Petrophysical properties of igneous rocks in continental rift basins – a case study from the Mesozoic sequence of the Browse Basin, North West Shelf of Australia

Capturing the ubiquitous distribution and properties of igneous rocks is necessary to succeed in hydrocarbon exploration, field development and underground gas storage when dealing with magma-rich rift margins. In recent years, numerous researches have revealed detailed morphologies of intrusive and extrusive rock units embedded within sedimentary basins owing to advances in 3D seismic data. Outcrop studies have also provided deeper understandings of their occurrence and geometries. However, there has been comparatively little focus on the rock physics of igneous bodies and their relationships to seismic expression. To bridge this gap between the outcrop and the seismic information, we undertook a well-log-based petrophysical study of igneous rocks using subsurface dataset from the Browse Basin located in the Australian North West Shelf. In this contribution, we describe a classification of volcanic facies (e.g. lava flows, volcaniclastics, intrusive sills) based on well log motifs and textures apparent in borehole image data. Statistics of the petrophysical properties of each volcanic facies are also analysed in order to examine their correlation to seismic patterns. Our study implies the importance of detailed characterisation of igneous petrophysical properties of igneous rock units where concentrated within a sedimentary basin, which will help reconcile interpretations of seismic data.