Detailed Description:

Each Operator Group was examining different options for potential deepwater fields West of Shetland, with the overall aim of identifying optimum development scenarios for both oil and gas accumulations in water depths typically between 350 and 1200 metres (with extension to potential 2000m). The optimisation process was carried out in four different phases.

As part of phase 1, performed a concept screening and selection study. The study was to provide CAPEX and OPEX data for a number of surface facility concepts. This data was then incorporated into through-life economic models, so that the different development scenarios could be assessed and compared.

The objectives of this initial study work can be summarised as follows:

• generate an exhaustive list of possible / suitable candidate surface facility concepts (eg. Jacket, Gravity Base Structure (GBS), Tension Leg Platform (TLP), Compliant tower (CPT), semi-submersible (SSB), deep-water semi-sub (DDSS), spar, wellhead plus floating production (TLWP+FPSO) etc) for various topsides configurations / water depths;
• select front runner concepts;
• develop outline designs for selected concepts;
• estimate CAPEX and OPEX for selected concepts and components;
• develop full CAPEX and OPEX estimates for full development scenarios;
• identify technical and schedule risks;
• highlight areas of uncertainty and areas for further work.

Specific pre-established selection criteria were then applied resulting in the identification of a reduced number of "front-runner" concepts. Typical comparative criteria are tabulated below.

In the second step these front runners were developed into outline designs, encompassing the key cost drivers for each concept, for nine combinations of water depth and topsides configurations. Cost and schedule estimates for each concept design case were then developed in the third step. Selected typical concepts are presented in the 6 graphics provided below.

In the fourth step in conjunction with each individual Operator Group, these concepts were combined with other cost components, (eg. subsea, storage, drilling etc.) to form economic models of complete field development scenarios. These were then costed and discounted appropriately in order to rank all potential development options.

Areas where further development was required were identified as follows:

• Mooring Technology: Taut line mooring systems will replace conventional catenary mooring systems in water depths beyond 800-1000 m. New synthetic materials (aramide, polyester, etc.) are being developed and the following areas need to be addressed:
  • long term strength,
  • fatigue of termination details and bending at touch down,
  • long term line elasticity,
  • abrasion resistance on sea bed,
  • offshore handling to avoid damage.
  In addition vortex induced vibrations in taut line moorings need to be studied and new design criteria need to be developed.
• Design and construction of vessel hulls: The DDSS and SPAR require study into:
  • construction methods,
  • deep draught towing,
  • deck installation,
  • ballasting systems to maintain draught during oil export.
• Riser Technology: Flexible riser technology is currently in service at 1000 m in mild conditions (Brazil) and about to be applied at 500 m in harsh conditions (Foinaven, West of Shetland). The development of alternative riser types is required, such as the hybrid deep water riser and the steel catenary riser. Moreover, improved analysis methods for assessing riser response to multi-directional currents, vortex induced vibration and wave loading also need to be developed.
• Oil Export Technology and Infield Tanker Operations: The existing export systems such as UKOLS (Ugland Kongberg Offloading System) and STL (Submerged Turret Loading) are theoretically feasible in deep water but require additional work to confirm the designs.
• TLP Tether Technology: TLP tethers require study work on the analysis of springing and ringing, vortex induced vibration and tether excursions. Installation methods in deep water also need to be developed.
• Environmental Conditions: Environmental data for the Northern Atlantic needs to be collected and developed into design criteria. Present wave and current theories need to be adapted to these new environmental conditions.