defined as:
D =
Equation 7;
where Sc is a scaling factor corresponding to the fraction of the drill bit 44
which contacts the
material being drilled. For example, estimating that only 5% of the drill bit
surface is in
contact with the material being drilled, . An
appropriate value of scaling/safety
factor can be introduced to the dynamic force, Pd, according to the material
being drilled so
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as to ensure that the crack propagation zone does not extend too far from the
drill bit 44, and
consequently compromising borehole stability and reducing the borehole
quality.
[0029] Another factor to consider is that the resonant frequency changes when
drilling
through different rock types. The compressive strength can be related to an
optimal
frequency range. It was therefore considered that the lower frequency range
can be in
relation to changing rock properties, looking at the right hand side of
Equation 5 and
introducing a factor, Sf:
U5,18000-7Anj) f 5101 (D i751800 0 II-A Equation
8.
[0030] Referring now to Figure 2, shown in a side sectional view is an
alternate example of a
drilling system 10A used in forming a wellbore 12A in a formation 14A. In this
example, the
drilling system 10A includes many of the same elements of the drilling system
10 of Figure
1, that is, a drill string 16A in the wellbore 12A, a rotary table 18A, drill
pipe 20A, a derrick
22A, a BHA 24A having a housing 26A, and sidewalls 27A on the housing 26A.
Further
making up the BHA 24A are compartments 28A1_n in the housing 26A, and
bulkheads 30A1_õ
at opposing axial ends of the compartments 28A1. A generally cylindrically
shaped ram
assembly 32A is coaxially disposed in the housing 26A having axial sidewalls
33A and radial
walls 34A1_n that are transversely mounted within sidewalls 33A. Axially
between the radial
walls 34A1_n are compartments 36A1_n in which actuators 37A1_n are provided
and that include
reactive members 38A1-n. Resilient members 40A1_n provided in the compartments
36A1_n
exert a biasing force against reactive members 38A1-n.
[0031] A difference between the embodiments of Figures 1 and 2 concerns the
bit 44A. As
shown, bit 44A is made up of a main bit 52A having an axial bore 54A extending
therethrough. An inner bit 56A is included with the main bit 52A that
reciprocates within
bore 54A. Here, the inner bit 56A has an upstream end that attaches to a lower
end of ram
assembly 32A via a connecting rod 58A. Thus, in this example, actuating the
reactive
members 38A1, 38A2,..., 38An generates a resultant force in ram assembly 32A
which
transfers only to inner bit 56A to reciprocate it within the main bit 52A.
Further, main bit
52A is shown mounted to a lower end of housing 26A.
[0032] Because housing 26A is not axially motivated by actuators 37A1, main
bit 52A does
not axially reciprocate in response to operation of actuators 37A1_n and thus
generally
maintains its axial distance from the lower end of drill string 16A. Instead,
main bit 52A is
limited to rotation within wellbore 12A, much like a standard drill bit.
Further, cutters 60A,
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62A are shown respectively formed on the downhole ends of inner bit of 56A and
outer or
main bit 52A. In bits that rotate about their axes, the radial speed of the
bit, and thus the
cutters on the bit, becomes lower with proximity to the bit axis. Meaning the
region of a bit
proximate its axis is less effective for rotational drilling that regions of
the bit distal from the
bit axis. An advantage of focusing the axial vibration of the effective bit
area towards its
inner radius is that when the cutters 60A on the inner bit 56A are out of
contact with the
formation 14 (due to reciprocation of the inner bit 56A), the amount of
cutting force per bit
surface area lost is less than that if an outer portion of the bit 44A is
moved away from the
formation 14. As such, adding the axial vibration and forces on the ensuing
rock enhances
the operational functionality of the bit 44A of Figure 2. Examples exist where
cutters 60A,
62A are formed from composites, such as poly-crystalline diamond.
[0033] Figure 3 is an axial sectional view of an example of the BHA 24 taken
along lines 3-3
of Figure 1. In this example, a coil 64 is shown between ram assembly 32 and
reactive
member 381. As is known, selectively energizing the coil 64 with electricity
generates an
electrical field that as explained above axially elongates the reactive member
381. Electricity
for energizing the coil 64 can be from surface, such as from controller 48 or
power supply 50
(Figure 1), from a battery (not shown) included with the bottom hole assembly
24, or from a
downhole generator (not shown) that converts fluid flow to electricity. As
shown reactive
member 381 coaxially inserts into a sleeve 66 that can provide
protection/isolation for the
reactive member 381. Further illustrated are supports 68 that extend radially
between the ram
assembly 32 and housing 26. Annular spaces 70 are defined in the
circumferential spaces
between adjacent supports 68 and the radial spaces between the ram assembly 32
and housing
26. In an example of operation, drilling fluid flows downhole within the
annular spaces 70,
and back uphole within an annulus 72 between the outer surface of the housing
26 and walls
of the wellbore 12.
[0034] Figures 4A and 4B provide in a side sectional view an example of how
the drill bit 44
of the drilling system 10 reciprocatingly contacts the bottom 74 of the
wellbore 12, thereby
creating fractures in the formation 14. Referring specifically to Figure 4A,
here the drill
string 16 of the drilling system 10 is disposed in the wellbore 12 in a
retracted mode so that
the bit 44 is spaced away from a bottom 74 of the wellbore 12. In the
retracted mode, the
members 381-n are in an unelongated state. In an example where members 381-n
are
magnetostrictive material, the members 381-n are not energized and electricity
from controller
48 or power supply 50 is not being transmitted to the members 38i_n. Referring
now to
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Figure 4B, the members 381õ are depicted in an elongated state. In an
embodiment where the
members 381, are made from magnetostrictive material, the elongation can be
due to applied
electricity, such as from controller 48A or power source 50. In the elongated
state of Figure
4B, the members 381, 382, 383, and 38n, have elongated over their lengths
shown in Figure 4A
by the respective distances D1, D2, D3, and Dri=
[0035] Further illustrated is that the bit 44 has moved a distance DBIT in the
wellbore 12. As
described above, the movement of the bit 44 is in response to movement of the
members 381õ
via the coupling between the members 381õ and ram assembly 32 (Figure 1).
