U.S. patent application number 12/578916 was filed with the patent office on 2011-04-14 for fixed bladed drill bit force balanced by blade spacing.
Invention is credited to David R. Hall, Davido L. Hyer, Casey Webb.
Application Number | 20110083906 12/578916 |
Document ID | / |
Family ID | 43853942 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110083906 |
Kind Code |
A1 |
Hall; David R. ; et
al. |
April 14, 2011 |
Fixed Bladed Drill Bit Force Balanced by Blade Spacing
Abstract
In one aspect of the present invention a force balanced drill
bit may comprise a bit body comprising a plurality of fixed blades,
each blade comprising cutters defining a cutter profile. Junk slots
may be disposed between the blades and define the blade boundaries.
The blade boundaries may be spaced apart sufficiently to achieve
force balance. In another aspect of the present invention a method
of designing a downhole fixed bladed bit comprises the steps of
modeling a fixed bladed bit by inputting blade and cutter
parameters into a computer program, performing a force balance on
the modeled fixed bladed bit, and modifying at least one blade
parameter to adjust the force balance. The parameters for modeling
a fixed bladed bit include cutter placement on a plurality of
blades integrally formed in a bit body and a position for each
blade.
Inventors: |
Hall; David R.; (Provo,
UT) ; Webb; Casey; (Spanish Fork, UT) ; Hyer;
Davido L.; (Springville, UT) |
Family ID: |
43853942 |
Appl. No.: |
12/578916 |
Filed: |
October 14, 2009 |
Current U.S.
Class: |
175/378 |
Current CPC
Class: |
E21B 10/42 20130101;
E21B 10/00 20130101 |
Class at
Publication: |
175/378 |
International
Class: |
E21B 10/00 20060101
E21B010/00 |
Claims
1. A force balanced drill bit, comprising: a bit body comprising a
plurality of fixed blades, each blade comprising cutters defining a
cutter profile; and junk slots disposed between the blades and
defining blade boundaries; wherein the blade boundaries are spaced
apart sufficiently to achieve force balance.
2. The force balanced drill bit of claim 1, further comprising at
least one nozzle disposed on the bit body and aiming into a junk
slot.
3. The force balanced drill bit of claim 2, further comprising a
plurality of nozzles disposed on the bit body wherein each junk
slot corresponds to an individual nozzle aiming into the junk
slot.
4. The force balanced drill bit of claim 3, wherein the blade
boundaries are spaced sufficiently apart to receive the plurality
of nozzles.
5. The force balanced drill bit of claim 1, wherein the cutter
profile is defined by a number of cutters, spacing of the cutters,
type of cutters, back rake, and side rake.
6. The force balanced drill bit of claim 1, wherein the cutters are
evenly spaced along the cutter profile.
7. The force balanced drill bit of claim 1, wherein the cutters
comprise flat shear type cutters.
8. The force balanced drill bit of claim 1, wherein the cutters
comprise conical shaped cutters.
9. The force balanced drill bit of claim 1, wherein the cutters
comprise both flat shear type cutters and conical shaped
cutters.
10. The force balanced drill bit of claim 1, wherein the cutters
comprise polycrystalline diamond.
11. The force balanced drill bit of claim 1, wherein the blade
boundaries are not evenly spaced.
12. The force balanced drill bit of claim 11, wherein the cutter
profile is such that if the blade boundaries were evenly spaced
then the drill bit would no longer be force balanced.
13. The force balanced drill bit of claim 1, wherein the bit body
comprises a center axis and each of the plurality of blades is
disposed around the center axis.
14. The force balanced drill bit of claim 13, wherein blade
boundaries are spaced such that the blades are within six degrees
of an even spacing around the center axis.
15. The force balanced drill bit of claim 1, wherein each blade
comprises a blade profile defined by a starting position, curvature
radii and/or angular length, a bit depth and a bit diameter.
16. The force balanced drill bit of claim 15, wherein each blade
comprises a similar blade profile.
17. The force balanced drill bit of claim 1, further comprising a
jack element disposed intermediate the plurality of fixed
blades.
