UNIVERSAL TUBING HANGER SUSPENSION ASSEMBLY AND WELL COMPLETION SYSTEM AND METHOD OF INSTALLING SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention The invention relates primarily to a subsea wellhead assembly for an oil and gas well, and more particularly relates to a universal tubing hanger suspension assembly for use in a subsea wellhead assembly. The invention also relates to tubing hanger suspension assemblies for land based wellhead assemblies.

2. Description of the Prior Art A typical subsea wellhead assembly includes a wellhead housing installed at the sea floor. With a drilling blowout preventer (BOP) stack installed on the wellhead housing, the well bore is drilled while successively installing concentric casing strings in the well bore. Typically, each successive casing string is cemented at its lower end and includes a casing hanger sealed with a mechanical seal assembly at its upper end in the wellhead housing.

hi order to produce the cased well, a production tubing string and tubing hanger is typically run into the well bore through the BOP stack, and the tubing hanger is landed, sealed and locked in the wellhead housing and/or the casing hanger. Upon sealing the bore(s) extending through the tubing hanger, the BOP stack is removed, and a Christmas tree is lowered onto the wellhead housing. A Christmas tree is an oilfield term which refers to an assembly of control valves and chokes positioned at the top of a well to control the flow of oil and gas. It is vitally important to the operation and safety of the well that the proper connections are remotely formed between the Christmas tree, the wellhead housing, and the tubing hanger.

In a conventional completed well system, the Christmas tree is connected to the top of the wellhead housing over the tubing hanger. The tubing hanger supports at least one production tubing string which extends into the well bore. The tubing hanger provides a production bore within the tubing string and a conduit that communicates with the annulus

surrounding the tubing string and inside the innermost or production casing string. In addition, a tubing hanger includes at least one vertical production bore for communicating fluid between the tubing string and a corresponding production bore in the Christmas tree, and typically at least one vertical annulus bore for communicating fluid between the tubing annulus and a corresponding annulus bore in the Christmas tree. The tubing hanger may additionally include one or more service and control conduits for communicating control fluids and well chemicals through the tubing hanger or electrical power to devices or positions located in or below the tubing hanger.

A tubing hanger conventionally is sealed and rigidly locked into the wellhead housing or component in which it is landed. In a well having a conventional Christmas tree, the tubing hanger is landed in the wellhead housing. The tubing hanger typically includes an integral locking mechanism which, when activated, secures the tubing hanger to the wellhead housing or a profile in the casing hanger. The locking mechanism ensures that any subsequent pressure from within the well acting on the tubing hanger will not cause the tubing hanger to lift from the wellhead housing thereby resulting in an unsafe condition.

There are a limited number of subsea wellhead equipment manufacturers worldwide. Currently, the primary manufacturers of subsea wellhead housings are ABB Vetco Gray, Cooper Cameron Corp., Dril-Quip, FMC and Kvaerner. Each of the primary manufacturers has its own proprietary wellhead housing and casing hanger designs, dimensions and details. Quite frequently, a well is completed on Manufacturer A's wellhead housing and casing hangers using a tubing hanger and/or Christmas tree from Manufacturer B. However, since Manufacturer A's housing and casing hanger design is proprietary, Manufacturer B may not be able to connect its tubing hanger and/or Christmas tree to Manufacturer A's housing without a license fee from Manufacturer A in order to design Manufacturer B's equipment to properly interconnect and mate with Manufacturer A's wellhead housing and casing hanger. This results in a substantial amount of additional engineering and costs or additional equipment (such as a tubing spool) when electing to purchase Manufacturer B's equipment for use with Manufacturer A's wellhead housing. Since each wellhead housing/system manufacturer has multiple models of housings and casing hangers with different proprietary details, it is not practical or economical for other

manufacturers to build up an inventory of equipment for installation on other manufacturers' wellhead equipment. In addition to the added costs, it also increases the delivery time which is often vitally important to the well owner.

3. Identification of Objects of the Invention A primary object of this invention is to provide a subsea well completion system that is adapted for use with wellhead housings from all manufacturers.

Another object is to provide a tubing hanger assembly adapted for positioning in the wellhead housing independently of any proprietary details of the wellhead housing.

Another object is to provide a universal tubing hanger assembly that is adapted for use in a plurality of wellhead housings.

Another object of the invention is to provide a universal tubing hanger assembly adapted for use in wellhead housings of two or more manufacturers.

Another object is the invention is to provide a tubing hanger assembly arranged and designed for placement in a wellhead housing of a land bored well such that the tubing hanger assembly is independent of proprietary details and dimensions of this wellhead housing.

Another object of the invention is to provide a method for installing a universal tubing hanger assembly in a wellhead housing where knowledge of landing surfaces in the wellhead housing is unavailable.

SUMMARY OF THE INVENTION

The invention is embodied in a tubing hanger suspension assembly for an oil and gas well completion system and a method of installing same. The tubing hanger suspension assembly for either a subsea well or a land well includes a tubing hanger housing which is positioned in the wellhead housing. The tubing hanger assembly includes a sealing and lockdown mechanism which provides sealing and load support of the production tubing at a position below this wellhead housing in the production casing string. A stab sub assembly connected between the upper end of the tubing hanger suspension assembly and lower end of the Christmas tree assembly provides downhole hydraulic and electric functionality and annulus access to the production tubing.

