Note: Descriptions are shown in the official language in which they were submitted.
CA 02523325 2005-10-12
FLOW ALLOCATION IN DRILL BITS
BACKGROUND
The present invention relates generally to earth boring drill bits. More
particularly, the
present invention relates to methods and apparatus used to allocate and
control fluid flow
through and around earth boring drill bits. Still more particularly, the
present invention relates to
methods that use hydraulic analysis to determine the fluid flow through and
around earth boring
drill bits and apparatus that provide for the adjustment or variation of
certain drill bit parameters
in order to allocate and control the fluid flow.
In rotary drilling applications, an earth boring drill bit is disposed at the
end of a rotating
drill string. A fluid is pumped down through the drill string to the bit,
where it exits the bit
through one or more nozzles or ports. The interaction of the fluid with the
drill bit and the
surrounding formation is an important aspect of drill bit design and
performance. This system of
interaction is known as "bit hydraulics." Evaluation of bit hydraulics
generally comprises
analyzing three primary functions of the hydraulics, namely: cutting structure
cleaning/cooling;
bottom hole cleaning; and cuttings evacuation.
Cutting structure cleaning is the ability of the hydraulic fluid to remove
formation
materials from the bit's cutting structure. Accumulation of formation
materials on the cutting
structure can reduce or prevent the penetration of the cutting structure into
the formation.
Cutting structure cooling is the ability of the hydraulic fluid to remove
heat, which is caused by
contact with formation, from cutting elements in order to prolong cutting
element life. Bottom
hole cleaning is the ability of the hydraulic fluid to remove cut formation
materials from the
bottom of the hole. Failure to remove formation materials from the bottom of
the hole can result
in subsequent passes by cutting structure to re-cut the same materials, thus
reducing cutting rate
CA 02523325 2005-10-12
and potentially increasing wear on the cutting surfaces. Cuttings evacuation
is the ability of the
hydraulic fluid to move cut formation particles away from the area immediately
surrounding the
drill bit. Failure to circulate formation cuttings up the annulus and away
from the drill bit can
also lead to reduced penetration rates and premature wear of cutting surfaces.
The three functions of bit hydraulics should be properly addressed through bit
hydraulic
design to provide for best overall bit performance. However, because each
drilling situation may
be significantly or slightly different depending on many factors, careful
consideration should be
paid to the bit hydraulic system design. The drilling situation depends on
factor that include, but
are not limited to, the bottom hole assembly, drilling fluid type, rig
capability, formation type,
drilling rate, and drilling depth.
Also playing an important role in this bit hydraulics system design is the
style or method
by which fluid is discharged from the bit. Commonly, a nozzle receptacle
receives an erosion
resistant, replaceable nozzle through which fluid is discharged. This
receptacle oftentimes is an
integral feature of the bit made during the manufacturing process and offers
means for
orientation and retention to the separate nozzle part when installed. Common
means of nozzle
retention include by screw thread, snap-ring, or nail, however other means do
exist.
Nozzle selection is an important step in designing a bit hydraulics system.
Fundamental
selection aspects include the nozzle orifice diameter and nozzle design.
Nozzle orifice diameter,
or nozzle size, directly relates to the nozzle's ability to restrict flow and
create desired pressure
loss. In addition to diameter, the total-flow area (TFA) of a nozzle can be
used as a basis for
nozzle size selection and can be determined by calculating the cross sectional
area of the nozzle
at its exit. In cases of difficult to measure geometry, TFA can be determined
experimentally and
presented as an equivalent-TFA relative to some known situation. In general,
increasing orifice
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diameter or TFA of a nozzle can result in a higher efficiency nozzle having
less fluid restriction
and a smaller magnitude pressure loss for a given flowrate.
