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WARNING: This information is provided to FMC customers solely to illustrate the operation of FMC equipment. It does not provide complete information for service or maintenance. Improperly performed service, maintenance, or installation could cause serious injury or death. FMC equipment is to be installed, serviced and maintained only by trained, authorized FMC personnel. © 2005 FMC Technologies, Inc

Vertical Tree Installed on a Tubing Head

Installing the tubing hanger in a tubing head provides a number of advantages over installing the tubing hanger directly into the wellhead.

Tubing head advantages include:

- Can serve as cross over from a competitor’s wellhead system to allow identical tubing hangers and trees to be used with the tubing head and FMC wellhead systems.

- Provides new landing, lock down and sealing profiles for the tubing hanger that have not been exposed to drilling operations.

- Can provide annulus access below the tubing hanger - Provide passive orientation for the tree

- Allows connection and testing of the flow lines prior to installing the tree - Allows retrieval of the tree without disconnecting the flow lines

Typical GLL Tubing Head

Tubing head disadvantages include:

- Higher CAPEX.

- Additional leak path between the wellhead and tubing head interface.

- Additional stack up height that can add to the loading on the wellhead system when the subsea BOP or completion equipment is installed.

The tubing hanger lands, locks down and seals in the tubing head. Annulus access past the tubing hanger can be provided through a port in the tubing head below the tubing hanger that is sealed with a ROV-operated gate valve. The GLL tubing head has a funnel down interface with the wellhead and a funnel up interface with the BOP stack and tree. Flowline connection may also be attached to the tubing head assembly. The tree interfaces to the tubing head with a second intermediate flowline connector so that the tree can be installed and retrieved without affecting the primary flowline connection. The tubing hanger’s slim design allows it to be installed or retrieved through smaller bore risers, which use smaller, less expensive completion vessels if desired.

When a tubing head is used, annulus access can be routed below the tubing hanger in a manner similar to that used in the horizontal Subsea tree . This can simplify the annulus access through the tubing hanger. The annulus would be isolated by series 100 metal sealing gate valves with hydraulic actuators or by manual valves operated by ROV.

Passive orientation of the tubing hanger can also be provided by an integral 360 degree mule shoe bushing (helix) integral to the tubing head. The graphic below shows the typical annulus flow path arrangement in a tubing head.

Typical GLL Tubing Head Vertical Subsea Tree Arrangement

The vertical tree system has a dual vertical bore for production and annulus access.

The production and annulus bores in the tubing hanger would have a wire line plug profile to allow a plug to be installed while the subsea

BOP is removed and the Subsea tree is installed.

The dual bore would also be in the Subsea tree valve block and vertical pressure barrier barriers would be provided by

FMC series 100 metal sealing gate valves, Production and annulus master and swab valves would provide the dual vertical barriers to the environment. Production and annulus wing valve blocks, chokes and flow

loops would be connected to the side of the Subsea tree valve block.

The top profile of the vertical tree would provide and interface profile (typically a 13-5/8” hub) for the lower riser package

and emergency disconnect package. The graphic at left shows the vertical tree system tool package system.

Tubing

RE-ENTRY HUB WITH PRODUCTION

& ANNULUS BORES PRODUCTION MASTER & SWAB

VALVE HYDRAULIC ACTUATORS ANNULUS MASTER & SWAB VALVE

HYDRAULIC ACTUATORS

The vertical tree valve block assembly would include the production and annulus series 100 metal sealing gate valves and hydraulic actuators. The hydraulic

actuators are designed for water depths up to 3000 meters hence they are

designated M3000 type actuators. The valves are normally set up to be fail safe close on loss of hydraulic operating pressure. In some cases the valves can be set to be fail safe open. This is typically done (failsafe open) with a cross over valve to allow circulating to be done via the production and service flow lines. The graphic below shows a typical vertical tree valve block arrangement.

The vertical tree system tubing hanger lands, locks, and seals inside the wellhead housing or tubing head. Metal to metal seals isolate the production annulus. A rigid lock down mechanism on the tubing hanger prevents any movement in the metal seals during production due to pressure or temperature cycles. Movement of the seals could cause premature failure of the metal seals. Elastomer back up seals is also provided on the tubing hanger. The graphic below shows the major features of the vertical tubing hanger.