The well completion system according to the invention is arranged and designed for use with wellhead housings from all manufacturers. The tubing hanger suspension assembly of a preferred embodiment includes a tubing hanger housing positioned in the wellhead housing independently of any proprietary details of the wellhead housing. The preferred embodiment of the tubing hanger suspension assembly is "universal", i.e., adapted for use in a plurality of wellhead housings, including wellhead housings of two or more manufacturers.

According to the invention, a tubing hanger assembly is installed in a wellhead housing where the wellhead housing supports a casing hanger connected to a casing string which lines a wellbore. A tubing hanger assembly is provided with a tubing hanger housing having an outer diameter arranged and designed to fit within the bore of the wellhead housing. The tubing hanger assembly includes a tubular member and a lockdown assembly carried by the tubing hanger housing, both of which are arranged and designed to fit within the casing string. The tubing hanger housing positioned within the wellhead housing and the tubular member and lockdown assembly positioned within the casing string until a bottom surface of the tubing hanger housing is positioned a few inches above a top end of the casing hanger. The lockdown assembly is activated against the interior of the casing string. As a result, the tubing hanger assembly is supported vertically by the lockdown assembly engagement of the casing string at a position below the tubing hanger housing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The objects, advantages, and features of the invention will become more apparent by reference to the drawings which are appended hereto and wherein like numerals indicate like parts and wherein an illustrated embodiment of the invention is shown, in which:

Fig. 1 is a schematic sectional elevation view showing a cased well bore, a wellhead housing, a blowout preventer ("BOP") stack connected to the wellhead housing, and casing strings with casing hangers landed in the wellhead housing;

Fig. 2 is a schematic sectional elevation view showing a tubing hanger suspension assembly according to a preferred embodiment of the present invention lowered into a cased well bore and wellhead housing with a tubing hanger running tool;

Fig. 2A is an enlarged view of the lower portion of Fig. 2;

Fig. 3 is an enlarged schematic sectional elevation view of a preferred embodiment of the sealing and lockdown assembly of the tubing hanger suspension assembly of Figs. 2 and 2A;

Fig. 4 is a view similar to Fig. 2 with the sealing and lockdown assembly set in the casing string and a retrievable plug set in the production tubing;

Fig. 5 is a schematic sectional elevation view showing a preferred embodiment of a subsea tree with a stab sub connected to the universal tubing hanger suspension assembly and wellhead housing;

Fig. 6 is a sectional elevation view of the stab sub connected to the universal tubing hanger assembly according to a preferred embodiment of the present invention, the arrows indicating an annulus flowpath;

Fig. 7 is a section view of the stab sub taken along lines 7-7 of Fig. 6; Fig. 8 is a view similar to Fig. 6 showing passageways for the chemical injection and subsurface safety valve controls;

Fig. 9 is an enlarged view of the upper portion of Fig. 8; and

Fig. 10 is a sectional elevation view of a portion of the tubing hanger suspension assembly according to another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE

INVENTION

An embodiment of the invention is described in detail with specific reference to the drawings. This invention concerns completion of a well that has been drilled and which has its bore hole lined with casing. Although the written description below and the attached drawings illustrate the invention embodied in a subsea well, the invention can also be embodied in a well on land. Referring to Fig. 1, a typical drilled well bore B is shown extending from the sea floor F down to a zone Z, typically communicating with a reservoir of hydrocarbon fluids. The well bore B is shown having a series of tubular strings of casing pipe extending from the sea floor F down into the bore B as is well known in the art. The series of pipe strings, beginning from the outermost string, includes a conductor housing 12, a wellhead housing 14, a first or outer casing string 16 with hanger 16a, and an inner or production casing string 18 with hanger 18a. The well depicted in Fig. 1 is representative of a typical well for purposes of illustrating the present invention; nevertheless, the invention is not limited to wells of this precise configuration. The drawing figures are not drawn to scale due to the tremendous depths to which wells are drilled.

Still referring to Fig. 1, the top of the conductor housing 12 is preferably above the sea floor F. The wellhead housing 14, preferably a high pressure housing, extends above the conductor housing 12. Preferably, the top of the wellhead housing 14 is about ten feet above the sea floor F. The wellhead housing 14 typically includes an external profile (not shown) for connection with a connector 20a of a blowout preventer ("BOP") stack 20 and an oilfield Christmas tree as described below. Typically, the casing hangers 16a and 18a are landed and secured in the wellhead housing 14.

Although not shown, the wellhead housing 14 typically includes several internal profiles, dimensions and details for landing, locking and sealing the stacked casing hangers 16a, 18a in the wellhead housing 14. Each wellhead manufacturer has several wellhead housings with corresponding casing hangers for each wellhead housing. As a result, the casing hangers 16a, 18a installed in the wellhead housing 14 are typically

manufactured by the same company since each manufacturer's wellheads and casing hangers are different from those of any other manufacturer.

Following the setting of the casing as shown in Fig. 1, a prior art tubing hanger assembly is typically run in the conventional well. Although not shown, a typical prior art tubing hanger assembly for a conventional well (i.e., a well in which the tubing hanger in landed in the wellhead housing) includes a housing having a string of production tubing extending from the housing substantially down to the production zone Z. A typical prior art tubing hanger installed in the wellhead housing of Fig. 1 lands on one or more shoulders 18b in the production casing hanger 18a. The weight of the suspended tubing string is supported by the production casing hanger 18 a. Although not shown, the prior art production casing hanger 18a includes internal profiles, dimensions and details for landing, locking and sealing a typical prior art tubing hanger in the production casing hanger 18 a. Similar to the above, each casing hanger manufacturer has its own proprietary configuration with respect to mating and connecting with the tubing hanger. As a result, in a typical conventional well, the tubing hanger is usually manufactured by the same manufacturer of the casing hanger(s) which is also typically the same as the wellhead housing manufacturer.

