U.S. patent application number 11/829752 was filed with the patent office on 2008-01-31 for method of designing blowout preventer seal using finite element analysis.
This patent application is currently assigned to HYDRIL COMPANY LP. Invention is credited to Shafiq Khandoker.
Application Number | 20080027693 11/829752 |
Document ID | / |
Family ID | 39523225 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080027693 |
Kind Code |
A1 |
Khandoker; Shafiq |
January 31, 2008 |
METHOD OF DESIGNING BLOWOUT PREVENTER SEAL USING FINITE ELEMENT
ANALYSIS
Abstract
A method of manufacturing, certifying, and optimizing a seal for
a blowout preventer. The method includes generating a finite
element analysis seal model, smoothing the finite element analysis
seal model, and analyzing a strain plot of the smoothed finite
element analysis seal model based upon a displacement
condition.
Inventors: |
Khandoker; Shafiq; (Houston,
TX) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
HYDRIL COMPANY LP
3300 North Sam Houston Parkway East
Houston
TX
77032
|
Family ID: |
39523225 |
Appl. No.: |
11/829752 |
Filed: |
July 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60847760 |
Sep 28, 2006 |
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60820723 |
Jul 28, 2006 |
|
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60862392 |
Oct 20, 2006 |
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60912809 |
Apr 19, 2007 |
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Current U.S.
Class: |
703/7 |
Current CPC
Class: |
G06F 30/23 20200101;
B29C 35/0222 20130101; E21B 33/06 20130101; B29C 35/0288 20130101;
G06F 2111/10 20200101; Y10T 137/5983 20150401; B29L 2031/265
20130101 |
Class at
Publication: |
703/007 |
International
Class: |
G06G 7/48 20060101
G06G007/48 |
Claims
1. A method of manufacturing a seal of a blowout preventer, the
method comprising: selecting a seal design; generating a first
finite element analysis seal model from the selected seal design;
smoothing the first finite element analysis seal model; analyzing a
strain plot of the smoothed first finite element analysis seal
model based on a displacement condition; and manufacturing a
seal.
2. (canceled)
3. The method of claim 1, wherein the smoothing comprises modifying
at least one of an internal corner and an external corner of a
rigid material insert of the first finite element analysis seal
model.
4. (canceled)
5. The method of claim 1, wherein the smoothing comprises modifying
a compression face of an elastomeric body of the first finite
element analysis seal model.
6. The method of claim 1, wherein the smoothing comprises modifying
an end of a flange of a rigid material insert of the first finite
element analysis seal model.
7. The method of claim 1, wherein the smoothing comprises modifying
an end of a web of a rigid material insert of the first finite
element analysis seal model.
8. The method of claim 1, wherein the smoothing comprises modifying
a side of a flange of a rigid material insert of the first finite
element analysis seal model.
9. The method of claim 1, wherein the smoothing comprises modifying
a side of a web of a rigid material insert of the first finite
element analysis seal model.
10. The method of claim 1, further comprising: generating a second
finite element analysis seal model based on the analyzed strain
plot of the smoothed first finite element analysis seal model; and
analyzing a strain plot of the second finite element analysis seal
model based on the displacement condition.
11. (canceled)
12. The method of claim 10, wherein at least one of the first
finite element analysis seal model and the second finite element
analysis seal model converges within a tolerance of about 1%.
13. The method of claim 10, wherein at least one of the first
finite element analysis seal model and the second finite element
analysis seal model converges within a tolerance of about 0.5%.
14. The method of claim 10, wherein a volume of an elastomeric body
of the second finite element analysis seal model is maintained
substantially constant with the volume of the smoothed finite
element analysis seal model.
15. The method of claim 1, wherein a volume of an elastomeric body
of the first finite element analysis seal model is maintained
substantially constant during smoothing.
16. The method of claim 1, wherein the seal comprises an elastomer
and a rigid material.
17-20. (canceled)
21. The method of claim 1, wherein the displacement condition
comprises strain of at least about 300%.
22. (canceled)
23. The method of claim 1, wherein the strain plot comprises one of
maximum principal strain, axial strain, and shear strain.
24. The method of claim 1, wherein the strain plot comprises a
cross-sectional view of the first finite element analysis seal
model.
25. A method to certify a seal of a blowout preventer, the method
comprising: generating a first finite element analysis seal model;
smoothing the first finite element analysis seal model; analyzing a
strain plot of the smoothed first finite element analysis seal
model based upon a displacement condition; and comparing the strain
plot of the smoothed first finite element analysis seal model
against at least one specified criteria.
26. The method of claim 25, further comprising: generating a second
finite element analysis seal model based on the analyzed strain
plot; analyzing a strain plot of the second finite element analysis
seal model based on the displacement condition; and comparing the
strain plot of the second finite element analysis seal model
against the at least one specified criteria.
27. The method of claim 26, further comprising smoothing the second
finite element analysis seal model.
28. The method of claim 25, wherein the seal comprises an elastomer
and a rigid material.
29. (canceled)
30. The method of claim 29, wherein the industry requirements
comprise API 16A/ISO 13533:2001.
31. A method of optimizing a seal of a blowout preventer, the
method comprising: smoothing a first finite element analysis seal
model; analyzing a strain plot of the smoothed first finite element
analysis seal model based upon a displacement condition; generating
a second finite element analysis seal model based on the analyzed
strain plot of the smoothed first finite element analysis seal
model; smoothing the second finite element analysis seal model;
analyzing a strain plot of the second smoothed finite element
analysis seal model based upon a displacement condition; and
repeating the analyzing and generating of smoothed finite element
analysis seal models until an optimized seal model is reached.
32. The method of claim 31, wherein the seal comprises an elastomer
and a rigid material.
33. The method of claim 31, wherein a volume of the first finite
element analysis seal model and a volume of the second finite
element analysis seal model are substantially the same.
34. The method of claim 31, wherein the optimized seal model is
compared against at least one specified criteria.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the following
provisional applications under 35 U.S.C. 119(e): U.S. Provisional
Patent Application Ser. No. 60/820,723 filed on Jul. 28, 2006; U.S.
Provisional Patent Application Ser. No. 60/847,760 filed on Sep.
28, 2006; U.S. Provisional Patent Application Ser. No. 60/862,392
filed on Oct. 20, 2006; and U.S. Provisional Patent Application
Ser. No. 60/912,809 filed on Apr. 19, 2007, all of which are
incorporated by reference in their entirety herein.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments disclosed herein generally relate to blowout
preventers used in the oil and gas industry. Specifically,
embodiments selected relate to methods of designing and
manufacturing seals for use in blowout preventers, in which the
seals may include elastomer and a rigid material.
[0004] 2. Background Art
[0005] Well control is an important aspect of oil and gas
exploration. When drilling a well, for example, safety devices must
be put in place to prevent injury to personnel and damage to
equipment resulting from unexpected events associated with the
drilling activities.
[0006] Drilling wells involves penetrating a variety of subsurface
geologic structures, or "layers." Occasionally, a wellbore will
penetrate a layer having a formation pressure substantially higher
than the pressure maintained in the wellbore. When this occurs, the
well is said to have "taken a kick." The pressure increase
associated with a kick is generally produced by an influx of
formation fluids (which may be a liquid, a gas, or a combination
thereof) into the wellbore. The relatively high-pressure kick tends
to propagate from a point of entry in the wellbore uphole (from a
high-pressure region to a low-pressure region). If the kick is
allowed to reach the surface, drilling fluid, well tools, and other
drilling structures may be blown out of the wellbore. Such
"blowouts" may result in catastrophic destruction of the drilling
equipment (including, for example, the drilling rig) and
substantial injury or death of rig personnel.
[0007] Because of the risk of blowouts, devices known as blowout
preventers are installed above the wellhead at the surface or on
the sea floor in deep water drilling arrangements to effectively
seal a wellbore until active measures can be taken to control the
kick. Blowout preventers may be activated so that kicks are
adequately controlled and "circulated out" of the system. There are
several types of blowout preventers, the most common of which are
annular blowout preventers (including spherical blowout preventers)
and ram blowout preventers. Each of these types of blowout
preventers will be discussed in more detail.
