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.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

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.

2. Description of the Related Art

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.

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,

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

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.

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.

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.

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

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.

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.

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.

FIG. 3 is an end view of the stacked casing hanger assembly of FIG. 1.

FIG. 4 is an end view of an alternate stacked hanger assembly in accordance with another embodiment of the present disclosure.

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.

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.

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.

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

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_X extending therethrough. As used herein, the terms “longitudinal” and “axial” or variants thereof generally describe a direction parallel to the longitudinal axis A_X, and the term “radial” or variants thereof generally describes a direction that is substantially perpendicular to the longitudinal axis A_X.

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.

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.

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.

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.

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.

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.

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_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.

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.

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.

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.

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.

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.

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.

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 A₀ (FIG. 7) and a 0.0056 inch inward radial displacement of point “U” at point B₀ (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.

A divergence is observed at points A₁ and B₁ 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 A₁, a 0.28 inch axial displacement of point “U” is observed, and at point B₁, a 0.0165 inch radial displacement is observed. The 0.0165 inch radial displacement at point B₁ 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 A₁ and B₁) 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.

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.

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; anda 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; anda 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; anda 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.