OS5B-3:CONTROLS ON THE BASE OF GAS HYDRATES OFFSHORE MAURITANIA: DETERMINED BY 3D SEISMIC IMAGING OF THE BOTTOM SIMULATING REFLECTION

    High-resolution 3D seismic data from offshore Mauritania provide accurate information on seismic amplitude characteristics and the distribution of a bottom simulating reflection (BSR). On seismic sections the BSR is discontinuous, composed of alternating high and low seismic amplitudes. On the amplitude map of the BSR, the amplitude bands are curvilinear and they dip towards different directions. The high amplitude bands are interpreted to be mostly caused by the presence of free gas trapped below the base of gas hydrates, potentially in regularly spaced beds of coarser sediments. The changes in the planform geometry of the bands provide evidence of lateral changes in the ambient conditions that control the depth of the BSR. These changes occur due to variable water depth of the slope, impingement of salt diapirs and canyon cutting at the seabed. This paper exemplifies that mapping the BSR on 3D seismic data can provide a wealth of information on lateral changes in the position of the base of the gas hydrate stability zone (BHSZ).