Another element for nozzle selection is nozzle design. Some nozzles are
designed to
discharge fluid streams with very little jet expansion resulting in more
concentrated and efficient
energy delivery whereas other designs, such as diffusers, encourage diffusion
and mixing and
still others significantly redirect the discharging fluid stream. The large
number of nozzle designs
available exists to facilitate adjusting bit performance in the various
different drilling
applications and situations.
As an alternative to replaceable nozzles, the discharge location may comprise
a nozzle
port, which is a fluid passageway formed between the internal portion of the
bit and the bit
exterior. Ports generally do not allow the end-user flexibility to adjust its
configuration. In most
instances, the port's configuration is adjusted by modifying the passage
geometry and is
implemented in manufacturing. Similarly, as with replaceable nozzles, the
larger TFA ports are
less restrictive and thus produce lower magnitude pressure losses. Also, as
with replaceable
nozzles, various port designs are available for a large variety of intended
drilling applications.
There are two predominate types of rock bits, namely roller cone rock bits and
rotary
drag bits. Commonly, drag bits are referred to as polycrystalline diamond
cutter (PDC) bits
since cutters contain polycrystalline diamond on the cutting surface. Drag
bits are often
characterized by cutters grouped and placed on several blades. Many drag bit
designs include
primary blades, secondary blades, and sometimes even tertiary blades, where
the primary blades
are generally longer and start at locations closer to the bit's rotating axis.
The blades project
radially outward from the bit body and form flow channels therebetween. Drag
bits also include
nozzles or fixed ports that serve to inject fluid into these flow passageways.
As fluid is injected
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CA 02523325 2005-10-12
from the nozzles and flows through the flow channels, the fluid removes
cuttings and cleans the
cutting structure. The fluid carries the cuttings through the flow channels
and upwards into the
annulus through the passageways formed by the blades of the drill bit and the
surrounding hole,
which are commonly known as "junk slots." The movement of fluid through the
junk slots is an
important factor in the performance of the drill bit.
Thus, there remains a need to develop methods and apparatus that provide
improved bit
hydraulic performance by providing for an evaluation the allocation of flow
across the bit as well
as bit design features that allow for adjusting and controlling the allocation
of flow in order to
overcome some of the foregoing difficulties while providing more advantageous
overall results.
SUMMARY OF THE PREFERRED EMBODIMENTS
The preferred embodiments include methods for designing drill bits having bit
parameters that provide a substantially balanced flow among a plurality of
flow paths. A method
for designing a drill bit comprises modeling a domain between a drill bit and
a surrounding
wellbore. A region is defined within each of a plurality of flow paths through
which fluid travels
through the domain. An allocation of flow among the plurality of flow paths
through the domain
is determined and the drill bit is modified such that the allocation of flow
is substantially uniform
among the plurality of flow paths. A drill bit comprises a bit body having a
plurality of blades
projecting there from, wherein at least one blade has a greater length than at
least one other
blade. A plurality of nozzles, or ports, are disposed on the bit and a
plurality of junk slots are
formed between adjacent blades so that the flow of fluid through each of the
plurality of junk
slots is substantially uniform.
Thus, the present invention comprises a combination of features and advantages
that
enable it to overcome various problems of prior devices. The various
characteristics described
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CA 02523325 2005-10-12
above, as well as other features, will be readily apparent to those skilled in
the art upon reading
the following detailed description of the preferred embodiments of the
invention, and by
referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more detailed description of the preferred embodiment of the present
invention,
reference will now be made to the accompanying drawings, wherein:
Figure 1 is a bottom view of a drag bit;
Figure 2 is a flowchart representing a method for designing a drill bit have a
substantially
uniform allocation of flow;
Figure 3 illustrates the flow areas through the junk slots of a drag bit;
Figure 4 is a graph representing the allocation of flow through the junk slots
of a drag bit;
Figure 5 illustrates one embodiment of a drag bit having multiple nozzles in a
single junk
slot;
Figure 6 illustrates nozzle parameters for a single nozzle of a drag bit;
Figure 7 illustrates one embodiment of a drag bit having nozzles with adjusted
nozzle
parameters;
Figure 8 illustrates a nozzle having a shallow seat depth;
Figure 9 illustrates a nozzle having an increased seat depths;
Figure 10 illustrates a drag bit having nozzles with adjusted seat depths;
Figure 11 illustrates a drag bit with increased blade fill; and
Figure 12 is a visual representation of the allocation of flow through the
junk slots of two
different bit designs.
