An innovative concept for deep water oil production platform design

Abstract

As more oil and gas are discovered in deep water, the offshore industry has become increasingly interested in the design of deep water offshore production facilities. A new design concept tentatively called FPSOT (Floating Production, Storage and Off loading Tower) is studied in this thesis. Instead of using a single large cylindrical structure as in the spar configuration, the FPSOT utilizes a jacket-type framed structure supported by a buoyancy/storage tank deep below the ocean surface. This new structure concept is suitable for water depths up to 1000 meters or more. 20000 tons of concrete and 67000 tons of oil, serving as ballast, provide a good stability of the structure. The stored oil, used as a ballast, can also be replaced by sea water. The deck and the drilling/production equipment of 10000 tons are supported by a framed structure made of small cylindrical members. Because of the smallness of these cylindrical members, wave forces on the upper structure is very small. The forces on the lower structure (buoyancy/ballast tank), which is deeply submerged, are also small. Thus, the platform will be very stable even in a very severe sea state, with maximum surge and heave motions are less than two meters and the pitch motion is always smaller than one degree. All the natural frequencies are very small (less than 0.055 rd/sec). All the calculations are performed for regular and random waves. It was found that the platform motions were extremely small even in stormy waves as compared to the other platform configurations. A model with a scale 1:60 of this concept has been built and tested in deep water wave at the Offshore Technology Research Center on campus. The experimental and theoretical results are very close. A comparison is performed between this new concept and a spar buoy of same draft, weight, buoyancy and catenary system. The motions of the FPSOT, specially in pitch, are smaller than the spar buoy. Thus, this new concept is proved to be feasible and to be a very interesting approach for the future offshore platform design.