Orientation between the tubing hanger and subsea tree is critical to ensure correct engagement and make up of the production, annulus, down hole hydraulic and electrical connections.

For GL & GLL applications orientation is typically provided by a hydraulic pin that is installed to one of the side outlets on the subsea BOP stack. This pin interfaces with a helix profile on a tubing hanger orientation joint (THOJ)

connected to the top of the tubing hanger running tool, When a tubing head is used a passive orienting mechanism can be made integral to the tubing head using a 360 degree helix profile.

Fine alignment between the subsea tree and the tubing hanger can be provided by

alignment slots in the tubing hanger that engage mating keys in the subsea tree connector. This positively aligns the tree stabs prior to engagement with tubing hanger.

Horizontal Tree Systems

As describes earlier, in a horizontal tree system the tubing hanger lands inside the horizontal tree body (the composite valve block)

Two types of horizontal tree systems have been provided to date.

The first generation of horizontal trees (HXT) utilized a tubing hanger landed in the tree with an internal tree cap installed above the tubing hanger. Both landed, locked and sealed independent from the other. Dual vertical barriers to the environment has been provided by a wire line plug set in the tubing hanger and by a solid internal tree cap or by an internal tree cap with a wire line plug profile. In some cases the internal tree cap has been provided with a ball valve operated by the running tool.

All manufacturers of this type of tree (separate tubing hanger and internal tree cap) experienced problems with debris when installing the internal tree cap. Operational requirements meant that the tubing hanger was installed through the drilling riser and BOP first and a wire line plug installed. The tubing hanger running tool was then retrieved to be used to run the internal tree cap. When the internal tree cap was run it was often found that debris had been dislodged from inside the drilling riser and accumulated on top of the tubing hanger and wire line plug preventing the internal tree cap from being installed.

Considerable rig time was then involved in running special flushing tools to wash out the debris before the internal tree cap could be installed. This rig down time cost operators lots of money.

To overcome the debris problems the latest generation of horizontal trees called the enhanced horizontal tree (EHXT™) was developed. The EHXT utilized an extended length tubing hanger that could incorporate two vertical wire line plugs to provide a dual barrier to the environment. This eliminated the need for the independent internal tree cap.

WIRE LINE PLUGS WIRE LINE PLUG

BALL VALVE

TUBING HANGER INTERNAL TREE CAP

The drawings below show the different tubing hanger arrangement for the HXT and the EHXT. The traditional HXT shows the separate tubing hanger and internal tree cap in this case with integral ball valve. The EHXT shows the extended tubing hanger with the two wire line plugs installed.

FMC has standardized on the EHXT design and no longer propose the HXT to customers unless specifically requested for example when a customer may want to add another same again tree design to an existing field.

In a horizontal tree system the tubing hanger orients, land, locks and seals inside the tree composite valve block. The lower extension on the tree provides a 360 degree mule shoe (helix) profile for orienting the tubing hanger. No orienting mechanism is required in the subsea BOP stack as is the case with vertical tree completion systems.

The EHXT composite valve block assembly provides integral product master, annuls master, annulus access valves. Wing valve blocks bolted to the composite valve block provide the wing valves and cross over valve. These wing valve blocks also allow mounting of pressure/temperature transducers and chemical injection valves as required.

Metal to metal seals are located above and below the production side outlet of the tubing hanger to isolate the side exit production bore in the tree composite valve block.

The down hole hydraulic and electric connections are routed through the EH-5 penetrator couplers on the side of the tubing hanger. These interface with the EH-5 radial penetrator on the side of the composite valve block. In the Gulf of Mexico the hydraulic and electric connections also exit the top of the tubing hanger to allow operation and monitoring of the down hole functions through the tubing hanger running tool when the tubing hanger is being run. A maximum of 9 down hole functions can be provided when two EH-5 penetrators are used. One of the hydraulic ports through the EH-5 penetrators is used to monitor between the upper and lower wire line plugs set in the EHXT tubing hanger.

