U.S. patent application number 13/849872 was filed with the patent office on 2014-09-25 for thin wall active casing hanger.
This patent application is currently assigned to Vetco Gray Inc.. The applicant listed for this patent is VETCO GRAY INC.. Invention is credited to Nicholas P. Gette.
Application Number | 20140284048 13/849872 |
Document ID | / |
Family ID | 50543699 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140284048 |
Kind Code |
A1 |
Gette; Nicholas P. |
September 25, 2014 |
Thin Wall Active Casing Hanger
Abstract
A wellbore system includes a housing assembly and first and
second position casing hangers supported by the housing assembly. A
load member is provided that is adapted to extend between the first
position casing hanger and the housing assembly to enable the
housing assembly to support the first position casing hanger. The
second position casing hanger is stacked onto the first position
casing hanger, and an interface is defined between the first and
second position casing hangers to aid in alignment and
centralization of the second position casing hanger during
installation. The interface also provides radial support to the
first position casing hanger and enables loads associated with the
second position hanger to be transferred to the housing assembly
through the load member.
Inventors: |
Gette; Nicholas P.;
(Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VETCO GRAY INC. |
Houston |
TX |
US |
|
|
Assignee: |
Vetco Gray Inc.
Houston
TX
|
Family ID: |
50543699 |
Appl. No.: |
13/849872 |
Filed: |
March 25, 2013 |
Current U.S.
Class: |
166/208 |
Current CPC
Class: |
E21B 33/04 20130101;
E21B 23/01 20130101 |
Class at
Publication: |
166/208 |
International
Class: |
E21B 23/01 20060101
E21B023/01 |
Claims
1. A wellhead system comprising: a wellhead with a bore; a first
position casing hanger in the bore and comprising an upper end, a
lower end, and an axial passage, the lower end of the first
position casing hanger including a first connector connected to a
first casing string; a second position casing hanger in the bore
and comprising an elongated annular body that extends into the
axial passage of the first position casing hanger, and a second
connector connected to a second casing string; and a centralizing
ring set in an annular space between the elongated annular body and
the first position casing hanger, so that when the first position
casing hanger deflects radially inward in response to axial loads,
the centralizing ring supports the first position casing
hanger.
2. The wellhead system of claim 1, wherein the first position
casing hanger is supported by at least one upward-facing shoulder
defined within the bore of the wellhead, and wherein the
centralizing ring defines a support surface that is disposed at a
longitudinal elevation of the at least one upward-facing
shoulder.
3. The wellhead system of claim 2, wherein the at least one
upward-facing shoulder comprises a toothed profile that selectively
receives a radial expandable load member therein, and wherein the
support surface of the centralizing ring is disposed longitudinally
between upper and lower ends of the toothed profile.
4. The wellhead system of claim 1, wherein the first position
casing hanger includes a circumferential shelf extending around an
upper end thereof, wherein the second position casing hanger
includes an upper end extending radially outward from the elongated
annular body and defining a downward-facing ledge thereon, the
downward-facing ledge abutting the circumferential shelf to support
the second position casing hanger.
5. The wellhead system of claim 1, wherein an annular space is
between a support surface of the centralizing ring and the first
position casing hanger when the first position casing hanger is
unloaded.
6. The wellhead system of claim 1, wherein an interference fit is
established between a support surface of the centralizing ring and
the first position casing hanger when the first position casing
hanger is unloaded.
7. The wellhead system of claim 1, wherein the axial passage
selectively receives a drill bit prior to installation of the
second position casing hanger.
8. The wellhead system of claim 1, wherein the centralizing ring
includes a lower taper extending between an exterior surface of the
elongated annular body and a support surface defined at a radially
outer edge of centralizing ring for guiding the second position
casing hanger to a central location with respect to the axial
passage of the first position casing hanger.
9. The wellhead system of claim 1, wherein the centralizing ring
includes a plurality of radially spaced segments defining flow
channels therebetween, and wherein a support surface defined around
an outer periphery of the centralizing ring is interrupted by the
flow channels.
10. The wellhead system of claim 9, wherein the flow channels
occupy about half a cross-sectional area of an annulus defined
between an exterior surface of the elongated body and the first
position casing hanger.
11. The wellhead system of claim 1, wherein the centralizing ring
defines a continuous support surface circumscribing the
centralizing ring, and where at least one bore extends
longitudinally through the centralizing ring to provide fluid
communication through the centralizing ring.
