Development of an API 17TR8 Compliant 18-3/4 Subsea Wellhead System rated to 20,000 psi and 350°F

摘要

As the industry' progresses into deeper waters with reservoirs that require more complicated well designs, there is an increasing need for equipment that can withstand higher pressures, temperatures, casing loads, and structural and cyclic loads. A 20,000 psi 350°F rated 18-3/4" wellhead system has been developed to meet those needs. The system was designed and qualified to API 17TR8 with the addition of rigorous internal design and testing requirements. The system design is based on the field-proven technology of a legacy 20,000 psi 350°F 18-3/4" wellhead system (reference OTC paper 19694) which completed development in 2008, prior to the release of API 17TR8. This API 17TR8 compliant wellhead system can support a total of 4,400,000 lb of casing weight inside the high-pressure wellhead housing, including up to 2,400,000 lb of intermediate casing weight in the first position and up to 2.000.000 lb in the second position. The system is provided with annulus seal assemblies (ASA) designed and tested through an extensive qualification plan made up of industry required testing in addition to testing identified by a detailed Failure Modes, Effects, and Criticality Analysis (FMECA). Operators can install and test the first position and second position ASAs, up to 20,000 psi, in a single trip with the use of a specially designed single trip tool. A spring-loaded tool and wear bushing also allows the operators to test the blowout preventer (BOP) to 20,000 psi while isolating the ASAs. The design of each component involved detailed elastic-plastic finite element analysis (FEA) per ASME BPVC Sec. VIII, Div 3 and a rigorous qualification plan generated through the FMECA process. The goal of this paper is to provide an overview of the development (verification and validation) of the 20,000 psi 350°F wellhead system per API 17TR8 and the independent third party (I3P) review as required by BSEE for an HPHT wellhead system.