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CA 02523325 2005-10-12
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In one class of embodiments, the present invention includes methods and
apparatus that
allow a drill bit to be designed, analyzed, and constructed such that flow is
substantially uniform
among several flow paths that carry fluid away from the drill bit. Figure 1
illustrates a drag bit
comprises a bit body 12 having three primary blades 14, three secondary blades
16, and six
nozzles 18. Primary blades 14 have a greater length than secondary blades 16
and extend closer
to the bit's central axis. Junk slots 19 are formed around the circumference
of bit body 12
between blades 14, 16. Nozzles 18 are disposed on bit 10 generally between
blades 14, 16. In
operation, drilling fluid flows through nozzles 18, past blades 14 and 16, and
through junk slots
19 as it moves up the annulus toward the surface. As discussed above, the
drilling fluid acts to
cool the cutting structures and to remove cuttings from the blades as well as
from the bottom of
the hole as the hole is being drilled.
Analysis and experience has shown that the distribution or allocation of fluid
through the
junk slots is not easily predictable. For instance, in a conventional six-
bladed bit having six,
symmetrically arranged blades, junk slots, and nozzles, one would think each
junk slot would
receive an amount of fluid equivalent to the other slots (i.e. 16.7% of the
total flow through the
annulus). However, it has been learned that the fluid distribution for any
junk slot could easily
have values of 25%, 10%, or 5% due to the interaction between the fluid, bit
geometry, and
nozzle configuration.
Therefore, embodiments of the present invention include methods that allow a
drill bit to
be designed, analyzed, and constructed such that flow is substantially
uniformly allocated among
the several flow paths that carry fluid away from the drill bit. Embodiments
of the present
invention include methods that allow a designer to use computational fluid
dynamics (CFD) to
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CA 02523325 2005-10-12
evaluate drill bit performance. Once a drill bit design is chosen, that design
can then be analyzed
using CFD to determine the bit's hydraulic performance, including the
allocation of flow among
several flow paths. The analysis of the hydraulic performance of the bit can
be performed as a
set of fluid flow and other conditions that are based on identified drilling
parameters or other
criteria. CFD analysis tools allow detailed analysis of the fluid flow field
through and around the
drill bit structure and bottom hole region. CFD analysis can provide data that
can be used to
generate information as to the fluid velocity, pressure, turbulence,
direction, temperature, and
other fluid characteristics within the modeled volume.
To analyze a drill bit using CFD, a model is generally designed in a CAD
system or other
applicable software which creates a set of bounding surfaces which encapsulate
the fluidic area
of interest. Typically the bounding surfaces, known as the physical domain,
will comprise the
drill bit and an area representing the drill string, the bore hole that is
being drilled, the hole
bottom, and an exiting surface up the bore hole, which can be represented by
an annular ring
between the borehole and the drill string. Once the bounding surface model is
complete, a mesh,
which may be constructed of various element types, is created in meshing
software. This mesh is
called the computational domain, or domain, and is used by the CFD solver to
calculate a
solution comprising the fluidic properties at each element, or cell, within
the domain. Once the
solver has completed a solution, fluidic properties can be determined at any
location within the
confines of the domain. In order to better understand the allocation of flow
through the domain,
methods of analysis and design processes using regions defined within the
domain has been
developed as a part of certain embodiments of the current invention.