12. A wellhead system comprising: a wellhead housing; an upper
hanger mounted in an axial bore in the wellhead housing; a lower
hanger mounted in the axial bore and circumscribing the upper
hanger, and comprising sidewalls that deflect radially inward in
response to axial loading of the upper hanger; and a centralizing
ring strategically disposed adjacent to where the sidewalls deflect
and between the upper and lower hangers.
13. The wellhead system of claim 12, wherein the upper hanger is
stacked onto the lower hanger such that weight suspended from the
upper hanger is transferred to the lower hanger.
14. The wellhead system of claim 12, wherein the centralizing ring
includes a longitudinally elongated support surface defined at a
radially outer edge thereof.
15. The wellhead system of claim 12, wherein the centralizing ring
is strategically disposed in a longitudinal support region from
which a weight suspended from the first hanger is transferred to
the wellhead housing.
16. The wellhead system of claim 12, wherein at least one fluid
flow channel extends longitudinally through the centralizing
ring.
17. A wellhead system, comprising: a wellhead with an axial bore; a
first position casing hanger in the bore and comprising an axial
passage; a first casing string connected to the first position
casing hanger; a second position casing hanger in the bore and
comprising an elongated annular body that extends into the axial
passage of the first position casing hanger; a second casing string
connected to the second position casing hanger; a centralizing ring
in an annular space between the elongated annular body and the
first position casing hanger, so that when the first position
casing hanger deflects radially inward in response to axial loads,
the centralizing ring supports the first position casing hanger; an
annular load ring comprising an inner profiled circumference that
engages an outer surface of the first position casing hanger, and
an outer profiled circumference that engages an inner surface of
the wellhead within the axial bore to define a longitudinal support
region; and a first channel in the wellhead that intersects the
axial bore above and below the longitudinal support region.
18. The wellhead system of claim 17, further comprising a second
channel in the second position casing hanger extending between the
axial bore and the axial passage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates in general to mechanisms for
supporting a casing string from a wellhead. More specifically, the
invention relates to a stacked casing hanger assembly for providing
a load capacity in a compact space while facilitating
installation.
[0003] 2. Description of the Related Art
[0004] In an oil or gas well, a wellhead will generally be located
on the ground surface, or on the sea floor for a subsea well. The
wellhead is a tubular member having an axial bore. At least one
load shoulder is usually disposed within the bore for supporting
casing string. In deep wells, there will generally be more than one
casing string extending into the well, and one or more load
shoulders may be provided for supporting each one of the casing
strings.
[0005] Often, once a well is drilled to a certain depth, a first
casing string is lowered through the axial bore of the wellhead and
supported by a first casing hanger on a first load shoulder in the
wellhead. Cement is pumped down the first casing string and back up
an annulus surrounding the first casing string to cement the first
casing string within the well. The well may then be drilled to
deeper depths at a smaller diameter, and a second casing string may
be lowered through the wellhead and the first casing string to
extend below the first casing string. A second casing hanger at the
top of the second casing string may positioned in the wellhead and
supported by an upper surface of the first casing hanger. In some
techniques, the entire weight of the second casing string and
second casing hanger is transmitted through the first casing hanger
to the first load shoulder. In other techniques, a second load
shoulder is provided to support a portion of the weight of the
second casing string while a portion of the weight is also
transmitted through the first casing hanger to the first load
shoulder. The second casing string may then be cemented into
place,
[0006] In addition to supporting the weight of the casing strings,
the casing hangers must also generally support high pressures from
tests of equipment placed above the casing hangers, and working
loads associated with producing from the well. For at least this
reason, casing hangers must be fairly robust. Casing hangers must
also generally provide a large drift size to permit passage of
additional casing strings, drilling implements or other equipment
therethough. To allow for the passage of larger pieces of
equipment, walls of the casing hangers are thin, which may limit
the load carrying capacity of a casing hanger in some
instances.
SUMMARY OF THE INVENTION
[0007] Described herein is a wellbore system including first and
second position casing hangers supported in a wellhead. A load
member is provided that is adapted to extend between the first
position casing hanger and the housing assembly to enable the
housing assembly to support the first position casing hanger. The
second position casing hanger is stacked onto the first position
casing hanger, and an interface is defined between the first and
second position casing hangers at a longitudinal elevation of the
load member to provide radial support to the first position casing
hanger. The interface also aids in alignment and centralization of
the second position casing hanger during installation.
