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Long restricted to land acquisition, simultaneous source methodology has now been proven in a marine environment.
In land seismic acquisition, simultaneous sources have revolutionized the way surveys are acquired, providing much greater sampling and consequently better imaging. Why hasn't this been done in the marine environment?
Well, it hasn't been for lack of trying. WesternGeco researchers have been studying the implementation of marine simultaneous source acquisition since before WesternGeco became a company. But they had to overcome some fairly significant hurdles.
At first it was commodity prices. "We invented this just before the big downturn came in '98 and '99," said Craig Beasley, chief geophysicist for WesternGeco and a Schlumberger fellow. "That lasted until about 2004 in the seismic industry, so it came at a bad time in terms of interest for new technology."
Along with the downturn, the cost of the acquisition was a tough hurdle to jump. At the time, marine simultaneous source acquisition was envisioned as a multivessel operation which required adding another shooting boat and incurring that cost. Fortunately, with the advent of wide-azimuth (WAZ) surveys, multivessel operations became more common. As more companies saw the benefits of WAZ, the simultaneous source concept began to gain momentum.
The result is the first commercial job using simultaneous sources in a marine survey. Conducted by WesternGeco for Apache and its partners offshore Australia, Beasley characterizes the technique as "a complete revolution in acquisition technology."
"With every additional source you put out, you increase the productivity of the seismic crew in a linear fashion," he said. "If you shoot two sources, you collect twice as much data."
Dave Monk, global director of geophysics and distinguished advisor for Apache, said his company first started considering marine simultaneous sources in 2010 while doing tests at the Forties field in the North Sea. Monk said Apache acquired a test to understand the concept and to see if it was feasible. Those tests gave the company confidence to try the acquisition methodology in a commercial setting. It wasn't as simple as throwing another source boat into the water. In fact, the survey was done on a single vessel usually configured with flip-flop sources. "It's not what we would have predicted would be our first commercial job," Beasley said. "But it's pleasing to see the technology demonstrated in that challenging environment because it opens the door for simultaneous sources in virtually any marine acquisition." Another challenge was develop ing a separation algorithm that would capture the signal with as little residual imprint as possible. To test this, WesternGeco simulated simultaneous-source data from real data. "We had real noise and real data problems, but we knew the real answer," Beasley said.
The announcement might seem overshadowed by WesternGeco's other big announcement, the introduction of IsoMetrix marine isometric seismic technology. The new marine acquisition system outputs isometrically sampled point-receiver data in both the crossline and inline directions. But Monk said the two technologies are complementary.
"I hold out a lot of hope for what they've done," he said. "There is absolutely no reason why you shouldn't use IsoMetrix technology with a simultaneous source."