This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 30667, “How Technology Enables a Lower Cost for Subsea Tiebacks,” by Fabrice Bacati, Giorgio Arcangeletti, SPE, Bruno Breuskin, Saipem, et al., prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4-7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission.
The traditional subsea tieback model is evolving, supported by advances in flow assurance that allow tiebacks over much longer distances and by the introduction of new technologies that increase overall cost effectiveness. Paper OTC 30667 discusses several of these technologies, their maturity status, and how they can be integrated economically.
During the past 15 years, operating companies have relied increasingly on effective subsea field-development solutions to eliminate the need for traditional platforms or vessels with topside processing facilities, particularly in geographically remote areas and small-pool developments of maturing brownfield areas. Technical and economic challenges include flow assurance and the cost of the umbilical and flowlines, which increase with length. These aspects, together with others independent of length, such as power and space availability, affect project economics significantly.
Technologies developed recently or in their final stage of qualification can help not only in solving technical challenges but also in finding cost-effective configurations, either through reduction or re-apportioning of capital and operational expenditures, extension of reserves recoverability, or reduction of associated risks.
The complete paper outlines several configurations, beginning with those enabled by conventional technologies, and compares them to those enabled by the new technologies. Each section of the complete paper discusses the subject technology’s composition, application, maturity, and impact on cost effectiveness.
Subsea boosting systems that ensure pressure to enable production flow for the life of the field have matured during the last 10 years. Boosting can reduce backpressure at wellheads, and also can transport the production fluid at higher pressure to minimize flowline diameter and control possible instability issues. For gas fields, recovery can be increased by allowing the reservoir to deplete and then using compression to produce the field over a longer time. Currently, several boosting systems operate internationally.
The type of pump technology used depends on the fluid to be boosted and the performance required. Single-phase pumps are used for water injection and oil boosting up to 15% of gas/volume fraction (GVF). Hybrid pumps are used for GVF up to 30%, and multiphase pumps for up to 95%. Subsea compressors are used for higher GVF.