A Christmas tree is a set of valves, fittings, and spools that regulates the flow of fluids from an oil or gas well. It’s installed at the top of the well, connecting to the wellhead. It is named for its resemblance to a decorated tree at Christmas.
Many times, the words Christmas Tree and Wellhead are used interchangeably; however, a wellhead and Christmas tree are entirely separate pieces of equipment. A wellhead must be present in order to utilize a Christmas tree and is used without a Christmas tree during drilling operations. Producing surface wells that require pumps (pump jacks, nodding donkeys, etc.) frequently do not utilize any tree due to no pressure containment requirement.
How it works
- The Christmas tree controls the flow of fluids from the well to the surface production facilities.
- It also allows tools to be lowered through the tubing to perform subsurface work.
- The Christmas tree regulates production flow rates and ensures operational efficiency.
Types of Christmas trees
- Surface trees: Used in surface wells, these trees connect to the wellhead that’s visible on the surface.
- Subsea trees: Used in offshore drilling, these trees can be vertical or horizontal.
What it’s used for? Oil exploration and production, Water injection wells, Water disposal wells, Gas injection wells, and Condensate wells.
Tree complexity has increased over the last few decades. They are frequently manufactured from blocks of steel containing multiple valves rather than made from multiple flanged valves.
The primary function of a tree is to control the flow into or out of the well, usually oil or gas.
A tree often provides numerous additional functions including chemical injection points, well intervention means, pressure relief means (such as annulus vent), tree and well monitoring points (such as pressure, temperature, corrosion, erosion, sand detection, flow rate, flow composition, valve and choke position feedback, connection points for devices such as down hole pressure and temperature transducer (DHPT).
WHAT PURPOSE DOES A TREE SERVE?
On producing wells, injection of chemicals or alcohols or oil distillates to prevent and 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 application on a producing or non-producing well in order to sustain economic “production” volumes of gas from other well(s) in the area (field). The control system attached to the tree controls the downhole safety valve ( scssv , dhsv , sssv ) while the tree acts as an attachment and conduit means of the control system to the downhole safety valve.
As you can see even on this Christmas Tree Diagram there are five valves. The Kill Wing valve, the Swab valve, the production wing valve, the upper master valve, and lower master valve. When the operator, well, and facilities are ready to produce and receive oil or gas, valves are opened and the release of the formation fluids is allowed to flow into and through a pipeline. It is important to understand where these valves are located and what role they play in getting gas from the wellbore to the customer.
PARTS DEFINED
- The two lower valves are called the master valves (upper and lower respectively) because they lie in the flow path, which well fluids must take to get to surface .
- The lower master valve will normally be manually operated, while the upper master valve is often hydraulically actuated.
- 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 injection of fluids such as corrosion inhibitors or methanol to prevent hydrate formation.
- The valve at the top is called the swab valve and lies in the path used for well 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 We hope this has helped you understand the difference between wellhead and Christmas trees better; however if you have any questions feel free to contact us with any questions. We do not sell Wellhead equipment or Christmas Tree equipment; although we do sell natural gas processing equipment and oil production equipment.
