FRANCE: CGG maintains commitment to Brazil, takes 4D to Gulf of Mexico

Winter is normally the flat season for seismic acquisition offshore. By January, however, CGG had already secured more than 50% of its global capacity for 2002, guaranteeing full occupancy for five of its vessels through to spring.

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Winter is normally the flat season for seismic acquisition offshore. By January, however, CGG had already secured more than 50% of its global capacity for 2002, guaranteeing full occupancy for five of its vessels through to spring. The exception is the CGG Mistral, currently in Germany for a major upgrade program.

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Artist's impression of the newly upgraded CGG Mistral.
Click here to enlarge image

According to Rollin Delzer, Vice President Business Development Offshore, "This is a record backlog for CGG, both from a proprietary and a spec viewpoint. Most of the workload for the first half of this year is in the Western Hemisphere, mainly in the Gulf of Mexico and Brazil."

CGG has been active in Brazil since 1968 and has maintained a presence there while others have come and gone. Delzer points out that in late 1998, "there was one CGG-owned vessel in action off Brazil. By the end of 1999, there were 23 vessels operating, and by the end of 2001 there were three, two of which were ours.

"This is a market that moves up and down. Even though the sector has been opened to western companies, Petrobras remains the major player." CGG has maintained a strong working relationship with Petrobras over the years and is better attuned than most to Brazil's complex environmental regulations, which can hamper seismic and drilling activity.

Since late summer, the CGG Harmattan has been working for Petrobras on what is claimed to be the world's largest high-resolution 3D survey, covering an area of over 2,700 sq km in the Campos Basin. Petrobras' aim is to "ring fence" the field being surveyed with high quality seismic to improve imaging and understanding of the producing reservoir. The survey also will form the baseline for future 4D programs to monitor the reservoir's performance.

"Most of our work is in the Santos and Campos basins, although we've just been awarded a substantial project in the Amazon Basin. Our intention is to maintain two vessels in Brazil throughout 2002," says Delzer.

In the Gulf of Mexico, the CGG Symphony is two months into a one-year, multi-client spec survey across the entire Garden Banks area, deploying 9,000-m streamers. "Some of our clients in this sector are long established, but for this project we're working with a few international clients new to the Gulf of Mexico." The CGG Amadeus has been acquiring high-resolution 3D seismic for BP and ExxonMobil over the Thunder Horse Field in the Mississippi Canyon in the Gulf of Mexico, the main aim being to map the complex, largely subsalt reservoirs and their associated geology.

On January 5, the Mistral went into drydock in Bremerhaven, Germany, for an upgrade to a 10 digital Sercel "Solid Seal" recording system capability. The operation involves a complete re-building of the seismic deck and propulsion system. The re-built ship will be 95 m long and 23 m wide, with a cruising speed of 13 knots. It will be the first fully solid streamer vessel in the company's fleet. The Mistral has at least one firm assignment in Morocco later this season and will be joined in Europe by the CGG Fohn, which is currently in Brazil.

West Africa, which is normally active for seismic acquisition in winter, has been a depressed market of late. "Some vessels are down there, but only shooting multi-client spec surveys," says Delzer. "We don't have a dedicated vessel in that region this year, although we're hoping for renewed activity from the fourth quarter onwards." CGG is also looking hard at Southeast Asia and Eastern Canada, where there are good prospects for acquisition activity.

4D processing

As for services, "the development of 4D, time-lapse surveys for field monitoring has been the talk of the town the past couple of years," says Guillaume Cambois, Executive Vice President for Data Processing and Reservoir Services. "Since the first successful offshore tests in 1997, Shell and BP have been the most advanced operators, mainly in Europe. Shell uses the technique on Draugen in the Norwegian Sea and on Gannet in the UK North Sea. BP's main applications to date are Forties and Foinaven, West of Shetland."

CGG has worked with both operators on these projects. "We have two dedicated processing centers at BP and Shell's premises in Aberdeen working exclusively on 4D processing. Certain fields are already undergoing their fourth generation of 4D surveys, so the technique must be working." The collaboration with BP has extended to the Gulf of Mexico.

Last summer, CGG introduced an "integrated" 4D data processing and reservoir monitoring service involving the use of tools such as surface-consistent matching, 4D stratigraphic inversion, 4D amplitude versus offset (AVO), 4D depth imaging, and 4D multi-component. The aim is to provide improved information, particularly for mature fields, on pressure and saturation changes, movement of fluid contacts, mapping of flow pathways, and undrained compartments.

Another new service is A+ processing, claimed to be the first fully anisotropic seismic data processing service to exploit the Earth's anisotropy to generate a sharper and more focused reservoir image. "Anisotropy causes the speed of sound in rocks to vary with the direction of wave propagation. Within a series of horizontal layers, the wave traveling vertically will be slowed by internal bouncing, while the wave traveling horizontally will be 'tunneled' and will therefore travel much quicker," Cambois says.

"Our seismic cables are employing longer offsets to image salt domes in the Gulf of Mexico. The waves, in turn, are travelling much longer distances horizontally. Previously, it was not possible to tell whether the velocities of horizontal waves were faster than the vertical ones. A+ solves this problem. Also, because of these longer offsets, you can get much wider angles, a benefit for AVO studies. This leads to improved hydrocarbon detection, and better positioning of dipping events."

CGG has invested in over 6,000 CPUs of Intel server clusters in its London and Houston processing hubs, giving it a 10-fold increase in its global seismic data processing capacity. This is in line with its main competitor, Western Geco, and perhaps a little ahead of the others.

CGG is also re-examining the use of "turning waves" to image the salt base more accurately. "It's been known for some time that these waves exist," says Cambois, "but they are very difficult to record and process. Now, with the advent of longer streamers, these waves can effectively be used for imaging. The top of a salt canopy is generally much rougher than the base. Which means that direct waves are diffracted and very little energy bounces back from the base. Turning waves dive through the sediment and, thanks to the gradual velocity increase, turn back up. They get reflected from the base of salt and follow a reverse path to be recorded by the surface sensors. With these waves, it is possible to accurately image the base of salt without actually going through the salt. We can now obtain a clear picture of salt structures for the first time."

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