Referring still to Fig. 1, the BOP stack 20 is shown having the connector 20a, a vertical bore 20b, a plurality of rams 2Or, a choke line 20c and a kill line 20k. There are several types and configurations of BOP stacks 20 that are suitable for use with the wellhead housing 14. The bore 20b of the BOP stack 20 is shown with a diameter approximating the diameter of the wellhead housing 14. However, the BOP bore diameter need only have a diameter that is the same as or slightly greater than the diameter of any tool or well component that must pass through the BOP stack 20 for a desired installation or work over operation. The term "work over" is used to designate one or more of a variety of remedial operations on a producing well for the purpose of restoring or increasing production.

Although not necessary, it may be desirable to determine the distance between the top end 18c of the production casing hanger 18a and the upper face 14a of the wellhead housing 14. The depth of the top end 18c is typically determined from the known depth

(dimensions) of the BOP stack 20. A typical wellhead housing 14 has approximately 24" to 36" between the housing upper face 14a and the top end 18c of the production casing hanger 18a.

Preferably, the length D between the top of one of the plurality of BOP rams 2Or, for example ram 2Or' in Fig. 1, and an inner face 2Of of the BOP wellhead connector 20a is measured and known. This length D is referred to as the "space out" dimension for reasons which will be explained below. The inner face 2Of of the wellhead connector 20a is typically adjacent to or abutting the upper face 14a of the wellhead housing 14 when the BOP stack 20 is mounted on the wellhead housing 14.

A universal tubing hanger suspension assembly 10 according to a preferred embodiment of the present invention is shown in Figs. 2 and 2 A. The tubing hanger suspension assembly 10 includes a string of production tubing 22 connected to a tubing hanger housing 24. The production tubing 22 defines a production tubing bore 22a extending axially through the tubing 22. The tubing hanger housing 24 includes a production bore 24a in fluid communication with the production tubing bore 22a. The production bore 24a extends substantially vertically through the tubing hanger housing 24. As previously discussed, the production tubing string 22 typically extends down to the production zone Z. The production tubing string 22 may include a subsurface safety valve 26 at a desired depth within the well bore B.

The tubing hanger housing 24 also preferably includes an annulus passageway 24b extending through the tubing housing hanger 24. In the preferred embodiment, an annulus isolation valve 28 is included in the tubing hanger housing 24. The annulus isolation valve 28 is arranged and designed to seal and close off the annulus passageway 24b.

Referring to Fig. 2 A, the universal tubing hanger suspension assembly 10 preferably includes a tubing hanger lower assembly 32 at a lower end of the tubing hanger housing 24. The lower assembly 32 may be connected to or integral with the tubing hanger housing 24. The lower assembly 32 preferably includes a sealing and lockdown assembly 34. The lower assembly 32 is preferably a tubular member having a throughbore. The tubular member 32 may be a pipe or a mandrel having a bore

therethrough. The tubing hanger lower assembly 32 preferably extends around the production tubing string 22 with a production annulus 32a defined therebetween. While the production tubing string 22 preferably has a length such that its lower end extends approximately to the production zone Z, the tubing hanger lower assembly 32 preferably has a length substantially less than the length of the tubing string 22. Preferably, the length of the lower assembly 32 is less than 50% the length of the tubing string 22, more preferably less than 25% the length of the tubing string 22, and most preferably less than 15% the length of the tubing string 22.

Since the length of the tubing string 22 is dependent on the depth of the production zone Z, the length of the lower assembly 32 relative to the tubing string 22 varies from well to well. Preferably, the lower assembly 32 has a length in the range of 1' to 1,500', more preferably in the range of 1' to 300', and most preferably in the range of 5' to 100'.

Preferably, the sealing and lockdown assembly 34 is carried by the tubing hanger lower member 32. Preferably, the sealing/lockdown assembly 34 is located near the lower end of the tubing hanger lower member 32. An enlarged view of the sealing/lockdown assembly 34 is shown in Fig. 3. Preferably, the sealing/lockdown assembly 34 includes an enlarged outside diameter tubular portion 36 which is slightly less than the inside diameter of the production casing 18. In the preferred embodiment, the sealing/lockdown assembly 34 includes a sealing apparatus 38 and a movement prevention locking apparatus or lockdown apparatus 40. The sealing apparatus 38 and the lockdown apparatus 40 may be contained within a unitary assembly or may be separate assemblies. In wells having a subsurface safety valve 26, the sealing apparatus 38 is positioned in the casing string 18 above the subsurface safety valve 26. The lockdown apparatus 40 is also above the subsurface safety valve.

In the preferred embodiment, the lockdown apparatus 40 includes elements or slips, which may be metallic or non-metallic, adapted to engage the interior of the production casing 18. When engaged, the lockdown apparatus 40 engages the interior of the casing 18 and "fixes" or prevents vertical movement of the tubing hanger suspension assembly 10 relative to the production casing 18.

