Subsea Field Development Schemes Integrating Subsea Chemical Storage and Injection Systems: Benefits and Challenges for Long Tiebacks

摘要

Chemical injection in subsea fields is a consolidated practice to solve or prevent flow assurance issues that may occur linked to hydraulic, thermal and operability requirements, especially in transient conditions. The traditional approach adopted to supply chemicals to a subsea tieback is to position the chemical injection system, including pumps and storage, on the platform/FPSO, transporting the chemicals subsea through the umbilical or the chemical lines in case of high flow rates, and performing chemical distribution subsea up to the injection points. In the development of a long subsea tieback, costs for the umbilical system tend to increase based on its length and complexity. Moreover, pressure drops and control of chemical delivery pressures and flowrates through such a long umbilical can be extremely challenging, together with the risk of umbilical line blockages and their related issues. The design resolution to enlarge the diameter of the chemical conduits in umbilicals leads to an increase in unit weights and, combined with the umbilical length, additional costs and packing and installation challenges. These factors drive the need to review the conventional chemical injection system architecture and to make the development of a long tieback sustainable from the point of view of cost and technology. To overcome these major criticalities, the chemical injection system can be placed subsea, possibly close to the injection points. Recently, Saipem has mapped the typical chemical demand for a representative size oil fields, with the main aim of defining a subsea chemical injection system architecture and its related main components. The main result of this exercise is the definition of a configurable architecture for subsea chemical storage, injection and refilling facilities to be located close to the subsea users, based on operating consideration suitable for offshore and deepwater scenarios. A "building block" approach is followed together with a certain degree of equipment standardization, where possible, allowing for a flexible system that can be adapted and tailored to the specific field. Technology development status has been also considered and specific Saipem technologies, currently under qualification or being patented, have been considered and integrated in the concept.