[0008] Annular blowout preventers typically use large annular,
rubber or elastomeric seals having metal inserts, which are
referred to as "packing units." The packing units may be activated
within a blowout preventer to encapsulate drillpipe and well tools
to completely seal an "annulus" between the pipe or tool and a
wellbore. In situations where no drillpipe or well tools are
present within the bore of the packing unit, the packing unit may
be compressed such that its bore is entirely closed. As such, a
completely closed packing unit of an annular blowout preventer acts
like a shutoff valve. Typically, packing units seal about a
drillpipe, in which the packing unit may be quickly compressed,
either manually or by machine, to affect a seal thereabout to
prevent well pressure from causing a blowout.
[0009] An example of an annular blowout preventer having a packing
unit is disclosed in U.S. Pat. No. 2,609,836, issued to Knox,
assigned to the assignee of the present invention, and incorporated
herein by reference in its entirety. The packing unit of Knox
includes a plurality of metal inserts embedded in an elastomeric
body, in which the metal inserts are completely bonded with the
elastomeric body. The metal inserts are spaced apart in radial
planes in a generally circular fashion extending from a central
axis of the packing unit and the wellbore. The inserts provide
structural support for the elastomeric body when the packing unit
is radially compressed to seal against the well pressure. Upon
compression of the packing unit about a drillpipe or upon itself,
the elastomeric body is squeezed radially inward, causing the metal
inserts to move radially inward as well.
[0010] Referring now to FIG. 1, an annular blowout preventer 101
including a housing 102 is shown. Annular blowout preventer 101 has
a bore 120 extending therethrough corresponding with a wellbore
103. A packing unit 105 is then disposed within annular blowout
preventer 101 about bore 120 and wellbore 103. Packing unit 105
includes an elastomeric annular body 107 and a plurality of metal
inserts 109. Metal inserts 109 are disposed within elastomeric
annular body 107 of packing unit 105, which are distributed in a
generally circular fashion and spaced apart in radial planes
extending from wellbore 103. Further, packing unit 105 includes a
bore 111 concentric with bore 120 of blowout preventer 101.
[0011] Annular blowout preventer 101 is actuated by fluid pumped
into opening 113 of a piston chamber 112. The fluid applies
pressure to a piston 117, which moves piston 117 upward. As piston
117 moves upward, piston 117 translates force to packing unit 105
through a wedge face 118. The force translated to packing unit 105
from wedge face 118 is directed upward toward a removable head 119
of annular blowout preventer 101, and inward toward a central axis
of wellbore 103 of annular blowout preventer 101. Because packing
unit 105 is retained against removable head 119 of annular blowout
preventer 101, packing unit 105 does not displace upward from the
force translated to packing unit 105 from piston 117. However,
packing unit 105 does displace inward from the translated force,
which compresses packing unit 105 toward central axis of wellbore
103 of the annular blowout preventer 101. In the event drillpipe is
located within bore 120, with sufficient radial compression,
packing unit 105 will seal about the drillpipe into a "closed
position." The closed position is shown in FIG. 5. In the event a
drillpipe is not present, packing unit 105, with sufficient radial
compression, will completely seal bore 111.
[0012] Annular blowout preventer 101 goes through an analogous
reverse movement when fluid is pumped into opening 115 of piston
chamber 112, instead of opening 113. The fluid translates downward
force to piston 117, such that wedge face 118 of piston 117 allows
the packing unit 105 to radially expand to an "open position." The
open position is shown in FIG. 4. Further, removable head 119 of
annular blowout preventer 101 enables access to packing unit 105,
such that packing unit 105 may be serviced or changed if
necessary.
[0013] Referring now to FIGS. 2, 3A, and 3B together, packing unit
105 and metal inserts 109 used in annular blowout preventer 101 are
shown in more detail. In FIG. 2, packing unit 105 includes an
elastomeric annular body 107 and a plurality of metal inserts 109.
Metal inserts 109 are distributed in a generally circular fashion
and spaced apart in radial planes within elastomeric annular body
107 of packing unit 105. FIGS. 3A and 3B show examples of metal
inserts 109 that may be disposed and embedded within elastomeric
annular body 107 of packing unit 105. Typically, metal inserts 109
are embedded and completely bonded to elastomeric annular body 107
to provide a structural support for packing unit 105. The bond
between annular body 107 and metal inserts 109 restricts relative
movement between annular body 107 and inserts 109, movement which
is seen to cause failure of the elastomer within the elastomeric
annular body 107. More discussion of the bonds between elastomeric
bodies and metal inserts within a packing unit may be found in U.S.
Pat. No. 5,851,013, issued to Simons, assigned to the assignee of
the present invention, and incorporated herein by reference in its
entirety.
[0014] Referring now to FIGS. 4 and 5, an example of packing unit
105 in the open position (FIG. 4) and closed position (FIG. 5) is
shown. When in the open position, packing unit 105 is relaxed and
not compressed to seal about drillpipe 151 such that a gap is
formed therebetween, allowing fluids to pass through the annulus.
As shown in FIG. 5, when in the closed position, packing unit 105
is compressed to seal about drillpipe 151, such that fluids are not
allowed to pass through the annulus. Therefore, the blowout
preventer may close the packing unit 105 to seal against wellbore
pressure from the blowout originating below.
[0015] Similarly, spherical blowout preventers use large,
semi-spherical, elastomeric seals having metal inserts as packing
units. Referring to FIG. 6, an example of a spherical blowout
preventer 301 disposed about a wellbore axis 103 is shown. FIG. 6
is taken from U.S. Pat. No. 3,667,721 (issued to Vujasinovic and
incorporated by reference in its entirety). As such, spherical
blowout preventer 301 includes a lower housing 303 and an upper
housing 304 releasably fastened together with a plurality of bolts
311, wherein housing members 303, 304 may have a curved, spherical
inner surface. A packing unit 305 is disposed within spherical
blowout preventer 301 and typically includes a curved, elastomeric
annular body 307 and a plurality of curved metal inserts 309
corresponding to the curved, spherical inner surface of housing
members 303, 304. Metal inserts 309 are thus disposed within
annular body 307 in a generally circular fashion and spaced apart
in radial planes extending from a central axis of wellbore 103.
[0016] Additionally, ram blowout preventers may also include
elastomeric seals having metal inserts. The large seals are
typically disposed on top of ram blocks or on a leading edge of ram
blocks to provide a seal therebetween. Referring now to FIG. 7, a
ram blowout preventer 701 including a housing 703, a ram block 705,
and a top seal 711 is shown. With respect to FIG. 7, only one ram
block 705 is shown; typically, though, two corresponding ram blocks
705 are located on opposite sides of a wellbore 103 from each other
(shown in FIG. 8). Ram blowout preventer 701 includes a bore 720
extending therethrough, bonnets 707 secured to housing 703 and
piston actuated rods 709, and is disposed about central axis of a
wellbore 103. Rods 709 are connected to ram blocks 705 and may be
actuated to displace inwards towards wellbore 103. Rams blocks 705
may either be pipe rams or variable bore rams, shear rams, or blind
rams. Pipe and variable bore rams, when activated, move to engage
and surround drillpipe and/or well tools to seal the wellbore. In
contrast, shear rams engage and physically shear any wireline,
drillpipe, and/or well tools in wellbore 103, whereas blind rams
close wellbore 103 when no obstructions are present. More
discussion of ram blowout preventers may be found in U.S. Pat. No.
6,554,247, issued to Berckenhoff, assigned to the assignee of the
present invention, and incorporated herein by reference in its
entirety.
[0017] Referring now to FIG. 8, ram blocks 705A, 705B and top seals
711A, 711B used in ram blowout preventer 701 are shown in more
detail. As shown, top seals 711A, 711B are disposed within grooves
713 of ram blocks 705A, 705B, respectively, and seal between the
top of ram blocks 705 and housing 703 (shown in FIG. 7). As
depicted, ram block 705A is an upper shear ram block having top
seal 705A, and ram block 705B is a lower shear ram block having top
seal 705B. When activated, ram blocks 705A, 705B move to engage, in
which shears 715A engage above shears 715B to physically shear
drillpipe 151. As ram blocks 705A, 705B move, top seals 705A, 705B
seal against housing 703 to prevent any pressure or flow leaking
between housing 703 and ram blocks 705A, 705B.
