Integrated Interpretation of Magnetics and Seismic Datasets in the Outer Browse Basin (Australia)

Abstract

Exploration permit WA-314-P is located on the outer edge of the Browse basin and previous exploration wells have drilled thick volcanic intervals, which occlude reservoir development in the targeted Jurassic section. Recent exploration has focused on an outboard anticlinal trend that straddles the divide between the Caswell sub-basin and the frontier Seringapatam sub-basin. In using geophysical methods to detect the presence of volcanics, it is prudent not to rely on just one approach. A broadband 3D seismic survey was acquired over the anticlinal trend and interpreted using conventional techniques with ties to nearby well control using legacy 2D and 3D seismic. Meanwhile, 3 pre-existing magnetics datasets were merged with allowance for acquisition differences between each survey. This revealed a small and low intensity anomaly over the main prospect when compared to the broad and high intensity anomalies surrounding wells that drilled thick volcanics. Magnetic modeling and inversion evolved in parallel with the seismic interpretation, beginning with the modeling of a 2D profile along a regional seismic line intersecting a well that encountered a thick volcanic section. Magnetic susceptibility values for use in the models were established using a hand-held susceptibility meter and cuttings from one of the nearby wells. This enabled several diverse models to be rapidly tested and also helped to establish which horizons would be required for 3D inversion of the magnetics data. Inversion of the magnetics data was tested on several 2D profiles allowing inversion parameters and constraints to be refined before attempting a 3D inversion using the final depth horizons mapped across the study area on both 3D and 2D seismic. Along the way, we noticed that the magnetic anomalies (high susceptibility bodies) became more clearly defined and these were then imported into the seismic interpretation package to check for consistency with the final 3D depth model. The magnetic anomalies near the prospect are (fortunately) quite small and were typically observed along mapped faults and so we interpret these to be minor intrusives. Using structural restoration, their age can be shown to correspond to the most intense period of volcanism (Jurassic) in the Browse basin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015