Development of the 18-3/4" × 16-5/8" Drill Through Subsea Wellhead System for Pre-Salt Búzios Field
Authors: Maldonado Oscar , Mo Wenxi , de Freitas Pinto Thiago , Weidlich Marcos Correa , de Santana Pinto Thiago , de Resende Delton Lustosa , Dória André Santos 
Published: April 2024

Abstract
This paper describes the design methodology implemented during the wellhead system development for the Petrobras Búzios project. The project required an increase in the subsea wellhead system's capabilities, including pressure containment, load-carrying capacities, and endurance testing, surpassing those of past projects. The wellhead system included components featuring a reduced outside diameter of the equipment that allows the wellhead components to be deployed through the Production Adapter Base (PAB) which will eliminate Blowout Preventer (BOP) trips, leading to a savings of up to five days per well.
A fit-for-purpose wellhead system was developed for use with a PAB that incorporated enhanced performance in structural loading and endurance that leveraged new sealing technology, combining cost reduction in well construction with an increase in integrity. The wellhead system has been fully verified using advanced analysis tools and validated with full-scale load and pressure testing to endurance cycle standards defined by the Búzios life-of-field performance. Industry leading seal validation standards were set for the project and met to account for strenuous operational design requirements. Total system development included the system hardware design, validation testing, bore protection equipment design, and installation tooling design.
The full wellhead system was designed by analysis and utilized 3D models to accurately capture load distribution and interaction of the complex components within the system assemblies. Further refined analysis was used to optimize performance based upon validation test results that led to successfully completing all seal validation requirements to the Petrobras specifications inclusive of a 200-cycle endurance test followed by performance envelope validation. In addition, the system further met the high operational and technical standards of other Dril-Quip subsea wellhead systems, such as single trip installations of casing hangers and seal assemblies. The system does not require additional lockdown devices to be installed either in tandem or separately while meeting 1.8-million-pound hanger and Seal Assembly lockdown requirements. Eliminating the need for extra lockdown devices has the potential to further expedite well construction by approximately one day.
The Búzios project requirements challenged equipment providers to explore new methods of learning and design optimization to meet the overall project schedule. The final output required to meet the project challenge was a new 18-3/4″ × 16-5/8″ 15,000 psi rated wellhead system that provides the industry with the highest combination of pressure capacity, lockdown capacity, and endurance testing. This pivotal technology is instrumental in enhancing operational savings by eliminating both BOP (Blowout Preventer) trips and the lockdown sleeve trip, thereby unlocking greater efficiency in operations. In this paper, we delineate the multifaceted challenges encountered in the development of the 18-3/4" × 16-5/8" Drill Through Subsea Wellhead System and highlight the innovative solutions that were devised to overcome these obstacles. An in-depth exploration of the engineering hurdles is presented, alongside a description of the systematic approach and novel methodologies employed to ensure the project's success and its alignment with the stringent requirements of the Búzios field development. Furthermore, these advancements not only underscored Dril-Quip's commitment to engineering excellence but also established the company as the first to market with this pioneering technology, setting a new benchmark in the industry.