Abstract
The Schiehallion and Loyal oil fields located in Quad 204, and neighbouring Foinaven, all west of the Shetland Isles, are the first group of North Sea deep-water fields to be developed and together form a huge subsea development. As part of the Quad204 Project Schiehallion and Loyal are being re-developed to extend field life and this requires infill drilling, replacement of some subsea infrastructure and replacement of the Floating Production, Storage and Offloading vessel (FPSO) to service the extended scope. The reservoirs will remain shut-in for a period of up to three years whilst the FPSO Schiehallion is disconnected, the site is prepared and the new FPSO is hooked-up.
There are fifty-two wells (25 producers and 27 injectors) and this is the first time that bp has shut-in a field for so long at such scale. Many wells access mature, water-flooded, multi-layer reservoirs which have been flowing for 15 years. The infill drilling programme will be providing additional well-stock and production for the new FPSO but the majority of the rate at restart will be supplied by the existing wells so it is essential that the fields are prepared carefully and left in a healthy and predictable state for the shut-in and subsequent restart.
Fifteen years of production has created differential oil depletion both areally and vertically between layers. Factors to be considered include: minimising hydrogen sulphide development in the reservoir, maintaining the Christmas trees that reside within the hydrate-forming envelope, existing well issues and corrosion treatments for preservation. The shut-in of the fields is complicated by the requirement for continued low-levels of production for the purposes of cleaning the FPSO cargo tanks – and continued injection support whilst cleaning.
This paper discusses the preparation and planning for the reservoir activities and the coordination of reservoir management with facilities requirements during the shut-in of the wells.
