3-D visualisation of transpressional structures in the eastern Otway Basin

Abstract

The application of new technology and concepts to exploration in the eastern offshore area of the Otway Basin has recently resulted in two gas/condensate discoveries. Exploration for hydrocarbons in BHP Petroleum's permits VIC/P30 and VIC/P31 began in 1991. Geotechnical studies conducted by BHPP during the gazettal phase of the VIC/P31 acreage indicated the presence of a previously unrecognised compressional structural setting. A 2-D seismic grid was shot over this area which confirmed these concerns. The area displays extreme structural complexity, due to a history of reactivation closely linked to localised episodic compression and regional extension. The "Eric The Red" anticlinal structure is a product of these forces and was drilled unsuccessfully for hydrocarbons in early 1993. Accurately resolving the complex three-dimensional structural problem in the Eric The Red area with 2-D seismic data on Landmark presented major difficulties. In the ideal case, the most structurally plausible model would be generated with a three dimensional interpretation of the 2-D seismic. Through BHP Research, state-of-the-art 3-D computer visualisation technology was employed to assist in interpretation. Visualisation of 2-D seismic data in 3-D is not known to have been previously attempted with this technology. Mapped time surfaces and fault planes from the original Landmark/Zycor interpretation were sliced through the 3-D volume as part of the visualisation exercise. The "VoxelGeo" software utilised has the added capability of rendering the data volume transparent up to a specified amplitude threshold. This enabled detailed examination of zones and surfaces of interest. The 3-D visualisation concept is currently at the forefront of developments in computer-based geophysical interpretation. In addition to seismic amplitude data other attributes, such as phase, instantaneous frequency and velocity, are available for the 3-D imaging of seismic data.