OPT 2005 - Flowlines Installation on Kristin - New Techniques

摘要

This paper describes the unique challenges related to the pipeline scope of work performed by Technip under the Statoil Kristin Marine Operations contract. Six 10" flowlines and four bundled 3.5" service lines and umbilicals were installed by the Technip Offshore vessel Apache, a 12" oil export line was also installed by the Skandi Navica under a subcontract to Subsea. This scope included a significant number of challenges related to the implementation of reliable flowline systems and to the mitigation of loads on manifolds and other structures connected to the pipelines. The Kristin field is the most extreme HPHT subsea field developed in Norway to date, 170 degC reservoir temperature and 91 lbarg pressure, and has required the qualification and implementation of a number of new technologies by the operator.For flow assurance of the 13%Chrome 10" flowlines a system has been developed employing the direct electrical heating (DEH) method. Experiences from previous DEH projects and 13%Cr material pipelines in general, have been used to optimise the general layout of the Kristin field and to improve technical details. Anode tubes for CP protection of the flowlines and earthing of the DEH system were developed for the flowlines. In addition external mechanical protection of the DEH cable was utilised for the first time. These measures have resulted in a significant number of new operations on the pipeline construction vessel, Apache. This paper describes the new techniques employed, the reasons for their development and the benefits gained. The Service Line/Umbilical system made use of single termination heads connecting both the steel core umbilical and the 3.5" ID scale squeeze injection line. Although not a new concept, the application in the Kristin field involved far heavier dimensions on the piggyback product than the carrier product causing significant installation and tie-in challenges. Interface loads to structures connected to flowlines have been a major topic for all tie-in operations on Kristin. Recent experience with similar hubs has resulted in the introduction of extra limitations on interface loads both during installation and operation. These have been found to be governing for the design and tie-in of expansion loops between the flowlines and manifolds. The paper describes the methods adopted to achieve a controlled loading situation such that the risk of overloading was minimised. Techniques employed to solve similar loading issues on the combined service line and umbilical bundles are also described.