Riser concerns creating headaches elsewhere
Jeremy Beckman
Editor, Europe
Installation contractors are marshalling their resources in West Africa for at least 15 new deepwater projects. Physically, the challenge can be met, according to the market leader Stolt Offshore. Financially, problems may arise if operators over-extend their technical brief.
Stolt Offshore has had first-hand experience of these issues with two current projects off Angola and Nigeria. Girassol Phase 1 was one of the world's most ambitious deepwater programs, involving untried insulation and connection technologies and a large vessel spread. But the concept proved to be technically and economically sound.
Bonga is also extending frontiers, as the region's first development incorporating steel catenary risers. However, detailed engineering rev-ealed phenomena previously unknown to the industry, with unavoidably high rectification costs. These were borne by Stolt Offshore under the terms of the contract, denting the company's recent third quarter figures.
This episode caused Stolt to question the value of EPIC contracts, although the company has not scaled back its bids for future projects in the region. It is in the frame for at least four imminent deepwater subsea packages, in addition to its work on three current major developments.
Bundle behavior
In cooperation with Bouygues Offshore and Doris Engineering, Stolt was responsible for most of the subsea engineering and flowline installations on Girassol. According to Olivier Carre, the company's vice president for deepwater development, "overall, things have worked out quite well since the field started up in December 2001. We understand that the main problem on the FPSO is due to actual production being on or above design capacity. As for the flowline bundles, we know that they have done significant tests in terms of thermal behavior. But apart from the insulation cover on some flowline flanges, which we will rectify in the next few months, the system has behaved better than expected. Temperatures within the bundles have been higher than expected, well above 2°C after 16 hours."
The extent of Girassol Phase 2, due onstream by mid-year, is now well defined, but the numbers of wells to be connected will depend on the results of ongoing development drilling. The work scope involves installation of three further flowline bundles to tie in the Jasmim field to the northwest of the FPSO. As in Phase 1, these have been fabricated in Soyo on the northern Angolan coast. The first was towed out to the field just before Christmas and the fifth one completed by mid-January. From pulling of the bundle from the beach to arrival at Girassol takes four-five days on average.
"During Phase 1, we had to fine-tune positioning of the bundles to make sure they settled in the defined target areas. Being 3 km long, they are quite heavy. It took some time to understand how the bundles were behaving. During Phase 2, this experience allowed a smooth and problem-free operation, despite pulling of some bundles under the FPSO."
Erha development schematic.
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Among the vessels committed to Phase 2 are the Seaway Explorer and Seaway Legend, both involved in survey work relating to the bundle-towing route and also in the towing operation.
Stolt's flagship construction vessel Polaris was mobilized to the field early last month to perform J-lay of production and injection lines, plus installation of spool pieces and six manifolds. The Explorer will undertake all connections using the company's patented Matis spool flange connection system.
"This is now field-proven technology," Carre said. "Basically, Phase 2 will be a repeat of what we did on Phase 1."
Stolt Offshore also entered the design competition for tieback of the Rosa field to the Girassol facilities. According to Carre, the thermal requirements for Rosa's flowlines will be more stringent, mainly due to the greater distance between these wells and the FPSO. This would necessitate improvements to the riser towers in this case (if selected), with stronger insulation for the flowlines.
Dalia's thermal demands are also tougher.
"With Girassol, we could afford a temperature loss of 1° per km on the seabed, and 1° within the riser towers, not including the loss induced by pressure drop. However, on Dalia, we can only permit a half-degree loss on the seabed and half a degree within the towers (again, if selected). This is due to a combination of the distance of the well locations from the Dalia FPSO, and also the fact that the temperature at the wellhead will be lower than Gira-ssol's crude. But TFE wants the same temperature on arrival as for Girassol."
As on Girassol, Stolt has teamed up with Bouygues Offshore (now assimilated into Saipem) for the subsea design phase.
"We have a technical advantage in this case, as we have proven that our system has already worked for one year. For the competition to produce riser towers, they would need a yard. Although Technip-Coflexip has a plot of land in Lobito, it can't be used for riser tower fabrication." Stolt/Saipem have also conducted model tests to validate their concept.
As for other upcoming projects off Angola, Stolt completed its work for BP's block 18 design competition last July, offering an improved riser tower concept. This block also contains multiple discoveries, with a central FPSO to be located on Plutonio.
