Innovative technologies for 3,000-m water depth
Peter Howard Werhteim
Special Correspondent
Cenpes, the R&D center of Brazil's state- owned Petroleo Brasileiro SA (Petro-bras), is working on new concepts to make production feasible from new deepwater discoveries.
"The program is also geared to reduce costs in production developments and to reduce lifting costs in currently producing fields at water depths beyond 1,000 meters," says Dr. Jacques Braile Saliés, Petrobras' coordinator of the company's ultra-deepwater R&D program, called Procap-3000.
Petrobras is the world's main oil producer in deepwater and plans to reach a 1.8 MMb/d production in 2005 and 2.2 MMb/d by 2007, when the country hopes to reach oil self-sufficiency, according to Petrobras officials.
3D visualization allows designers to see how units behave in the real environment while still in the concept stage.
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Petrobras had proven reserves of 12.6 Bboe in Brazil, plus 1.9 Bboe abroad at year-end 2003, according to SPE criteria.
"Of these reserves, 66% are located offshore in less than 300-m water depth, while only 26% lie below 300 m. The onshore reserves represent only 8%. Considering that 33% are beyond 1,500-m water depth, future discoveries will demand a high degree of technology to be reached in a short period of time," Saliés says.
Flowlines, risers, completion risers, boosting, and subsea equipment will likely be the major technical challenges, according to Saliés.
"These and the projects chosen for Procap-3000 play a key role in ultra-deepwater prod-uction, not only in Brazil, but also in deepwater developments all over the world," Saliés says.
Petrobras will invest $100 million in Procap-3000 projects by year-end 2004.
Focusing R&D
One project that will benefit from this investment is a numerical offshore tank (TPN), which provides for a wide range of programs for simulating behavior for offshore units.
The advantages of the TPN include a strong graphical interface for developing models with important and hard-to-define data stored in databases and full 3D visualization of the results with stereoscopic facilities.
In the visualization room, designers see how the units behave in the real environment even when the designs are only in the conceptual stage, Saliés says.
Another project that will see investment dollars is the flexible riser system for ultra-deepwater. Petrobras believes that flexible pipes have to be further developed to reach deeper waters. The new concept investigates the use of composite materials, thermal insulation, mechanical performance, and new riser configurations to reduce weight and related loads.
Petrobras adopted the free-hanging steel catenary riser (SCR) configuration as a cost-effective alternative for oil and gas exportation in deepwater fields where large-diameter flexible risers present technical and economic limitations. According to Saliés, this concept is considered to be an available technology for semisubmersible application.
Petrobras has pursued R&D projects with European companies and Brazilian universities in order to study different configurations of steel risers using flexibilization elements.
In hopes of overcoming the limitations of cost and technology limitations of the flexible and rigid risers, Cenpes is investing in new concepts for production and export risers and pipelines within a project called alternative riser systems for ultra-deepwater.
Among the new concepts is the free standing hybrid riser (FSHR), Saliés says. The FSHR consists of a vertical rigid tube with a large buoy at the top and an anchored base on the sea bottom. The vertical rigid tube and the platform are connected through a jumper, a concept that avoids axial compression in the riser and provides thermal insulation for well production and export lines, he says.
Another alternative is the passive and heated pipe-in-pipe (riser and flowline) concept. The line between the christmas tree and the platform should be designed to guarantee flow assurance during the whole period of operation of the oil field. Pipe-in-pipe is a good solution to this kind of completion system, Saliés says. The heated pipe-in-pipe can be used in regions where hydrate and wax formations are expected.
The subsea pipeline heating system associated with the subsea electrical submersible pumping concept consists of employing the same electrical umbilical to alternatively power the subsea electrical submersible pump system during normal production and a subsea electrical heating system during a shutdown. Developed to operate for 20 years, the system is designed to take the fluid inside the pipeline out of the hydrate formation risk zone in less than 12 hours. The prototype installation and first oil are scheduled for 4Q 2006, Saliés says.
Petrobras' research and development center is investigating new technologies for deepwater production.
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Another Cenpes project is subsea equipment installation by cable in 3,000-m water depth. The project includes using a vessel with relative low cost compared to conventional rigs capable of operating in such water depths. This method was developed and successfully employed for Roncador manifold deployment. In spite of using a drilling rig with a nominal limitation of 1,000-m water depth, this procedure allowed the manifold installation at 1,885 m water depth and could conceivably reach depths beyond, Saliés says.
Ultra-deepwater exploitation is always associated with expensive rigs and high flow rate subsea wells making workover riser efficiency play an important role in reducing costs.
Petrobras has been using the drill pipe riser to perform completions and workovers at water depths to 2,000 m.
Although far more efficient than the conventional completion riser, the drill pipe riser's operational experience showed that it was worthwhile, Saliés says. The key issue is the control umbilical and related equipment such us hang-off equipment and clamps, which presented problems deemed to be critical at 3,000 m. The definition phase and technical specification were recently concluded, and prototype manufacturing is now under development.
New floating platform concept
Petrobras is preparing a new technology to face the challenge of producing heavy crude at 1,800-m water depth. The new concept is the Monobr floating platform.
Cenpes expects to finish the concept by year-end 2004 in cooperation with São Paulo University (USP) and with the support of other Brazilian universities and engineering companies.
"The Monobr is the first prototype of a family of mono-column hulls to support production plants. This model has no oil storage capacity. It receives and exports production, 200,000 bbl of heavy crude through steel catenary risers (SCR)," says naval engineer Isaías Quaresma Masetti of Cenpes and USP.
"Monobr is similar to a spar buoy, but has a shallower draft of around 45 m. The inertia and dynamic characteristics of the hull compensate the wave excitation forces. The total displacement is close to 160,000 tons," Masetti says.
Variations of hull diameter and a lower skirt increase the added mass and inertia. A moonpool, with a small diameter outlet, provides out-of-phase forces to mitigate the vertical and angular motions of the hull.
The geometry of the hull is not complex and can be constructed with the technology available in shipyards' facilities. The primary construction material is DnV NV36-HS steel, which can be produced by Brazilian mills. This choice results in a small cost increase with a reasonable reduction in steel weight.
The ability to build the structure in Brazil is one of the strongest arguments for the Monobr design.
