A subsea Christmas (X-Mas) tree is composed of valves that are connected to a subsea wellhead. This is to provide a controllable interface between the well and the production facilities. It has valves that are used for testing, servicing, regulating, as well as choking the stream of oil, gas and other liquids going up from the well.
There are different types of Christmas trees that are used for production or maybe water or gas injection. The configurations will be different basin on the projects or field developments. Let us look at the basic information and the differentiation of the horizontal and the vertical X-Mas tree.
Important Functions of Subsea Xmas Tree
The subsea Xmas tree enables the flow of the fluid from the well and also the injection of water or gas from the surface to the injection tree. This normally includes the protection fluids like inhibitors for corrosion or hydrate prevention. The Xmas tree will also stop the flow of the fluid that is produced or injected using the valves. This will also control the flow of the fluid through a choke if needed. And of course, the Xmas will monitor the surrounding levels of the tree like the pressure, annulus pressure, temperature, sand direction, and so on.
The Two Types of Xmas Tree
Christmas tree has two types which will depend on the configuration of valves; the Vertical Xmas Tree and the Horizontal Xmas Tree.
- Vertical Xmas Tree. On this tree, the master valves will be located above the tubing hanger. The swab valves, as well as the master valves, will be stacked together vertically. The production, as well as the annulus bore, will be found laying on the body of the tree. The well completion should be finished before attaching the vertical Xmas tree. Because of this, the Xmas tree can be removed without having to recover the downhole completion. The Vertical Xmas tree is usually suggested for subsea fields because of its flexibility with the installation and operation.
- Horizontal Xmas Tree. Unlike the Vertical Xmas tree, the valves of the Horizontal Xmas tree should be located on the lateral sides of the horizontal tree. This will allow easy well intervention as well as tubing recovery. This is the best choice for the wells that need interventions most of the time. The tubing hanger is installed in the tree body, and not on the wellhead. The Horizontal Xmas tree is attached to the wellhead even before the completion of the well is done.
Horizontal vs Vertical: The Difference
Between the two types of Xmas tree, there are notable differences between the two. This includes the configuration as well as the installation equipment. The installation and the repair sequence would be different as well. These two has different purposes, so the operating philosophies are also different.
The Horizontal Xmas tree advantages are different from those of the Vertical Xmas tree. The vertical tree does not require the removal of the wireline plug when a well needs an intervention. This is best for fields that don’t have to do a workover. It is simpler and cheaper as well compared to the other Xmas tree type. On the other hand, the Horizontal Xmas tree is better for fields that would need a lot of workovers. But here, you can use a larger bore tubing. And this tree is much shorter compared to the other one.