Identification of a Triassic anomaly in deep water of Northern Carnarvon Basin, Australia

The deep-water area of the Beagle Depression in the Northern Carnarvon Basin is at an early exploration stage. Cygnet anomaly, which was found in Triassic strata, has not only the paleotectonic background of developing carbonate reefs, but also the possibility of being volcanic rocks. In order to distinguish whether the Cygnet anomaly is volcanic rock or reef, a set of four-step analytical techniques was applied in this area. (1) Seismic facies analysis. Based on the interpretation of 3D seismic data, comprehensive seismic attributes as well as seismic facies, the shape of the Cygnet anomaly was identified. (2) Inner structure analysis. The inner structure of the Cygnet anomaly was dissected by using waveform clustering and 3D visualization techniques. (3) Gravity and magnetic analysis. The gravity and magnetic properties of the Cygnet anomaly were identified by carrying out gravity and magnetic seismic inversions. (4) Regional volcanic activity analysis. Combined the restoration of paleo-structure, the analysis of lithofacies paleogeography and the investigation of regional volcanic activity, the volcanic activity period and time were confirmed. Finally, it was concluded that the probability that the Cygnet anomaly is igneous rock was high, and some important seismic facies such as volcanic channel facies, volcanic intrusive facies, overflow facies and pyroclastic sedimentary facies were identified. This set of anomalous body identification technology in a pre-drilling deep-water area has a good application. It can identify anomalous body characteristics in the early exploration stage and optimize drilling investment.