This paper presents experience of subsea and marine systems gained from the first four years of production from the Ivanhoe/Rob Roy fields focusing particularly on those areas which are different from a fixed platform development.
As an introduction the overall field layout is described and the success of the development is demonstrated by summarising availability of the facilities. The paper then describes the field development work since first oil, together with the inspection, repair and re-design work that have been necessary to ensure this success. The description includes work on all facilities on the sea bed, work on marine systems, and subsea well servicing. If thus includes the hull, stability and damage stability, bilge and ballast systems, subsea Christmas trees, moorings, flexible risers, flowlines and jumpers, valves, chokes, electro-hydraulic control system, umbilicals, downhole gauges, etc.
The information can be used to lead towards more cost effective developments in the future.
The Ivanhoe/Rob Roy fields came on stream in July 1989 and have now been producing successfully for nearly four years. Typical production rates are in the region of 70,000 bpd.
The fields are located in the UK sector Block 15/21a approximately 110 miles north east of Aberdeen in 140m of water.
The layout of the field facilities is shown in Figure 1. From the centrally located Floating Production Facility, designated AH001, a flexible riser system (Fig. 2) connected to a Riser Base Manifold (RBM) conveys fluids up and down to the sea bed. From the RBM oil and gas export lines go to the Claymore and Tartan platforms respectively and infield flexible flowlines travel approximately 1.6 kms to the Ivanhoe and Rob Roy manifolds. There are a total of 16 subsea wells clustered around the manifold; Rob Roy manifold has 6 producers and 3 injectors (Fig. 3) and the Ivanhoe manifold has 4 producers and 3 injectors (Fig. 4).
The electro-hydraulic control system consists of a dynamic umbilical at the aft end of the AH001, splitting three ways to distribution units and control modules on each manifold (Fig. 5). The control system also recovers data from a range of pressure and temperature gauges.
The vessel is moored on station by a twelve point multi-component system (Fig 6), with the position being monitored by an acoustic system and also by reference to line lengths and tensions. The vessel draught, trim and stability are altered and maintained by a bilge and ballast system.