The following discussion uses a drag bit as an example but the principles and
methods
discussed herein are equally applicable to other types of bits, including
roller cone bits. For
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CA 02523325 2005-10-12
example, in analyzing roller cone bits, the designer may want to have
substantially uniform flow
in the annular space above the gage, which is the outermost surface of the
drill bit. In this case,
instead of looking at flow allocation in junk slots, one may examine flow
allocations in certain
angular intervals around the bit.
As discussed above, certain drill bit designs utilize fixed ports for
discharging fluid into
the wellbore. In the case when both fixed ports and replaceable nozzles are
used on a bit, the
adjustment of fluid discharge sizes, orientations and locations can involve
both port and nozzle
configurations. When the term nozzle is used herein it is understood that it
refers to a
replaceable nozzle, a fixed outlet port, and any other location from which
fluid is discharged
from the drill bit.
Referring now to Figure 2, one such design process 20 utilizes CFD to simulate
the flow
within a domain. In this method, the first step comprises selecting a drill
bit design 22 that may
comprise a hydraulic configuration including one or more bit design
parameters. In general, bit
design parameters are defined as any aspect of the nozzle or port parameters
and/or bit geometry
parameters that can be changed so as to influence the behavior of the fluid as
it circulates
through and around the drill bit. Examples of nozzle or port parameters
include, but are not
limited to, quantity, design, size, location, angular orientation, seat depth,
and arrangement.
Examples of bit geometry parameters include, but are not limited to blade
height, width, and
length, blade shape, bit body geometry, bit interior geometry, and number of
blades. Other bit
geometry parameters may also include, profile, height, and width of blade and
blade-fill,
transition between body and blades, shape, height, and width of junk slots and
waterway, and
side-rake, back-rake, location and orientation of cutters.
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CA 02523325 2005-10-12
Once the drill bit design is selected, the domain between the drill bit and
the surrounding
wellbore is modeled 24. Modeling the domain may further comprise constructing
a
computerized CAD model of a portion of the drill bit and wellbore, generating
a mesh, which is
also called the computational domain or domain, to represent the space between
the drill bit and
the surrounding wellbore, and establishing boundary conditions for the domain.
A CFD solver is
then utilized to simulate flow through the modeled domain and generate a CFD
solution. The
CFD solution comprises data representing the flow of fluid through the domain
including the
associated fluidic properties.
Once the CFD solution is complete, a plurality of regions is defined 26 within
the flow
paths of fluid moving away from the bit. As an example, Figure 3 illustrates a
drag bit 32
disposed in a wellbore 34 where a plurality of regions 36A-F have been defined
within the junk
slots of bit 32. Using the CFD solution, the flow allocation among the
plurality of regions can be
determined. The flow through each region can be represented by a volumetric
flow rate, a mass
flow rate, a fluid velocity, or any other fluidic property that provides a
representation of fluid
flow behavior.
Once the plurality of regions is defined, the base fluidic properties can be
found. For
example, in one embodiment, each of the regions co-planar surfaces defined
within a junk slot.
The fluidic property of interest for each region is the volumetric flow rate
passing through the
defined surface. Generally, the volumetric flow rate through the region is
found by integrating
the normal velocity over the area of the surface. Depending on the direction
of the velocity
vector at each point along the surface, the fluid may be moving upward from
the surface or
downward from the surface In this case, up and down do not indicate up and
down relative to
gravity but rather opposing directions relative to the local surface normal
direction. In one case,
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CA 02523325 2005-10-12
a designer may be interested in the amount of fluid that is moving up and the
amount of fluid that
is moving down. In another case, the designer may also be interested in the
volume of the fluid
moving up versus the volume moving down which could also be displayed in the
form of a ratio
Q°P/Qa~«,. The designer may be further interested in looking at ratios
relative to the total flow
moving through the plane, which may be determined as Q,°, _ (abs(Q"p) +
abs(Qa°w")).
Moreover, the designer may be interested in looking at the net flow rate of
fluid through the
region defined in the junk slot, which may be determined as Q"ec = Q°p -
Qa°"~, In other
embodiments, the fluidic property of interest may be the upward flowing
velocity vectors and/or
the downward pointing velocity vectors..
