Overview of Wellhead and X-Mas Tree Assembly
Wellhead equipment refers to the Christmas tree, tubing head, casing head, and related components - equipment used for suspending, supporting, controlling, and regulating during oil and gas production operations. As critical production equipment, the performance of wellhead equipment directly impacts the safe and efficient operation of oil and gas wells.
Design Standards for Wellhead Equipment and Christmas Trees
1. API Spec 6A Wellhead and X-Mas Tree Assembly, 21st Edition 2018
2. ISO 10423-2022 Wellhead and Christmas Tree Equipment
3. GB/T 22513-2023 Petroleum and Natural Gas Industries - Wellhead and Christmas Tree Equipment
4. API Std 6AR Repair and Remanufacture of Wellhead and Christmas Tree Equipment, 2nd Edition 2019
5. SY/T 7694-2023 Repair and Remanufacture of Wellhead and Christmas Tree Equipment
These standards specify the performance requirements, dimensions, interchangeability, design, materials, testing, inspection, welding, marking, handling, storage, transportation, procurement, repair and remanufacturing for wellhead and Christmas tree equipment used in the petroleum and natural gas industries. Recommended practices are also provided.
Excluded from the scope are field operations, field testing, repair of wellhead and Christmas tree equipment (except weld repairs associated with manufacturing), and tools for installation and servicing like running, testing, cleanout, and lubricator tools.
The standards define four product specification levels (PSLs): PSL 1, 2, 3, and 4. PSL 3G covers supplementary design requirements for PSL 3 products requiring gas test pressures. PSL designations define different technical quality levels.
API 6A Definitions for Wellhead and X-Mas Tree Assembly
① Wellhead - The entire permanent assembly of equipment from the uppermost casing head outlet to the lowermost tubing head adapter flange.
②Casing Head Housing - Equipment connecting the top joint of surface casing to suspend and seal the casing string.
③Casing Head Spool - Equipment installed above another casing head to suspend and seal an intermediate casing string.
④Tubing Head Spool - Equipment installed above the uppermost casing head to suspend and seal tubing and the tubing-casing annulus.
⑤Hanger (Mandrel-Type) - Device used to suspend a casing or tubing string by connecting to the head via threads.
⑥ Hanger (Slip-Type) - Mechanism using wedging slips inside the casing head to grip and suspend the casing string.
⑦ Tubing Head Adapter - Equipment providing the transition at the top of the tubing head to accept the bottom connection of the Christmas tree.
⑧ Top Connector - The uppermost component of the Christmas tree allowing communication with the tree's vertical bore.
⑨ Gate Valve - Valve assembly with a closure mechanism at 90° to the flow bore to shut off flow.
⑩ Full Bore Valve - Valve whose trim bore equals or exceeds the valve body bore.
⑪Surface Safety Valve - Automatic fail-close valve assembly at the wellhead.
⑫ Choke - Device used to restrict, control, and regulate fluid flow rates and pressures.
⑬Plug Valve - Valve with closure perpendicular to flow bore, sealing when rotated 90°.
⑭Swab Valve/Crown Valve - Uppermost valve in the Christmas tree vertical bore above production outlets.
⑮ Actuator - Mechanism for remote or automatic operation of a valve or choke.
⑯ Back Pressure Valve - Check valve run through the christmas tree to prevent well fluids flowing out of the tubing string.
⑰ Blind Flange - Solid flange without a bore used to seal off flanged or studded outlets and connections. May have test ports.
⑱ Body - Any part of wellhead/tree equipment designed to contain or expose bore pressure and fluids, including end and outlet connections.
⑲ Bonnet - Pressure-containing closure for the body, excluding end and outlet connections.
⑳ Valve Removal Plug - Threaded plug installed in the wellhead to permit removal of the gate valve under pressure.
Functions of Wellhead and X-Mas Tree Assembly
①Suspend and support casing, tubing, and downhole tools while sealing the tubing-casing annulus
②Control and regulate production rates via chokes for production management
③Facilitate well interventions like wireline, perforating, acidizing, testing, etc.
④Monitor tubing pressure
⑤Provide safety functions
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