Converting semi-submersible drilling units to long term site specific Floating Production Service is becoming more frequent. This paper will present the latest classification and other regulatory requirements for this type of service.
The paper concentrates on Gulf of Mexico service and offers information regarding ABS interaction with Government Authorities such as USCG, MMS and flag states such as Panama and Liberia. ABS requirements for production risers, subsea templates and the role of ABS as a CVA for MMS are also discussed.
Fatigue assessment methods and joint detail enhancement are discussed together with surveys that are necessary to ensure that the unit will be capable of operating in one location for an extended period of time.
In recent years the offshore industry has been confronted with rising costs. Less expensive and more efficient methods of oil production needed to be developed.
With the down-turn in drilling activity world wide and the enormous cost of upgrading semi-submersibles in the North Sea to meet the latest HSE requirements, drilling contractors are pursuing alternative usage for older semi-submersibles. One such operation is floating production.
Oil companies are also concerned about the cost of production in marginal and deep water fields and are now seriously looking at semi-submersibles as an efficient and cost effective method for oil production.
Drilling units were first used for production in the mid 1970's, with the Transworld 58 in the North Sea and a number of jack-ups and semi-submersibles in Brazil. These however were treated as drilling units and were normally brought into sheltered waters for intermediate and special surveys where inspections and, if necessary, repairs could be made.
In the mid 1980's oil companies were looking for a more permanent installation that would reduce the high costs of design, construction and installation of fixed structures or tension leg platforms. Semi-submersibles are ideally suited, provided some modifications are carried out and the revised design is analyzed so that the service life can be for a period up to 20 years without disruption of the oil production.