AKPO: The Subsea Production System

Abstract It has been said " All deep water offshore projects are challenging??. Nowhere in the world do projects have such high commercial pressures as those which take on the challenge of Deep Water. Rarely if ever can it be said that any one field is a repeat of another. Each therefore raises its own issues which each development must solve anew. Some lessons are the same, and we forget them at our peril. Some are new challenges, and we then call on our experience of the past to rise to meet them, and hence all our experience is necessary. In the case of Akpo, many of the issues were totally new and we called on all of our experience of Deep Water fields in the Gulf of Mexico and West Africa. The Akpo field in block OML 130, 200 km offshore Nigeria is in 1400 m water depth. It is a gas/condensate field with high pressures and high temperatures. One of the greatest challenges is to ensure that condensate and gas in multiphase flow reach the production facilities without being stopped by hydrates and wax and scale deposition. The technical challenges alone are significant, but when set against the background of increasing oil prices and high commercial pressure on the suppliers from more than one operator and more than one field, the challenges take on a new dimension. Added to that for Akpo were the issues of resources of personnel and manufacturing capacity in a very buoyant market as well as the new challenge of manufacturing in Nigeria. This paper also addresses the challenges of the Subsea Production System of the AKPO development. It shows how the conceptual design principles are encapsulated in the simple acronym - RAM and how these lead to some key issues. The second most important issue facing all Subsea decisions is the fact that the cost of installation - whether by Drilling Rig or by Installation Vessel - FAR exceeds (in most cases) the cost of the equipment itself. Added to that is the cost of the lost production. This cost is effectively tripled if equipment has to be retrieved and then re-installed. No Subsea Engineer ever wants to see their equipment return to the surface. Nevertheless - things do go wrong even on a single well - and in a system as large as Akpo, the opportunities for something to go wrong increase. Such is the inevitable nature of large Systems. The ability to recover and install was seen as vital. Design for installation was a vital strategy in the design process. This lead to design in order to minimize installation - and retrieval - costs. The overall Field Layout, showing the full subsea network and its connection to the FPSO is shown in Figure 1.