[0008] According to one aspect of the invention, a wellhead system
includes a wellhead with a bore. A first position casing hanger is
in the bore and includes an upper end, a lower end and an axial
passage. The lower end of the first position casing hanger includes
a first connector connected to a first casing string. A second
position casing hanger is in the bore and includes an elongated
annular body that extends into the axial passage of the first
position casing hanger, and a second connector connected to a
second casing string. A centralizing ring is set in an annular
space between the elongated annular body and the first position
casing hanger, so that when the first position casing hanger
deflects radially inward in response to axial loads, the
centralizing ring supports the first position casing hanger.
[0009] According to another aspect of the invention, a wellhead
system includes a wellhead housing, an upper hanger mounted in an
axial bore in the wellhead housing, and a lower hanger mounted in
the axial bore and circumscribing the upper hanger. The lower
hanger includes sidewalls that deflect radially inward in response
to axial loading of the upper hanger. A centralizing ring is
strategically disposed adjacent to where the sidewalls deflect and
between the upper and lower hangers.
[0010] According to another aspect of the invention, a wellhead
system includes a wellhead with an axial bore, a first position
casing hanger in the bore and comprising an axial passage, a first
casing string connected to the first position casing hanger, a
second position casing hanger in the bore and comprising an
elongated annular body that extends into the axial passage of the
first position casing hanger, a second casing string connected to
the second position casing hanger, and a centralizing ring in an
annular space between the elongated annular body and the first
position casing hanger, so that when the first position casing
hanger deflects radially inward in response to axial loads, the
centralizing ring supports the first position casing hanger. The
wellhead system also includes an annular load ring comprising an
inner profiled circumference that engages an outer surface of the
first position casing hanger, and an outer profiled circumference
that engages an inner surface of the wellhead within the axial bore
to define a longitudinal support region. A first channel in the
wellhead intersects the axial bore above and below the longitudinal
support region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above-recited features,
aspects and advantages of the invention, as well as others that
will become apparent, are attained and can be understood in detail,
a more particular description of the invention briefly summarized
above may be had by reference to the embodiments thereof that are
illustrated in the drawings that form a part of this specification.
It is to be noted, however, that the appended drawings illustrate
only preferred embodiments of the invention and are, therefore, not
to be considered limiting of the invention's scope, for the
invention may admit to other equally effective embodiments.
[0012] FIG. 1 is a partial cross-sectional view of a wellhead
system including a stacked casing hanger assembly including first
and second position casing hangers installed in a high pressure
wellhead in accordance with one example embodiment of the present
invention.
[0013] FIG. 2 is a detailed cross-sectional view an interface
between the first and second position hangers as identified as an
area of interest in FIG. 1.
[0014] FIG. 3 is an end view of the stacked casing hanger assembly
of FIG. 1.
[0015] FIG. 4 is an end view of an alternate stacked hanger
assembly in accordance with another embodiment of the present
disclosure.
[0016] FIG. 5 is a simplified representation of example loading
conditions applied to the wellhead system of FIG. 1, which includes
first and second position casing hangers having the interface of
FIG. 2 established therebetween.
[0017] FIG. 6 is a simplified representation of an alternate
wellhead system including first and second position casing hangers,
which do not have the interface of FIG. 2 established
therebetween.
[0018] FIG. 7 is a chart indicating the longitudinal displacement
of the first position casing hangers of FIGS. 5 and 6 resulting
from loading the first position casing hangers as indicated in
FIGS. 5 and 6.
[0019] FIG. 8 is a chart indicating the radial displacement of the
first position casing hangers of FIGS. 5 and 6 resulting from
loading the first position casing hangers as indicated in FIGS. 5
and 6.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0020] Referring generally to FIGS. 1 and 2, a wellhead system 10
includes a wellhead housing assembly 12 and a stacked casing hanger
array 14 supported therein. The wellhead system 10 defines a
longitudinal axis A.sub.X extending therethrough. As used herein,
the terms "longitudinal" and "axial" or variants thereof generally
describe a direction parallel to the longitudinal axis A.sub.X, and
the term "radial" or variants thereof generally describes a
direction that is substantially perpendicular to the longitudinal
axis A.sub.X.
[0021] The wellhead housing assembly 12 includes an outer housing
18 and a high pressure housing or high pressure wellhead 20 having
an axial bore 22. The stacked casing hanger array 14 is an
arrangement of two casing hanger assemblies 26, 28 including a
first position casing hanger 26 and a second position casing hanger
28. The second position casing hanger 28 is "stacked" on the first
position casing hanger 26 as described in greater detail below. In
this example embodiment, a lockdown bushing 29 is optionally
disposed above the second position casing hanger 28. In other
embodiments (not shown), additional casing hanger assemblies may be
stacked on the second position casing hanger 28.