[0018] Referring now to FIGS. 9A and 9B, top seals 711A, 711B are
shown in more detail. As shown particularly in FIG. 9A, top seals
711A, 711B comprise an elastomeric band 751, elastomeric segments
753 attached at each end of elastomeric band 751, and a metal
insert 755 disposed within each elastomeric segment 753. Top seal
705A for ram block 705A (i.e., the upper shear ram block) may also
include a support structure 757 connected between elastomeric
segments 753. As shown in a cross-sectional view in FIG. 9B, metal
insert 755 disposed within elastomeric segment 753 has an H-shaped
cross-section. The H-shaped cross-section of metal insert 755
provides support and optimal stiffness to elastomeric segment 753.
Furthermore, it should be understood that top seals 711A, 711B may
be used with either pipe rams, blind rams, or shear rams (shown in
FIG. 8).
[0019] Referring now to FIG. 10, a ram block 705A with a top seal
and a ram packer 717A used in ram blowout preventer (e.g., 701 of
FIG. 7) are shown. FIG. 10 is taken from U.S. Publication No. US
2004/0066003 A1 (issued to Griffen et al. and incorporated herein
by reference in its entirety). Instead of a shear rams (shown in
FIGS. 7 and 8), FIG. 10 depicts a pipe ram assembly having a
variable bore ram packer 717A comprised of elastomer and metal. As
shown, variable bore ram packer 717A comprises an elastomeric body
761 of a semi-elliptical shape having metal packer inserts 763
molded in elastomeric body 761. Metal packer inserts 763 are
arranged around a bore 765 of elastomeric body 761. As mentioned
above with respect to pipe rams or variable bore rams, when
activated, ram packer 717A (along with a corresponding ram packer
oppositely located from ram packer 717A) moves to engage and
surround drillpipe and/or well tools located in bore 765 to seal
the wellbore.
[0020] For any seal mechanism comprising elastomers and metal in
blowout preventers (e.g., packing units in the annular and
spherical blowout preventers and top seals and ram packers in the
ram blowout preventer), loads may be applied to contain pressures
between various elements of the blowout preventers. For example,
with respect to the annular blowout preventer shown in FIG. 1, as
the fluid force is translated from piston 117 and wedge face 118 to
packing unit 105 to close packing unit 105 towards central axis of
wellbore 103, the fluid force generates stress and strain within
packing unit 105 at areas and volumes thereof contacting sealing
surfaces (e.g., wedge face 117 and drillpipe 151) to seal against
wellbore pressure from below. The stress occurring in packing unit
105 is approximately proportional to the fluid force translated to
packing unit 105.
[0021] As stress is incurred by blowout preventer seals, the
material of the seals will strain to accommodate the stress and
provide sealing engagement. The amount of strain occurring in the
material of the seal is dependent on a modulus of elasticity of the
material. The modulus of elasticity is a measure of the ratio
between stress and strain and may be described as a material's
tendency to deform when force or pressure is applied thereto. For
example, a material with a high modulus of elasticity will undergo
less strain than a material with a low modulus of elasticity for
any given stress. Of the materials used in blowout preventer seals,
the metal inserts have substantially larger moduli of elasticity
than the elastomeric portions. For example, the modulus of
elasticity for steel (typically about 30,000,000 psi; 200 GPa) is
approximately 20,000-30,000 times larger than the moduli of
elasticity for most elastomers (typically about 1,500 psi; 0.01
GPa).
[0022] Historically, when examining, designing, and manufacturing
seals for blowout preventers, such as packing units for blowout
preventers, the locations and amounts of stress and/or strain
(i.e., stress concentrations, strain concentrations) occurring
within the seal have been the largest concern and received the most
attention and analysis. As the seal is subject to loads (e.g.,
repetitive and cyclic closures of a packing unit of an annular
blowout preventer about a drillpipe or about itself), the magnitude
and directions of the stresses and strains occurring across the
seal are evaluated to determine the performance of the seal. A
common technique used for this evaluation is finite element
analysis ("FEA"). Specifically, the FEA may be used to simulate and
evaluate the stress and/or strain concentrations which occur across
the seal under given displacement conditions.
[0023] Traditionally with FEA, seals for blowout preventers are
modeled with finite elements to determine the performance of the
seal under various displacement conditions. For example, using FEA
modeling, the packing unit of an annular blowout preventer may be
simulated with a displacement condition to move into the closed
position around a drillpipe, in which the packing unit would be
compressed between the piston and the removable head from the
annular blowout preventer and the drillpipe. The FEA model may be
used to produce a strain plot of the seal (packing unit in this
example) to display the strain concentrations within the seal under
that specific displacement condition.
[0024] However, this evaluation of the strain concentrations may
not result in the most accurate prediction and representation of
the performance of the seals used in blowout preventers. Typically,
the seals used in blowout preventers experience extremely high
amounts of strain from the stresses that may be incurred. For
example, when a packing unit is compressed into the closed position
to seal about a section of drillpipe, an elastomeric body of the
packing unit may experience strains in excess of 300% in the areas
of the strain concentrations. Further, in a case where no drillpipe
is present, the packing unit may begin experiencing strains of
about 400-450% in seating about itself These elevated strains,
especially when repetitively and cyclically performed upon the
packing seal, usually lead to the ultimate failure of the seal.
[0025] Furthermore, as described above, the metal and elastomers
used for seals in blowout preventers typically have large
differences in their moduli of elasticity. Because of this
difference between the moduli of elasticity, when bonded together,
the metal will tend to control the "flow" and deformation of the
elastomers in the seals when compressed in the blowout preventers.
With the large amounts of strain, especially the strain resulting
from repetitive and cyclic displacements, coupled with the
significant difference between the moduli of elasticity of the
seal's materials, FEA evaluating strain concentrations may not
accurately represent the capabilities of the seals.
[0026] In FEA applications, the seal comprising a rigid material
and elastomer may be represented by a geometrically similar
representation consisting of many finite elements (i.e. discrete
regions), commonly referred to as a mesh. The finite elements
interact with one another to model the seal and provide simulated
data and results for various displacement conditions. However, the
finite elements within areas of high stress and/or strain (i.e.,
stress and/or concentrations) with substantial differences between
materials' moduli of elasticity may improperly deform. Common
improper deformations of the finite elements that may occur include
the elements collapsing upon themselves, distorting without bound,
or sustaining losses in stress, strain, and/or energy. These, in
addition to other improper deformations of the finite elements may
produce inaccurate results for the stress and strain occurring
across the model.
[0027] Historically, when the FEA is producing erroneous results,
the number of finite elements of the mesh is increased for better
resolution in at least some selected locations (e.g., areas of high
stress or strain concentration). Thus, it is common for areas with
stress and/or strain concentrations to receive more localized
"attention" when modeling in FEA than other areas. However, this
process may allow the analysis to become inherently localized on
the areas of the seal models with the stress and/or strain
concentrations, leading to solutions that may be narrowly
constructed and/or inaccurate. For example, it is common PEA
practice to increase the number of elements of (and thus further
complicate) the seal model in the areas of these concentrations to
increase the accuracy of the simulated stress and strain within the
concentration regions. The same may also be done for a seal model
in the areas of strain concentrations. However, it should be
understood that by increasing the number of elements, or decreasing
the mesh size, the solution time and the amount of computing power
required may be increased. This may lead to solution stalling (due
to computational error) and/or the generation of inaccurate
results.
[0028] Referring now to FIG. 11, a graph displaying strain (y-axis)
versus number of iterations (x-axis) within FEA is shown.
