The primary function of a Christmas tree is to manage the flow of oil and gas from the well. It serves several key purposes:
Flow Control: Regulating the flow rate of oil and gas to optimize production.
Pressure Management: Maintaining appropriate pressure levels within the well to prevent blowouts.
Separation of Fluids: Allowing for the separation of oil, gas, and water as they are extracted.
Safety Measures: Providing emergency shut-off capabilities to prevent uncontrolled releases of hydrocarbons.
In producing wells, injection of chemicals, alcohols, or oil distillates to prevent or solve production problems (such as blockages) may be used.
A tree may also be used to control the injection of gas or water injection applications on a producing or non-producing well in order to sustain economic "production" volumes of gas from other wells (s) in the area (field).
The control system attached to the tree controls the downhole safety valve while the tree acts as an attachment and conduit means of the control system to the downhole safety valve.
Components of a Christmas Tree
A typical Christmas tree is composed of a master gate valve, a pressure gauge, a wing valve, a swab valve, and a choke. The Christmas tree may also have a number of check valves.
At the bottom, we find the casing head and casing hangers. The casing will be screwed, bolted, or welded to the hanger. Several valves and plugs will normally be fitted to give access to the casing. This will permit the casing to be opened, closed, bled down, and, in some cases, allow the flowing well to be produced through the casing as well as the tubing. The valve can be used to determine leaks in the casing, tubing, or packer, and will also be used for lift gas injection into the casing.
The tubing hanger (also called a donut) is used to position the tubing correctly in the well. Sealing also allows Christmas tree removal with pressure in the casing.
There are wells drilled into the reservoir, and the central conductor, along with the surrounding jackets/annulus, rises up to the production deck/cellar deck of the platform. On top of the wellhead, an assembly of valves is placed, which has the form of a cross. This assembly of valves together with the flanges is called a wellhead Christmas tree.
The Christmas tree has many Manual valves and a number of actuated valves. The actuated valves usually found on the Christmas tree are as follows:
Sub-Surface Safety Valve:
The Sub-Surface Safety valve is a hydraulic operated valve, the location of which is below sea level, above the sea bed. The actuator of this valve needs to be very small, as it gets enclosed within the Annulus of the conductor. The actuator is usually hydraulically operated. The control line for the hydraulic supply for the SSSV runs within the conductor and terminates at a connection on the Christmas tree.
Surface Safety Valve or Master Valve:
This isolates the tree from the production tubing. The Christmas tree has two master valves referred to as the upper and lower master valves. The lower master valves are opened first and closed last. This ensures a minimal flow of hydrocarbon over the valve seat, thus protecting it from abrasive particles and ensuring a good seal is maintained.
In most cases, the lower master valve is manually operated and the upper master valve is operated via a hydraulic or pneumatic actuator and is connected to the emergency shutdown system. The actuators are fail-safe in operation. The valve is held open by oil or pressure against a compressed coil spring.
The master gate valve is a high-quality valve. It will provide a full opening, which means that it opens to the same inside diameter as the tubing so that specialized tools may be run through it. It must be capable of holding the full pressure of the well safely for all anticipated purposes. This valve is usually left fully open and is not used to control flow.
A master valve is the first actuated valve on the Christmas tree, located above the Mezzanine deck of the platform. The Actuator is bigger and can be pneumatic or Hydraulic, based on the Christmas tree requirement.
The pressure gauge: The minimum instrumentation is a pressure gauge placed above the master gate valve before the wing valve. In addition, other instruments such as temperature will normally be fitted.
Wing Valve:
The wing valve comes on the arm of the Christmas tree, on the line where the flow line starts. The actuator is again hydraulic or pneumatic based on the requirement. The wing valve can be a gate valve or a ball valve. When shutting in the well, the wing gate or valve is normally used so that the tubing pressure can be easily read.
Christmas trees may be manufactured with one or two wing valves. One valve is permanently connected to the hydrocarbon process system and is fitted with a hydraulic or pneumatic actuator. The other valve is manual in operation and permits the injection of chemicals or gases into the well without disturbing production pipework.
Both valves are offset from the vertical lines so that a clear entry into the well is maintained through the swab valve for wireline work. The flow of gas from the well is regulated by wing valve operation or by choking fitted above the wing valve.
Hydraulic tree wing valves are usually built to be fail-safe closed, meaning they require active hydraulic pressure to stay open.
The right-hand valve is often called the flow wing valve or the production wing valve because it is in the flow path the hydrocarbons take to production facilities.
The left-hand valve is often called the kill wing valve. It is primarily used for the injection of fluids such as corrosion inhibitors or methanol to prevent hydrate formation.
Well Service Valve:
The Well Service Valve may be present on some Christmas trees, where Diesel pumping is required for initial start-up. It is on the other arm of the Christmas tree, and usually, the size is lesser than that of the wing valve.
The valve at the top is called the swab valve and lies in the path used for good interventions like wireline and coiled tubing. A 'Choke' is a device, either stationary or adjustable, used to control the gas flow, also known as volume, or create downstream pressure, also known as back pressure.
The Wellhead valves are all controlled by a Well Head Control panel, which gives the hydraulic & pneumatic supply for opening/closing these valves. There is logically built in the WHCP for allowing the safe closure of all these wellhead valves, in case of an emergency, either due to process upset or due to emergency/fire. In addition to these valves, the other instrumentation which is associated with the Christmas tree is the Pressure gauges and Transmitters for monitoring the Annulus pressures, the Flowing Tube Head Pressure, etc.
As a premier manufacturer of Christmas Tree, Vigor upholds the API 6A standards rigorously in both production and inspection processes. Each product is thoroughly tested before dispatch to ensure compliance with these high standards. Additionally, Vigor tailors shipping packaging for each product, ensuring meticulous wrapping to prevent any potential damage during transit. Our dedicated shipping department oversees the entire shipment process, maintaining strict control to guarantee a seamless experience. At Vigor, our commitment to reducing risks and minimizing customer inconvenience drives us to earn your trust through exceptional products and unparalleled service quality. If you are interested in our offerings, please do not hesitate to contact us for professional products and top-notch service.
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