[0022] The stacked casing hanger array 14 is supported in the axial
bore 22 by engagement between a load member 30 and the high
pressure wellhead 20. In this example embodiment, the load member
30 is an inwardly-biased, expandable C-ring that is installed on
the first position casing hanger 26 prior to installation into the
high pressure wellhead 20. Once installed in the high pressure
wellhead 20, the load member 30 interacts with an actuation member
32 such that the load member 30 expands radially outwardly to
extend between the first position casing hanger 26 and the high
pressure wellhead 20. The engagement of load member 30 with the
high pressure wellhead 20 is described in greater detail in
commonly owned, U.S. application Ser. No. 12/415,198 to Nicholas P.
Gette et al., filed Mar. 31, 2009, the entire disclosure of which
is hereby incorporated by reference herein for all purposes.
[0023] The high pressure wellhead 20 as shown includes a toothed
profile 34 in the axial bore 22, which defines a plurality of
upward-facing shoulders 36. A corresponding exterior toothed
profile 40 is provided on the load member 30, which is received in
the toothed profile 34 of the high pressure wellhead and supported
on the upward-facing shoulders 36. The first position casing hanger
26 also includes a toothed profile 44 having downward-facing
shoulders 46. A corresponding interior toothed profile 48 on the
load member 30 is received within the toothed profile 44 of the
first position casing hanger 26, and engages the downward-facing
shoulders 46 to support the first position casing hanger 26.
[0024] The high pressure wellhead 20 also includes a plurality of
channels 50 defined therein extending from a port 52 disposed above
the toothed profile 34 and a port 54 disposed below the toothed
profile 54 and the actuation member 32. The ports 52, 54 provide
fluid communication between the axial bore 22 of the high pressure
wellhead 20 and the channels 50 to permit drilling mud, cement or
other well fluids to pass through the wellhead system 10, and
bypass the interface between toothed profile 34 and toothed profile
44.
[0025] The first position casing hanger 26 includes a threaded
lower end 60, which provides a connector from which a first casing
string 61 is suspended. An upper end 62 of the first position
casing hanger 26 provides a circumferential shelf 64 extending
around an axial passage 66 extending longitudinally through the
first position casing hanger 26. The second position casing hanger
28 is supported by the circumferential shelf 64 and extends into
the axial passage 66.
[0026] Still referring to FIGS. 1 and 2, the second position casing
hanger 28 includes a threaded lower end 70 from which a second
casing string 71 is suspended. An elongated body 72 of the second
position casing hanger 28 is received within the axial passage 66
of the first position casing hanger 26 and extends longitudinally
through the toothed profile 44. An upper end 74 of the first
position casing hanger 28 extends radially outward from the
elongated body 72 and includes a downward-facing ledge 76. The
downward-facing ledge 76 abuts the circumferential shelf 64 on the
first position casing hanger 26 to support the second position
casing hanger 28. The upper end 74 of the second position casing
hanger 28 extends radially to the high pressure wellhead 20. In the
example embodiment depicted in FIG. 1, the upper end 74 is devoid
of a load member for supporting the second position casing hanger
28 directly from the high pressure wellhead 20. In other
embodiments (not shown) a load member may be provided on the upper
end 74. Channels 78 are provided through the upper end 74 of the
second position casing hanger 28 to provide fluid communication
between the axial bore 22 of the high pressure wellhead 20 and the
axial passage 66 of the first position casing hanger 26. An axial
bore 80 extends longitudinally through the second position casing
hanger 28.
