3-D seismic surveying in the Otway Basin

Abstract

The Tilbooroo seismic survey, recorded in early 1993, is the first 3-D survey acquired in the Otway Basin. It was preceded by an extensive study to optimise acquisition parameters in a cost-effective manner. This survey followed-up the minor oil recovery from fractured basement intersected by the exploration well Sawpit-1 and forms part of an integrated geological and geophysical analysis of the structural history of the Saw-pit area. Evaluation of this fracture play requires accurate prediction of the orientation and intensity of the basement fault and fracture pattern. The 3-D data, sampled at a spacing of 15 m inline by 30 m crossline, are acquired over a 44 km2 area. Land use is mainly pasture land, but also extends into the Coonawarra vineyards. There were numerous obstacles ? swamps, fences, buildings, no-access areas, vineyards ? that challenged ingenuity in the planning, acquisition and processing stages of the survey. The 3-D seismic data are acquired at less than one quarter of the fold and twice the group interval of 2-D data, yet have a vastly superior signal-to-noise ratio. Confident interpretation of the basement fault pattern, combined with structural analysis of fault attributes and knowledge of the present day stress field, indicates the basement fracture play would be best evaluated by a deviated well with a southwest azimuth.