The sealing apparatus 38 includes a sealing element, which may be made of elastomerics or other materials (including composites) or a metal seal, adapted to form an annular seal between the production casing 18 and the tubular portion 36, as for example, by compression. The sealing apparatus 38 and the lockdown apparatus 40 may be independently activated or jointly activated. Preferably, the activation and de-activation of the lockdown apparatus 40 and the sealing apparatus 38 is hydraulically controlled through ports 42a and 42b as explained below. The activation and de-activation may also be electronically, mechanically, or electrically activated or de-activated.

As shown in Fig. 2A, preferably one or more hydraulic control lines 44 extend through the tubing hanger housing 24 to provide hydraulic control to devices below the tubing hanger housing 24. For example, hydraulic control lines may be required to activate and de-activate the sealing apparatus 38 and the lockdown apparatus 40. Also, a hydraulic control line 44a may be required to run to the subsurface safety valve 26.

Preferably, these hydraulic control lines 44 are run in the production annulus 32a between the lower member 32 and the production tubing string 22 as shown in Fig. 2 A. The subsurface safety valve hydraulic control line 44a is preferably in an annulus 22b between the production casing string 18 and the production tubing string 22 below the lower end of the sealing and lockdown assembly 34 as shown in Fig. 2A.

Referring again to Figs. 2 and 2A, the tubing hanger suspension assembly 10 is preferably lowered into the cased well bore B and wellhead housing 14 with a tubing hanger running tool 30. The tubing hanger running tool 30 is adapted to lock into the upper end of the tubing hanger housing 24. The tubing hanger running tool 30 preferably includes a production bore 30a which extends through the running tool 30 and communicates with the tubing hanger production bore 24a. The tubing hanger running tool 30 also preferably includes an annulus access bore 30b which communicates with the tubing hanger annulus passageway 24b and hydraulic lines 30c communicating with the hydraulic lines 44 of the tubing hanger housing 24. The tubing hanger running tool 30 preferably includes lines for downhole hydraulics and chemical injection (not shown) for communication with similar lines in the tubing hanger housing 24.

The tubing hanger running tool 30 preferably includes an upper mandrel 46 having a space out mandrel adjust nut 48 or similar mechanism at an upper portion. Preferably, the nut 48 or the mandrel 46 and nut 48 are adjustable in length for reasons as explained below. As explained above with reference to Fig. 1, the space out dimension D is the measured and known distance between the top of BOP rams 2Or' and the inner face 2Of of the wellhead connector 20a of the BOP stack 20. This space out distance D is constant for the BOP stack 20 and is preferably measured before lowering the BOP stack 20 into the water. As shown in Fig. 1, the space out distance D also corresponds to the distance between the top of the BOP rams 2Or' and the upper face 14a of the wellhead housing 14 when the BOP stack 20 is connected to the wellhead housing 14.

Referring to Fig. 2, the adjust nut 48 and the upper mandrel 46 of the tubing hanger running tool 30 are preferably "adjusted" before commencing the "running" or installation operations of the tubing hanger suspension assembly 10. The mandrel 46 and adjust nut 48 are adjusted such that the tubing hanger housing 24 is received at the desired elevation in the wellhead housing 14 when the adjust nut 48 contacts the partially closed BOP rams 2Or' as shown in Fig. 2. The adjust nut 48 in the preferred embodiment has an outer diameter greater than the outer diameter of the upper mandrel 46. As the tubing hanger suspension assembly 10 approaches its desired depth, the larger diameter adjust nut 48 "bottoms out" on the rams 2Or' which are closed to a diameter smaller than the diameter of the adjust nut 48 but larger than the mandrel diameter.

Referring to Figs. 2 and 2A, the preferred installation operation of the tubing hanger suspension assembly 10 includes the lowering, through a riser (not shown) and BOP stack 20, of the production tubing string 22, the sealing and lockdown assembly 34, the tubing hanger lower tubular member 32, and the tubing hanger housing 24 with the tubing hanger running tool 30 and an installation tubing string 50, preferably drill pipe. The BOP ram 2Or' is partially closed after the tubing hanger housing 24 and lower portion of the tubing hanger running tool 30 passes. With the ram 2Or' closed or partially closed against the upper mandrel 46, the lowering operation continues until the adjust nut 48 contacts the ram 2Or' and stops the tubing hanger running tool 30 at the predetermined distance. The predetermined distance properly positions the tubing hanger housing 24 at a prescribed elevation relative to the wellhead housing 14. In the preferred embodiment of

the invention, the predetermined distance properly positions the tubing hanger housing 24 within the wellhead housing 14. For example, the predetermined distance may locate the upper end of the tubing hanger housing 24 within an inch or two above or below the top surface of the wellhead housing 14. With the adjust nut 48 contacting the ram 2Or ¹ , the tubing hanger lower tubular member 32 and the sealing and lockdown assembly 34 are vertically held in position in the production casing string 18.

