U.S. patent application number 15/377339 was filed with the patent office on 2017-06-22 for force stacking assembly for use with a subterranean excavating system.
This patent application is currently assigned to Aramco Overseas Company B.V.. The applicant listed for this patent is Aramco Overseas Company B.V., Geoprober Ltd.. Invention is credited to Ben Bamford, Scott Fraser.
Application Number | 20170175446 15/377339 |
Document ID | / |
Family ID | 57708855 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170175446 |
Kind Code |
A1 |
Fraser; Scott ; et
al. |
June 22, 2017 |
Force Stacking Assembly for Use with a Subterranean Excavating
System
Abstract
A force stacking assembly for use with an earth boring system
that includes a series of actuators that each generate a force, and
that are arranged to create a combined force that is cumulative of
all of the actuators. The actuators include members that react in
response to an applied stimulus, such as from an electrical current
or magnetic field. The members are arranged in series in a hollow
housing, planar bulkheads are transversely mounted in the housing.
Each of the members have an end axially abutting a corresponding
bulkhead. Ends of each member distal from it corresponding bulkhead
couple to a ram member, that in turn couples to a drill bit.
Energizing the members causes each to exert a force against the ram
member, which is transferred to the bit.
Inventors: |
Fraser; Scott;
(Aberdeenshire, GB) ; Bamford; Ben; (Aberdeen,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Aramco Overseas Company B.V.
Geoprober Ltd. |
The Hague
Aberdeen |
|
NL
GB |
|
|
Assignee: |
Aramco Overseas Company
B.V.
The Hague
NL
Geoprober Ltd.
Aberdeen
GB
|
Family ID: |
57708855 |
Appl. No.: |
15/377339 |
Filed: |
December 13, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62268752 |
Dec 17, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 1/00 20130101; E21B
28/00 20130101; E21B 4/12 20130101; E21B 4/06 20130101; E21B 6/04
20130101; E21B 7/24 20130101 |
International
Class: |
E21B 4/12 20060101
E21B004/12; E21B 6/04 20060101 E21B006/04; E21B 1/00 20060101
E21B001/00 |
Claims
1. A system for excavating within a wellbore comprising: 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.
2. The system of claim 1, wherein 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.
3. The system of claim 2, wherein when the actuators are
selectively extended, the drill bit is axially displaced an amount
substantially equal to axial elongation of one of the
actuators.
4. The system of claim 1, wherein the actuators comprise members
made from an activatable material that elongates in response to
applied electricity.
5. The system of claim 4, wherein the activatable material
comprises a substance selected from the group consisting of a
piezoelectric material, a magnetorestrictive material, and
combinations thereof.
6. The system of claim 1, wherein the drill bit comprises 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 an
activated state.
7. The system of claim 1, wherein the actuators are axially
elongated when selectively activated.
8. The system of claim 1, wherein the housing is hollow and
bulkheads are formed within 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.
9. The system of claim 8, wherein the ends of the actuators that
couple with the housing are in abutting contact with the
bulkheads.
10. The system of claim 1, wherein planar radial walls are provided
inside of the 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.
11. The system of claim 1, wherein the ram assembly coaxially moves
within the housing when the actuators are selectively extended.
12. A method of excavating within a wellbore comprising: rotating a
drill string in the wellbore that comprises 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 the drill bit away from
the drill pipe an urged distance that is substantially the same as
the designated distance.
13. The method of claim 12, wherein the actuators are elongated at
a frequency that comprises a resonant frequency selected from the
group consisting of a resonant frequency of the drill string and a
resonant frequency of a formation that surrounds the wellbore.
14. The method of claim 12, wherein selectively elongating each of
the actuators a designated distance comprises directing electricity
to a magnetorestrictive member disposed in an actuator that axially
expands and generates one of the actuating forces.
15. The method of claim 12, wherein the portion of the drill bit
urged away from the drill pipe comprises an inner bit that is
proximate an axis of the drill bit.
16. The method of claim 12, wherein at least a portion of the drill
bit comprises 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.
17. A system for excavating within a wellbore comprising: 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.
18. The system of claim 17, wherein the actuators comprise members
having material that is responsive to an application of
electricity.
19. The system of claim 18, wherein the bottom hole assembly
further comprises 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.
20. The system of claim 19, wherein the bottom hole assembly
further comprises 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.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application of, and
claims priority to and the benefit of, co-pending U.S. Provisional
Application Ser. No. 62/268,752, filed Dec. 17, 2015, the full
disclosure of which is hereby incorporated by reference herein for
all purposes.
BACKGROUND
[0002] 1. Field of the Disclosure
[0003] 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.
[0004] 2. Description of Prior Art
[0005] 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.