Specifically, the simulated strain displayed on the y-axis may be a
magnitude of a principal strain occurring in a specific direction
simulated across a finite element of a seal model for a given
displacement condition. For example, those having ordinary skill in
the art will recognize that the y-axis of the graph may display the
magnitude of a principal strain (e.g., strain occurring in the
direction of the z-axis; shear strain occurring in the plane of the
y-axis and the z-axis) occurring within a finite element when the
seal model is simulated with a displacement condition (e.g.,
closing of a packing unit about a drillpipe). Further, the number
of iterations displayed on the x-axis refers to the amount of
simulations of FEA used when modeling the seal. As such, each
"iteration" refers to a single execution of the FEA process to
simulate a displacement of the seal for the blowout preventer, thus
determining the magnitude of strain of the finite element of the
seal model.
[0029] In this approach, the resolution of the finite elements in
the mesh (seal model) is increased with each iteration.
Specifically, as mentioned above, it is ordinary practice to
increase the resolution of the finite elements of the mesh in
regions that experience large amounts of stress and/or strain.
However, because of the characteristics of metal reinforced
elastomer seals, such localized analysis may result in an FEA
stress and/or strain output that fails to correlate to an
experimentally observed solution. Furthermore, because of the
complexity, the FEA stress and/or strain output may not even be
capable of converging to a solution at all.
[0030] As shown, theoretical strain of the finite element occurring
in the direction of the simulated principal strain from the y-axis
in FIG. 11 is determined and shown for a seal of a blowout
preventer under the displacement condition. As the number of
iterations increases for the FEA model, the simulated strain
solution produced (i.e., a trend line of strain points found from
each iteration produced using FEA) thereby may not correspond and
converge with the theoretical strain under a comparable
displacement condition. A tolerance band of .+-. about 1% of the
theoretical strain is shown to indicate a range that may be
acceptable for the simulated strain solution to converge within.
This concept of convergence of FEA stress and/or strain output may
be understood as when the simulated stress/strain solution reaches
a solution within the tolerance band, the simulated stress/strain
solution continues to stay within the tolerance band as further
iterations of the solution are continued.
[0031] Therefore, as shown, when designing and manufacturing high
strain elastomeric seals containing rigid inserts, there may be a
significant discrepancy between the theoretical stress and strain
predicted by FEA and actual stress and strain. Thus, current
modeling and analysis techniques for blowout preventer seals may
not provide adequate information to improve their design and
manufacture.
SUMMARY OF INVENTION
[0032] In one aspect, embodiments disclosed herein relate to a
method of manufacturing a seal of a blowout preventer. The method
comprises selecting a seal design, generating a first finite
element analysis seal model from the selected seal design,
smoothing the first finite element analysis seal model, analyzing a
strain plot of the smoothed first finite element analysis seal
model based on a displacement condition, and manufacturing a
seal.
[0033] In another aspect, embodiments disclosed herein relate to a
method to certify a seal of a blowout preventer. The method
comprises generating a first finite element analysis seal model,
smoothing the first finite element analysis seal model, analyzing a
strain plot of the smoothed first finite element analysis seal
model based upon a displacement condition, and comparing the strain
plot of the smoothed first finite element analysis seal model
against at least one specified criteria.
[0034] Further, in another aspect, embodiments disclosed herein
relate to a method of optimizing a seal of a blowout preventer. The
method comprises smoothing a first finite element analysis seal
model, analyzing a strain plot of the smoothed first finite element
analysis seal model based upon a displacement condition, generating
a second finite element analysis seal model based on the analyzed
strain plot of the smoothed first finite element analysis seal
model, smoothing the second finite element analysis seal model,
analyzing a strain plot of the second smoothed finite element
analysis seal model based upon a displacement condition, and
repeating the analyzing and generating of smoothed finite element
analysis seal models until an optimized seal model is reached.
[0035] Other aspects and advantages of the embodiments disclosed
herein will be apparent from the following description and the
appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1 is a cross-sectional view of an annular blowout
preventer.
[0037] FIG. 2 is a cross-sectional view of a packing unit for an
annular blowout preventer.
[0038] FIG. 3A is a perspective view of a metal insert for a
packing unit for an annular blowout preventer.
[0039] FIG. 3B is a side view of an alternative metal insert for a
packing unit for an annular blowout preventer.
[0040] FIG. 4 is a cross-sectional view of a prior art packing unit
for an annular blowout preventer shown in a relaxed position.
[0041] FIG. 5 is a cross-sectional view of a packing unit for an
annular blowout preventer in a closed position.
[0042] FIG. 6 is a cross-sectional view of a spherical blowout
preventer.
[0043] FIG. 7 is a cross-sectional view of a ram blowout
preventer.
[0044] FIG. 8 is a perspective view of ram shears for a ram blowout
preventer.
[0045] FIG. 9A is a perspective view of a top seal for ram blocks
of a ram blowout preventer.
[0046] FIG. 9B is a cross-sectional view of a top seal for ram
blocks of a ram blowout preventer.
[0047] FIG. 10 is a perspective view of a variable bore ram packer
for a ram block of a ram blowout preventer.
[0048] FIG. 11 is a graphical representation of strain versus the
number of FEA iterations.
[0049] FIG. 12 is a flow chart depicting a method of manufacturing
a seal for a blowout preventer in accordance with embodiments
disclosed herein.
[0050] FIG. 13 is a cross-sectional, axial profile of an annular
packing unit in a two-dimensional plot (using x and z axes) in
accordance with embodiments disclosed herein.
[0051] FIG. 14 is a cross-sectional, radial profile of an annular
packing unit in a two-dimensional plot (using x and y axes) in
accordance with embodiments disclosed herein.
[0052] FIG. 15 is a portion of a seal model of an annular packing
unit in a three-dimensional plot (using x, y, and z axes) in
accordance with embodiments disclosed herein.
[0053] FIG. 16 is a portion of a seal mesh of an annular packing
unit in a three-dimensional plot (using x, y, and z axes) in
accordance with embodiments disclosed herein.
[0054] FIG. 17A is an end view of a metal insert for a packing unit
for an annular blowout preventer.
[0055] FIG. 17B is an end view of a metal insert for a packing unit
for an annular blowout preventer in accordance with embodiments
disclosed herein.
[0056] FIG. 18A is a top view of a metal insert for a packing unit
for an annular blowout preventer.
[0057] FIG. 18B is a top view of a metal insert for a packing unit
for an annular blowout preventer.
[0058] FIG. 19A is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0059] FIG. 19B is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0060] FIG. 20A is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0061] FIG. 20B is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0062] FIG. 21A is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0063] FIG. 21B is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0064] FIG. 22 is a graphical representation of strain versus
number of FEA iterations in accordance with embodiments disclosed
herein.
[0065] FIG. 23A is a strain plot of a seal model of an annular
packing unit with selective de-bonding in accordance with
embodiments disclosed herein.
[0066] FIG. 23B is a strain plot of a seal model of an annular
packing unit with selective de-bonding in accordance with
embodiments disclosed herein.
[0067] FIG. 24A is a strain plot of a seal model of an annular
packing unit with selective de-bonding in accordance with
embodiments disclosed herein.
[0068] FIG. 24B is a strain plot of a seal model of an annular
packing unit with selective de-bonding in accordance with
embodiments disclosed herein.
[0069] FIG. 25A is a strain plot of a seal model of an annular
packing unit with selective de-bonding in accordance with
embodiments disclosed herein.
[0070] FIG. 25B is a strain plot of a seal model of an annular
packing unit with selective de-bonding in accordance with
embodiments disclosed herein.
[0071] FIG. 26 depicts a computer system used to design seals for
blowout preventers in accordance with embodiments disclosed
herein.
[0072] FIG. 27A is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0073] FIG. 27B is a strain plot of a seal model of an annular
packing unit in accordance with embodiments disclosed herein.
[0074] FIG. 28 is a seal model of an annular packing unit in
accordance with embodiment disclosed herein.
DETAILED DESCRIPTION
[0075] In one aspect, embodiments disclosed herein relate to a
method of manufacturing a seal for a blowout preventer. In another
aspect, embodiments disclosed herein relate to a method of
optimizing a seal for a blowout preventer that incorporates using a
strain plot in the method. In another aspect, embodiments disclosed
herein relate to a method of certifying a seal model for a blowout
preventer using FEA to produce a strain plot after the model has
been smoothed and bulk analyzed in response to a displacement
condition.