"This is not the most difficult in terms of flow assurance," Carre said. "It's somewhere in bet-ween Girassol and Dalia."
However, the schedule for the development has since slipped. Tender documents had been promised for last September. BP and its partners may have their reasons, but as Carre pointed out, continuing uncertainties can cause problems for contractors.
"You set up a team, there are a lot of manhours expended, then you have to disband the team. So there is no continuity."
Escalating costs
Bonga's FPSO is similar in scope to Girassol's, with a 300,000-ton hull and 17,000 tons of topsides. As stated earlier, it is also West Africa's first FPSO project to be developed with steel catenary risers (SCRs). However, Shell's preparatory work fell a little short, leading to Stolt's profits warning statement.
"The partners said that they were concerned, but we still didn't see any clear result," Carre said. "It's been difficult for us. We've had to change the design, invest in new equipment to tackle the problem, but no one is sharing the expense. And the cost in rectifying it is substantial."
Stolt Offshore is responsible for construction and installation of the flowline bundles for the continuing Girassol development.
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Carre will not divulge what the problem was – "why should we tell everyone else what we discovered?" – but he insists that the project schedule will not be affected.
"We discussed the problem with Shell, the engineering is complete, and we are now fabricating the system's various elements," Carre said. "All the pipes have been produced. In this case, model tests were not as important as for Girassol, as SCRs are much simpler than riser towers. The insulation is more conventional, being wrapped around the pipes. We have performed tests on the efficiency of the insulation. Now we are doing site integration tests with ABB and Shell, so the project is moving forward.
"The first phase of offshore operations is due to start in April. The Polaris will lay some flowlines, assisted by the Legend for survey activities. Work should be completed in June. Then, we will wait for the FPSO to arrive in the fall. The Polaris will then complete the flowline installations. These will comprise 28 km in total of 10-in. and 12-in. diameter. We have completed pre-qualification of automatic UT, a new technique for weld examination for this type of line."
Originally, Stolt had planned a reel lay operation, but decided to switch to J-lay due to cancellation of a proposed pipe-reeling base. This was to be built on Snake Island on a 12-hectare site owned by Nigerdock. However, this operation was subsequently privatized, and the reel-base did not materialize in the required time frame.
According to Carre, there was fierce competition among contractors for the Bonga SCR, "to demonstrate that you would be the first to make the concept work." Stolt's subsequent experience helped it clinch the award for the SCRs and flowlines for the Erha project last October. Erha, operated by Esso Exploration and Production Nigeria, is situated in 1,200 m of water in offshore production license 209. Stolt's remit is to engineer, fabricate, install, and pre-commission 26 km of flowlines and risers. These will eventually link 24 subsea wells to a 165,000 b/d FPSO, under construction in the Far East and Nigeria.
There will be two subsea drill centers (east and west) linked to an FPSO via production, water, gas injection, gas lift, and production test lines. Globestar is fabricating the spools connecting the flowlines to the subsea manifold, and 45 suction anchors, of which four will be used to moor two dedicated semisubmersible drilling rigs this May. Stolt will additionally fabricate and install the floater's cable/chain mooring system. The Seaway Polaris will begin installing the anchors for the drilling rig in May. Next year, the moorings for the FPSO will be pre-installed, and when the floater arrives on location in mid-2005, installation of umbilicals, risers, flowlines, and export lines will follow.
"As to how we clinched this work, I see three winning parameters," Carre says. "First, we put together a team with a lot of experience in deepwater that could answer all Exxon-Mobil's questions. Second, the quality of our answers to their questions was appreciated. Third was our experience with SCRs on Bonga. ExxonMobil, however, shifted less risk onto us than did TFE or Shell. Instead of a design competition where you have to do everything, they gave us a basic design. It's our responsibility to check their design and make sure there are no mistakes. And if we find some discrepancies, there is a mechanism in our contract that allows us to adjust it compared with what we originally bid."
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This engineering phase is due to be completed by the summer.
Elsewhere off Nigeria, Stolt has been pre-qualified to bid for another deepwater floater development, Akpo, and is currently awaiting the bid package. Operator TFE is deliberating over whether to adopt SCRs for this project.
"Some operators still have concerns over SCRs for this environment," Carre explained. "It depends what you consider the maximum allowable movement for an FPSO, due to the prevailing swell from the southwest in the Gulf of Guinea. Some see small variations in the swell, while others see a wider range. If true, this would lead to greater movements."
