Estimation of Uncertainties in Fault Lateral Positioning on 3D PSDM Seismic Image - Example from the NW Australian Shelf

Abstract

We present a two-step sequence to estimate uncertainties in lateral positioning of fault planes on 3D PSDM seismic images. The first step provides an approximate evaluation of what causes the uncertainties, how uncertainties are distributed in 3D space and what to expect within our target zones. At this step we create a qualitative 3D volume of lateral fault position uncertainties that depend on complexity of the overburden and the seismic acquisition parameters. In the second step we focus on a single fault of practical interest. Based on the results of the first step we modify the existing 3D PSDM anisotropic velocity model by introducing additional anomalies that cause maximal changes to the lateral position of the fault on seismic image. Then we iteratively re-migrate a small sub-volume around the fault and check the PSDM images and residual moveout. We assess how far the velocity changes can move the image of the fault and still satisfy the available seismic data. The second step gives more reliable quantitative uncertainty estimations for a single location within the general uncertainty volume produced in the first step. We use a real multi-azimuth 3D seismic dataset from the North-West Australian shelf to illustrate this sequence.