18. The force balanced drill bit of claim 17, wherein the bit body
comprises a center axis and the jack element is disposed on the
center axis.
19. The force balanced drill bit of claim 18, wherein the jack
element is used in a jack steering system.
20. The force balanced drill bit of claim 18, wherein the jack
element is used in a jack hammering system.
Description
BACKGROUND OF THE INVENTION
[0001] Rotary drag bits are a type of fixed bladed drill bit that
are typically used to shear rock with a continuous scraping motion.
A typical fixed bladed bit will comprise a bit body, several blades
protruding from the bit body, and a plurality of cutters fixed on
the exposed edge of each of the blades. These cutters may be formed
from any hard and abrasive material but are generally composed of
polycrystalline diamond compact (PDC). A fixed bladed bit may be
rotated in an earthen formation allowing the cutters to engage the
rock and debris to be removed via the vacant spaces between the
blades.
[0002] Fixed bladed bits may be designed to optimize cutter
efficiency. Methods of designing fixed bladed bits for optimal
cutter efficiency may include performing a force balance. A force
balance comprises summing the forces on each cutter and calculating
the imbalance of forces in relation to the bit. Once a force
balance has been performed, modifications may be made to the
locations and orientations of the cutters to adjust the forces
acting on the bit. This process may be performed several times
during the design of a fixed bladed bit.
[0003] One such method for designing a rotary drag bit for optimal
cutter efficiency is disclosed in U.S. Pat. No. 4,815,342 to Brett,
which is herein incorporated by reference for all that it contains.
Brett discloses a method for modeling and building drill bits where
an array of spatial coordinates representative of selected surface
points on a drill bit body and on cutters mounted thereon is
created. The array is used to calculate the position of each
cutting surface relative to the longitudinal axis of the bit body.
A vertical reference plane which contains the longitudinal axis of
the bit body is established. Coordinates defining each cutter
surface are rotated about the longitudinal axis of the bit body and
projected onto the reference plane thereby defining a projected
cutting surface profile. In manufacturing a drill bit, a
preselected number of cutters are mounted on the bit body. A model
of the geometry of the bit body is generated as above described.
Thereafter, the imbalance force which would occur in the bit body
under defined drilling parameters is calculated. The imbalance
force and model are used to calculate the position of an additional
cutter or cutters which when mounted on the bit in the calculated
position would reduce the imbalance force. A cutter or cutters is
then mounted in the position or positions so calculated.
[0004] Another such method for designing a rotary drag bit for
optimal cutter efficiency is disclosed in U.S. Pat. No. 6,672,406
to Beuershausen, which is herein incorporated by reference for all
that it contains. Beuershausen discloses methods including
providing and using rotary drill bits incorporating cutting
elements having appropriately aggressive and appropriately
positioned cutting surfaces so as to enable the cutting elements to
engage the particular formation being drilled at an appropriate
depth-of-cut at a given weight-on-bit to maximize rate of
penetration without generating excessive, unwanted torque on bit.
The configuration, surface area, and effective back rake angle of
each provided cutting surface, as well as individual cutter back
rake angles, may be customized and varied to provide a cutting
element having a cutting face aggressiveness profile that varies
both longitudinally and radially along the cutting face of the
cutting element.
BRIEF SUMMARY OF THE INVENTION
[0005] One embodiment of the present invention comprises a force
balanced drill bit. Such a drill bit may comprise a bit body
comprising a plurality of fixed blades, each blade comprising
cutters defining a cutter profile. Junk slots may be disposed
between the blades and define the blade boundaries. The blade
boundaries may be spaced apart sufficiently to achieve force
balance.
[0006] Nozzles may be disposed on the bit body such that they aim
into the junk slots. Each nozzle may aim into a given junk slot.
The blade boundaries may be spaced sufficiently apart to receive a
plurality of nozzles.
[0007] The cutter profile may be defined by the number of cutters,
spacing of the cutters, type of cutters, back rake, and side rake.
