IMPROVED STRUCTURAL RESOLUTION FROM 3D SURVEYS IN AUSTRALIA

Abstract

Two marine seismic three-dimensional (3D) surveys were carried out in the Gippsland Basin during 1980. The results of these surveys illustrate the improved structural resolution that can be obtained by 3D migration in complex areas, and also the great detail with which a structure can be defined by the dense data volume given by a 3D survey.

Certain aspects of data collection and processing are particularly critical in achieving a successful 3D survey. Line spacing and depth-point spacing must be related to the maximum dips and reflection frequencies expected, and accurate navigation and streamer positioning are essential. Correct migration of the data is highly dependent on obtaining the proper migration velocities, and these are derived from the stacking velocity analysis by a form of 3D modelling.

Sections and Seiscrop' horizontal time slices from the surveys demonstrate that in areas of complex three-dimensional structures, 3D seismic methods are necessary to properly image the reflection energy. The Seiscrop sections also show how the dense spatial sampling of 3D data is required to map these complex structures with adequate resolution for the most effective planning of a drilling programme.