Seismic Uncertainty and Ambiguity

The link between seismic data and subsurface properties suffers from an intrinsic ambiguity, i.e., that many reservoir models fit the same data within the noise. In some pathological cases, this may cause biases in the interpretation of the structure of the earth models used in exploration and reservoir management. Inversion techniques for large seismic data sets encountered in the oil industry are well established and are assumed to be reliable. Although this is generally true, thanks to integrated knowledge from geology and other geophysical data, there is, in some cases, still a significant risk that traditional approaches may end up finding only part of the models which can explain the observed data, overlooking potentially different scenarios and, moreover, hampering a correct uncertainty quantification. This phenomenon is often observed in practice when different inversion contractors arrive at significantly different results from the same data sets. The impact of the unavoidable non-uniqueness should be assessed when performing inversion of seismic data. We investigate the magnitude of the ambiguity problem in seismic modelling of chalk reservoirs by explicitly taking ambiguity into account in the inverse problem. Our study is based on a careful selected test case from the the Danish North Sea sector.