The cutters may be flat shear type cutters, conical shaped cutters,
or a combination of various types of cutters. The cutters may be
comprised of polycrystalline diamond or other super hard materials
known in the art. Since the force balance is achieved by the
spacing of the blade boundaries, the cutters may be evenly spaced
along the cutter profile.
[0008] The blade boundaries may not be evenly spaced. In fact, the
cutter profile may be such that if the blade boundaries were evenly
spaced then the drill bit would no longer be force balanced. The
drill bit may comprise a center axis and each of the plurality of
blades disposed around the center axis may be spaced such that the
blades are within six degrees of an even spacing around the center
axis.
[0009] Each blade may comprise a blade profile defined by a
starting position, curvature radii and/or angular length, a bit
depth and a bit diameter. Each blade may comprise a similar blade
profile or varying blade profiles.
[0010] A jack element may be disposed intermediate the plurality of
fixed blades. The jack element may be disposed on the center axis.
The jack element may be used in a jack steering system or jack
hammering system.
[0011] Another embodiment of the present invention comprises a
method of optimizing fixed bladed bit efficiency during the design
stage by adjusting the locations and orientations of blades, rather
than cutters, on the bit. Such a method may comprise the steps of
modeling a fixed bladed bit by inputting blade and cutter
parameters into a computer program, performing a force balance on
the modeled fixed bladed bit, and modifying at least one blade
parameter to adjust the force balance. The parameters for modeling
a fixed bladed bit may include cutter placement on a plurality of
blades integrally formed in a bit body and a position for each
blade.
[0012] The step of modeling a fixed bladed bit using a computer
program may include creating a blade profile, a cutter profile, and
a blade layout. The blade profile may be defined by first selecting
a blade profile type from a definite number of blade profile types
which may include profiles containing: three distinct curvatures,
at least one linear edge in between a plurality of curvatures, or
at least one curvature in between a plurality of linear edges. The
blade profile may then be defined by a starting position, curvature
radii, curvature angular length, bit depth and bit diameter. The
cutter profile may be defined by the number of cutters, spacing of
the cutters, type of cutters, back rake, and side rake. The blade
layout may be defined by the number of blades, blade thickness, and
blade offset.
[0013] After the blade and cutter parameters have been inputted,
selected parameters may be allowed to be manually manipulated.
These parameters may include the side rake, back rake, profile
offset, normal offset, cutter diameter, cutter length, blade
rotation, and starting cutter placement.
[0014] After the fixed bladed bit has been modeled, a force balance
on the fixed bladed bit may be performed. This force balance may
comprise summing the forces on each cutter and calculating the
imbalance of forces in relation to the bit. The force balance may
be dependent upon an inputted depth of cut value. Upon performing
the force balance, the computer program may visually display force
vectors representing the forces acting on each cutter. Reduction of
the imbalance of forces resulting from the force balance may be
achieved by adjusting the position of at least one blade. The at
least one blade may have an angular displacement within six degrees
of its original position. The cutter parameters and the blade
profile may remain the same while the blade parameters of the fixed
bladed bit are modified.
[0015] The steps of performing a force balance and modifying at
least one blade parameter may also be performed on a modeled fixed
bladed bit inputted from an external source. Performing a force
balance may also comprise accounting for forces generated by a jack
steering system. After modeling or inputting a fixed bladed bit,
performing a force balance, and repositioning at least one blade on
the fixed bladed bit, the fixed bladed bit may be outputted to a
computer aided design computer program.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross-sectional side view of an embodiment of a
drill string.
[0017] FIG. 2 is a perspective view of an embodiment of a fixed
bladed bit.
[0018] FIG. 3 is a front view of an embodiment of a fixed bladed
bit.
[0019] FIG. 4a is a perspective view of an embodiment of a modeled
fixed bladed bit.
[0020] FIG. 4b is a perspective view of another embodiment of a
modeled fixed bladed bit.
[0021] FIG. 5 is a perspective view of an embodiment of a computer
display.
[0022] FIG. 6a is a 2-dimensional view of an embodiment of a blade
profile.
[0023] FIG. 6b is a 2-dimensional view of another embodiment of a
blade profile.
[0024] FIG. 6c is a 2-dimensional view of another embodiment of a
blade profile.
