Ultra deepwater floating production facility for Makassar Strait
Gde Pradnyana
Jafar Korloo
Gde Pradnyana, BPMIGAS,
Jafar Korloo, Chevron
Developments of Indonesia’s oil and gas prospects in the deepwater areas of Makassar Strait have unique challenges for floating systems using dry tree units. Despite benign wind and wave conditions, the area is subjected to strong persistent currents. The combination of deepwater currents and large number of risers introduces unique design challenges.
The Makassar Strait is protected by the Philippine Islands in the north and the Indonesian Islands in the south. The wind and waves are quite benign ranging in the 0.5 m to 1.5 m wave height range with wind speeds of 10 to 20 kts for the normal operating conditions.
The current conditions in the Makassar Strait are of prime concern for their effect on the floating facilities as well as on the subsurface elements such as risers. The importance of current has resulted in long-term collection of current data at every potential installation site for at least one year.
A typical data set taken over a one-year period consists of 20,000 current profiles. One of the challenges facing the designer is the interpretation and reduction of the current data to a manageable data set and the application for overall loading and fatigue calculation due to vortex induced vibration (VIV).
Dry tree concepts
A dry tree development has the wellheads in air at deck level of the facility. The wells are drilled and serviced from the production platform either by a stand-alone facility or by tender-assisted drilling. The key requirement of a dry tree floating system is the ability to accommodate the risers and associated stroke arising primarily from heave, transitional motions of the floater, and tidal changes.
For dry trees, the motions of the floating facility relative to the risers need to be restricted. Risers must be tensioned through connections to the deck and/or by buoyancy cans. Therefore, only concepts with low motions (particularly heave and roll) are suitable for dry tree operations.
The dry tree concepts suitable for application in the Makassar Strait are TLP, spar, semi, dry tree barges, and a number of other low-heave-response type concepts. However, it is the TLP design for the West Seno development that has been used first in Indonesia’s Makassar Strait.
Comparative cost assessment
Careful consideration should be given to the maturity of the concept, transportation and installation issues, and the procurement issue when selecting a floating system concept.
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Volume 66 Issue 2
February 2006
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