In 2001 an extensive research program led by BP’s research and development group concluded that improved subsalt seismic imaging required the acquisition of seismic information from all directions around a reservoir; hence the term wide-azimuth seismic. Because no viable deepwater wide-azimuth seismic acquisition system existed at that time, the BP team set out to proactively develop this capability using autonomous ocean bottom seismic (OBS) nodes.

OBS nodes are autonomous seismic recording units that are placed in an array on the sea floor. The nodes are deployed to and recovered from the seafloor in depths up to 9,800 ft (3,000 m) by remotely operated vehicles (ROVs) that are tethered to a ROV support vessel on the ocean surface.

Each node has a seismic sensor, recording system, batteries, clock and memory for storing

Illustration of Fairfield autonomous seafloor node system. (Image courtesy of BP)
the recorded seismic data. They will record seismic data continuously as seismic sources near the ocean surface shoot into them from any desired direction. Autonomous nodes offer tremendous flexibility for deployment around congested facilities and rugged seafloor terrain. These two characteristics, autonomy and the recording of seismic data from all directions of the compass, are critical technical characteristics of this innovative technology that enable the solution of this urgent industry problem in the appraisal and development of deepwater subsalt reservoirs.

After executing several prototype sea trials with different manufacturers, BP selected the Fairfield Industries OBS node design in late 2004. The goal was to conduct a full-scale wide-azimuth seismic survey over the Atlantis field in the Gulf of Mexico beginning in 2005.

Case study
BP, the operator of Atlantis field, and its partner, BHP Billiton, commissioned Fairfield Industries to acquire a full-scale seismic survey using Fairfield’s autonomous node system. The survey successfully concluded in March 2006.
The performance of the OBS node system exceeded expectations in this harsh environment.

The offshore team deployed and recovered nodes at each of 1,628 target locations spread over 95 sq miles (247 sq km) during the 5-month period. “No node left behind,” the motto of the offshore team, was successfully executed. The nodes themselves, delivered directly from the factory to the deepwater Atlantis location, proved highly reliable, with 99.3% recording 100% of the required seismic data.

This was the largest ROV-based subsea equipment deployment and recovery operation in terms of number of units and areal coverage. The Atlantis OBS node survey was the largest deepwater OBS survey ever recorded. It clearly demonstrated the technical and commercial viability of a new deepwater wide-azimuth seismic acquisition technology in a very challenging environment (infrastructure, steep terrain, winter weather).

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