[0025] FIG. 7 is a 2-dimensional view of an embodiment of a cutter
profile.
[0026] FIG. 8 is a perspective view of another embodiment of a
modeled fixed bladed bit.
[0027] FIG. 9 is a 2-dimensional view of an embodiment of another
cutter profile.
[0028] FIG. 10 is a perspective view of another embodiment of a
modeled fixed bladed bit.
[0029] FIG. 11 is a 2-dimensional view of an embodiment of force
vectors displayed upon performing a force balance.
[0030] FIG. 12 is a perspective view of another embodiment of a
modeled fixed bladed bit.
[0031] FIG. 13 is a top view of another embodiment of a modeled
fixed bladed bit.
[0032] FIG. 14 is a front view of a cutter.
[0033] FIG. 15 is a 2-dimensional view of another embodiment of a
cutter profile.
[0034] FIG. 16 is a perspective view of an embodiment of a computer
display.
[0035] FIG. 17 is a flow chart representing an embodiment of a
method of designing a downhole fixed bladed bit.
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED
EMBODIMENT
[0036] Moving now to the figures, FIG. 1 displays a cross-sectional
side view of an embodiment of a downhole drill string 101. The
downhole drill string 101 may be suspended by a derrick 102 within
an earthen formation 105. The drill string 101 may comprise one or
more downhole components 104 including a fixed bladed bit 100
linked together and in communication with an uphole assembly 103.
The drill string 101 may be rotated at the derrick 102 causing the
fixed bladed bit 100 to engage the earthen formation 105. The fixed
bladed bit 100 may comprise a rotary drag bit that may shear rock
within the earthen formation 105 with a generally continuous
scraping motion. The fixed bladed bit 100 may also comprise
non-drag bits that may fail the rock by other methods.
[0037] FIG. 2 shows a perspective view of an embodiment of a fixed
bladed bit 100. The fixed bladed bit 100 comprises a bit body 200,
several blades 201 protruding from the bit body 200, and a
plurality of cutters 202 fixed on an exposed edge of each of the
blades 201. These cutters 202 may be formed from any hard and
abrasive material but are generally composed of polycrystalline
diamond compact (PDC). The cutters 202 may be flat shear type
cutters, conical-shaped cutters, or other cutter geometries known
in the art. Suitable conical-shaped cutters are manufactured under
the brand name Stinger.RTM. by Novatek Inc., 2185 S. Larsen
Parkway, Provo, Utah 84606. As the fixed bladed bit 100 is rotated
in an earthen formation, the cutters 202 may engage rock within the
earthen formation and debris may be removed via the vacant spaces,
known as junk slots 220, between the blades 201. If the fixed
bladed bit 100 comprises flat shear type cutters then the fixed
bladed bit 100 may comprise a rotary drag bit and may shear rock
with a generally continuous scraping motion. If the fixed bladed
bit 100 comprises conical-shaped cutters then the fixed bladed bit
100 may cleave chunks of rock from a formation.
[0038] The fixed bladed bit 100 may also comprise a jack element
210. The jack element 210 may form part of a jack steering system
where the fixed bladed bit 100 is urged in a desired direction by
the jack element 210. The desired direction may change throughout
the drilling process. The jack element 210 may also form part of a
jack hammering system where the jack element 210 oscillates back
and forth to help break up the formation.
[0039] FIG. 3 shows a front view of an embodiment of a fixed bladed
bit 100. The fixed bladed bit 100 may comprise nozzles 230 disposed
on the bit body 200 and aiming into junk slots 220. In the
embodiment shown, each individual nozzle 230 aims into an
individual junk slot 220. Also in the embodiment shown, the jack
element 210 is disposed on a center axis 250.