A secondary tubing hanger lock down mechanism is installed above the tubing hanger in the EHXT system. This mechanism can be part of an ROV installed internal tree cap or can be provided by an independent secondary lick down mechanism (THISL). The EHXT can be configured for GL and GLL applications The graphic below shows the EHXT landed on a UWD-15 wellhead system with the tree lower extension (isolation sleeve) engaged and sealed inside the upper casing hanger in the wellhead.

The graphic below shows the major features of the EHXT tubing hanger.

Down hole electric and hydraulic connections between the EHXT and the tubing hanger is provided by the EH-5 radial penetrator mechanism. As the designation indicates up to 5 connections can be provided through the penetrator. This can be a combination of hydraulic and electrical functions as required.

Two EH-5 penetrators can be used on the EHXT if required. One of the hydraulic ports through the EH-5 penetrator is used to monitor pressure between the wire line plugs set in the tubing hanger. The EH-5 penetrator (s) has a center shaft connected to the ROV panel on the tree to allow rotary operation by an ROV. The mechanism also has an emergency release mechanism operated by the ROV in the event that the rotary mechanism cannot be used. The graphic below shows the features of the EH-5 mechanism,

Positive and accurate orientation of the tubing hanger inside the EHXT is critical to correct alignment of the production side outlet on the tubing hanger and correct make up of the hydraulic and electrical connections between the tubing hanger and the EHXT EH-5 radial penetrator(s).

Primary (rough) orientation is provided by the large orienting key on the bottom of the tubing hanger engaging the 360 degree mule shoe in the bottom of the EHXT and secondary fine alignment is provided by the fixed alignment key on the body of the tubing hanger that engaged a milled slot in the bore of the composite valve block. The graphic below shows the primary and secondary orienting mechanisms.

In the EHXT system vertical barriers to the environment are provided by wire line set metal sealing plugs that land, lock down and seal inside the tubing hanger.

These plugs are Halliburton SSP plugs and provide a rigid lock down mechanism to ensure long term reliability of the metal seals. FMC provide the straight bore metal seals (SBMS-2) for these plugs. The drawing below shows the major features of the Halliburton SSP plug assembly.

EHXT vs. VXT

The decision to use a vertical or horizontal is dependent on a number of factors. The following is a brief overview of some of the issues associated with the tree selection process. Typical tree decision drivers include:

CAPEX and OPEX Considerations

Installed CAPEX and Life of Field OPEX Comparison

Workover Time Comparison in 6000 ft Of Water

With the development of “smart well” completions that require that sliding sleeves in the down hole production tubing be operated hydraulically the number of downhole control lines that can be accommodated through the tubing hanger becomes important. The following compares the EHXT and the VXT ability to handle down hole control lines.

The completion size that can be accommodated by the tree system is important especially in gas production where larger completion sizes may be required to handle the gas flow rates. The following is a brief overview of the completion size issues between EHXT and VXT tree systems

The following chart summarizes some of the advantages and disadvantages associated with the EHXT and VXT tree systems.

EHXT VXT

Advantages

Suitable for large bore 7”> gas wells One less BOP trip (Drill Through completion) Tubing hanger landed in wellhead (or tubing head)

Can be installed on competitors wellhead (X-tubing/tugging head)

Allows intervention without a rig Uses rig riser system Reduced wellhead loading

Simplified rig interface Metal sealing gate valves for environmental barriers (not filed installed like wireline plugs) Suitable for SMARTWELL technology Suitable for SMARTWELL technology

Passive TH orientation Tubing intervention simpler as no wireline lugs need to be retrieved

Allows Work over without pulling tree or disconnecting flowlines

Installed CAPEX considered to be lower than EHXT

Flow base typically not required

Wellhead casing hanger rigidizing mechanism integral to the tree

Flexibility of design to accommodate natural flow, gas lift, water injection & ESP

Disadvantages

Requires additional BOP trip May require BOP modification for TH orientation mechanism

Requires an SSTT and landing string Requires lead impression tool run to verify TH

In document Gestión de la Calidad, del Conocimiento y de la Innovación en Salud: (página 93-102)