[0006] 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 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.
SUMMARY
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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 the drill bit away from the drill
pipe an urged distance that is substantially the same as the
designated distance.
[0011] 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.
[0012] 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.
BRIEF DESCRIPTION OF DRAWINGS
[0013] 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:
[0014] FIG. 1 is a sectional view of an example of a drilling
system having actuators for delivering an axial force to a drill
bit.
[0015] FIG. 2 is a sectional view of an alternate example of the
drilling system of FIG. 1.
[0016] FIG. 3 is an axial view of an example of the drilling system
taken along lines 3-3 of FIG. 1.
[0017] FIGS. 4A and 4B show an example of the drilling system of
FIG. 1 respectively in a retracted and an extended
configuration.
[0018] FIGS. 5A and 5B show an example of the drilling system of
FIG. 2 respectively in a retracted and an extended
configuration.
[0019] 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.
DETAILED DESCRIPTION
[0020] 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.
[0021] 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.
[0022] Shown in a side sectional view in FIG. 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 A.sub.X of BHA 24. The
outer surface of sidewalls 27 resembles a cylindrical shape. Inside
of housing 26 are elongate compartments 28.sub.1-n that are formed
in series. The compartments 28.sub.1-n are defined between planar
bulkheads 30.sub.1-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 A.sub.X of the bottom hole assembly 24 and extend
generally parallel with sidewalls 27 of housing 26. Similar to the
bulkheads 30.sub.1-n in housing 26, are planar radial walls
34.sub.1, 34.sub.2 that extend radially between the sidewalls of
the ram assembly 32 at axially spaced apart locations to form
compartments 36.sub.1-n within ram assembly 32.
[0023] BHA 24 further includes actuators 37.sub.1-n that
selectively apply a cumulative force against the housing 26, and an
opposing force against ram assembly 32. More specifically,
actuators 37.sub.1-n of FIG. 1 are made up of reactive members
38.sub.1-n, that in the illustrated embodiment are disposed in
housing 26. Further illustrated is that each of the reactive
members 38.sub.1-n have an end that is coupled with the housing 26
via contact with an associated bulkhead 30.sub.1-n. Examples of the
reactive members 38.sub.1-n 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 37.sub.1-n such as hydraulic
or pneumatic. Changes in size include becoming longer, shorter,
wider, thinner, or combinations thereof. Example constituents of
the reactive members 38.sub.1-n 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 38.sub.1-n couples with the ram assembly 32 via
resilient members 40.sub.1-n where each of the resilient members
40.sub.1-n are in contact with the ram assembly 32. In the example
of FIG. 1, resilient member 40.sub.1 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 40.sub.2 mounts on radial wall 34.sub.1, resilient
member 40.sub.3 mounts on radial wall 34.sub.2, and resilient
member 40 mounts on radial wall 34.sub.n. Examples of the resilient
members 40.sub.1-n include springs, Belleville washers, elastomeric
members, combinations thereof, and the like. In an alternate
embodiment, resilient members 40.sub.1-n are not included so that
the ends of the reactive members 38.sub.1-n directly contact the
ram assembly 32.
[0024] 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 FIG. 1,
is a controller 48 which connects to a communication means 49 for
communicating signals and/or electrical power to the reactive
members 38.sub.1-n. In one example of operation, reactive members
38.sub.1-n 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
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 38.sub.1-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 38.sub.1-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 38.sub.1-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.
[0025] Thus selectively generating forces against ram assembly 32
with reactive members 38.sub.1-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 38.sub.1-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 38.sub.1-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 38.sub.1-n
rather than a sum of all of their elongations. In one example,
controller 48 energizes actuators 37.sub.1-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 operate
controller 48 so that the actuators 37.sub.1-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.
[0026] 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 37.sub.1-n are arranged in
series, the resulting force is as though the actuators 37.sub.1-n
were in parallel, that is, the resulting force is substantially
equal to the sum of force exerted by each of the actuators
37.sub.1-n. Moreover, in an example the axial displacement of the
bit 44, due to the cumulative axial displacement of the actuators
37.sub.1-n is substantially the same as if the actuators 37.sub.1-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.
