Development of Subsea Safety Systems to Allow Well Testing In European Frontier Areas

Abstract

Abstract Offshore well testing operations in the North Sea have, for many years, been confined to the shallow areas of UK and Norwegian continental shelf with water depths ranging from 100 to 1,000ft. Rig selection of these operations has been primarily moored vessels. New discoveries in the Frontier areas have moved the operations into the deep water regions north of Ireland and west of Shetland where water depths range from 2,500 to 10,000ft. The under-explored regions of the Barents and Norwegian Seas also provide extreme weather conditions in addition to a wide range of water depths. The deeper water prospects have moved operators to the use of dynamically positioned vessels. The combination of high frequency and severity weather systems, deep water and the potential of rapid vessel movement create unique challenges for well testing subsea safety systems. Subsea safety systems (or as often termed subsea landing strings) are critical to maintaining well integrity during any period were there is the potential to flow hydrocarbons. They typically consist of a lubricator valve to allow in-well tool deployment, a subsea test tree to provide dual-barrier well containment and a disconnect function, and a retainer valve to secure test string contents in the event of a disconnect or shear situation. To ensure all functional goals are achieved in the conditions found in European Frontier regions, several features of available string types need to be taken into consideration. The key features that are desirable in these challenging operating environments are: Rapid disconnect capability through the use of electro-hydraulic controlsDisconnect capability under string tensionUmbilical protection systemMultiple disconnect methodsAt-tree and below-tree chemical injectionValves capable of cutting coil tubing These features are not commonly available in landing strings provided for the shallower and more benign conditions found elsewhere in Europe. The technologies required can be developed from the experiences from other deep water regions (such as West Africa and Brazil) and the most extreme North Sea conditions