New Method for Managing Hydrates in Deepwater Tiebacks

Abstract

Abstract This paper will discuss holistic application and integration of existing technology to manage hydrate formation and potential blockage in subsea tiebacks. The paper will cover how careful examination of the nature of the reservoir fluids and properties can be used to advantage in subsea field developments to facilitate strategies different from "first principal" techniques such as chemicals and insulation that are aimed at preventing hydrate formation altogether. In many developments such methods would be expensive potentially to the point of preventing economic development of a particular asset. In the present work a combination of modern flow and thermodynamic simulation tools in conjunction with judicious testing to verify key assumptions have been used to develop an operational hydrate management philosophy of "doing nothing" under certain circumstances. In fact it is suggested that hydrates can form without any significant blockage risk to operations. The concept is based on allowing hydrates to form in a limited fashion. Aspects of the concept have been discussed and demonstrated in field and laboratory applications within industry forums such as the Deepstar Flow Assurance program. Introduction Many considerations enter into the flow assurance philosophy and design for a given project development. Of the many tasks, the planning for managing hydrate formation usually requires the most effort in terms of time and planning. Hydrate mitigation and management in a deepwater oil system typically ends up being comprised of a collection of strategies that involve thermal management (eg. insulation of subsea equipment and flowlines to retain heat and provide cooldown time), chemical injection (eg. pumping methanol and or low dosage hydrate inhibitor during shutdowns and restarts), pressure reduction (eg. blowdown), and fluid composition management (eg. dead oil displacement during extended shutdowns). The hydrate management philosophy therefore has a significant impact on hardware design and operating procedures.