Vito Project: Hull / Mooring Design & Platform Installation

Abstract

In 2009, the Vito field was discovered in more than 4,000 ft of water approximately 150 miles offshore from New Orleans, Louisiana. The project produces from reservoirs nearly 30,000 feet below sea level. This paper provides an overview of the Hull & Mooring system, executing a minimum technical scope to produce a simplistic design. This paper is part of a Vito Project series at OTC 2023, and the other papers are listed in the references. The original Vito project execution strategy was to replicate the Shell mega-project of Appomattox. As the industry and market began to change in 2015, the project faced significant financial hurdles, and the project team decided to refresh the design concept to reduce cost and simplify. The team regrouped to propose a smaller semi-submersible Floating Production System (FPS) with a simplistic mooring design. The Topsides was designed to be lifted as a single module, with a payload of less than 10,000 st to enable competitive tendering process. The redesigned FPS concept was moored with 12 taut, chain – polyester – chain mooring line system utilizing an in-line mooring tensioner, removing the traditional mechanically complicated and space demanding "on-vessel" winch systems. Vito employed a passive hull system, with all ballasting occurring over the top without hull penetrations. There were no pump rooms within the hull as equipment is accessed from top of column, removing the need for regular hull access to maintain equipment. The hull compartmentation also followed a simple approach, containing only 12 ballast tanks to reduce fabrication cost. The hull design also included simplified ring stiffening for columns which eliminated the traditional orthogonally stiffened systems. Additionally, the structure utilized an upper column frame structure to support the topsides deck and served as a bracing for supporting columns at the top for squeeze-pry loads and bracing for supporting columns during dry tow. The simplification of the stiffening system and topsides deck support design reduced interfaces between hull and topsides and also opened up options for fabrication of topsides and hull. Key challenges included developing installation methods without traditional FPS mooring chain jacks and increasing installation options by not requiring a large installation derrick barge and enabling use of common anchor handler vessels. The project experienced fabrication delays due to COVID-19, which required creative solutions transporting the FPS from Singapore to the Gulf of Mexico. The design team enabled the use of various heavy transportation vessels (HTV), ultimately settling on a smaller HTV modified with four 25 ft outriggers.