[0040] FIGS. 4a and 4b show perspective views of an embodiment of a
modeled fixed bladed bit 300. While designing a fixed bladed bit, a
computer program may be used to model the fixed bladed bit
digitally. One of the advantages of creating a modeled fixed bladed
bit 300 is that calculations may be performed on the modeled fixed
bladed bit 300 without the expense of building a physical fixed
bladed bit. In order to model a fixed bladed bit, parameters may be
inputted into a computer program to form a blade profile 303 and a
cutter profile 304. The blade profile 303 is a 2-dimensional
outline of an individual blade 201. The cutter profile 304 is a
layout of the positioning of a plurality of cutters 202 placed on a
blade profile 303. FIG. 4a shows a perspective view of an
embodiment of a modeled fixed bladed bit 300 with PCD shear cutters
301 and FIG. 4b shows a perspective view of an embodiment of a
modeled fixed bladed bit 300 with PCD conical-shaped cutters
302.
[0041] FIG. 5 shows a perspective view of an embodiment of a
computer display 500. When designing a downhole fixed bladed bit
with a computer program, a user may first choose a blade profile
type from a definite number of blade profile types as shown on a
computer display 500. In the embodiment shown, blade profile 410,
blade profile 411, and blade profile 412 are available for the user
to chose. Option buttons 501 may be used to select a blade profile
type.
[0042] FIGS. 6a, 6b, and 6c are 2-dimensional views of embodiments
of blade profiles 410, 411, and 412 respectively. Each blade
profile 410, 411, and 412 has a first linear edge 401 and a second
linear edge 402. The first linear edge 401 terminates at a first
end point 403 and the second linear edge 402 terminates at a second
end point 404. The first linear edge 401 and the second linear edge
402 may be connected by a plurality of combinations of curvatures
and linear edges as shown in the following embodiments. FIG. 6a
shows a 2-dimensional view of an embodiment of a blade profile 410
comprising at least one linear edge 405 between a plurality of
curvatures 406. FIG. 6b shows a 2-dimensional view of an embodiment
of a blade profile 411 comprising at least one curvature 407
adjacent a linear edge 408. FIG. 6c shows a 2-dimensional view of
an embodiment of a blade profile 412 comprising three distinct
curvatures 409.
[0043] FIG. 7 shows a 2-dimensional view of an embodiment of a
cutter profile 304. The cutter profile 304 may be formed from a
blade profile 303 with the addition of a plurality of cutters 202.
The cutters 202 may be placed on the blade profile 303 according to
cutter profile 304 parameters that may include: number of cutters
202, spacing of cutters 202, type of cutters 202, back rake, and
side rake. In the embodiment shown, the cutters 202 are equally
spaced throughout the cutter profile 304. In other embodiments, the
cutters 202 may be uniquely spaced throughout the cutter profile
304 and in accordance to other inputs.
[0044] FIG. 8 is a perspective view of another embodiment of a
modeled fixed bladed bit 300. A user may manually manipulate the
parameters of the modeled fixed bladed bit 300. The user may
manually manipulate individual cutters 202 or individual blades
201. In the embodiment shown, a cutter 701 has been modified. Each
cutter 202 on the fixed bladed bit 300 is a PCD shear cutter with
the exception of cutter 701 which is a PCD conical-shaped cutter.
The user may manually manipulate the parameters consisting of: type
of cutter 202, side rake, back rake, profile offset, normal offset,
cutter 202 diameter, cutter 202 length, blade rotation, and cutter
202 placement starting diameter. The cutter 202 placement starting
diameter indicates that a first cutter on its corresponding blade
will be located at a set length away from the center of the fixed
bladed bit.
[0045] FIG. 9 shows a 2-dimensional view of another cutter profile
800. This embodiment of a cutter profile 800 shows how parameters
can be manually manipulated with respect to the profile offset and
the normal offset. The cutter profile 800 is formed from a blade
profile 303 with the addition of a plurality of shear cutters 801
and a plurality of conical shaped cutters 802. The profile offset
is a distance which offsets a cutter position along the cutter
profile 800. As seen in the figure, a shear cutter 803 has been
offset along the cutter profile a distance 804. Therefore the
profile offset is the distance 804 in between the shear cutter 803
and the shear cutter 805. The normal offset can be seen with the
conical-shaped cutter 806. The normal offset is a distance which
offsets a cutter position along a vector normal to the cutter so as
to raise or lower a cutter. The conical-shaped cutter 806 must be
raised a distance 807 along a vector normal to the cutter so that
the conical-shaped cutter 806 can be on the same cutting level 808
as the shear cutter 809. The normal offset is typically used to
bring conical-shaped cutters to the same cutting level as shear
cutters; however the normal offset can also be used for any other
application which requires at least one cutter 801 to be offset
along a vector normal to the cutter 801.
