Imaging septaria geobody in the Boom Clay using a Q-compensated reverse-time migration

Abstract

The Boom Clay is being investigated as a host rock for disposal purposes of radioactive wastes. Although the formation is relatively uniform and homogeneous, there are embedded septaria bodies (carbonates) or layers of septaria that may constitute a problem regarding the integrity of the clay. It is therefore essential to locate these geobodies, particularly with seismic experiments. Since the medium shows strong attenuation it is necessary to correct for this amplitude loss if true amplitudes of the reflections are required when imaging these bodies after the stack. To achieve this task, we implement a reverse-time migration algorithm based on a dispersionless anelastic rheology, that is, the phase velocity and attenuation factor are frequency independent, and back-propagation is performed with a negative quality factor, Q. The algorithm is tested on synthetic data. For this we assume that the septaria are diffractors generating waves synchronously to simulate a stacked seismic section, that is, the result of an exploding-reflector experiment. In this case, back-propagation is stopped when all the diffraction points are imaged at the same time. The examples consider layers of septaria and isolated septaria embedded in homogeneous and inhomogeneous Boom Clay with zones of low Q. The amplitude of the geobodies is recovered and the resolution is improved, even in the presence of noise.