Abstract

East Coast Basin (ECB) is situated on an active convergent margin that has been influenced by a long subduction history between the Pacific and Australian plates. Exploration activity in the onshore region of this area is shown by 40 wells with over 300 hydrocarbon seeps indicating the presence of an active hydrocarbon system. On the other hand, the offshore area has only three wells, all of which encountered significant gas shows. Regarding the offshore area, one of the problems is less understanding of migration pathway leading to uncertainty in prospect identification.

This study tries to approach this issue by identifying the relationship between regional tectonic framework, pathways for fluid to flow and hydrocarbon potential in the offshore ECB particularly in the thrust triangle zone within this area. While 2D and 3D seismic analysis has identified the tectonic features, palinspastic reconstruction, complemented with recent knowledge of regional tectonics, was performed to represent reasonable solutions for the tectonic evolution of offshore ECB. On the other hand, seismic observations complimented by seismic attribute analysis identify fluid related features related to faults in the offshore area.

Analysis of the datasets indicate four main tectonic events in the offshore area consisting of (1) Pre-Miocene deposition in passive margin settings, (2) Early-Middle Miocene deposition while thrust faults formed in the compressional phase, (3) Late Miocene deposition while listric faults formed in the extensional phase and (4) Pliocene-Holocene deposition with structural inversion in the compressional phase until recent. On the other hand, observations of chimneys associated with listric faulting indicates the Late Miocene extensional phase created migration pathway for fluid to flow from Cretaceous-Paleogene source rock. An assessment of trapping configuration, as well as a presence of high amplitude anomaly bounded by reactivated fault in the study area, offers a promising late Miocene prospect in the offshore ECB. Understanding the tectonic evolution, fluid related features and hydrocarbon potential within the offshore ECB provides insight into the petroleum system as well as potential prospectivity identification in this area.

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