[0027] A centralizing ring 82 is provided on the second position
casing hanger 28, and extends radially outward from an exterior
surface 84 of the elongated body 72. The centralizing ring 82 is
provided at a longitudinal distance from the downward-facing-ledge
76 such that when the second position casing hanger 28 is installed
into the wellhead system 10, the centralizing ring 82 is disposed
at a longitudinal elevation of at least one of the upward-facing
shoulders 36, and between upper and lower ends of the load ring 30
and toothed profiles 34, 44. Thus, the centralizing ring 82 is
disposed within a longitudinal support region "R;" which defines an
axial distance where the first position casing hanger 26 engages
the high pressure wellhead 20. The weight of the first position
casing hanger 26 and any weight suspended therefrom is transferred
to the high pressure wellhead 20. Opposing axial surfaces of the
centralizing ring 82 are profiled to define a lower taper 85 and an
upper taper 86, which project obliquely to a circumferential
support surface 88. The support surface 88 is substantially
parallel to axis A.sub.X, and corresponds with a shape of the axial
passage 66 of the first position casing hanger 26. The centralizing
ring 82 extends into the axial passage 66 of the first position
casing hanger 26 such that an annular clearance "C" is defined
between the circumferential support surface 88 and a wall of the
axial passage 66. In this example embodiment, the annular clearance
"C" is about 0.015 inches. In other embodiments (not shown) the
centralizing ring 82 is configured to provide any slightly positive
annular clearance "C." For example, clearances "C" in the range of
about 0 to about 0.125 inches are provided in some embodiments. In
other embodiments, a slightly negative annular clearance "C," i.e.,
a slight interference fit may be established between the support
surface 88 and the first position casing hanger 26.
[0028] As depicted in FIG. 3, the centralizing ring 82 includes a
plurality of segments 82A, spaced around the second position casing
hanger 28. Each of the segments 82A extend radially outward from
the exterior surface 84 of the second position casing hanger 28 to
the support surface 88. The support surface 88 is generally shaped
to correspond to the shape of the axial passage 66 of the first
position casing hanger 26. Flow channels 66A are defined in the
axial passage 66 of the first position hanger 26 between the
segments 82A. In this embodiment, flow channels 66A occupy about
half a cross-sectional area of an annulus defined between the
exterior surface 84 and the first position casing hanger 26, with
the segments 82A occupying the other half. The flow channels 66A
interrupt the support surface 88. As described in greater detail
below, the support surface 88 provides radial support to the first
position casing hanger 26.
[0029] In an example of operation, a wellbore is drilled to a first
depth and the high pressure housing 20 is installed. The first
position casing hanger 26 is installed in the high pressure housing
20 with the first casing string 61 suspended therefrom. The weight
applied by the first position casing hanger 26 on the load ring 30
causes the load ring 30 to engage the actuation member 32 and
radially expand to transfer the weight of the first casing string
61 to the high pressure housing 20. Prior to installation of the
second position casing hanger 28, the axial passage 66 of first
position casing hanger 26 provides a relatively large passageway
into the wellbore (for passage of drill bits and drilling
equipment, surveying or test devices, etc.) in comparison to
conventional casing hangers with similar nominal sizes. The axial
passage 66 has a relatively large diameter, since a wall thickness
"T" of the first position casing hanger 26 is relatively small. The
wall thickness "T" is relatively small since first position casing
hanger 26 does not need to support the weight of both casing
strings 61, 71 alone since the centralizing ring 82 provides radial
support to the first position casing hanger 26 once loaded with the
weight of the second casing string 71. Thus, prior to installation
of the second position casing hanger 28, the first position casing
hanger 26 allows relatively large equipment to be lowered into the
wellbore and provides operators with options that might not be
available with a smaller axial passage 66.
[0030] After the first position casing hanger 26 is installed, the
wellbore is drilled to a second depth, and the second position
casing hanger 28 is lowered into the axial passage 66 with the
second casing string 71 suspended therefrom. As the centralizing
ring 82 passes the circumferential shelf 64 on the first position
casing hanger 26, the lower taper 85 guides the elongated body 72
of the second position casing hanger 28 into a central location
within the axial passage 66. The downward-facing ledge 76 rests on
the circumferential shelf 64 such that the weight of the second
casing string 71 is transferred to the first position casing hanger
26 and to the high pressure wellhead 20 through the load ring 30.
As a result of the weight of the first and second casing strings
61, 71 as well as axial forces associated with testing performed
above the first position casing hanger 26, e.g., a pressure test of
a blow-out preventer (not shown), the first position casing hanger
26 is elastically or plastically deformed to exhibit radial inward
displacements. The support surface 88 on the centralizing ring 82
provides radial support to the first position casing hanger 26,
such that the first position casing hanger 26 may support larger
axial loads than the first position casing hanger 26 would
otherwise support in the absence of centralizing ring 82.
[0031] As depicted in FIG. 4, an alternate embodiment of a
centralizing ring 90 provides a continuous support surface 92 that
extends circumferentially around the entire centralizing ring 90.
Bores 94 extend longitudinally through the centralizing ring 90 to
provide fluid communication through the centralizing ring 90.
