DISCover - Broadband Towed Streamer Acquisition

Abstract

In this paper we present a new method for broadband marine acquisition and processing capable of imaging deep targets while maintaining full high frequency bandwidth data. The method uses a deep interpolated streamer coverage approach (DISCover), which comprises a conventional 3D shallow towed-streamer spread, and a deep streamer spread which is more sparsely sampled in the crossline direction. The measurement from the shallow streamer plane is complemented with a low frequency limited measurement from the deep streamer plane; In essence boosting the low frequencies of the shallow streamer measurement, which are heavily attenuated by the shallow tow ghost response. Because the deep streamers are only going to provide the low-frequency part of the bandwidth, we can more sparsely sample these data thus 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, characteristics suitable for deep imaging below attenuative overburdens. Velocity model building, imaging and impedance inversion also benefit from the broadband result. In addition, data acquired in this way are more robust to poor weather conditions than conventionally acquired data. Data from 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 6 m and two deeper streamers (below shallow streamers 2 and 5) towed at a depth of 20 m. The correct relative position of the streamers was controlled by means of streamer steering. A novel over/under source design was also used to bias source output toward low frequencies and further enhance the low-frequency signal-to-noise ratio of the acquired data.