SCHLUMBERGER’S new seismic acquisition technology is giving broadband marine acquisition a boost in efficiency, according to Ed Kragh, Schlumberger Cambridge Research programme manager.
Kragh and a team of colleagues told delegates at the recent EAGE conference in Amsterdam that the acquisition geometry involves towing several streamers at a shallow depth but only a sparse array of streamers at a deeper depth.
The result is frequency-rich data that maintains both ends of the marine spectrum without the high-frequency compromises that usually result from deep towing.
The Schlumberger team said that a sparse sampling needed for the low-frequency signals means fewer receivers are needed, and the combination of signals from different depth layers delivers an optimal solution
They pointed out that the DISCover (deep interpolated streamer coverage) towing geometry allows recovery of the low, mid and high-frequency ranges, supplying broadband acquisition, and is said to show great promise in areas with a complex overburden and/or deep targets.
Also, the additional low frequencies that the technique provides allow improved inversion of the data for rock properties.
Schlumberger said potential applications included improved imaging beneath highly absorptive overburdens such as basalt and salt, or acquiring data suitable for inversion to absolute rock properties. Data acquired in this way were also more robust to poor weather conditions than conventionally acquired data.
A 3D case study using this new acquisition method was acquired off the NW Shelf of Australia. The streamer spread consisted of six shallow streamers towed at a depth of 6m (20ft) and two deeper streamers (below shallow streamers 2 and 5) towed at a depth of 20m (65ft). Schlumberger said the resulting data exhibited both high resolution and deep penetration for subsalt and sub-basalt imaging, for example. In addition, inversion for acoustic impedance, imaging and velocity model building also benefited from the broadband result.