Morten Svendsen

Efficient broadband marine acquisition and processing for improved resolution and deep imaging

Summary We present a new method for broadband marine acquisition and processing. A 3D shallow towed-streamer spread is deployed, designed to optimize the mid- and high-frequency parts of the bandwidth. In addition, data are simultaneously acquired from a small number of deeper towed streamers. The depth of these deeper streamers is optimized for the low frequencies such that the combined overall bandwidth is enhanced. Because the deep streamers will only provide the low-frequency part of the bandwidth, we can more sparsely sample these data enabling efficient acquisition scenarios as fewer streamers are required. The data are combined in processing, optimizing the signal-to-noise ratio over the entire bandwidth. The resulting data exhibit 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 benefit from the broadband result. Data acquired in this way are also more robust to poor weather conditions than conventionally acquired data. Data for a 3D case study using this new acquisition method were acquired off the NW Shelf of Australia. The streamer spread consisted of six shallow streamers towed at a depth of 6m and two deeper streamers (below shallow streamers 2 and 5) towed at a depth of 20m.

Repeated Seismic Survey From the North Sea using New Streamer Technology

Seismic reservoir monitoring is now a well established technology. The method has a yet unrealized potensial which will open for wider use, if higher repeatability can be obtained. Wider applications could be more quantitative interpretations, monitoring over shorter time intervals and application of the technology to smaller, tighter and more complex reservoirs. Todays towed streamers impose basic limitations on repeatability, as streamer feather is hard to repeat and tow noise must be kept low. New streamer technology, called Q-Marine, involves single hydrophone sensor output instead of hardwired groups, improved acoustic positioning and horizontal steering of the streamers. This enables a better attenuation of tow noise, as induced from either swell or flow across the streamers. The horizontal steering makes repeated streamer positions possible. In the first full-scale use of the system, data will August 2000 be acquired over a major producing field in the North Sea, as a repeat of multi-streamer lines after a time-lapse of three years. This test is expected to show the increased monitoring power of the new system, with detection of only a few meters movement of saturation fronts.