Additionally,
in one example, the distances D1, D2, D3, and Dn (that can be referred to as
designated
distances) all have substantially the same value. Further in this example,
distance DBIT has a
value that is substantially the same as the value of any one of distances D1,
D2, D3, and Dr,.
Accordingly, in this example, the novel configuration of the housing 26 and
ram assembly 32
results in the distance DBIT not being a sum of the individual distances D1,
D2, D3, and Dn.
[0036] Further illustrated in Figure 4B are arrows that respectively represent
forces F381,
F382, F383, and F384 generated by the members 38iõ when being
actuated/elongated.
Another arrow represents force FBIT which is the force being transmitted to
drill bit 44 from
elongation of the members 381õ, and which is substantially equal to a
summation of forces
F381, F382, F383, and F384. As indicated above, ends of the members 38iõ
couple with the
housing 26, and opposing ends of the members 38iõ couple with the ram assembly
32. Thus
the ram assembly 32, the attached drill chuck 42, and drill bit 44, are moved
away from the
housing 26 and drill pipe 20 by elongating the members 381õ. Strategically
coupling the
members 38iõ with the ram assembly 32 via the radial walls 34iõ and housing 26
via the
bulkheads 30iõ allows for reciprocation of the drill bit 44 a distance
substantially the same as
the elongation of individual members 381õ while also exerting a cumulative
force onto drill
bit 44 so that its reciprocating force FBI"' is substantially the same as the
sum of forces F381,
F382, F383, and F384. An advantage of reciprocating the drill bit 44, while
also rotating the
drill bit 44, is that when the drill bit 44 is reciprocatingly thrust against
the bottom 74 of the
wellbore 12, fractures 76 are formed in the formation 14 adjacent the bottom
74 of the
wellbore 12. The fractures 76 can reduce inherent stresses in the formation
14, which
increases the amount of rock removed with each rotation of the drill bit 44,
that in turn
increases rate of penetration of the drilling operation.
[0037] Figures 5A and 5B show in a side sectional view an example of
reciprocating motion
of the drill bit 44A of Figure 2. In the example of Figure 5A the drill string
16A is in the
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retracted configuration with the members 38A1õ in an unelongated state.
Further, the inner
bit 56A is spaced upward from the bottom 74A of the wellbore 12A with its
cutters 60A out
of contact with the bottom 74A, while the main bit 52A is at the bottom 74A of
the wellbore
12A and its cutters 62A in rotating contact with the bottom 74A. In an example
where
members 38A1õ include magnetostrictive material, the members 38A1õ are not
energized and
electricity from controller 48A or power supply 50A is not being transmitted
to the members
38A1-n.
[0038] In the example of Figure 5B, the members 38A i_n are depicted in an
elongated state.
In an embodiment where the members 38A1_n are made from magnetostrictive
material, the
elongation can be due to applied electricity, such as from controller 48A or
power supply
50A. In the elongated state the members 38A1, 38A2, 38A3, and 38Aõ, have
lengthened over
that of their lengths in Figure 5A by the respective distances DIA, D2A, D3A,
and DiiA. Further
illustrated is that the inner bit 56A has moved a distance DBITA with respect
to the main bit
52A. In this example the main bit 52A is coupled with the housing 26A by a
threaded
connection 78A, and unlike the inner bit 56A, the main bit 52A does not
reciprocate with
movement of the ram assembly 32A. As described above, the movement of the
inner bit 56A
is in response to movement of the members 38Aiõ via the coupling between the
members
38A1õ and ram assembly 32A (Figure 2).
[0039] Additionally, in one example, the distances DiA, D2A, D3A, and DiiA
(that can be
referred to as designated distances) all have substantially the same value.
Further in this
example, distance DBITA has a value that is substantially the same as the
value of any one of
distances DiA, D2A, D3A, and Dr,A. An advantage to reciprocating a portion of
the cutting
surface of the bit 44A proximate the axis Ax is that the portions of the
cutting surface
proximate the axis Ax have a reduced excavating effectiveness than those
portions of the
cutting surface distal from the axis Ax. The bit 44A therefore can remain
substantially
effective in excavating even when the inner bit 56A is spaced away from the
bottom 74A
(Figure 5A). Moreover, the main bit 52A is shown creating fractures 76A in the
formation
14A adjacent the bottom 74A, which can improve the excavating efficiency of
the bit 44A as
a whole.
[0040] In embodiments where the actuators 371õ, 37A1_n, do not include the
members 381õ,
38A1,, the distances DBIT, DBITA will be substantially the same as elongation
of one of the
individual actuators 37i_n, 38A1õ rather than a sum of their distances.
Similarly, the
corresponding forces FBIT, FBITA on the bits 44, 44A will be substantially the
same as the sum
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of forces from the extended actuators 371-n, 37A1_n when the actuators 371-n,
37A1_n do not
include the members 381-., 38A1-n.
[0041] The embodiments described above are well adapted to carry out the
objects and attain
the ends and advantages mentioned, as well as others inherent. While a
presently preferred
embodiment has been given for purposes of disclosure, numerous changes exist
in the details
of procedures for accomplishing the desired results. These and other similar
modifications
will readily suggest themselves to those skilled in the art, and are intended
to be encompassed
within the spirit of the embodiments disclosed herein and the scope of the
appended claims.
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