Variable-depth streamer acquisition: broadband data for imaging, post and pre-stack inversion

Abstract

Variable-depth streamer acquisition is a broadband streamer acquisition technique where the depth profile of the streamer is optimized in order to ensure receiver ghost diversity, which in turn allows the deconvolution of the residual ghost at the imaging stage, pre-stack or post-stack. This technique allows the streamers to be towed at an average depth of several tens of meters, which combined with the use of solid streamers, ensures the raw data has an exceptionally good signal-to-noise ratio, especially at low frequencies. This variable-depth streamer acquisition and processing has been field-tested on a variety of locations, achieving bandwidth up to 6 octaves (2.5Hz -160 Hz). This broad bandwidth translates into improved results for the acoustic impedance inversion. The lack of low frequencies in conventional seismic data means that a low frequency model must be incorporated in the inversion process, obtained by interpolating low-passed filtered impedance logs between well locations. With variable-depth streamer data, high-resolution NMO-derived seismic velocities are used to define the low frequency model in a range 0-5Hz, while the reflectivity provides information from 2.5Hz. Variable-depth streamer data thus have the potential to fill the usual gap between the high frequencies of the seismic velocities and the low frequencies of the reflectivity, the 2.5-5 Hz octave being the overlapping zone. Pre-stack elastic inversion has also been performed, providing both impedance and Vp/Vs sections, proving the feasibility of pre-stack deghosting of variable-depth streamer data.