[0046] FIG. 10 is a perspective view of an embodiment of a modeled
fixed bladed bit 300. After a fixed bladed bit has been modeled, a
force balance may be performed. A force balance is a method of
determining the forces acting upon a drill bit while engaged. These
forces may be caused by weight-on-bit, torque, a steering system
such as a jack steering system, or other causes known in the art.
In order to perform a force balance, a depth-of-cut value may be
required to determine a weight-on-bit. The purpose of a force
balance is to eliminate unbalanced forces acting on a drill bit.
Unevenly balanced forces acting on a drill bit may cause cutters to
wear more quickly and also make the drill bit less effective. When
a force balance is performed, a weight-on-bit imbalance percentage
may be calculated. The weight-on-bit imbalance percentage is the
numerical value corresponding to the unbalanced forces acting on
the bit.
[0047] A Cartesian coordinate system comprising a z-axis 920,
y-axis 930 and x-axis 940 is shown as a reference for the forces
acting on the cutter 950. To perform a force balance, a tangential
force 901 may be calculated. The tangential force 901 may be then
separated into Cartesian vector components to obtain an x-component
of the tangential force 902 and a y-component of the tangential
force 903. A normal force 904 may also be calculated. The normal
force 904 can be split up into an axial force 905 and a radial
force 906. The axial force 905 is the force acting down upon the
cutter along the z-axis 920, note also that the axial force 905 is
the weight-on-bit that can be controlled during actual drilling.
The radial force 906 is the force acting towards the center axis of
the modeled fixed bladed bit 300. The radial force 906 may then be
separated into Cartesian vector components to obtain an x-component
of the radial force 907 and a y-component of the radial force 908.
The x-component of the tangential force 902 and the x-component of
the radial force 907 may be summed together (.SIGMA.x) and the
y-component of the tangential force 903 and the y-component of the
radial force 908 may be summed together (.SIGMA.y). A resultant
force (F.sub.res) 909 may then be calculated from .SIGMA.x and
.SIGMA.y by the equation:
(F.sub.res).sup.2=(.SIGMA.x).sup.2+(.SIGMA.y).sup.2
[0048] The weight-on-bit imbalance percentage (WOB %) may then be
calculated from the resultant force and the axial force (F.sub.ax)
905 from the following equation:
WOB %=(F.sub.res/F.sub.ax)*100
[0049] If the drill bit was completely balanced, the WOB % would be
zero. The WOB % is zero when the forces around the drill bit cancel
each other out.
[0050] FIG. 11 shows a 2-dimensional view of an embodiment of force
vectors 1000 that may be displayed when a force balance is
performed. Each force vector 1000 represents the magnitude of
forces acting on an individual cutter. The magnitude of the forces
acting on an individual cutter is dependent upon an area of each
individual cutter when engaged. The force vectors 1000 may be shown
on a standard Cartesian coordinate system 1001 with an x-axis 1002
and a y-axis 1003. The intersection 1004 of the x-axis 1002 and the
y-axis 1003 is the point that corresponds to the center of the
modeled fixed bladed bit. By using the standard Cartesian
coordinate system 1001, users can identify where the forces are
unbalanced and make adjustments in order to balance the forces and
minimize the WOB %. As shown in the figure, each force vector 1000
represents the forces acting on each cutter. When adjustments are
needed in order to balance the forces and minimize the WOB %, at
least one blade is rotated around the center axis. As the at least
one blade rotates, the forces acting on each cutter at the new
position can be represented by a new force balance. Therefore the
force vectors 1010 originate in a first position, then upon
rotating the blade, the force vectors 1010 end in a second
position.
