A subsea horizontal tree is designed so that all flow control valves are outside the central wellbore. A tubing hanger is located inside of a subsea horizontal tree body. A horizontal tree is well known as a workover friendly tree because it offers easy access for tubing retrieval because the valves are not located at the centre of the wellbore. Figure 1 shows an image of a horizontal subsea tree from GE oil and gas.
Figure 1 – Horizontal Subsea Tree Model VetcoGray M-Series MVXT and MHXT (Courtesy of GE Oil & Gas)
In the oil and gas industry, a Christmas tree is referred to as a series of valve & spool assembly fitted on top of the well. A Christmas tree is installed on top of the last casing spool on a surface well or the high pressure wellhead housing for a subsea well. Figure 1 demonstrates the diagram of a Christmas tree and wellhead of a surface wellhead. The Christmas part is located at the top part (a blue box) and the wellhead part is the lower section (a red box). Many people get confused about what a Christmas tree and a wellhead are and many times they think of them as the same thing.
Its functions are as follows;
- Allow reservoir fluid to flow from the well to the surface safely in a controlled manner.
- Allow safe access to the wellbore in order to perform well intervention procedures.
- Allow injections as water or gas injection.
- Provide access to hydraulic line for a surface control sub surface safety valve (SCSSSV)
- Provide electrical interface for instrumentation and electrical equipment for electrical submersible pump (ESP)
In this section, it will describe about a surface Christmas tree (Dry Tree) which is referred to as any Christmas tree used above water level. A Christmas Tree consists of a series of valves and the components are shown and described below; Continue reading