[0076] As used herein, a "rigid material" refers to any material
that may provide structure to a seal of a blowout preventer, both
metal and non-metal. Examples for a rigid material may include, but
are not limited to, steel, bronze, and high strength composites
(e.g., carbon composites, epoxy composites, thermoplastics).
Further, as used herein, a "seal" refers to a device that is
capable of separating zones of high pressure from zones of low
pressure. Examples of blowout preventer seals include, but are not
limited to, annular packing units, top seals, and variable bore
rams.
[0077] As mentioned above, techniques and models historically used
to design and manufacture seals having elastomer and rigid
materials for blowout preventers may not provide accurate
information to improve the performance of the seal's design.
Therefore, in designing, manufacturing, and certifying a seal for a
blowout preventer in accordance with embodiments disclosed herein,
a method including FEA of bulk strain and generating a strain plot
may be used to yield more accurate convergent results under a given
displacement condition. This FEA method, in addition to certain
techniques for generating and modifying the seal models, may more
accurately calculate the strain in the seal because it is tailored
to accommodate the large amounts of stress and strain experienced
by blowout preventer seals. Suitable software to perform such FEA
includes, but is not limited to, ABAQUS (available from ABAQUS,
Inc.), MARC (available from MSC Software Corporation), and ANSYS
(available from ANSYS, Inc.).
[0078] Specifically, embodiments and methods disclosed herein may
advantageously provide techniques for generating and analyzing seal
models within FEA to determine the seal's response under
displacement conditions characterized by large amounts of strain.
Methods disclosed herein may use a simplified seal design and/or
model of a seal to assist in the analysis of the seal. For example,
methods disclosed herein may avoid analyzing stress and strain
concentrations of a complex seal design by "smoothing" that
design.
[0079] As used herein, the term "smoothing" refers to various
techniques to simplify a complex geometry of a seal design for use
with FEA. These techniques may allow the analysis of a smoothed
model (i.e., a FEA model constructed from a smoothed design) to
correlate with experimentally observed conditions and to converge
to a definitive result when analysis of a non-smoothed model may
not. As such, a model constructed from a smoothed design may be
analyzed within FEA to determine an overall, or "bulk", strain
condition. By analyzing this bulk (i.e., non-localized) strain, the
performance, and/or possibly failure, of a seal under various
displacement conditions may be predicted with more accuracy.
Following the analysis of the smoothed model for the bulk strain
condition, knowledge obtained therefrom may be incorporated into a
(non-smoothed) seal design that is to be manufactured.
[0080] Referring now to FIG. 12, a flow chart depicting a method of
manufacturing a seal including an elastomer and a rigid material is
shown. As a first step 1210, properties of the seal's materials
(e.g., the elastomers and the rigid materials) are determined. The
material properties may either be determined through empirical
testing or, in the alternative, may be provided from commercially
available material properties data. Next, a three-dimensional seal
model (i.e., a mesh) for the seal is generated 1220. As such,
generating a seal model 1220 may also comprise importing a seal
design 1221 and subsequently smoothing the imported seal design
1222 to simplify FEA analysis.
[0081] Next, displacement conditions are simulated in FEA using the
smoothed seal model 1230. Preferably, these simulated displacement
conditions reflect the forces, load states, or strains that the
seal may expect to experience in operation. Further, after
simulating displacement conditions, a strain plot showing the
strain and deformation occurring in the seal model is generated and
analyzed 1240. Ideally, the strain plot shows the location and
amount of strain occurring in the seal model in response to the
simulated displacement conditions. The strain plot may be analyzed
and reviewed 1240 to determine the performance characteristics of
the seal model. If the seal model requires improvement, the method
may loop back to 1210 to determine material properties of another
material for the seal, or alternatively may loop back to 1220 for
generation and analysis of another seal model. This loop allows the
seal model to be further simulated in FEA to determine its
performance after further modifications or models. Otherwise, if
the seal model is considered acceptable and meets a specified
criteria, the seal model may be used to manufacture a seal for a
blowout preventer 1250.
[0082] In initial step 1210, the properties of the seal's materials
are determined. Of the materials, the elastomeric materials will
have lower moduli of elasticity than the rigid materials. Thus,
when the seal is subjected to large amounts of stress, the
elastomeric portion of the seal will strain more than the rigid
material portions. For example, when the packing unit in an annular
blowout preventer is stressed in the closed position, the
elastomeric body of the packing unit will strain significantly more
than the metal inserts. Because elastomers strain significantly
more than the rigid materials for any given stress input, it may be
especially important to determine the material properties of an
elastomer used in the seal, specifically the relationship between
stress and strain across the elastomer.
[0083] In viscoelastic materials under constant stress, the strain
may increase with time (i.e., creep). Conversely, under a constant
level of strain, the stress within viscoelastic materials decreases
over time (i.e., relaxation). Furthermore, higher levels of strain
and lower temperatures may lead to an increase in the moduli of
elasticity for viscoelastic materials. Elongation of a material
refers to the percentage change in length of a material. The
maximum amount of tensile strain to which a material may be
subjected, or elongated to, before failure is referred to as the
elongation at break. A material may have a high or low modulus of
elasticity, but may exhibit a low elongation at break such that the
material will fail without experiencing much strain. Further, the
tensile strength of a material is the maximum amount of stress (in
tension) a material may be subjected to before failure. As stress
is exerted upon the material, the material strains to accommodate
the stress. Once the stress is too much for the material, it will
no longer be able to strain, and the material fails. The failure
point of the material is known as the ultimate tensile
strength.
[0084] Furthermore, if cyclic displacements are applied to an
elastomeric material, hysteresis (phase lag) may occur, leading to
a dissipation of mechanical energy within the elastomeric material.
Hysteresis may occur when there is softening induced by stress.
This may be described as an instantaneous and irreversible
softening for a material that occurs when an applied displacement
increases beyond any prior maximum value, resulting in a shift of
the stress-strain curve of the material. This induced softening,
which may also be referred to as the Mullin's effect, is thought to
be at least partially attributed to the microscopic breakage of
links in a elastomeric material. This weakens the elastomeric
material during an initial deformation so that the material is, in
turn, weaker in subsequent deformations of the material.
[0085] Thus, in one embodiment of the present disclosure, to
determine at least one of the material properties of the elastomer
for the seal of the blowout preventer, as described above,
empirical testing of the elastomer may be used. Specifically, tests
may be performed to determine the properties of the elastomeric
material. Examples of tests that may be performed include, but are
not limited to, a uniaxial tension test, a uniaxial compression
test, a lap shear test, and a biaxial tension test. A uniaxial
tension test applies tensile load in one direction to a material
and measures the corresponding strain induced in the material. A
uniaxial compression test applies compressive load in one direction
to a material and measures the corresponding strain induced in the
material. A lap shear test applies shear loads to a material and
measures the corresponding shear strain of the material. Further, a
biaxial tension test applies tensile loads in two directions to a
material and measures the corresponding strain of the material. The
use of these tests, in addition to other tests commonly known in
the art, may assist in analyzing and determining the material
properties of the elastomer. Furthermore, it should be understood
by one of ordinary skill in the art, that as material properties of
most materials vary by temperature, the performance of multiple
tests at differing temperatures may be prudent to establish certain
material properties.
[0086] In step 1220, a model (i.e., a mesh) for the seal is
generated. When generating the model of the seal, design features
of the seal are chosen and applied to the model. For example, for a
packing unit for an annular blowout preventer, the number of
inserts used, the width of the rigid material inserts, and the
specific material used for the rigid material inserts may be chosen
when generating the seal model. The seal models may be created in a
computer aided design ("CAD") software package (e.g., AutoCAD
available from Autodesk, Inc., and Pro/Engineer available from
Parametric Technology Corporation) and imported into the FEA
software package or, in the alternative, may be generated within
the FEA packages (e.g., ABAQUS and PATRAN) themselves.
[0087] Referring now to FIGS. 13-16, a method of generating a seal
model in accordance with embodiments disclosed herein is shown.