Next, if desired, a well completion fluid is circulated in the well. Preferably, the BOP rams 2Or' are sealed around the upper mandrel 46. The well completion fluid is pumped from the rig down the kill line 20k of the BOP stack 20 and into the tubing hanger running tool annulus access bore 30b, the tubing hanger annulus passageway 24b, the lower member production annulus 32a and the production tubing annulus 22b and returned to the surface up through the production tubing bore 22a, tubing hanger production bore 24a, running tool production bore 30a and bore 50a of the installation tubing string 50. Alternatively, the completion fluid can be pumped down the installation tubing string bore 50a, the running tool production bore 30a, the tubing hanger and production string bores 24a and 22a and around the lower production packer 52 and up the annulus bores 22b, 32a to the tubing hanger annulus passageway 24b, the running tool annulus bore 30b and to the surface through the BOP choke or kill lines 20c, 20k. The completion fluid is circulated in the well prior to the lower packer 52 being set to form a seal between the production casing 18 and the production tubing 22 at the lower end of the well. It is to be understood that the above circulations of completion fluid can be conducted either prior to or after setting the sealing apparatus 38.

Next, the sealing and lockdown assembly 34 is activated, preferably hydraulically, via the hydraulic control lines to force the lockdown apparatus 40 (see Fig. 3) into tight locked engagement with the production casing 18. The engaged lockdown apparatus 40 prevents or substantially prevents relative vertical movement between the lower tubular member 32 and the production casing 18. Upon activation of the sealing apparatus 38, the sealing apparatus 38 forms a fluid- or gas-tight seal between the lower tubular member 32 and the production casing 18. The sealing and lockdown assembly 34 may include a set of slips having metal elements which grip the production casing 18. An elastomeric or other seal is preferably compressed by the set slips to form the fluid-tight seal. Preferably, the

sealing and lockdown assembly 34 is a modified packer assembly of the type conventionally used in wells to isolate production zones, etc. Such representative packer assembly technology is generally described in U.S. Patents 6,769,491; 5,988,276; 5,271,468; and 4,296,806, and commercially available from companies such as Halliburton Company, Baker Hughes Inc. and Weatherford/Lamb, Inc. Applicant incorporates by reference herein U.S. Patents 6,769,491; 5,988,276; 5,271,468; and 4,296,806 in their entirety.

hi this preferred embodiment of the invention, the sealing and lockdown assembly 34 engaged with the production casing 18 provides the sealing and load support of the universal tubing hanger suspension assembly 10 in the well. The sealing and lockdown assembly 34 provides vertical load support to support the universal tubing hanger assembly 10 and to resist upward forces that may be exerted against the assembly 10. This sealing, locking and suspension of the tubing hanger assembly 10 is accomplished and installed without having to know any critical and proprietary dimensions in the wellhead housing 14 and/or casing hangers 16a, 18 a. Furthermore, in this preferred embodiment the tubing hanger housing 24 is not required to, and preferably does not, lock or seal with either the wellhead housing 14 or the casing hangers 16a, 18 a.

With the sealing and lockdown assembly 34 activated and set, the seal may be pressure tested from above or below the sealing and lockdown assembly 34. The seal can be pressure tested from above by closing the anrmlus isolation valve 28 in the tubing hanger housing 24 and with the rams 2Or' sealed around the upper mandrel 46, pumping a fluid from the surface through the kill line 20k, down past open ram 2Or", around the outside of the tubing hanger running tool 30 within the BOP bore 20b, in the annular area between the wellhead housing 14 and the tubing hanger housing 24, and the annular area between the production casing 18 and the lower member 32.

Preferably, after the sealing and lockdown assembly 34 has been successfully tested, the lower packer 52 is set to seal off the production tubing annulus 22b near the bottom of the production tubing string 22. The lower packer 52 can be tested from below by opening the annulus isolation valve 28 and closing the BOP rams 2Or' and lower rams 2Or" around the tubing hanger running tool 30. To pressure test, pressure is built up by

pumping fluid down the installation tubing string bore 50a, the tubing hanger running tool production bore 30a, the tubing hanger production bore 24a and the production tubing bore 22a to beneath the packer 52. If, during the test, the packer 52 leaks fluid, pressure and fluid is taken up through the tubing annulus 22b, annulus valve 28 and annulus passageway 24b, between rams 2Or' and 2Or", and up the kill line 20k.

With reference to Fig. 4, preferably a closure member or plug 54 is lowered (e.g., via wireline) down the installation tubing string bore 50a and tubing hanger production bore 30a and set in the bore 22a of the production tubing 22. The closure member 54 is preferably a retrievable plug, and more preferably a wireline retrievable plug. In the preferred embodiment the closure member 54 is set in the production tubing 22 at a depth at or below the sealing and lockdown assembly 34. Alternatively, the closure member 54 may be set in the production tubing 22 at or above the sealing and lockdown assembly 34 or in the tubing hanger housing production bore 24a.

After setting and testing the sealing and lockdown assembly 34, the lower packer 52 and the closure member 54, and with the subsurface safety valve 26 and the annulus isolation valve 28 closed, the tubing hanger running tool 30 is disconnected from the tubing hanger housing 24 and retrieved to the surface. The BOP stack 20 is then removed from the wellhead housing 14.

Next, a tree assembly 60 is lowered from the upper surface of the water via a pipe string 50, preferably a drill string, and a tree running tool 56 as shown in Fig. 5. The tree assembly 60 is shown having a production bore 62, production master valve 64, production wing valves 66 and a production swab valve 68. The tree assembly 60 also includes an annulus bore 70 and an annulus master valve 72. The tree assembly 60 has a tree wellhead connector 60a adapted to seal and connect with the wellhead housing 14.

The preferred tree assembly 60 shown in Fig. 5 is generally referred to as a monobore tree; however, the invention is applicable not only to monobore trees but also dual bore and multi-bore trees and test frees. Additionally, while -the invention is particularly suited for subsea application, it can also find application for surface wells.

