Schlumberger Unveils New WAZ Seismic Process
Monday, June 30, 2008
Schlumberger released information concerning their new wide azimuth seismic process at the EAGE/SPE Rome 2008 Conference.
Wide azimuth, or WAZ, seismic surveys provide better illumination than traditional marine surveys in complex geologic areas by essentially "shining the light" on the formations from many directions. The "light" comprises seismic signals over a wide range of azimuths, or angles of incidence on the subsurface reflectors. WAZ surveys typically use multiple source and streamer vessels to obtain this advantage.
Nick Moldoveanu, geophysical advisor at Schlumberger, described a new acquisition technique at the recent meeting of the European Association of Geoscientists and Engineers (EAGE) in Rome. "The WAZ geometry is parallel," he told the delegates, "so the efficiency is affected by the line change or turn, where significant production time is lost, especially for smaller, development-type WAZ surveys."
The new method developed by Schlumberger, Coil Shooting, uses a circular geometry, with a single vessel sailing in overlapping circles, acquiring data constantly.
"Test results in the Gulf of Mexico proved that it is feasible to sail along circles maintaining constant streamer separation and positioning the receivers very accurately along the cable," Moldoveanu said. The test of this full azimuth technique (FAZ) was performed in April 2007 over an area previously examined using a parallel-geometry WAZ survey. Comparing the prestack depth migration results for the two surveys, Moldoveanu pointed out clearer detail below salt in the new circular geometry.
Moldoveanu told the group, "This idea dates back 20 years, but in the 1980s there were technical problems that forced its abandonment." The WesternGeco Q-Marine system has solved the problems of positioning accuracy, streamer control, noise attenuation, and the ability to image complex geology. With those issues solved, the Coil Shooting methodology is very efficient for FAZ towed-streamer acquisition because it requires only a single streamer vessel with a single source array, and it uses continuous acquisition. A simulation comparing circular and parallel WAZ surveys over a 900-km2 area showed the circular method was slightly faster and obtained almost double the number of shots.