July 2000 Vol. 221 No. 7  Exploration

Perry A. Fischer,  Engineering Editor

Western and Geco merge; streamers that can be steered

It was the premier news at EAGE in Glasgow: Schlumberger and Baker Hughes signed a Memorandum of Understanding (MOU) that would create a new company called Western Geco. Gary Jones, current president of Western Geophysical, would be its president. Schlumberger would pay $500 million in cash for a 70% stake in the new company, and Baker Hughes would have the right to make certain working capital reductions valued at about $100 million.

The new venture would own the vessels, data-processing assets, nonexclusive data libraries and other assets currently comprising the surface-seismic businesses of both companies. It would have had pro forma 1999 revenues of about $1.5 billion. The new company would control about 60% of marine 3-D survey capacity and could produce savings of $75 – $100 million a year, according to an analyst with Simmons & Co. For Baker Hughes, forming the joint venture resulted from concerns that its $4.8-billion 1998 acquisition of Western Atlas was too expensive and did not deliver projected benefits.

In this column in February, I wrote, "Unless there’s a quick upturn . . . industry consolidation is likely this year." But no one I’ve talked to expected it to be the two largest contractors. This puts pressure on the remaining three big players to consolidate, but I won’t make a prediction this time. Contract details have yet to be worked out, and government regulators have not had their say (although the Transocean Sedco Forex deal went through without a hitch). It is also uncertain just how much capacity this will remove from the market.

This may be negative for oil companies that have been enjoying the glut in capacity and the resulting low prices for services. These were the two largest investors in seismic research, and it is unlikely that their combined R&D budgets will be as large as when they were competitors. It could put an upward pressure on prices for services. For these reasons, competitors at EAGE were surprisingly upbeat – and they believed the merger would preoccupy management for the coming months. Thereafter, everyone’s crystal ball turns cloudy.

New type of streamer positioning. Schlumberger has developed a new type of streamer positioning and steering control system that allows lateral steering of the cables. Three new components allowed development of the new streamer steering system: cable-integrated steering devices; a built-in acoustic ranging system; and a new, integrated navigation system.

The system can steer cables up to 3° laterally from the natural, streamer feather angle. Although this seems small, by consistently applying a 3° angle, a high degree of streamer maneuverability is achievable. When this is coupled with the new acoustic network, streamers can be reliably positioned within 2–3 m – a significant improvement over conventional marine-seismic positioning.

   The inline steering device is integrated into – rather than clamped onto – the seismic cable at 400-m intervals. No longer called "compass birds," each steering device comprises a 1-m titanium body which contains sensors, electronics and wing actuators, and a pair of removable semicircular paddles. The device is powered via the streamer, but also has rechargeable backup batteries. Tests have confirmed that the new paddle-shaped devices are much less noisy in the seismic frequency band than comparable clamp-on birds and traditional, acoustic positioning systems.

   The acoustic ranging system consists of sources and receivers. The acoustic-positioning receiver network nodes comprise two receivers 50 m on either side of the steerable device. The largest separation between two receivers is 300 m. Future networks will be even denser, with 100-m receiver separation. Compasses in the steering devices only marginally increase accuracy with such a dense acoustic network; therefore, their use becomes optional.

   Integrated navigation system. The steering devices are controlled by software from the vessel using position data for each steering device obtained from the acoustic positioning system. The true position is then compared with the desired position, and a lateral force is computed and sent to each steering device. Control-system reliability is paramount, but the system can revert to neutral, lateral-force mode in the event of any main-system failures.

When the steering system is initialized, different steering strategies can be chosen based on the type of operation and survey configuration. The options allow optimizing for efficiency, optimal coverage or minimizing streamer-tangling risk, or a combination of these.

   Client benefits. In addition to reduced noise due to the new steering-device design, selecting tangling-avoidance strategy can allow crossline separation surveys down to 25 m without significant risk of streamer tangling, thereby permitting high-resolution surveys when the client so desires. Infilling – where the vessel is required to deviate on a subsequent pass to fill in missing coverage due to streamer drift – will be greatly reduced or eliminated. Post-mission positioning will likely become obsolete because of the accuracy of this online cable steering.

Vessel turn-around time will be shortened due to improved cable steering. Obstacle avoidance will be safer, since the vessel can take a path well away from platforms and such, while the streamers can be steered closer for better coverage. In 4-D surveys, streamer cable positioning can vary with each survey; this is one of the greatest impediments to repeatability. By using previous navigation data, streamer positions can be steered to the same positions in prior surveys, thereby greatly reducing that noise source in 4-D processing.

The new, streamer control system has been tested extensively in the Caspian Sea on conventional streamers. A second-generation system is being developed with the ability to detect and acquire more acoustic ranges for more-accurate positioning.

Comments? Write: fischerp@gulfpub.com