[0032] Referring now to FIGS. 5 and 6, example loading conditions
are illustrated on a simplified depiction of the wellhead system 10
(FIG. 5), which includes a centralizing ring 82, and on an
alternate embodiment of a wellhead system 100 (FIG. 6), which is
devoid of, a centralizing ring. The example loading conditions were
utilized by a finite element analysis to describe the expected
stresses and strain on various components of the wellhead systems
10, 100. Example results of the finite element analysis are
illustrated in FIGS. 7 and 8.
[0033] An axial constraint AC1 is assigned to the high pressure
wellhead 20 on a lower socket surface thereof. The axial constraint
AC1 represents a reference location on the wellhead systems 10, 100
from which relative displacements of the various components of the
wellhead systems 10, 100 are measured as the first position casing
hanger 26 is loaded. An axial constraint AC2 is also applied to an
upper surface of the second position casing hangers 28 (FIGS. 5)
and 102 (FIG. 6). Although some axial displacement may be expected
in the upper surfaces of the second position the casing hangers 28,
102, for the purpose of analysis, the axial constraint AC2
maintains the second position casing hangers 28, 102 in an
approximate position where the centralizing ring 82 is axially
between upper and lower ends of the load ring 30. A first load
MPC-1 is applied to the lower end 60 of the first position casing
hanger 26, which represents the weight of a first casing string 61
(FIG. 1) suspended from the first position casing hanger 26. A
second load MPC-2 is applied to the circumferential shelf 64 of the
first position casing hanger 26 and represents the weight of a
second casing string 71 (FIG. 1) suspended from the second position
casing hanger 28, as well as forces applied to the first position
casing hanger 26 from testing performed above the first position
casing hanger 26.
[0034] Referring now to FIGS. 7 and 8, together with FIGS. 5 and 6,
the axial and radial displacements of the first position casing
hanger 26 are plotted against the axial load applied to the first
position casing hanger 26. Lines L1 and L3 correspond to the
wellhead system 10 (FIG. 5), and represent the displacements of a
point "U" on the first position casing hanger 26, which is adjacent
the centralizing ring 82. Lines L2 and L4 correspond to the
wellhead system 100 (FIG. 6) and represent the displacements of the
point "U" on the first position casing hanger when centralizing
ring 82 is not provided. The first load MPC-1 of 2 million pounds
of casing weight applied to the lower end 60 of the first position
casing hanger 26 induces a 0.28 inch axial displacement of point
"U" as represented at point A.sub.0 (FIG. 7) and a 0.0056 inch
inward radial displacement of point "U" at point B.sub.0 (FIG. 8).
At a loading of 2 million pounds, the axial and radial
displacements of the point "U" are the same for the wellhead system
10, which includes the centralizing ring and the wellhead system
100, which is devoid of a centralizing ring.
[0035] A divergence is observed at points A.sub.1 and B.sub.1 where
the second load MPC-2 of 6.76 million pounds is applied to the
circumferential shelf 64 of the first position casing hanger 26. At
point A.sub.1, a 0.28 inch axial displacement of point "U" is
observed, and at point B.sub.1, a 0.0165 inch radial displacement
is observed. The 0.0165 inch radial displacement at point B.sub.1
is greater than the 0.015 inch the clearance "C" defined between
the support surface 88 of the centralizer ring 82 and the first
position casing hanger 26. Thus, the point "U" contacts the support
surface 88 of the centralizer ring 82, and the centralizer ring 82
provides radial support to the first position casing hanger 26.
Additional loads applied to the first position casing hanger 26
induce lower axial and radial displacements at point "U" in
wellhead system 10 where the centralizer ring 82 is provided than
in wellhead system 100 where the centralizer ring is not provided.
The additional loads applied to the first position casing hanger
26, that generate the axial and radial displacements plotted in
FIGS. 7 and 8 (above points A.sub.1 and B.sub.1) are applied to the
lower end 60 and the circumferential shelf 64 of the first position
casing hanger 26 in proportion to the 2 million pound MPC-1 and the
6.76 million pound MPC-2.
[0036] The present invention described herein, therefore, is well
adapted to carry out the objects and attain the ends and advantages
mentioned, as well as others inherent therein. While a presently
preferred embodiment of the invention has been given for purposes
of disclosure, numerous changes exist in the details of procedures
for accomplishing the desired results. These and other similar
modifications will readily suggest themselves to those skilled in
the art, and are intended to be encompassed within the spirit of
the present invention disclosed herein and the scope of the
appended claims.
* * * * *