Abstract The Northern Carnarvon Basin (NCB) located on Australia's North West Shelf hosts an extensive (∼40 000 km 2) intrusive igneous complex related to Mesozoic rifting and break-up. Using an extensive suite of modern 3D seismic reflection surveys, we have mapped this intrusive system across the NCB. We identify three predominant intrusion morphologies: stacked sheets of large interconnected sill intrusions (up to ∼170 km long) and smaller (8–30 km long) isolated, strata concordant intrusions, which often interact with normal faults emplaced into deltaic sedimentary rocks, and variably sized (10–40 km long) saucer-shaped intrusions emplaced into marine shales, spread across seven zones (geographically constrained groups of intrusions of a specific morphology). We consider the zones’ margin-parallel orientation, suggesting control by subcrustal extensional processes during rifting, and the variation in intrusion morphology between these zones, suggesting a dominant control by host rock mechanical properties. We integrate previous work with our observations, constraining emplacement to between the Kimmeridgian and Valanginian, coinciding with key phases of margin evolution. Finally, we assess the impact of this intrusive complex on local petroleum systems. There is likely little to no adverse impact on source rock maturation or reservoir contamination by CO 2 , but there is a spatial dissociation between the location of groups of intrusions and the gas fields, particularly in the Exmouth Plateau. This suggests that migrating hydrocarbons may be blocked, baffled and/or redirected by emplaced igneous rocks.

Abstract The Browse Basin is one of Australia's major hydrocarbon provinces, where significant discoveries have been made in recent decades including the Ichthys and Prelude fields, which accounted for ∼15% of the cumulative Australian liquified natural gas (LNG) production in 2019–20. This rift basin hosts extensive Mesozoic intrusive and extrusive igneous rocks, having been identified from both well and seismic data, and which are recognized as one of the key challenges for exploration and production activities in this region. Their impact on petroleum exploration is demonstrated by the number of wells which encountered unpredicted or thicker than expected igneous rock units both within and adjacent to target sections. This study therefore aims to document the reasons of such unexpectedness, and to develop capability to predict the occurrence of igneous rock units prior to drilling in the Browse Basin and other rift settings that contain igneous rocks. Multiple case studies of uncommercial exploration wells are developed by integrating petrophysical and seismic reflection data, focusing in particular along the outboard part of the basin where igneous rocks are most prevalent. Our study highlights the importance of understanding petrophysical, spatial and chemical heterogeneities of igneous rocks in basins to explain their emplacement and distribution, and thereby predict their occurrence prior to exploration and development activities.