Figure 5 shows the tree assembly 60 with a tree-to-tubing hanger stab sub assembly 74 providing various interconnections between the tree assembly 60 and the universal tubing hanger suspension assembly 10. The stab sub assembly 74 is preferably installed in the lower end of the tree assembly 60 before lowering the tree assembly 60 to the wellhead housing 14. The stab sub assembly 74 includes a production bore 74a in sealed engagement with the tree production bore 62 and forms a sealed engagement with the tubing hanger housing production bore 24a upon the installation of the tree assembly 60 on the wellhead housing 14. Similarly, the stab sub assembly 74 also includes an annulus bore 74b in sealed engagement with the tree annulus bore 70. The annulus bore 74b forms a sealed engagement with the tubing hanger annulus bore 24b upon the installation of the tree assembly 60. One or more hydraulic control lines 74c are preferably in the stab sub assembly 74 and provide connection to hydraulic lines 24c, 44a and 44b (Fig. 9) for the control of downhole equipment and devices. Additionally, other ports or lines, such as a chemical injection line, may be provided in the stab sub assembly 74. Use of the term "lines" in reference to the hydraulics and chemical injection is meant to include either tubing or bores or ports in solid members, as for example the tubing hanger housing 24 or stab sub assembly 74.

Fig. 6 shows a preferred embodiment of the stab sub 74 connected to the universal tubing hanger housing 24. A pair of annulus isolation valves 28 are shown in the tubing hanger housing 24. The right side of Fig. 6 shows the right valve 28 in the closed position to close the annulus passageway 24b, and the left side shows the left valve 28 in the open position to open the annulus passageway 24b. Preferably the left and right isolation valves 28 assume the same position and are operated together. As shown in Figs. 6 and 7, the stab sub 74 preferably includes a pair of annulus bores 74b in order to provide a sufficient cross sectional annular flow area, typically the combined area being equivalent to the cross sectional area of a 1.5" to 2" diameter hole. The lower ends of the annulus bores 74b are in fluid communication with each other by a peripheral groove or gallery 74b'. Similarly, the upper ends of the annulus bores 74b are in fluid communication with each other by a peripheral groove or gallery 74b". Alternatively or additionally, the tree assembly 60 may also include a peripheral groove for providing fluid communication to the tree annulus bore 70 and the annulus master valve 72 (Fig. 5). The annulus flowpath P from below the

sealing and lockdown assembly 34 to the tree assembly 60 with the annulus isolation valve 28 open is indicated by the arrows in Fig. 6.

Figures 8 and 9 show passageways for the chemical injection and hydraulic or subsurface safety valve (SSSV) controls. The section views of Figs. 8 and 9 have been angularly rotated relative to the section view of Fig. 6. As shown in Fig. 9, the stab sub 74 includes separated passageways for the hydraulic controls 74c for the subsurface safety valve 26 and for chemical injection 74d. Similar galleries as described above are preferably provided for each. Seals are preferably provided between each of the galleries to maintain segregation between the various passageways.

hi the preferred embodiment, the widths (measured along the longitudinal axis of the stab sub 74) of the peripheral grooves or galleries are larger than the respective diameters of the bores 74b, 74c and 74d to allow communication between the respective passageways over a range of vertical spacing variations between the tubing hanger housing 24 and the tree assembly 60. For example, the vertical elevation of the tubing hanger housing 24 relative to the wellhead housing upper face 14a is predetermined and set via the running tool upper mandrel 46 and adjust nut 48 as described above. The tree assembly 60 is installed on the wellhead housing 14. The stab sub assembly 74 provides the fluids and controls linkage between the tubing hanger housing 24 and the tree assembly 60. Since the stab sub 74 is preferably joined to the tree assembly 60 prior to lowering the assembly, it is important that all of the fluids/controls connections between the tubing hanger housing 24 and the stab sub 74 automatically mate when the tree assembly 60 is secured to the wellhead housing 14. The enlarged widths of the peripheral grooves or galleries described above permits the desired mating over a range of distances between the tree assembly 60 and the tubing hanger housing 24. Preferably, the galleries allow the stab sub assembly 74 to properly mate and communicate over a vertical distance range of approximately 1" to 3".

The galleries, as described above with respect to the preferred embodiment, allow the tree assembly 60, the stab sub assembly 74 and the tubing hanger housing 24 to communicate and mate with each other independently of the angular orientation of the separate components. This "non-oriented" characteristic of this apparatus simplifies the

running and installation of the subsea components. The invention may also be used with oriented subsea components.

With the tree assembly 60 secured and tested, the closure member 54 (see Fig. 4) is retrieved to the surface through the bores of the production tubing 22, tubing hanger 24, stab sub assembly 74, Christmas tree assembly 60, tree running tool 56 and the installation tubing string 50.

