Petroleum Geo-Services ASA (PGS), Oslo, completed a four-component (4C) 3D seismic survey of a 45 sq km area of giant Roncador oil field in as much as 1,860 m of water off Brazil.
This is industry’s first ultradeepwater 4C survey, and the water depth is triple that of previous 3D surveys in the Campos basin, said PGS, which shot the survey for Petroleo Brasileiro SA (Petrobras). Processing will be finished in September.
The three-boat survey used ocean-bottom cables 6 km long deployed from the Bergen Surveyor seismic vessel and steered into position with a real-time acoustic navigation system.
The crew steered the 4C sensors landed within 0.8% of the water depth of their planned positions without using remotely operated vehicles, PGS said. The Ocean Explorer served as the recording vessel.
Roncador target sands occur at 3,000-3,700 m and are difficult to map and interpret with conventional compressional, or longitudinally vibrating, seismic waves.
A 4C survey makes use of laterally vibrating (shear) energy introduced in the subsurface when compressional energy propagating downward through water reaches the sea floor.
PGS hopes to use information from the converted waves to plot reservoirs transparent to compressional waves in Roncador and nearby Albacora field. It also hopes to validate several oil-water contacts.
Before the survey, most of the cables, many of them 3 years old, were replaced with new ones and a specially designed deepwater cable-handling system was installed on the Bergen Surveyor.
The deepest previous Campos basin 3D survey was the Viola survey, PGS said. ✦