- Schematic shows modifications to the Bongkot riser platform as part of the phase IIIa production expansion program.
Bongkot, 18 km northeast of Songkhla in the Gulf of Thailand, was planned from the outset as a phased development. Phase I production started in July 1993 at 150 mcf/d, rising to 350 mcf/d for the Phase II start-up early in 1996. Gas is contracted to Thai mainland distributor PTT, the exploration arm of which is also a 40% partner in the development.
Operator Total and its other partners stalled for a while over commercial terms for the current Phase IIIa, but these were finally agreed last August. The extra supplies are being sourced partly from Ton Sak, a satellite field to the north-east of Bongkot which was discovered in 1994.
As engineering supervisor, Doris has in fact built in 15% extra flexibility beyond the newly contracted rate, providing potential export capacity through the existing production and riser platforms of 623.5 mcf/d. Of this, 220 mcf/d will be contributed by the new compression train. Further equipment add-ons will allow condensate throughput to rise to 13,000 b/d, and water treatment capacity to 14,500 b/d.
In total, an extra 2,500 tons of modules have to be accommodated, rather than building a second production facility. At the same time, installation of the modules must be arranged to cause only minimal disruption to existing production (a few days at most).
One reason that Doris is able to effect these changes is its roll-on contract for Bongkot. Early in the field's life, production was not predicted to rise as fast as it has done. However, the reservoir and surrounding area have proven fertile for finding new gas. To make sense of the changing data, Doris engineers work with Total in an integrated team in Paris which can respond quickly in design terms whenever a new sales agreement is reached.
Doris president Dominique Michel also makes the point that the existing Bongkot production facilities were designed to accommodate future installations. Adding the new modules only involved minor modifications to the established platforms. Nevertheless, the modules that were selected had to be restricted in size, due to space limitations.
The two new wellhead platforms will be installed from the end of this year to the north-west and north-east of the Bongkot complex. Development drilling will then ensue. Both are small structures of similar design, weighing around 1,500 tons with 12 production well slots. Thai Nippon Steel in Bangkok is the fabricator.
As for the existing facilities, most of the add-ons will occur on the production platform. The upper deck will house the new compression train, which will comprise
- a third Nuovo Pignone, two-stage turbo-compressor, skid mounted on the north-west corner of the platform, and identical to the two current turbo-compressors
- a glycol regeneration package on the south-west of the platform
- a third turbo-generator on the south side.
Down on the main deck, a new third-stage separator will be added to aid condensate stabilization. Various control systems will also be inserted. Further down on the lower deck, liquid handling capacity will be raised through installation of an oily water flash drum and extra hydrocyclones. And two existing condensate export pumps will be replaced by four new ones. Finally, on the platform's west and east faces, a third glycol contactor and a new module housing scrubbers will be added.
The bridge-linked, first-stage riser platform will receive an additional separator and slug catcher, and an HP flare KO drum. A new control room is also planned for the quarters platform. Produced condensate will be stored on a floating storage vessel.
Phase IIa took 50,000 manhours to design, but there is already talk of a Phase IIIb getting under way next year, which might involve up to five wellhead platforms and over 50 wells.
Doris is also at the engineering forefront of several brand new field developments in the western hemisphere. As part of the Grand Banks Alliance, it will be responsible, with Brown and Root, for the ice-resistant steel hull for the Terra Nova FPSO vessel. Design details are still being finalized while operator Petro-Canada awaits project sanction from the Canadian government.
Michel sees possibilities for four to five more floater-based developments off Newfoundland. "Semisubmersibles are not feasible because of the need to disconnect all risers and mooring lines quickly to prevent iceberg impact. The only solution to me is a turret-moored ship. Also, you can't have storage on a semi."
In the Gulf of Mexico, Doris' Compliant Piled Tower concept has been chosen for Amerada Hess' Garden Banks 260 project. The platform is currently under construction by McDermott/Aker Maritime and will be installed later this year. Texaco has also chosen a CPT for the development of one of its fields in the Gulf.
Finally, the Doris/ Bibby Line Group company, Offshore Design Engineering, has been working on oil and gas production concepts for Texaco and Amerada Hess fields west of Shetland, in waters ranging from 400-1,200 meters.
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