Specifically, as shown, a model of packing unit 105 of an annular
blowout preventer may be generated from a seal design created using
CAD software. As shown in FIG. 13, cross-sectional, axial profiles
1301 of a seal design may be generated of annular packing unit 105
in a two-dimensional plot (using x and z axes). Packing unit 105
includes elastomeric body 107 and rigid (e.g., metal) material
insert 109 with bore 111. Multiple radial and axial cross-sectional
profiles may be generated to represent different sections of the
seal. For example, profiles may be generated of the sections of a
packing unit 105 that do or do not have metal inserts 109.
[0088] From here, as shown in FIG. 14, in addition to generating
cross-sectional, axial profiles 1301, cross-sectional, radial
profiles 1401 of the seal design may be generated to represent
different radial sections of the seal in a two-dimensional plot
(using x and y axes). Because of the symmetry of packing unit 105,
only a radial portion of cross-sectional, radial profiles 1401, as
shown, may need to be generated. Then, as shown in FIG. 15, by
combining axial and radial profiles 1301, 1401, a three-dimensional
seal design 1501 may be generated to represent at least a portion
of packing unit 105 in a three-dimensional plot (using
corresponding x, y, and z axes from FIGS. 13 and 14). In
three-dimensional seal design 1501, metal inserts 109 and
elastomeric body 107 are generated as separate bodies which may
interact with one another. Depending on the complexity of the
design of the seal (i.e., packing unit in this case), more profiles
1301, 1401 of the seal may be generated for more detail in seal
design 1501.
[0089] Further, as shown, seal design 1501 and model or mesh 1601
(discussed below) may only represent a radial portion of packing
unit 105. However, the remainder of packing unit 105 may be easily
generated by taking advantage of the symmetrical geometry of
packing unit 105. Those having ordinary skill in the art will
appreciate that in the case of radially symmetric models, symmetric
portions and profiles may be used and replicated to simplify the
generation of the model.
[0090] Referring now to FIG. 16, seal design 1501 created using CAD
software may be imported into FEA software to generate a model or
mesh 1601 of numerous finite elements 1603. Finite elements 1603 of
mesh 1601 work together to simulate a seal and a packing unit when
stresses and forces are applied. Finite elements 1603 of
elastomeric body 107 of packing unit 105 will simulate and respond
to stress and forces (i.e., they will exhibit strain) corresponding
to the material properties of the elastomeric material.
[0091] Similarly, finite elements 1603 of metal inserts 109 of
packing unit 105 will simulate and respond to stress and forces
corresponding to the material properties of the metal inserts.
Thus, finite elements 1603 deform and strain to simulate the
response of the different materials (e.g., elastomers and rigid
materials) of the seal in accordance with their material
properties. While finite elements 1603 are shown as eight-noded
elements (i.e., brick elements), finite elements of any shape known
in the art may be used.
[0092] Further, while generating a seal model 1220, a number of
smoothing techniques may be used on the seal design 1222. In many
circumstances, as mentioned above, analyzing the actual
manufactured geometry of the seal using FEA may lead to
complications when large amounts of stress and strain are
simulated. Particularly, as manufactured, the geometry of metal
seal components include radiused corners and other
stress-concentration reducing features to more evenly distribute
stress across the component as it is loaded. However, it has been
discovered that these techniques may adversely affect FEA models in
FEA in that they increase the complexity of the model and may
prevent the FEA from producing accurate results. Therefore, a seal
model generated from a smoothed design may include removing
as-manufactured stress concentration features in an effort to
improve the results of FEA.
[0093] In one embodiment, the seal design's rigid material may be
modified (i.e., smoothed) to reduce their complexity. Referring now
to FIG. 17A, an end view of a metal insert 1701 including flanges
1703 connected by a web 1705 is shown. Metal insert 1701 typically
includes radiused internal corners 1707 and squared external
corners 1709. However, in one embodiment of smoothing a design, the
corners of the metal insert may be modified. For example, referring
now to FIG. 17B, an end view of a metal insert 1711 design
including flanges 1713 connected by a web 1715 in accordance with
embodiments disclosed herein is shown. In smoothing the design,
internal corners 1717 may be modified to reduce or eliminate their
radii (as shown) in an attempt to simplify a subsequently
constructed model. Further, in smoothing the seal design, external
corners 1719 may be modified to add or increase their radii (also
shown) in an attempt to simplify a subsequently constructed model.
A seal model constructed in this manner may be analyzed for bulk
strains such that the FEA may produce more accurate and definitive
results than would be possible using the former, more "localized"
approach.
[0094] Furthermore, in another embodiment, instead of smoothing the
design by modifying internal and external corners of the rigid
material insert, the smoothing may include modifying the shape of
the rigid material insert and its position within the elastomeric
body. Referring now to FIG. 18A, a top view of a metal insert 1801
disposed within a portion of an elastomeric body 1802 of an annular
packing unit is shown. Flange 1803 and web 1805 (outline shown) of
metal insert 1801 shown has a rectangular outline, in which flange
ends 1804A, 1804B of flange 1803 and web ends 1806A, 1806B of web
1805 are defined by straight edges. Ends 1804A, 1806A are radially
closer to central axis 103 than ends 1804B, 1806B.
[0095] However, referring to FIG. 18B, the shape and orientation of
the metal insert may be smoothed for bulk strain analysis. In FIG.
18B, a top view of a metal insert 1811 disposed within a portion of
an elastomeric body 1802 of an annular packing unit in accordance
with embodiments disclosed herein is shown. As shown, flange 1813
and web 1815 (outline shown) of metal insert 1811 have arcuate ends
to define a radial outline centered about central axis 103.
Specifically, sides 1814C, 1814D of flange 1813 may follow along
radial lines 1817 extending radially out from central axis 103.
Sides 1816C, 1816D of web 1815 may similarly follow along radial
lines (not shown). With this, flange ends 1814A, 1814B disposed
between flange sides 1814C, 1814D and web ends 1816A, 1816B
disposed between web sides 1816C, 1816D may then follow an arcuate
path to have an arc, bow, or bend, as shown. Preferably, arcuate
ends 1814A, 1814B, 1816A, 1816B follow radial paths 1818 defined
about central axis 103. Thus, as shown, a width of flange 1813 and
web 1815 increases when following along their sides 1814C, 1814D,
1816C, 1816D from ends 1814A, 1816A to ends 1814B, 1816B. As such,
a seal model constructed in this manner may be able to more
accurately simulate strain during FEA to produce more accurate and
definitive results.
[0096] Further still, the elastomeric body of the seal design may
be smoothed as well. Referring again to FIG. 15, elastomeric body
107 includes a compression face 108 corresponding to wedge face 118
of piston (117 of FIG. 1). When piston 117 is activated, wedge face
118 contacts and compresses packing unit 105 to seal the well. In
one technique, the seal design may be smoothed by modifying the
compression face to have approximately the same angle as the wedge
face of the piston. Alternatively, the wedge and compression faces
may be modified to increase a contact region therebetween. By
modifying the compression face, the wedge face, or both, a seal
model constructed therefrom may be able to more accurately simulate
strain for the strain plots during FEA. As the compressive face of
the elastomeric body would otherwise have a different angle than
the wedge face of the piston, the output of the FEA may be
simplified to produce more accurate or definitive results when
displaced.
[0097] Those having ordinary skill in the art will appreciate that,
in addition to these described smoothing techniques and
modifications, other techniques may be used as well in addition.
For example, in another embodiment, the web of the rigid material
insert may be modified, such as hollowing the web of the insert, as
long as the rigid material insert provides sufficient structural
support for the seal to sustain the forces applied thereto when
under any and all displacement conditions.
[0098] Preferably, when generating the seal models in step 1220,
especially when smoothing the seal design 1222 of the seal model,
the volume of the elastomeric body and the rigid material inserts
of the seal model remains substantially constant. If the volume
does not remain constant, the results and simulated strain from the
strain plots created by the FEA may not be accurate or consistent.
For example, when applying a force to an element, the force upon
the element will stress the element, causing the element to strain
to accommodate the stress. The stress applied to the element,
though, is directly proportional to the force applied to the
element and inversely proportional to the area or volume of the
element. Thus, if the force applied to the element increases and/or
the volume of the element decreases, the stress will
correspondingly increase in the element.
