Pioneer Design of Unmanned Utility Buoy to Unlock Challenging Subsea Tiebacks in Asia

Abstract

A floating Normally Unmanned/Unattended Installation (NUI) or "utility buoy" can provide key services to overcome flow assurance and control constraints directly at the well site. The objective of this paper is to explore how implementing an NUI can enable development of a typical Southeast Asian subsea tieback that could otherwise be considered uneconomical. The approach is based on using Buoyant Production Technologies Ltd. (BPT) floating NUI solution to provide power, chemicals, and control to subsea developments. This removes the need for a long umbilical and potentially costly host modification to accommodate a subsea tieback. A case study is presented to explore the benefits of the NUI. A low power utility buoy is sized to cater for well control and chemical injection. This simple subsea tieback is compared to a conventional approach with an umbilical to a host facility. An assessment of procurement, fabrication, installation, and operation phases is performed to identify the advantages of the utility buoy. The floating NUI design is such that fabrication location is flexible allowing for local fabrication near to the field. In addition, the transportation and installation can be performed by small locally available vessels, resulting in a cost-effective solution, and reduced environmental emissions. Material and equipment selection are focussed on high reliability and low maintenance requirements. This allows for less frequent inspection and maintenance visits, which reduces personnel risk and results in low lifecycle cost. A low power utility buoy shows significant benefits compared to a long umbilical. Combined with the flexibility and re-deployment capabilities, the buoy solution can benefit long tiebacks, as well as early production schemes. An NUI is seen as an enabler for mature regions dominated by subsea tiebacks to feed existing hubs. The improved economics, local fabrication opportunity and reusable profile all adds to the flexibility which will be needed as tiebacks become longer and developments more technically challenging and complex.