Subsea Hybrid Loop: Operating Philosophy And Technical Challenges

Most deepwater oil fields are currently developed using a field-proven pigging loop configuration. Such a configuration based on two production lines enables to implement a reliable operating strategy. With smaller fields to be developed and longer tie-back distances to production hubs, operators are facing more and more demanding technical challenges such as the duration of transient operations, increased hydrate risk and solid deposits management. In the context of investigating alternate configurations for deepwater fields development, a field architecture based on a single production line looped with a water injection line has been technically assessed. This new architecture, called Hybrid Loop, is similar to Greater Plutonio operated by BP where a production line is looped with a service line; however the Hybrid Loop concept differs from the Greater Plutonio reference as it makes use of the injection water to displace the production flowline content. By eliminating the need of two production lines, this configuration provides new field architecture options while bringing additional technical advantages. However, from an operating point of view, the Hybrid Loop is different from the Conventional Loop. In particular, transient operations and relevant flow assurance issues must be carefully evaluated. In the frame of conceptual and feasibility studies performed by TOTAL and SAIPEM, Hybrid Loop transient operations and flow assurance have been assessed up to a level demonstrating the technical feasibility of the operating philosophy. Therefore, the objective of this paper is to describe the Hybrid Loop configuration, discuss the operating philosophy and flow assurance challenges and provide information on the required subsea hardware. The Hybrid Loop configuration can be implemented on fields where water injection is required for reservoir pressure management. For such fields, the paper will also highlight the main incentives to use Hybrid Loops