2D PP/PS-stereotomography: Application to a real 2D-OBC dataset
M. Alerini, G. Lambaré, R. Baina, P. Podvin and S. Le Bégat
Journal name: Geophysical Prospecting
Issue: Vol 56, No 2, March 2008 pp. 213 - 227
Info: Article, PDF ( 1.7Mb )
It has been shown on an ‘ideal’ synthetic dataset that PP/PS-stereotomography can estimate an accurate velocity model without any pairing of PP- and PS-events. The P-wave velocity model is first estimated using PP data and then, fixing this velocity field, the S-wave velocity is estimated using the PS data. This method needed to be evaluated further and we present here the first application of PP/PS-stereotomography to a real dataset: the 2D East-West Mahogany OBC line (Gulf of Mexico). We are here confronted with data which do not fit our working assumptions: coherent noise (due to an approximate separation of PP- and PS-events and some remaining multiples), probably some anisotropy and 3D effects. With a careful selection of the stereotomographic picks, which allows one to decrease the effect of the picked coherent noise by the automatic picker, our application can demonstrate the relevance of our approach in the upper part of the profile, where anisotropy and 3D effects might be low. We can thus estimate, without any pairing of PP- and PS-events, a velocity field which provides not only flat common image gathers, but also PP- and PS-depth migrated images located at the same positions. For the deeper part of the profile, a significant shift in depth appears. In addition to possible anisotropy, 3D effects and a more complex velocity field (‘salt body’), this is due to the quality of the PZ- and X-components profiles: The PZ-component profile where the PP-stereotomographic picking is performed, is polluted by conflicting converted or multiple events and the X-component profile, where the PS-stereotomographic picking is performed, is highly noisy. This study emphasizes the need to develop accurate selection criteria for the stereotomographic picks.