Next Generation HP/HT Wellhead Seal System Validation
Authors: Brown Lucas , Witwer Bruce 
Published: April 2017

As the industry's need for upstream oil and gas equipment designed and engineered to work in deeper water and harsher environments grows, so does the importance of challenging the thoroughness of wellhead system validation testing. With virtually no ability for operators to standardize on wellhead system configurations (ie, casing sizes, weights, BOP stacks, rigs, riser systems, etc.), the capability of these systems must be equally comprehensive. Increased flexibility in individualized components may be realized through more effective validation testing which would serve to minimize the need for specialty equipment. Current industry requirements are not prescriptive enough to ensure that certain claimed capabilities of these systems are effectively validated in such a manner as to accurately reflect the as-installed scenarios of the components, most notably with respect to the subsea casing hanger/seal lockdown performance. This paper proposes what the authors believe should be considered the standard industry requirements for validating subsea seals/casing hangers, for casing hangers held in place by mechanical means, within the next generation of wellhead systems. The proposed requirements are intended to meet the demands of current and future wells. In the development of these propositions, many challenges are illustrated in association with effectively producing testing methodology which accurately reflects the field operations for the equipment being qualified.

The subsea wellhead system functions in a dynamic, complex environment; however, the qualification process of this system commonly employs relatively static test fixtures. The test configurations for this equipment may lack assemblies which would prevent hardware movement generated by thermal growth, annulus pressure buildup and/or other factors due to the conditions of normal or even extreme/survival (e.g. worst-case discharge) events. These critical seal/casing hanger barriers within the next generation wellhead system are presented, discussed and shown with exhaustive validation efforts necessary to evaluate relevant failure modes and the ability to standardize across various wellhead configurations. Within the wellhead system, loads are typically resultant of a combined state including pressure and temperature. The validation of these components is aimed at defining the performance of the system in these states while detailing the limitations that one performance aspect may have on another.

Well-defined subsea seal/casing hanger validation testing requirements to accurately simulate the installed configuration are provided. Loads are applied independent of pressure within these assemblies, and in doing so, the performance of the components have been defined throughout a distinct operating envelope of combined loads and pressures. The operational envelopes validated by this testing offer the information a well designer needs to ensure that the hardware selected is suitable for a variety of applications.

The antiquated claims of not being able to provide metal-to-metal sealing in dynamic applications are dispelled based on performed validation testing of a metal-to-metal seal (with no elastomeric/thermoplastic elements) which accurately represents field scenarios, in which combined pressure/temperature, load and hanger movement are applied. The need for costly equipment installed within the system to withstand certain dynamic conditions is shown to be unnecessary with a fully defined high capacity casing hanger/seal lockdown operational envelope.