Page 103 - Well Control for Completions and Interventions

Figure 3.7 Conventional mono-block Christmas tree on an offshore platform.

Table 3.2 Christmas tree valve function
Valve name Function

Lower master valve The lower master is not normally used for day-to-day
(LMV) operations. It is left open and only used to provide a
barrier if other valves in the tree have failed.
Upper master valve This is the valve that is normally used to open and close
(UMV) the wellbore. On many trees the UMV is operated by a
hydraulic (or pneumatic) actuator. The actuator is
configured for “fail-safe closed” operation, and
connected to the facilities automated shut-down panel.
Swab valve (SV) The swab valve (sometimes called the crown valve) is
normally closed while the well is producing (injecting).
It gives access to the wellbore during interventions,
where it used as one of two mechanical barriers (the
UMV being the other).
Flow wing valve Used, along with the UMV, to control flow from the well.
(FWV) Like the UMV, many wing valves are fitted with fail-safe
actuators and are tied into the facility ESD system.
Kill wing valve This valve enables fluid to be pumped into the tubing. As
(KWV) the name suggests, it allows the well to be killed while
the flowline is still attached. It is also used to pump
stimulation and inhibition chemicals down the well,
probably a more common application.
The tree cap Sometimes called the swab cap, the tree cap is a high
pressure cap with the same working pressure as the tree
body. It is removed to allow intervention pressure control
equipment to be rigged upon the well. Most tree caps
have “quick union” type thread, compatible with those
used on intervention pressure control equipment.