Abstract

This paper revisits the problem of receiver deghosting, showing that for optimal signal-to-noise ratio it should be performed post-stack rather than pre-stack, as is the usual practise. A new deghosting algorithm is described, based on computing both a migration and a mirror migration and performing a joint deconvolution of the two. This method is true amplitude, as it is able to extract the true deghosted reflectivity, i.e. the reflectivity that would have been obtained had the water surface not been reflecting. The paper then describes how this new technique provides a method of deghosting data acquired with ghost notch diversity, such as slant streamer acquisition. We revisit this acquisition technique with two modifications. Firstly, we optimize the streamer-depth profile in order to ensure diversity for all reflector depths, resulting in a variable- depth streamer rather than a slant streamer. Secondly, since we recognize that stacking performs imperfect deghosting, leaving a residual ghost, we use our new deghosting technique to perform residual deghosting. This variable-depth streamer acquisition and processing has been employed in several locations. Here, we show results from West African, where a 2.5- 150Hz bandwidth was achieved, and Western Australia. The broad bandwidth translates into improved results for acoustic impedance inversion. Variable-depth streamer data has 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 overlap zone.