Once the fluidic property data from the individual regions is collected, it
can then be
processed to determine the allocation of flow among the junk slots or other
flow paths. The
allocation of flow can then be presented as a visual representation, such as a
graph, plot, contour,
or other visual representation that is easy to understand and analyze.
Refernng back to Figure 2,
once the fluidic property and allocation of flow has been determined, it can
be evaluated 28 by
comparing it to a pre-established design criterion (e.g. a maximum standard
deviation) or by
comparing it to results from a baseline configuration or other solved
hydraulic configurations
with similar bit body and cutting structure designs in order to look for
beneficial fluidic
properties and allocation of flow.
In certain embodiments, it is desirable to provide a substantially uniform
flow among the
plurality of flow paths through the domain. As it is used herein,
substantially uniform flow is
where the standard deviation of the fluidic property among the plurality of
flow paths is less than
10%. Preferably, substantially uniform flow is where the standard deviation is
less than 5% and
more preferably where the standard deviation is less than 3%.
CA 02523325 2005-10-12
Figure 4 shows results from computational fluid dynamics (CFD) simulation for
the flow
distribution in the junk slots 36A-F. Junk slot 36A, 36C, and 36E have much
stronger flow rates
relative to the other junk slots. The standard deviation 38 of the percentage
of flow rates is 11°/o
and indicates a higher than desired non-uniformity of flow through the
different junk slots 36A-
F. The high non-uniform flow rates through the junk slots may cause
undesirable fluid
circulation above the drill bit. The junk slots with lower flow rates (36B, D,
F) will typically
have a larger degree of fluid circulation within the junk slots. This intra-
slot circulation may
form loops such that cuttings carried away through the high flow rate junk
slots from the hole-
bottom are circulated back to the hole-bottom through the junk slots with
lower flow rates.
Referring back to Figure 2, based on the evaluation of the flow allocation,
the drill bit
design can then be modified 30. Once the drill bit design is modified, the
method shown in
Figure 2 can be run again with a modified domain being modeled between the new
drill bit
design and the surrounding wellbore. Again, a plurality of regions is defined
in the same
locations to evaluate the flow allocation. This process is repeated until the
evaluation 28 of the
series of simulations indicate a preferential interior surface parameter, or
set of parameters, for
the final design. In this manner, the modified drill bit design can be
evaluated to determine if the
changes made improved the flow allocation and drill bit performance.
There are several approaches to improve the uniformity of the flow
distribution in the
junk slots. These approaches can include, but are not limited to, adjusting
one or a combination
of bit design parameters comprising nozzle parameters and/or bit geometry
parameters. Because
the selection and installation of nozzles is often undertaken in the field, in
certain embodiments,
it may be desired to achieve improved uniformity of flow distribution by
modifying bit
parameters independent of nozzle size. For example, in certain embodiments,
substantially
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CA 02523325 2005-10-12
uniform flow may be achieved in a multiple blade drag bit that has one nozzle
per blade by
configuring the nozzles such that the radial locations, nozzle seat depth,
nozzle skew and profile
angles are substantially the same and modifying the blade geometry, such as
blade length or
thickness, including where at least one of the blades does not extend to bit
center.
In other embodiments, a bit design may have a plurality of primary blades and
a plurality
of secondary blades. The primary blades extend closer to the bit's central
axis than the
secondary blades. The bit has a set of primary nozzles associated with the
primary blades and a
set of secondary nozzles associated with the secondary blades. To generate a
substantially
uniform flow through the junk slots, the primary nozzles may be located
further inboard (i.e.
closer to the central axis) and have less profile angle and/or less (i.e.
shorter) seat depth than the
more radially outboard secondary nozzles.