[0027] The velocity of the mass m of the bottom hole assembly 24
changes by .DELTA.v during impacts of the oscillator of period
.tau., due to the contact harmonic force F=P.sub.d sin(.pi.t/.tau.)
which is governed by Equation 1, for the changing momentum of the
system.
m .DELTA. v = .intg. 0 .tau. P d sin ( .pi.t .tau. ) dt = P d ( 2
.tau. .pi. ) . Equation 1 ##EQU00001##
[0028] In one example, the uniaxial 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;
U.sub.S=P.sub.d/A.sub.e, Equation 2;
where A.sub.e is the effective area, which in an example is assumed
to be about 5% of the area of the hole drilled.
m .DELTA. v = P d ( 2 .tau. .pi. ) = 1 2 U s 0.05 D 2 .tau. , ( by
substituting Eqn . 2 into Eqn . 1 ) . Equation 3 ##EQU00002##
[0029] Assuming that the drill bit 44 performs a harmonic motion
between impacts, in this example the maximum velocity of the drill
bit is V.sub.m=A.omega., where A is the amplitude of the vibration
and .omega.=2.pi.f is its oscillation frequency in rad/s. Assuming
further that the impact occurs when the drill bit 44 has maximum
velocity V.sub.m and that the drill bit 44 stops during the impact,
then .DELTA.v=V.sub.m=2A.pi.f. Accordingly in this example, the
vibrating mass is expressed as:
m = 0.05 D 2 U s .tau. 4 .pi. Af . Equation 4 ##EQU00003##
[0030] The period of the impact, .tau., 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,
.tau. is estimated to be about 1.0 percent of the period of
oscillation, that is, .tau.=0.01/f. By substituting .tau. into
Equation 4 a lower bound estimation of the resonant frequency that
can provide enough impulse for the impacts is given by Equation 5
as follows.
f = D 2 U s 8000 .pi. Am . Equation 5 ##EQU00004##
[0031] 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, S.sub.f, with
appropriate value less than 1.0 can be applied to the frequency as
a precautionary measure.
[0032] The dynamic force, P.sub.d, applied to the oscillation
system can be calculated by rearranging Equation 2 and can be
expressed as follows:
P.sub.d=A.sub.eU.sub.S=.pi./4(D.sub.e.sup.2U.sub.S) Equation 6;
where in this example D.sub.e is an effective diameter associated
with effective area (A.sub.e) 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, D.sub.e, can
be defined as:
D.sub.e= {square root over (S.sub.C)}D Equation 7;
where S.sub.C 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, D.sub.e= {square root over
(0.05)}D. An appropriate value of scaling/safety factor can be
introduced to the dynamic force, P.sub.d, according to the material
being drilled so 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.
[0033] 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, S.sub.f.
{square root over
((D.sup.2U.sub.S/8000.pi.Am)))}.ltoreq.f.ltoreq.S.sub.f {square
root over ((D.sup.2U.sub.S/8000.pi.Am)))} Equation 8.
[0034] Referring now to FIG. 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 FIG. 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 28A.sub.1-n the housing 26A,
and bulkheads 30A.sub.1-n at opposing axial ends of the
compartments 28A.sub.1-n A generally cylindrically shaped ram
assembly 32A is coaxially disposed in the housing 26A having axial
sidewalls 33A and radial walls 34A.sub.1-n that are transversely
mounted within sidewalls 33A. Axially between the radial walls
34A.sub.1-n are compartments 36A.sub.1-n which actuators
37A.sub.1-n are provided and that include reactive members
38A.sub.1-n Resilient members 40A.sub.1-n provided in the
compartments 36A.sub.1-n exert a biasing force against reactive
members 38A.sub.1-n.
[0035] A difference between the embodiments of FIGS. 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 38A.sub.1, 38A.sub.2,
. . . , 38A.sub.n 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.
[0036] Because housing 26A is not axially motivated by actuators
37A.sub.1-n, main bit 52A does not axially reciprocate in response
to operation of actuators 37A.sub.1-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, 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 FIG. 2. Examples exist where cutters 60A, 62A are
formed from composites, such as poly-crystalline diamond.
[0037] FIG. 3 is an axial sectional view of an example of the BHA
24 taken along lines 3-3 of FIG. 1. In this example, a coil 64 is
shown between ram assembly 32 and reactive member 38.sub.1. As is
known, selectively energizing the coil 64 with electricity
generates an electrical field that as explained above axially
elongates the reactive member 38.sub.1. Electricity for energizing
the coil 64 can be from surface, such as from controller 48 or
power supply 50 (FIG. 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 38.sub.1 coaxially inserts into a sleeve 66 that can provide
protection/isolation for the reactive member 38.sub.1. 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.
[0038] FIGS. 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 FIG. 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 38.sub.1-n are in an unelongated state. In an example
where members 38.sub.1-n are magnetostrictive material, the members
38.sub.1-n are not energized and electricity from controller 48 or
power supply 50 is not being transmitted to the members 38.sub.1-n.
