Dongying Boru Mechanical Equipment Co.,Ltd
Wellhead – More Than Just a Structure
A wellhead is defined as the essential equipment assembly located at the opening of a well, responsible for regulating the extraction of hydrocarbon derivatives from underground formations, preventing leaks, and controlling pressure. It typically consists of a casing head, tubing head, and a Christmas tree for monitoring and controlling the flow of fluids from the well.
In the world of oil & gas, a wellhead may seem like a group of valves and connections but in reality, it’s a complete system designed for one purpose: safe, efficient, and controlled production.
Every part of it — from the casing head to the Christmas tree assembly — is there for a reason. Whether it's containing pressure, supporting the well, or managing the flow, understanding this system is essential for any field engineer.
Wellheads and Xmas trees are one of the most vital pieces of equipment in a subsea production system. The subsea wellhead system performs the same general functions as a conventional surface wellhead. It supports and seals casing strings, as well as supports the BOP stack during drilling and the subsea tree after completion.
A subsea Xmas tree is basically a stack of valves installed on a subsea wellhead to provide a controllable interface between the well and production facilities. It is also called a Christmas tree, cross tree, X-tree, or tree. Subsea Xmas tree contains various valves used for testing, servicing, regulating, or choking the stream of produced oil, gas, and liquids coming up from the well below. There are various types of subsea Xmas trees, which can be either used for production or water/gas injection. Configurations of subsea Xmas trees can be different according to different projects and field developments.
Subsea wellhead system and Xmas trees are normally designed mainly according to the standards and codes below:
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API 6A, Specification for Wellhead and Christmas Tree Equipment
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API 17D, Design and Operation of Subsea Production Systems—Subsea Wellhead and Tree Equipment
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API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations
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API RP 17H, Remotely Operated Vehicle (ROV) Interfaces on Subsea Production Systems
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API RP 17G, Design and Operation of Completion/Workover Risers
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ASME B31.3, Process Piping
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API 5L, Specification for Line Pipe
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ASME B31.8, Gas Transmission and Distribution Piping Systems
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ASME BPVC VIII, Rules for Construction of Pressure Vessels—Division 1 and 2
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AWS D1.1, Structural Steel Welding Code
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DNV RP B401, Cathodic Protection Design
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NACE MR-0175, Petroleum and Natural Gas Industries—Materials for Use in H2S-Containing Environments in Oil and Gas Production
