Although not part of subsurface equipment , the Christmas tree is usually the first component encountered by a workover/completion crew. The Christmas tree is a series of valves, flanges, choke body and connectors that allow the controlled flow of produced fluids.
Applications usually dictate what type of Christmas tree will be needed. There are many different designs and complexities of Christmas trees. Simple units, such as a pump jack setup, may consist of a stuffing box with
no valves. Complex tress may have numerous master and wing valves. Factors taken into account in tree design include pressure, surface environment and temperatures, other types of produced fluids, down hole envoronment, fluid temperatures and economics.
The tree should be lubricated on a regular schedule. Good maintenance minimizes complications during production. It also leads to smoother repair and removal.
The basic components of the Christmas tree include the following:
- PRESSURE GAUGE: Pressure gauges allow well pressures to be monitored. Tubing pressure and casing or annular pressures are monitored with these gauges.
- GAUGE FLANGE (CAP): Provides a seal for the top of the tree and has provisions for a pressure gauge. When this flange is removed, it provides access to the tubing.
- CROWN VALVE (SWAB VALVE): The crown valve is used to shut off pressure and allow access to well for wireline, coil tubing, workover, etc, units to be rigged up.
- FLOW TEE (CROSS, TEE): The flow tee is used so that tools may be run into the hole while allowing production to the flow line.
- WING VALVE: A wing valve is used to shut off the well for most routine operations. These are the easiest to replace in case of damage or cutting out of the valve.
- CHOKE: The choke controls the amount of flow desired from the well.
- MASTER VALVES: master valves are the main shut off valves. They are open most vof the well’s life and are used as little as possible, especially the lower master valve.
- TUBING HANGER: A tubing hanger suspends or supports the tubing string, seals off the casing annulus, and allows flow to the Chirstmas tree.
- CASING VALVE: The casing valve gives access to the annulus between tubing and casing.
- CASING HANGER: A slip and seal arrangement that suspends, and seals off, the casing in the casing bowl.
- CASING: Casing is a pipe string that supports the wellbore to prevent it from caving in and prevents communication from one zone to another.
- TUBING: A pipe string that contains and allows the flow of fluid produced by the formation.
During a rig move in and rig up, extremme care must be taken not to damage the tree. Carelessness at this point could prove fatal to rig and/ or personnel.