Referring now to FIG. 4B, the members 38.sub.1-n are depicted in an
elongated state. In an embodiment where the members 38.sub.1-n 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 FIG. 4B, the members 38.sub.1,
38.sub.2, 38.sub.3, and 38.sub.n, have elongated over their lengths
shown in FIG. 4A by the respective distances D.sub.1, D.sub.2,
D.sub.3, and D.sub.n.
[0039] Further illustrated is that the bit 44 has moved a distance
D.sub.BIT in the wellbore 12. As described above, the movement of
the bit 44 is in response to movement of the members 38.sub.1-n via
the coupling between the members 38.sub.1-n and ram assembly 32
(FIG. 1). Additionally, in one example, the distances D.sub.1,
D.sub.2, D.sub.3, and D.sub.n (that can be referred to as
designated distances) all have substantially the same value.
Further in this example, distance D.sub.BIT has a value that is
substantially the same as the value of any one of distances
D.sub.1, D.sub.2, D.sub.3, and D.sub.n. Accordingly, in this
example, the novel configuration of the housing 26 and ram assembly
32 results in the distance D.sub.BIT not being a sum of the
individual distances D.sub.1, D.sub.2, D.sub.3, and D.sub.n.
[0040] Further illustrated in FIG. 4B are arrows that respectively
represent forces F38.sub.1, F38.sub.2, F38.sub.3, and F38.sub.4
generated by the members 38.sub.1-n when being actuated/elongated.
Another arrow represents force FBIT which is the force being
transmitted to drill bit 44 from elongation of the members
38.sub.1-n, and which is substantially equal to a summation of
forces F38.sub.1, F38.sub.2, F38.sub.3, and F38.sub.4. As indicated
above, ends of the members 38.sub.1-n couple with the housing 26,
and opposing ends of the members 38.sub.1-n 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 38.sub.1-n. Strategically coupling the
members 38.sub.1-n with the ram assembly 32 via the radial walls
34.sub.1-n and housing 26 via the bulkheads 30.sub.1-n allows for
reciprocation of the drill bit 44 a distance substantially the same
as the elongation of individual members 38.sub.1-n while also
exerting a cumulative force onto drill bit 44 so that its
reciprocating force F.sub.BIT is substantially the same as the sum
of forces F38.sub.1, F38.sub.2, F38.sub.3, and F38.sub.4. 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.
[0041] FIGS. 5A and 5B show in a side sectional view an example of
reciprocating motion of the drill bit 44A of FIG. 2. In the example
of FIG. 5A the drill string 16A is in the retracted configuration
with the members 38A.sub.1-n 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 38A.sub.1-n include magnetostrictive material, the
members 38A.sub.1-n are not energized and electricity from
controller 48A or power supply 50A is not being transmitted to the
members 38A.sub.1-n.
[0042] In the example of FIG. 5B, the members 38A.sub.1-n are
depicted in an elongated state. In an embodiment where the members
38A.sub.1-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 38A.sub.1,
38A.sub.2, 38A.sub.3, and 38A.sub.n, have lengthened over that of
their lengths in FIG. 5A by the respective distances D.sub.1A,
D.sub.2A, D.sub.3A, and D.sub.nA. Further illustrated is that the
inner bit 56A has moved a distance D.sub.BITA 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 38A.sub.1-n via the
coupling between the members 38A.sub.1-n and ram assembly 32A (FIG.
2).
[0043] Additionally, in one example, the distances D.sub.1A,
D.sub.2A, D.sub.3A, and D.sub.A (that can be referred to as
designated distances) all have substantially the same value.
Further in this example, distance D.sub.BITA has a value that is
substantially the same as the value of any one of distances
D.sub.1A, D.sub.2A, D.sub.3A, and D.sub.nA. An advantage to
reciprocating a portion of the cutting surface of the bit 44A
proximate the axis A.sub.X is that the portions of the cutting
surface proximate the axis A.sub.X have a reduced excavating
effectiveness than those portions of the cutting surface distal
from the axis A.sub.X. The bit 44A therefore can remain
substantially effective in excavating even when the inner bit 56A
is spaced away from the bottom 74A (FIG. 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.
[0044] In embodiments where the actuators 37.sub.1-n, 37A.sub.1-n,
do not include the members 38.sub.1-n, 38A.sub.1-n the distances
D.sub.BIT, D.sub.BITA will be substantially the same as elongation
of one of the individual actuators 37.sub.1-n, 38A.sub.1-n rather
than a sum of their distances. Similarly, the corresponding forces
F.sub.BIT, F.sub.BITA on the bits 44, 44A will be substantially the
same as the sum of forces from the extended actuators 37.sub.1-n,
37A.sub.1-n when the actuators 37.sub.1-n, 37A.sub.1-n do not
include the members 38.sub.1, 38A.sub.1-n.
[0045] 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.
* * * * *