[0099] Using this concept, the respective volumes of the
elastomeric body and the rigid material inserts preferably remain
substantially constant to provide accurate results. For example, if
the volume of the overall seal model has substantially changed from
the actual seal, the strain plots of the seal model may show an
increase in strain in the elastomeric body with corresponding
displacement conditions. Further, if the volume of the seal model
changes from the smoothing techniques applied to the seal design of
the seal model, such as increasing the volume of the elastomeric
body of the seal model during the smoothing process, the strain
plots of the smoothed model may show a decrease in simulated strain
with corresponding displacement conditions. Thus, if the volume of
the elastomeric body and the rigid material insert of the model of
the seal increases or decreases, the simulated strain in the model
would inherently change, independent if the seal model was modified
for any improvements. Furthermore, if the overall volume of the
seal remains consistent between non-smoothed and smoothed models
but the relative volumes of the elastomeric body and the rigid
inserts change, the strain plots may be similarly compromised.
[0100] Continuing now with step 1230, displacement conditions are
simulated upon a seal for a blowout preventer in FEA using the
generated seal model. Preferably, the simulated displacement
conditions are loads and strains the seal may expect to experience
in service. For example, a model of a packing unit of an annular
blowout preventer may require a simulated displacement condition
correlating to compressing into a closed position to seal about a
section of drillpipe. Further, if no drillpipe is present, the
model may experience a simulated displacement condition correlating
to compressing to close about itself to seal the bore.
[0101] In step 1240, a strain plot, showing strain and deformation
occurring in the seal model in response to displacement conditions
may be analyzed and reviewed to determine the performance of the
modeled seal. Referring now to FIGS. 19-21, cross-sectional strain
plots of a seal model in accordance with embodiments disclosed
herein are shown. Specifically, the seal model is of a packing unit
for an annular blowout preventer, in which packing unit model is
initially simulated with a displacement condition as closed about a
drillpipe 151. Then, the packing unit is shown in an original
condition before the packing unit is simulated with the
displacement condition, but the strain from the simulated
displacement condition is superimposed across the non-displaced
packing unit. This technique may be performed by calculating the
strain from each element of the seal model with the displacement
condition and showing the strain upon each corresponding element of
the seal model in the original condition. This may allow the strain
occurring in the packing unit under the simulated displacement
condition to be "mapped" back to its original location in the
packing unit.
[0102] Referring now to FIG. 19A, a strain plot of the packing unit
model shows the maximum principal log strain occurring in the seal
model with a simulated displacement condition of closing the
packing unit about drillpipe 151. In FIG. 19B, a strain plot of the
seal model shows the packing unit originally before the
displacement condition is simulated across the seal model in FIG.
19A, but the maximum principal log strain plot from FIG. 19A is
superimposed across the undistorted seal model. Specifically, the
strain of each element in the seal model in the displacement
condition in FIG. 19A is added to each element in the undistorted
seal model in FIG. 19B. This allows the strain plot to show where
the strain concentrations will be located when in an undisplaced
condition.
[0103] Similarly, referring to FIG. 20A, a strain plot of the
packing unit model shows the axial log strain occurring in the seal
model with a simulated displacement condition of closing the
packing unit about drillpipe 151. In FIG. 20B, a strain plot of the
seal model shows the packing unit originally before the
displacement condition is simulated across the seal model in FIG.
20A, but the axial log strain plot from FIG. 20A is superimposed
across the undistorted seal model.
[0104] Similarly still, referring to FIG. 21A, a strain plot of the
packing unit model shows the shear log strain occurring in the seal
model with a simulated displacement condition of closing the
packing unit about drillpipe 151. In FIG. 21B, a strain plot of the
seal model shows the packing unit originally before the
displacement condition is simulated across the seal model in FIG.
21A, but the shear log strain plot from FIG. 21A is superimposed
across the undistorted seal model.
[0105] As shown in FIGS. 19-21, the packing unit experiences large
amounts of strain to accommodate the closed position simulated
displacement condition simulated with the seal model. Because of
these large strains, the finite elements of the model or mesh may
not deform properly to converge to an accurate or definitive
result. However, by analyzing a bulk strain plot of a smoothed
model in step 1240, a definitive result may be found. FEA focusing
on the evaluation of bulk strain may be used to produce more
accurate results.
[0106] Referring now to FIG. 22, a graph displaying strain (y-axis)
versus number of iterations (x-axis) within FEA in is shown. The
simulated strain on the y-axis is a magnitude of the principal
strain in a specific direction simulated across a finite element of
the seal model for a given displacement condition. Further, the
number of iterations on the x-axis refers to the amount of
simulations of PEA used when modeling the seal. However, in
contrast to the FEA iterations of FIG. 11 whereby the model is
iteratively made more localized (i.e., complex), each iteration of
FIG. 22 may incrementally smooth the analyzed model (while
maintaining consistent volume) to make such analysis less complex
in nature. As such, as the analysis progresses from a more
localized strain analysis (i.e., the left side of the x-axis) to a
bulk strain analysis (i.e., the right portion of the x-axis), the
solution converges and is contained within a tolerance band of
about .+-.1%. Specifically, the FEA solution may be seen to
converge in FIG. 11 because when the simulated strain solution
reaches a solution within the tolerance band, the solution
continues to stay within the tolerance band even as more iterations
are continued. Desirably, the simulated strain of the seal model
may converge within a tolerance of at least about 0.5% of the
theoretical strain.
[0107] As such, in contrast to what one of ordinary skill in the
art would intuitively believe, a simplified, smoothed model may
produce a more convergent and accurate FEA solution than more
complex, detailed models. As shown in this embodiment, the
simulated strain produced using FEA correlates with experimentally
observed solutions and converges to a definitive and correct result
about the theoretical strain and within the tolerance band
limitations. As the number of iterations increases (and as the
model is further smoothed), the simulated strain solution produced
by the FEA corresponds to the strain found in the seal through
empirical testing. With these results, bulk strain FEA may provide
useful results for simulation of seals for blowout preventers to
further improve their designs.
[0108] For example, referring now to FIGS. 27A, 27B, and 28, strain
that a seal model will sustain when simulated with a displacement
condition may be shown on a strain plot when still in an
undisplaced condition. This technique allows strains to be
determined within areas and elements of the seal model while still
in the undisplaced condition. In FIG. 27A, an enlarged view of a
strain plot of a packing unit model shows the maximum principal log
strain occurring in the seal model with a simulated displacement
condition of closing the packing unit about drillpipe 151. Three
finite elements 2711, 2713, 2715 experiencing strain when simulated
with the closed displacement condition have been marked and
identified. In FIG. 27B, an enlarged view of a strain plot of the
seal model shows the packing unit originally before the
displacement condition is simulated across the seal model in FIG.
27A, but the maximum principal log strain occurring in the seal
model from the displacement condition in FIG. 27A is superimposed
across the seal model. As elements 2711, 2713, 2715 were marked
when in the displacement condition in FIG. 27A, elements 2711,
2713, 2715 may be followed back in FIG. 27B to determine their
original location within the seal model to graphically represent
the magnitude and direction of the strains they experience. FIG. 28
also shows the packing unit seal model and mesh from FIGS. 27A, 27B
with elements 2711, 2713, 2715. Using this and similar techniques,
the areas of the seal model with the strain concentrations may be
more easily determined to further improve the design of the seal
model as necessary.
[0109] Further, when analyzing the strain plot in step 1240, the
strain plots may be used to certify the seal model for use in a
blowout preventer. Specifically, the strain plots may be compared
against one or more specified criteria to determine if the
performance of the seal model meets necessary requirements.
Specified criteria, for example, may include performance
requirements, customer's requirements, or even industry
requirements for seals. Furthermore, such criteria may be compared
against the strain plots of an analyzed seal model to determine if
a seal manufactured in accordance with the model would be in
compliance with such requirements. For example, a customer may
require packing units of annular blowout preventers to be capable
of experiencing strains in excess of 300%. A strain plot of the
seal model packing unit in a closed position displacement
conditions may then be compared against the specified criteria to
determine if the seal model is capable of satisfying such
requirements.