Figure 10 shows a slight modification to the embodiment of the present invention shown and described above. In Fig. 10, a stop apparatus 80 is connected to the lower end of the tubing hanger housing 24. The stop apparatus 80 is preferably a ring member having an upper ring portion 82 and a lower ring portion 84. Each ring portion 82, 84 includes a threaded end 82a, 84a, respectively, adapted to engage each other. Preferably, the lower ring portion 84 has a lower beveled end 84b corresponding to the shoulder 18b in the production casing hanger 18a. Preferably, the length of the stop apparatus 80 can be adjusted by the threaded engagement of the ring portions 82 and 84 prior to installing the tubing hanger suspension assembly 10. Preferably, the length of the stop apparatus 80 is such that the lower beveled end 84b contacts the casing hanger shoulder 18b and transfers the weight of the tubing hanger suspension assembly 10 to the production casing hanger 18a. Thus, if the dimensions and location of the production casing hanger 18a relative to the wellhead housing 14 are known, the ring stop apparatus 80 may be employed to provide a downward stop when lowering and installing the tubing hanger suspension assembly 10. Furthermore, the ring stop apparatus 80 can be used in lieu of the adjust nut 48 of Fig. 2. The ring stop apparatus 80 does not provide a seal, and it does not provide resistance to upward forces — the seal and resistance to upward forces are still provided by the sealing and lockdown assembly 34.

Based upon the foregoing description of the invention, a "universal" set of subsea well components is achievable. For example, referring again to Fig. 1, a common size of wellhead housing 14 has an inside diameter (ID) of 18.625" or 18.75", depending on the manufacturer. The casing hangers 16a, 18a installed in these wellhead housings 14 are typically 24" to 36" below the upper face 14a of the wellhead housing 14. Thus, the tubing hanger housing 24 (Figs. 2, 2a) of the universal tubing hanger suspension assembly

10 can occupy a round cylindrical space of approximately 18.5" in diameter and 24" in height at the upper portion of the wellhead housing 14. Since the preferred tubing hanger housing 24 does not include a releasable locking mechanism for locking to the upper portion of the wellhead housing 14 (typical of conventional tubing hangers), the 18.5" diameter is substantially fully usable by the tubing hanger housing 24. This larger diameter of the wellhead housing 14 is advantageous because the "usable space" for the various bores and passageways required to pass through the tubing hanger housing is substantially greater than in conventional tubing hangers.

Preferably, the length of the stab sub assembly 74 (see Fig. 5, 6) is the same regardless of the type of wellhead housing 14 and casing hangers 16a, 18a on which the tree assembly 60 is being installed. This is accomplished due to using the space out dimension D to substantially uniformly position the tubing hanger 24 relative to the top of the wellhead housing 14 regardless of the wellhead housing type. This provides simplicity in design from wellhead to wellhead and allows for a "universal" stab sub assembly 74 used with the preferred tree assembly 60. Certainly, separate stab sub assemblies are required for different size production tubing.

Thus, it is to be understood that the universal tubing hanger suspension assembly 10, the stab sub 74 and the tree assembly 60 are capable of installation on various wellhead housings 14, and are, to a great degree, "universal" and "off the shelf items, eliminating significant engineering and fabrication costs incurred when installing Manufacturer A's tree assembly on Manufacturer B's wellhead housing. The present invention also eliminates the use of a tubing spool (wellhead connector and crossover wellhead housing) mounted to Manufacturer B's wellhead housing for carrying Manufacturer A's tubing hanger.

In the preferred embodiment of the present invention, the universal tubing hanger suspension assembly 10, the stab sub assembly 74 and the tree assembly 60 do not require angular orientation. This feature significantly simplifies the installation procedure. Nevertheless, the invention is not limited to non-orientation arrangements and may also be used with components requiring orientation with respect to each other. Techniques for orienting a tree assembly to a tubing hanger are well known in the art. One type of

suitable orientation technique is disclosed in U.S. Patent 5,544,707 and is hereby incorporated by reference. Another orientation technique is to modify the BOP stack 20 with a pin to orient the components as they pass through the BOP stack 20. Orientation of the components adds costs and complexity to the subsea installation process.

The present invention includes a tubing hanger suspension assembly 10 for an oil and gas well and a method of installing same. The tubing hanger suspension assembly 10 includes a tubing hanger housing 24 which is positioned in the wellhead housing 14. The tubing hanger assembly 10 includes a sealing and lockdown mechanism 34 capable of providing sealing and load support of the production tubing 22 in the production casing string 18. A stab sub assembly 74 connected to the upper end of the tubing hanger suspension assembly 10 and lower end of the Christmas tree assembly 60 provides downhole hydraulic and electric functionality and annulus access to the production tubing 22.

Using the BOP stack 20 for space out and placement of the tubing hanger assembly 10 negates the requirement for exact dimensions of the wellhead housing 14 for space out and also negates the need for any internal stack up dimensions to interface the subsea tree assembly 60 to the stab sub assembly 74. Preferably, space out of the tubing hanger assembly 10 is accomplished through an adjustable space out nut 48 at the top of the upper mandrel 46 of the running tool 30 in the BOP stack 20. Alternatively, the space out predetermined elevation of the tubing hanger assembly 10 can be accomplished using a ring stop apparatus 80, preferably adjustable, landing in the production casing hanger 18.

Using tubing packer technology for fixing the lower member elevation at a predetermined elevation through the BOP stack 20 rather than the wellhead housing 14 allows subsea tree interface in any industry wellhead system. The device or devices used in the system negates the use of the BOP stack 20 or the wellhead for orientation as well.

