Etude des variations de l'amplitude de la réflectivité du sous-sol après imagerie sismique en profondeur

In oil exploration, seismic reflexion imaging is commonly used. This method gives a first estimation of the structures of the sub-surface and also an estimation of the reflection coefficients changes which are related to changes in petrophysics parameters (density, compression and shear velocities). An analysis of these variations allows us to estimate the elastics parameters which are essential and complementary to the interpretation of the reservoirs. The classical processing consists in studying the amplitude variation directly on data recorded as a function of offset and time of propagation. The analysis is done using an inversion of a linear approximation of the Zoeppritz's equations governing the theoretical amplitude changes. In our case, we consider the analysis of the amplitude variation after the imaging step, directly in the depth domain. In order to success in this analysis, we propose a post-imaging processing before the amplitude versus angle analyse to compensate for erroneous migration velocity fields, interference of the wavelet in the case of thin bed and the wavelet stretching. This processing also gives us a skeleton which represents a depth interpretation of the geologic structure.