[0051] FIG. 12 shows a perspective view of another embodiment of a
modeled fixed bladed bit 300. At least one blade 201 may be rotated
in order to adjust the force balance. In the embodiment shown, a
blade 1100 is in an original position 1101. After a force balance
is performed, the blade 1100 may be rotated about a center of the
drill bit to a new position 1102. By rotating the blade 1100, the
force vectors may be adjusted and the force balance may become
substantially balanced. In the embodiment shown, the blade 1100
rotates about the center of the fixed bladed bit 300 within six
degrees with respect to the blade's 1100 original position 1101. It
is believed that by rotating at least one blade 201 while the
cutters 202 and the blade profile 303 remain unchanged the pattern
of cutting may remain the same.
[0052] FIG. 13 is a top view of another embodiment of a modeled
fixed bladed bit 300. In this embodiment, a blade 1100 is in an
original position 1101 and then is rotated to a new position
902.
[0053] FIG. 14 shows a front view of a cutter 202. The darkened
areas 1100 and 1101 represent the surface of the cutter that may
engage a formation. In the embodiment shown, area 1300 represents
the engaging surface before at least one blade is rotated about the
center of the fixed bladed bit and the area 1301 represents the
engaging surface after the rotation. The area a cutter engages
changes as at least one blade is rotated about the center of the
fixed bladed bit because the area a cutter engages is dependent
upon the cutters on the other blades. As at least one blade is
rotated about the fixed bladed bit, the blade's initial position in
relation to the other blades is changed and therefore the area a
cutter engages is affected which in turn affects the forces on the
cutters and the weight-on-bit imbalance percentage.
[0054] FIG. 15 shows a 2-dimensional view of another embodiment of
a cutter profile 304. The figure shows the cutter profile 1401
before the rotation of at least one blade about the center of the
fixed bladed bit and the cutter profile 1402 after the rotation. As
shown, the cutter parameters remain unchanged when modifying at
least one blade parameter.
[0055] FIG. 16 is a perspective view of an embodiment of a computer
display 500 showing the output from computer programs 1501 and
1302. Program 1501 comprises the previously described method of
modeling a fixed bladed bit 300, performing a force balance on the
modeled fixed bladed bit 300, and modifying the modeled fixed
bladed bit by rotating at least one blade 201 about the center of
the fixed bladed bit 300. Program 1502 is a computer aided design
computer program which may import the designed fixed bladed bit 300
from an external source and subsequently perform other functions on
it.
[0056] FIG. 17 shows a flow chart representing an embodiment of a
method 1600 of designing a downhole fixed bladed bit comprising the
steps of modeling 1601 a fixed bladed bit, performing 1602 a force
balance, modifying 1603 blades, and outputting 1604 to a computer
aided design computer program. The step of modeling 1601 a fixed
bladed bit includes inputting a plurality of blade and cutter
parameters that may be used to form a blade profile, a cutter
profile, and a blade layout. Parameters that may be used to form
the blade profile include: starting position, curvature radii,
curvature angular length, bit depth, and bit diameter. Parameters
that may be used to form the cutter profile include: number of
cutters, spacing of cutters, type of cutters, back rake, and side
rake. Parameters that may be used to form the blade layout include:
number of blades, blade thickness, and blade offset (measure of
spiral for a specific blade). Modeling 1601 a fixed bladed bit may
also comprise manually manipulating individual cutters or
individual blades using the parameters: side rake, back rake,
profile offset, normal offset, cutter diameter, cutter length,
blade rotation, and cutter placement starting diameter. The step of
performing 1602 a force balance may comprise inputting a
depth-of-cut value. When the force balance has been performed, the
vector fields for each cutter may be visually displayed. The step
of performing 1602 a force balance may be completed on a modeled
fixed bladed bit from step 1601 or may be performed on a modeled
fixed bladed bit inputted from an external source. The step of
modifying 1603 blades comprises rotating at least one blade
parameter to adjust the force balance.
[0057] Whereas the present invention has been described in
particular relation to the drawings attached hereto, it should be
understood that other and further modifications apart from those
shown or suggested herein, may be made within the scope and spirit
of the present invention.
* * * * *