The apparatus and methods described above are advantageous because they are suitable for use in wellhead housings 14 independent of proprietary details pertaining to the housing. The tubing hanger suspension assembly 10 of the preferred embodiment of the present invention eliminates the need to use wellhead housing or casing hanger landing shoulders for locking and sealing the tubing hanger housing 24 in position. The tubing

hanger suspension assembly 10 of the preferred embodiment of the present invention also eliminates the need to seal the tubing hanger housing 24 to the wellhead housing 14. The preferred embodiment eliminates these requirements by sealing, anchoring and locking the sealing and lockdown assembly 34 in the production casing 18 suspended by the casing hanger 18a in the wellhead housing or system.

The present invention provides simplicity and reduced costs in completing a subsea well. The tubing hanger housing 24 is preferably not locked to, sealed with, or supported by the wellhead housing 14. Thus, the wellhead housing 14 no longer needs the details, profiles, etc. related specifically to the tubing hanger housing 24. Furthermore, no internal profiles, etc. are required in the production casing string 18 for cooperating with the sealing and lockdown assembly 34. This provides flexibility to install the tubing hanger housing 24 at the desired elevation for ensuring the proper spacing to be bridged by the stab sub assembly 74 as it is lowered with the tree assembly 60. Even the final elevation of the sealing and lockdown assembly 34 in the casing string 18 can be varied over a substantial distance by changing the length of the lower member 32. Depending on various well related factors, the invention can be embodied in a plurality of sealing and lockdown assemblies 34 if deemed desirable.

The invention provides a substantial amount of additional cross sectional area available for use in the tubing hanger housing 24 which is a tremendous benefit. The tubing hanger housing 24 may have a diameter that approaches the inside diameter of the wellhead housing 14. The additional area allows ample space for an increased production bore or multiple production bores, annulus and various other ports and controls, etc. that are required or desired in a tubing hanger housing.

A description of some of the benefits derived from the preferred embodiment of the tubing hanger suspension assembly of the present invention follow:

For the customer/user, the wellhead becomes invisible to the completion. This provides savings to the user in two ways: engineering and hardware interfacing. Engineering is reduced in determining tubing hanger interfaces such as stack up tolerances

and dimensions and compatibility issues. Currently, this includes issues in subsea and surface completions.

• Engineering:

1. Engineering time spent on the interface is significant. Users spend approximately one man week on engineering the interface for their completion. This generally requires 2 engineers at a cost of $200 per/hour totaling $16,000 per manufacturer's interface. The cost for two wells is approximately $32,000 and for ten wells is $320,000.

2. A manufacturer supplying proprietary drawings to work the interface issues charges $10,000 for each drawing. Typically, a minimum of two drawings are required totaling $20,000. This is charged on a well by well basis even if the wells are identical and drawings are copied. If the user has two wells, the charge is $40,000 or if he has ten wells the charge is $200,000. The wellhead manufacturer charges these fees for access to its needed proprietary information which serves as a monetary incentive to the user to purchase the wellhead manufacturer's tubing hanger and Christmas tree as opposed to seeking the most economical/commercial solution to his subsea well completion. 3. This totals between $36,000 for one well and $520,000 for ten wells.

• Manufacturing and hardware interfaces:

1. To complete a well using conventional tubing suspension methods inside a wellhead where the wellhead is of a different manufacturer than the tree, the tree manufacturer's conventional tubing suspension system is not compatible with the wellhead. Therefore, the user's completion is rendered useless. This means the user's $1,300,000 to $2,000,000 completion is useless and he must purchase another tree at the cost of time, schedule and hardware. 2. If the well situation will allow the technical deficit, a crossover spool may be used. However, the same issues as expressed above

in Engineering are incurred. The crossover spool is mounted on the wellhead housing and is designed to accommodate the tubing hanger of the tree manufacturer. Ih addition to the added engineering cost, the hardware cost for the crossover is approximately $500,000 with approximately an additional

$1,500,000 to $7,000,000 in installation spread cost. This spread cost is dependent on water depth and geographic location. 3. Horizontal trees have been used to assist in this respect, hi a horizontal tree, the tubing hanger housing is landed and sealed in the tree (spool) as opposed to the wellhead housing. However, horizontal trees come with a price and engineering interface also. Typically, the horizontal tree is approximately $1,000,000 higher in cost as well as approximately $1,200,000 in ancillary tolling cost per well. 4. In the preferred embodiment of the tubing hanger suspension assembly of the present invention, the lockdown and sealing device is in the casing bore. This provides advantages in the following areas: cost and flexibility. Cost is reduced to the user because a single or multi-bore production tubing system can be used. This allows large stab subs to be used in the tree to bring multi-bores

(production, annulus and hydraulic ports) through stab sub mandrels for tree interface, thus saving approximately $500,000 to $7,000,000 in the tree and completion.

The invention, including the universal tubing hanger suspension assembly 10, is not limited to the preferred embodiments described herein. The universal tubing hanger suspension assembly 10 is not limited to the tubing hanger housing being received in the wellhead housing. Rather, the universal tubing hanger suspension assembly 10 can also be used in wells in which the tubing hanger is received in tubing spools or horizontal trees mounted on the wellhead housing. It is to be understood that the sealing apparatus 38, and optionally the lockdown apparatus 40, would still be positioned in the casing string 18.

Preferred embodiments of the tubing hanger suspension assembly, well completion system and method of installing same according to the present invention have thus been set forth. However, ^' the invention should not be unduly limited to the foregoing, which has been set forth for illustrative purposes only. Various modifications and alterations of the invention will be apparent to those skilled in the art, without departing from the true scope of the invention.