Moving to higher-capacity wellhead systems for high-pressure and high-temperature (HP/HT) environments will require a larger mandrel and conductor-casing size to accommodate the high loads encountered during drilling and production operations for normal-, extreme-, and survival-loading conditions. Numerous analytical studies with 3D finite-element analysis (FEA) and other advanced tools have been performed in an effort to determine the changes needed, and an innovative solution is presented for next-generation subsea-wellhead equipment.
The numerous functions that a wellhead system performs are enabled by a large number of parts and subassemblies with complex geometries and interfaces and complicated load paths. The only way to have a true understanding of the wellhead and have confidence in the design safety margin is by performing verification analysis and validation testing of rated, extreme, and survival capacities at the system level, and not only at the component and subassembly level. Testing only at rated conditions is insufficient to verify design margins and eliminate the possibility of unexpected events that can occur at higher load magnitudes.
Current industry standards that guide the design of wellheads require some general testing to be performed at rated capacity for components and subassemblies. However, unlike the standards for casing connectors below the mudline, there are no requirements to test the wellhead at a system level, nor to test the system to the limits (yield capacity) of the equipment, which would confirm the design margins. Casing connectors are tested per requirements that subject the connector to combined load testing of tension, compression, internal pressure, external pressure, and bending at ambient and elevated temperatures. It is logical that testing similar to casing-connector tests be performed on wellhead systems....
Next-Generation HP/HT Subsea-Wellhead-System-Design Challenges and Opportunities
15 March 2016