Subsea tiebacks of oil discoveries to existing host platforms are currently, and will continue to be, the most sanctioned deepwater projects because they are fast paced and profitable. Deepwater liquid subsea tieback distances today are technically constrained to about 35 km. Globally, there are numerous discoveries with recoverable reserves too small to justify a stand-alone development, between 35 km and 100 km of an existing host platform, that are effectively "stranded". This paper presents an integrated solution that reimagines the extended length tieback to enable the development of many of these prospects, using only field proven technologies.
The integrated solution consists of two major components: a) an Autonomous Subsea Tieback Enabling Platform (ASTEP), which is a Normally Unattended Installation (NUI) semisubmersible platform that is moored adjacent to the subsea wells and provides power, chemicals, and controls for the tieback, and b) an Active Thermally Managed (ATM) flowline system that ties back the subsea wells to the host platform. A description of the principal components (topsides, hull, mooring, risers, subsea systems, and ATM flowline) is provided along with details of the NUI platform, flow assurance management and low carbon emission power generation options.
The ASTEP Integrated Solution (ASTEP IS) enables commercial development of stranded liquid discoveries up to 100 km from a host platform, employing field proven technologies. The ASTEP IS:
Minimizes host platform brownfield modifications and associated production deferment,
Increases reservoir ultimate recovery by incorporating proven Enhanced Oil Recovery (EOR) methods,
Improves Environmental, Social, and Governance (ESG) and Health, Safety and Environment (HSE) development aspects,
Is readily adaptable to reservoir and regional conditions,
Can be repurposed for multiple deployments
The technical and commercial viability of the proposed integrated solution is demonstrated by a case study of a 30 km deepwater extended tieback to a host platform in the Gulf of Mexico (GoM).