Variable‐depth streamer acquisition: Broadband data for imaging and inversion

Abstract

Summary This paper starts by revisiting the receiver deghosting problem, showing that in order to be optimal in terms of signal-to-noise ratio, it should not performed as a preprocessing stage as it is done usually. A new deghosting algorithm is described, based on computing a migration together with a mirror migration, and performing a joint deconvolution of these two images. It is true amplitude, being able to extract the true deghosted reflectivity, that is the reflectivity that would have been obtained should the water surface be not reflecting. The paper then describes how this new method allows to deghost acquisitions based on pre-stack notch diversity, such as the slant streamer technique. We revisit this acquisition technique in two ways: firstly, we optimize the depth profile of the streamer to ensure diversity for all reflectors depths, leading to variable-depth streamer rather than slant streamer. Secondly, recognizing that the stack performs an imperfect deghosting, leaving a residual ghost, we perform the residual deghosting with our new deghosting technique. This variable-depth streamer acquisition and processing has been tested on several locations. Here, we show results from a West Africa acquisition, where a 2.5-150 Hz bandwidth was achieved. This broad bandwidth translates into improved results for the acoustic impedance inversion. Variable-depth streamer data seems to 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.