Technology Focus: Subsea Systems

Abstract

Technology Focus Alternative solutions to traditional subsea production systems received more attention when the oil price was so low that only a few potential subsea field developments seemed to be profitable. During the past few years, more focus has been on how to use existing infrastructure to get more oil and gas from reservoirs than originally planned with its own platform or floating production, storage, and offloading vessel. A subsea system with a long pipeline back to the nearest existing process plant with available capacity, in many cases, makes a field development economically attractive even at low oil prices. However, some challenges need to be overcome by new technology when oil, water, and gas are to be transported in long subsea pipelines. In oil fields that are currently being considered, the length of these pipelines is typically 20 to 50 km, but tieback distances in gas fields today can be up to 220 km, as described in one of the papers presented at OTC this year (OTC 29232). A major challenge in nearly all long subsea tiebacks is related to flow assurance. Hours, in some cases days, are required for the fluid to travel through a pipeline surrounded by cold water. The drop in temperature results in higher viscosity, wax deposition, and hydrate formation. The backpressure from friction losses and flow-regime effects also can restrict flow. Hence, innovative solutions are required to complement traditional subsea production systems that are based on natural flow to the surface. Various system alternatives have been proposed and developed, but the use of subsea multiphase pumps at the seabed has so far been the most successful solution. However, the development of a pumping system that can be used at great water depths involves much more than just packaging of motors and pumps for subsea applications. The system needs electrical power to be transferred over long distances, and with this comes equipment such as subsea connectors, transformers, switch gears, and frequency converters. The status of some of these technologies is described in this feature’s synopses. Recommended additional reading at OnePetro: www.onepetro.org. OTC 29232 Real-Time Subsea Hydrate Management in the World’s Longest Subsea Tieback by Christophe Vielliard, OneSubsea, a Schlumberger Company, et al. OTC 29647 Unlocking Subsea Reserves Through a System-Based Approach for Tieback Solutions by Kristian Mikalsen, National Oilwell Varco, et al. OTC 29307 Qualification and Case Studies of a Subsea Chemical Storage and Injection Unit by Art J. Schroeder Jr., Safe Marine Transfer, et al.