Cabezas de pozo

WELLHEADS

Wellheads for offshore wells fall into three main categories. 1. Marine Wellheads for Flcating drilling units. 2. Mudline Suspension/Surface Wellhead for ‘fixed bottom’ Jackup units. 3. A Hybrid System of 1 and 2 generally a special purpose design for specific applications.

MARINE WELLHEADS

This type of wellhead is located on the ocean floor level. Its primary funczions are: 1. 2. 3. Ta provide a termination of the casing strinm with’a means to connect the primary well pressure control equipment. Provide a means of guidance for the Blawaut Preventor s{ dance of any odc!itionalequipment such as a zucsea “tree ?rovide a means of suspending the various casing strin9s cnnuli. The floating rig lJS.Sdto drili the we~! is eauicmed with Q ack, and guiif required). and sealing the ., subsea 310wout pr%,..entorStcck- (80P).

MUDLINE SUSPENSION SYSTEMS (MLS)

See Figure 3. A stondard mudline suspension system is limited for all practical purposes to some types of bottom supported rig or platform are virtually the same as for a land aperation. In its standard form, it does nat allow for annu. Annulus sealing and “pressure rating crossover” conventional wellheads located at the surface. The drilling operations us sealing at the mudline. are provided by means of The system provides a means of suspending the various casing strings at the ocean floor or ‘mudline level’ and a means of allowing the ‘casing extensions’ fram the MLS to the surface wellhead to be removed. In this fashion, the well may either be recentered at a later date for ither: Subsea completions Tie back ta a platform

HYBRID SYSTEMS The third type of subsea “Wellhead”, termed for the purpose of this paper is a “Hybrid”.

SYSTEMS DESCRIPTIONS AND INSTALLATION PROCEDURE FOR FIGURE 7

The 30” is installed in a similar manner to that of the MLS system. The 30” housing is fitted with a three post guide frame, providing guidance at a later stage far the high pressure marine riser and later the Christmas tree

TUBING SUSPENSION SYSTEMS

The primary functions of a tubing hanger system for a closed pressure campietion are: suspend one provide a or more tubing strings; means to lock and seal into the housing wellhead or tubing spool to facilitate removal of the rig’s pressure control equipment; provide a means by which the hanger moy be run

CHRISTMAS TREE CONFIGURATIONS

A Christmas tree for subsea applications perfarms the following major tasks: Provides a primary means of control for well fluids through the master valve - upper master valve - swab or wire line valve and a wing valve. It may also be provided with a means of varying well flow or pressure stepdown by the inclusian of a choke. Provides a means of connection to the wellhead and sealing to same.

Bottom Adaptor/Connector Flange

lhis flange would provide primary interface with the wellhead and the Christmas tree valves. In its simplest form, it wauld look like the MLS (A) in which it is clamp profile, extended neck.

Christmas Tree Valves

Christmas tree valves and ancillary items for production tubing access usually, as with surface trees, the standard requirement is for a manual master valve, a remotely operated upper master valve, a cross, and remotely aperated wing valve.

ManuallyOperated

Valves Manually operated vaives are ‘marinised’ by basically protecting the handwheel stem from marine ~rowth with a cap. Remote (Failsafe) Operated Valves Remote (failsafe) operated valves, whilst using the same sealing campcnent design as the manual, are fitted with a failsafe operator.

Flow Control

If required, a choke or flow controller may be installed on the wing valve providing a pressure stepdawn before the flowline.

Christmas Tree Flow Manifolding

 Th= =:--1 e+ mnmt-$mlriin . =&8,,p&ea.,8WU,. ,V.wb,.g LS om where the f~Qwline is attached directly to the outlet af the tree.

Guide Structures The simplest type of tree would have no guide structure. guide can provide the following features if the wellhead guide base: However, o simple is +irted with a A means of ~uidance when installing the Cinristmastree - a completion on a marine wellhead wculd use the four post PGB (Permanent Guide 6ase) installed with the weilhead. A frame to which to anchor the flawline to allow flowline induced loads to be transmitted part 0+ the tree. Protection for the Easier har,dlingof Provide a base from Provide a means for 8. c~irectly thr6ugh guide frame to a str cturally strong tree components from anchor lines or fishing lines. the tree assemblies prior to ifist~ii~ti~fi. which divers could work.

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