Descripción de la propuesta

The Tubing Hanger is a completion component, which sits inside the Tubing Head Spool and provides the following functions:

• Suspends the tubing

• Provides a seal between the tubing and the tubing head spool

• Installation point for barrier protection

The Tubing Head Spool provides the following functions:

• Provides a facility to lock the tubing hanger in place .

• Provides a facility for fluid access to the' A 'annulus

• Provides an appropriate base for the completion Xmas Tree

Both the Tubing Hanger and Tubing Head Spool are prepared to allow the actuation of an SCSSV.

An example of a Tubing Hanger/Tubing Head Spool system is shown in Figure 1:21. Such Tubing Hanger systems allow completion tubing to be suspended in neutral (ie. all the tubing weight minus fluid buoyancy) or the tubing suspended in compression.

NOTE: Completion strings may be set in compression to accommodate for

tubing movement as a result of pumping cold fluids into the tubing, i.e. thermal contraction effects. For example, water injection wells may be set in compression prior to landing the hanger by installing additional tubing in the well. When the water injection system is operating, thermal effects will contract the string appropriate to the additional tubing installed. Setting a completion in compression requires that the tubing-to-packer arrangement be appropriate (packer systems will be discussed later).

NOTE: Completion strings may also be set in tension to compensate for

thermal expansion of the tubing due to production. Setting a completion in tension requires pulling the tubing in tension prior to production and dosing rams around a hanger nipple. The hanger nipple is run an appropriate distance below a Ram Type Tubing Hanger, See Figure 1:22, and the tension applied to the tubing string to remove tubing from the well equivalent to that expected from thermal expansion. Setting a completion in tension requires that the tubing-to-packer arrangement be appropriate (packer systems will be discussed later).

Completion Design

Completion Design

Completion Design 1.8.11 Xmas Tree

An Xmas Tree is an assembly of valves, all with specific functions, used to control flow from the well and to provide well intervention access for well maintenance or reservoir monitoring.

NOTE: The Xmas Tree is normally connected directly to the tubing hanger

spool that sits on the uppermost casing head spool. The whole assemblage of Xmas Tree, Tubing Hanger and uppermost Casing Head Spool is sometimes referred to as the Wellhead.

A Xmas Tree may be a composite collection of valves or, more commonly nowadays, constructed from a single block; See Figure 1:23. The solid block enables the unit to be smaller and eliminates the danger of leakage from flanges.

Typically, from bottom to top, an Xmas Tree will contain the following valves: Lower Master Gate Valve Manually operated and used as a last resort to shut in

a well.

Upper Master Gate Valve Usually hydraulically operated and also used to shut in a well.

Flow Wing Valve Manually operated to permit the passage of hydro- carbons to the production choke.

Kill Wing Valve Manually operated to permit entry of kill fluid to into the tubing.

Swab Valve Manually operated and used to allow vertical access into the tubing for well intervention work.

NOTE: Nowadays, all Xmas Tree valves are of the gate-valve type that

allows full bore access.

Completion Design

Completion Design

Completion Design

1.8.12 Production Packers

A production packer may be defined as a sub-surface component used to provide a seal between the casing and the tubing in a well to prevent the vertical movement of fluids past the sealing point, allowing fluids from a reservoir to be produced to surface facilities through the production tubing.

NOTE: By no means are all wells completed with production packers.

However, for the purposes of this course, only those packers used in well completions will be discussed.

The prime purpose of using a packer or packers in a well completion is as follows:

• To protect the casing from reservoir fluids

• To protect the casing from the effects of flowing pressures

• To isolate various producing zones

In general, packers are constructed of hardened slips which are forced to bite into the casing wall to prevent upward or downward movement while a system of rubberised elements contact the casing wall to effect a seal.

Production packers may be grouped according to their ability to be removed from a well, that is, retrievable or permanent.

Retrievable Production Packers

Are run on the tubing string and may be set mechanically or hydraulically. They are usually removed from the well by the application of mechanical forces. An example of a retrievable production packer is shown in Figure 1:25.

Permanent Production Packers

These may run in a variety of ways and become an integral part of the casing once set. A permanent packer may run as follows:

• On wireline and set in the casing using pyrotechnics to generate the forces required to set it in the casing

Or

• On pipe and set hydraulically by the application of tubing pressure. Figure 1:26 shows an example of this type of permanent packer.

NOTE: Both the above methods provide a disconnect mechanism from the

setting device. The setting device is removed from the well after the packer has been set. The completion string is then run into the well and a seal assembly stabbed into the polished bore of the packer.