Certain bits may also have more than two sets of nozzles with nozzles within a
set having
similar parameters that are different from parameters of nozzles within other
sets. Multiple-
blade drag bits may also have multiple nozzles per blade or more than one
nozzle in a given junk
slot. In certain embodiments, more than one nozzle may be positioned in a
given junk slot while
another junk slot has only a single nozzle. Refernng now to Figure 5, drill
bit 41 comprises
blades 43, junk slots 45 and 47, and nozzles 48. Two nozzles 48 are disposed
within junk slot 47
while junk slot 45 only has one nozzle 48. In certain embodiments, nozzles at
the same radius
may have substantially the same nozzle parameters such that the inner-most
nozzles have similar
parameters and outer-most nozzle have similar parameters, where the two sets
not being equal.
Refernng now to Figure 6, in one embodiment, the bit design can be modified by
adjusting one or more nozzle parameters. One such nozzle parameter is the
nozzle orientation,
or angular orientation, which in one case may be described as comprising the
skew angle 44 and
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CA 02523325 2005-10-12
profile angle 46. As the angular orientation increases, the nozzle is tilted
more radially outward
from the center of the bit body. In one example, the nozzle has a nozzle axis
along the center
line of the fluid flow path from the nozzle. The nozzle also has a nozzle
plane that is a plane
through the nozzle axis and parallel to the bit axis. The skew angle 44 is the
angle between the
nozzle plane and the plane through the bit axis and the intersecting point of
the nozzle axis and
the bit body. The profile angle 46 is the angle between the nozzle axis and an
axis on the nozzle
plane that is collinear to the bit axis. Another nozzle parameter is nozzle
location 48, which is
defined as the radial, axial, and angular location of the nozzle relative to
the bit's central axis. In
certain embodiments, adjusting the nozzle location of one or more of the
nozzles so that at least
one nozzle has a radial, axial, or angular location that is different than a
radial, axial, or angular
location of another nozzle may result in a substantially uniform flow. Those
skilled in the art
will appreciate that the invention is not limited by the example definitions
of nozzle orientation
and nozzle location provided above.
An example of a bit having adjusted nozzle parameters is shown in Figure 7
where bit 50
utilizes smaller angular orientations for nozzles 52 that are closer to
primary blades 54 so as to
direct fluid at the portions of the blades that are closer to the bit axis. As
a result, the
impingement angles formed by the primary jet axis and the hole-bottom profile
are close to
impingement angles of the secondary jets. Therefore, in certain embodiments,
adjusting the
angular orientations for one or more of the nozzles so that at least one
nozzle has a angular
orientation that is different than a angular orientation of another nozzle may
result in a
substantially uniform flow.
Another nozzle parameter that can be adjusted is seat depth, or how far the
nozzle is
recessed into the bit body. Referring now to Figures 8-10, an increased seat
depth for the
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CA 02523325 2005-10-12
nozzles further away from the bit axis can also be used to adjust the flow
distribution. Figure 8
shows a schematic of a nozzle 60 on a bit body 62 with "standard" nozzle seat
depth 64 relative
to the bit body surface 66. Figure 9 shows a nozzle 70 on a bit body 72 and
having an increased
seat depth 74 relative to the bit body surface 76. Figure 10 shows a six-blade
bit 80 where the
primary nozzles 82, which are closer to the bit axis, have a shallower nozzle
seat depth than
secondary nozzles 84. Therefore, in certain embodiments, adjusting the seat
depth for one or
more of the nozzles so that at least one nozzle has a seat depth that is
different than a seat depth
of another nozzle may result in a substantially uniform flow.
In one or more embodiments, smaller exit area nozzles can be used to provide
further
uniformity to the flow distribution. Smaller exit area nozzles may be desired
for use with those
junk slots that show a large flow rate when equal sized nozzles are used. In
other embodiments,
a nozzle having a design that creates a large flow rate through a particular
slot could be replaced
be a nozzle having the same nozzle exit area, but of somewhat hydraulically
inefficient design so
as to effectively reduce the flow rate through the junk slot. Conversely, an
exhibited low flow
rate could be remedied by replacing the nozzle with one having a more
hydraulically efficient
design to increase the flow. Thus, in certain embodiments, adjusting the size
or design of one or
more of the nozzles so that at least one nozzle has a size or design that is
different than a size or
design of another nozzle may result in a substantially uniform flow.