[0110] In another example, industry requirements, such as API
16A/ISO 13533:2001, may be used as specified criteria to compare
and certify a seal model. In particular, API 16A, Section 5.7.2
references a "closure test" for ram-type blowout preventers, while
API 16A, Section 5.7.3 references a closure test for annular-type
blowout preventers. Under API 16A/ISO 13533:2001, a packing unit
may be required to undergo six closures about the drill pipe and,
on a seventh closure, be capable of effectively sealing against
pressure of about 200-300 psi (1.4-2.1 MPa). Thus, displacement
conditions from industry requirements may be used in conjunction
with a simulation to determine if a seal is capable of satisfying
such requirements. Using methods and embodiments disclosed herein,
the seal model may then be certified by comparing the strain plots
of the seal model against these specified criteria.
[0111] If the seal model generated in step 1220 and analyzed in
step 1240 may be improved further (e.g., if the model does not meet
the specified criteria), the method may loop back to step 1210 to
determine material properties for another material of the seal, or
the method may loop back to step 1220 to have the seal model
regenerated or modified as necessary. This loop of generating the
seal model 1220 and analyzing the seal model 1240 may be repeated
several times until an "optimized" seal model is reached.
[0112] In one embodiment, selected portions of an elastomeric body
of a packing unit may be de-bonded from the rigid material inserts
when looping back and re-generating the seal model 1220 to reduce
to reduce the amount and location of strain. Typically, the
elastomeric body is completely bonded to metallic inserts for the
packing unit to maintain maximum rigidity, as discussed above with
respect to the prior art. However, if selected portions of the
elastomeric body are not bonded to the rigid material inserts, this
may reduce strain in the elastomer of the packing unit when the
packing unit is modeled in FEA to show the strain plots.
[0113] Referring now to FIGS. 23-25, strain plots of a smoothed
seal model having such selective de-bonding are shown.
Specifically, the seal model is of a packing unit for an annular
blowout preventer, in which packing unit model is initially
simulated with a displacement condition as closed about a drillpipe
151. Then, the packing unit is shown in an original condition
before the packing unit is simulated with the displacement
condition, but the strain from the simulated displacement condition
is superimposed across packing unit. This technique is similar to
FIGS. 19-21 from above. However, the elastomeric body of the seal
model in FIGS. 23-25 is additionally de-bonded from a back surface
109B behind a head 109A of metal insert 109.
[0114] Referring now to FIG. 23A, a strain plot of the packing unit
model with such a "selectively de-bonded" elastomeric body shows
the maximum principal log strain occurring in the seal model with a
simulated displacement condition of closing the packing unit about
drillpipe 151. In FIG. 23B, a strain plot of the seal model shows
the selectively de-bonded packing unit model originally before the
displacement condition is simulated across the seal model in FIG.
23A, but the maximum principal log strain plot from FIG. 23A is
superimposed across the undistorted seal model. This allows the
strain plot to show where the strain concentrations will be located
when in an undisplaced condition.
[0115] Similarly, referring to FIG. 24A, a strain plot of the
packing unit model with a selectively de-bonded elastomeric body
shows the axial log strain occurring in the seal model with a
simulated displacement condition of closing the packing unit about
drillpipe 151. In FIG. 24B, a strain plot of the seal model shows
the selectively de-bonded packing unit model originally before the
displacement condition is simulated across the seal model in FIG.
24A, but the axial log strain plot from FIG. 24A is superimposed
across the undistorted seal model.
[0116] Similarly still, referring to FIG. 25A, a strain plot of the
packing unit model with a selectively de-bonded elastomeric body
shows the shear log strain occurring in the seal model with a
simulated displacement condition of closing the packing unit about
drillpipe 151. In FIG. 25B, a strain plot of the seal model shows
the selectively de-bonded packing unit model originally before the
displacement condition is simulated across the seal model in FIG.
25A, but the shear log strain plot from FIG. 25A is superimposed
across the undistorted seal model
[0117] Each of the strain plots of the packing unit model with a
selectively de-bonded elastomeric body (i.e., FIGS. 23-25)
indicates less strain than the strain plots of the packing unit
model without selective de-bonding of the elastomeric body (i.e.,
FIGS. 19-21). Specifically, the volume of the elastomeric body
adjacent to the back surface of the head of the rigid material
insert indicates less strain in the strain plots of the seal model
when the elastomeric body is de-bonded from the rigid material
insert. Thus, as shown with the selectively de-bonded packing unit,
the seal model may be modified and regenerated to produce an
optimized seal model that reduces the location and amount of strain
occurring in the seal model.
[0118] Similar to above with respect to generating a seal model in
step 1220, when simulating displacement conditions across the seal
models 1230, it is preferable for the volumes of the seal model and
its components to remain substantially constant. If the volumes do
not remain constant, the results of the strain plots and simulated
strain in FEA may not correlate with experimentally observed
results or with one another, thereby providing inaccurate results.
For example, if the volume of the seal models of the packing units
shown in the strain plots of FIGS. 19-21 changes from the volume of
the seal models of the packing units shown in the strain plots of
FIGS. 23-25, it would be difficult to compare the strain plots
because of the added factor of the changing volume. As the volume
of the seal model of the packing unit increases or decreases, the
simulated strain in the packing unit inherently changes,
independent if the seal model was modified for any
improvements.
[0119] In step 1250, after being generated, analyzed, and possibly
re-generated (if necessary), the seal model may be used to
manufacture a seal for a blowout preventer 1250. Specifically,
using techniques known in the art, a seal based upon the
three-dimensional seal model may be manufactured for use in a
blowout preventer, such as a packing unit for an annular blowout
preventer or a top seal or variable bore ram packer a ram blowout
preventer. For example, the seal model of the packing unit for the
annular blowout preventer having selective de-bonding, as discussed
above and shown in FIGS. 23-25, may be manufactured for use in the
industry. The selective de-bonding packing unit generated in FEA
reduced the strain concentrations in the packing unit when in the
closed position, as compared to the packing unit shown in FIGS.
19-21. This selective de-bonding seal model may then be
manufactured for use or testing within a blowout preventer because
of its improved performance over the other packing unit shown from
the FEA.
[0120] Aspects of embodiments disclosed herein, such as generating
and analyzing a seal model of a seal for a blowout preventer using
FEA, may be implemented on any type of computer regardless of the
platform being used. For example, as shown in FIG. 26, a networked
computer system 3060 that may be used in accordance with an
embodiment disclosed herein includes a processor 3062, associated
memory 3064, a storage device 3066, and numerous other elements and
functionalities typical of today's computers (not shown). Networked
computer 3060 may also include input means, such as a keyboard 3068
and a mouse 3070, and output means, such as a monitor 3072.
Networked computer system 3060 is connected to a local area network
(LAN) or a wide area network (e.g., the Internet) (not shown) via a
network interface connection (not shown). Those skilled in the art
will appreciate that these input and output means may take many
other forms. Additionally, the computer system may not be connected
to a network. Further, those skilled in the art will appreciate
that one or more elements of aforementioned computer 3060 may be
located at a remote location and connected to the other elements
over a network.
[0121] Advantageously, methods and embodiments disclosed herein may
provide improved and more accurate results when using FEA. Methods
and embodiments disclosed herein use strain within FEA to determine
the performance characteristics of seals for blowout preventers
under simulated displacement conditions. This allows the finite
elements within the seal model to displace when accommodating large
amounts of strain.
[0122] Further, methods and embodiments disclosed herein may
provide techniques for analyzing, smoothing, simplifying, and
modifying seal models for use in FEA. Using these techniques, the
accuracy of the results of the strain plots created using FEA may
be improved. Additionally, using these techniques, the seal model
may be modified to reduce the amount and location of strain (e.g.,
strain concentrations) occurring in the seal model from the
simulated strain plots.
[0123] Furthermore, methods and embodiments disclosed herein may
provide for a seal for a blowout preventer with an increased
working lifespan. For example, the packing unit may be modeled with
simulated displacement conditions of repeated closures (i.e.,
repeatably closing the seal about a drillpipe or itself) to
determine design features that may extend the working lifespan
(i.e., number of closures) of the packing unit.
[0124] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
may be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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