The Limits of Narrow and Wide Angle AVA Inversions in Case of High Vp/Vs Ratios -Application to Seabed Characterization

Since its introduction in the oil and gas industry, amplitude versus angle (AVA) inversion has become a standard tool in hydrocarbon exploration. However, with the intensification of off-shore construction activity, applications of this method have also been extended to evaluate the elastic properties of seabed sediments. These sediments are often undercompated and characterized by very low Vs and high Vp/Vs ratios. The importance of Vp/Vs ratios is usually underrated in AVA inversion which is often applied with few misgivings in case of high Vp/Vs ratios. In this work, we derive the elastic properties of the seabed interface by applying AVA inversion to a 2D well-site survey acquisition. The limited water depth, the maximum offset of the seismic acquisition and the high frequency content of the data make it possible to consider two different ranges of incidence angles: 0-30 and 0-60 degrees. The limits of AVA inversion in case of high Vp/Vs ratios are discussed together with the benefits introduced by wide angle reflections in constraining the inversion. In particular, these reflections are essential to decrease both the cross-talk between the inverted parameters and the uncertainties in the Vp and density estimations, but they do not guarantee a reliable Vs estimation.