It has also been found that fluid can flow in and out of a given junk slot by
crossing the
blade, in particular the upper portion of the blade near the blade top. Thus,
in another
embodiment, a bit design parameter that can be adjusted is blade geometry,
such as the size and
shape of the blades. For example, additional supporting material can be added
to the back of the
blades or the blades can be made thicker. Not only does the additional
material support the
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CA 02523325 2005-10-12
cutting structure, the material can also prevent or reduce fluid flow across
the top of the blades.
Hence, fluid flows within each passage and junk slot with less interference
from cross-flow. The
added blade material may protrude as close as desired to the hole-bottom. One
embodiment of a
bit having adjusted blade geometry is shown in Figure 11, where bit 100
includes blades 104
having additional material 102 added to the upper portion of the blades.
Alternatively, in one or
more embodiments, secondary blades may extend closer to the bit axis so as to
reduce flow
interference between different flow passages and increase the uniformity of
flow. In other
embodiments, the blade geometries are formed such that fluid flow across the
top of the blades is
allowed such that the flow distribution in the junk slots is substantially
uniform.
Figure 12 shows a comparison of the flow distribution of a new configuration
and flow
distribution in the original configuration of Figure 1 (labeled Configuration
A). The embodiment
of configuration B has additional blade material and employs smaller angular
orientation and
smaller nozzle depth for one or more nozzles. Results are obtained from a CFD
analysis such as
that described in Figure 2. The standard deviation reduced from 11% to 3% for
the new
configuration. Thus, the new configuration is considered to have a more
uniform flow
distribution, or a balanced flow distribution. An even distribution of 16.7%
in each of the junk
slots with zero standard deviation as shown with the dash line.
Thus, embodiments of the present invention include apparatus and methods that
allow a
designer to establish a desirable flow allocation by adjusting various bit
design parameters. A
given drill bit design is analyzed to determine how the flow around the bit is
allocated among a
plurality of flow paths. Results of the analysis are then evaluated to
determine if the flow
allocation is within desirable limits. The bit design parameters can then be
altered to adjust the
flow allocation and the bit design analyzed again. Thus, this method provides
multiple design
CA 02523325 2005-10-12
iterations so as to determine the optimum flow allocation for a particular
drill bit design and
application.
Under this design methodology, the designer, using computer-aided design
software
and/or laboratory testing, can perform a thorough evaluation of the bit
hydraulics prior to testing
in the field, thus helping to prevent expensive downhole problems. This method
may include the
use of Computational Fluid Dynamics (CFD) software to determine the flow field
parameters
around a bit and a method of evaluation to determine the fluid flow around a
bit and identify
manufacturer controlled bit parameters that can be adjusted to control the
allocation of the fluid
flow.
In certain applications, the described flow allocation methodologies can be
used to create
specific situations other than uniform flow, such as biasing the flow
allocation toward one region
of the bit. For example, a five bladed bit may benefit from having flow
allocations of 23%, 18%,
23%, 18%, and 18% instead of the uniform 20%. This non-uniform allocation of
flow may be
desirable in addressing an area of the bit that has shown a need for
additional cooling or
cleaning.
While limited embodiments of this invention have been shown and described,
modifications thereof can be made by one skilled in the art without departing
from the scope or
teaching of this invention. The embodiments described herein are merely
examples and are not
limiting by the type and configuration of the drill bit. Many variations and
modifications of the
system and apparatus are possible and are within the scope of the invention.
For example, the
relative dimensions of various parts, the materials from which the various
parts are made, and
other parameters can be varied, so long as the apparatus retain the advantages
discussed herein.
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