Turritella FPSO - Design and Fabrication of the World’s Deepest Producing Unit

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27663, “Stones Development: Turritella FPSO—Design and Fabrication of the World’s Deepest Producing Unit,” by Blake Moore, Andrew Easton, Jonathan Cabrera, and Carl Webb, Shell International Exploration and Production, and Babu George, SBM Offshore, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. The Stones Project is in the emerging Lower Tertiary trend in the Gulf of Mexico ultradeep water. A floating production, storage, and offloading (FPSO) unit was selected for the floating production system to address the stepwise development of the Stones Field. The Turritella FPSO (Fig. 1) is the deepest floating production system in the world and presented many challenges to successful execution of the surface host facilities. Overview The Stones development is along the Walker Ridge protraction area in the deepwater Gulf of Mexico, in water depths ranging from 7,500 to 9,500 ft. The field was developed using a disconnectable FPSO tied to a subsea development. Nominal production capacities will be 60,000 B/D of fluids, 30,000 B/D of produced water, and 15 MMscf/D of associated gas. The FPSO design was based on the conversion of an existing Suezmax-scale, double-hull tanker. Design Key design decisions during front-end engineering and design (FEED) and pre-FEED in 2012 and 2011 established many of the key design criteria that guided the design of the FPSO. Riser selection—lazy-wave riser to buoy vs. free-standing risers: An early study identified lazy-wave risers as preferable over free-standing risers because of technical concerns related to flexible pressure ratings and commercial considerations. Disconnectable buoy: Early engagement with regulatory entities (e.g., the Bureau of Safety and Environmental Enforcement) determined that a disconnectable turret to allow the FPSO to escape a hurricane would be required to achieve regulatory approvals. Hull size—Aframax vs. Suezmax: Shell/regulatory requirements for a double hull and the applicable environmental-impact statement for FPSOs in the Gulf of Mexico limiting FPSO storage capacity to less than 1 million bbl led to the limitation of potential hulls. Deck space to accommodate planned topside facilities and turret led to the selection of a Suezmax. FPSO throughput: Technical limitations on riser sizes at the water depth for Stones established maximum throughput. The system choke point was in the risers, and the capacity of the topside matched the riser throughput limit.