Underground hydrogen storage (UHS) involves complex subsurface processes, where accurate modeling of density and viscosity is essential for reliable simulations. In this study, a comprehensive experimental databank of density and viscosity for pure hydrogen and binary hydrogen mixtures with potential cushion gases (CH4, N2, and CO2) is assembled. Using this databank, commonly applied cubic equations of state (EOS)-van der Waals, Peng-Robinson, and Soave-Redlich-Kwong-with and without Peneloux volume shift are systematically benchmarked against the GERG-2008 equation of state using both experimental data and a synthetic full-range thermodynamic grid, and their performance is evaluated through a multi-criteria assessment jointly considering density and viscosity predictions. The results show that GERG-2008 consistently outperforms cubic EOS in predicting density and viscosity, especially for H2-CO2 mixtures. While SRK and PR-Volume Shift show acceptable accuracy for density- particularly for H2-CH4 and H2-N2 mixtures-their performance in viscosity predictions, especially for H2-CO2 mixtures, is significantly less reliable. Nearly 200 times greater computational time for GERG-2008 compared to cubic EOS represents a clear trade-off between accuracy and computational efficiency. Newly optimized coefficients for the Lohrenz-Bray-Clark (LBC) viscosity model are proposed, dedicated separately for methane-hydrogen and carbon dioxide-hydrogen mixtures. These tailored coefficients enhance viscosity prediction accuracy within their respective systems. The findings highlight the limitations of cubic EOS in accurate thermophysical property modeling while showing favorable computational efficiency. This work also identifies gaps in experimental data and suggests directions for future research.

In multi-phase rifts, pre-existing structural fabrics that are formed during earlier rifting stages can influence fault growth during later deformation. Successive extensional episodes cause pre-existing faults to reactivate, leading to the propagation of fault planes and/or generation of branching faults in surrounding strata. Pre-existing faults can also locally control geometries (e.g., fault bends) and distributions of subsequent faults by creating stress and strain perturbations without exhibiting observable fault displacements (i.e., structural inheritance). Constraining the evolution of faults in multi-phase rift basins is crucial for understanding how accommodation spaces form and pathways for subsurface fluids (e.g., water, hydrocarbons, magma) develop during active deformation. However, due to structural complexity and limitations in data availability and resolution, capturing detailed fault geometries in time and space remains challenging. This study focuses on the structural framework of the central Browse Basin, the Australian North West Shelf, which experienced repeated phases of rifting throughout the Mesozoic. Using multiple surveys of a high-quality 3D seismic reflection dataset, this study demonstrates how successive extensional episodes shaped fault geometries and hence the structural configuration of the central Browse Basin. Key findings include: (1) the development of distinct fault patterns such as zigzag, rhomboidal, arc-shaped and en echelon geometries through reactivations of pre-existing Permian-Triassic faults; (2) a rotation in extensional stress orientation after the Late Jurassic, resulting in the deepening of WNW-ESE striking grabens; and (3) quantification of fault growth histories revealing variations in displacement and periods of activity, including the cessation of some major faults by the Late Jurassic. These insights provide a detailed tectono-stratigraphic evolution model for the central Browse Basin and offer broader implications for understanding fault behaviour in multi-phase rift systems globally.

Ancient submarine volcanic systems preserved within sedimentary basins provide opportunities to investigate the time and spatial distributions of intrusive and extrusive rocks, though existing work has largely focused on the geometrical features of submarine volcanic products, with limited interrogation of their interactions with sedimentary processes. This study investigates a buried submarine volcanic system within the Browse Basin, Australian North West Shelf. Through the integration of three-dimensional seismic reflection survey with borehole data, our study reveals intricate geometric features of a submarine volcano and lava channels, and their relationship to an associated intrusive network of Early Cretaceous age that has been preserved beneath similar to 3.5 km of sedimentary overburden. In planform, the volcano has a diameter >4.5 km with a preserved height reaching 650 m. Meandering lava-flow channels extend similar to 20 km southward of the volcanic edifice, forming lava lobes with pressure ridges at the flow termini. Abundant sheet intrusions, identified within underlying Jurassic and older strata, indicate a magma transport from the north. The localized accumulation of sills led to variations in palaeo-seafloor topography, influencing the direction of lava flows and post-volcanic sedimentation patterns. Our findings have a broad range of implications encompassing submarine volcanism and their impacts on basin dynamics.

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 breakup. 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 to 30 km long) isolated, strata concordant intrusions, which often interact with normal faults emplaced into deltaic sedimentary rocks; and variably sized (10 to 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 sub-crustal extensional processes during rifting; and, 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.

The application of high-resolution seismic reflection data has spurred major advances in knowledge of the emplacement of sub-volcanic mafic magma plumbing systems in sedimentary basins, highlighting the importance of interconnected sheet intrusions in facilitating lateral magma transport, the links between host rock mechanical properties and emplacement processes, and providing insights into how intrusive activity in basins impacts their resource potential. However, most studies have focused on Mesozoic-Cenozoic mafic magma plumbing systems situated along offshore rifted margins characterised by extensive subsurface datasets. The extensive Mesoproterozoic (c. 1300 Ma) Derim Derim Dolerite, which intrude the greater McArthur Basin in northern Australia, provide a unique opportunity to study the emplacement of a Proterozoic magma plumbing system due to its penetration by numerous hydrocarbon and mineral drillholes, in addition to seismic reflection coverage. Understanding the emplacement of this system is important because of its interactions with prospective unconventional shale reservoirs in the Velkerri and Kyalla Formations, which represent one of the world’s oldest known petroleum systems. This paper focuses on characterising the intrusion emplacement and magma plumbing system using an array of subsurface data, to constrain the distribution, morphology, and emplacement mechanisms of the Derim Derim Dolerite.The morphology of the large, strata-concordant intrusions encountered at shallow present-day depths (<2 km) in the greater McArthur Basin is indicative of greater original emplacement depths of >3–4 km, suggesting a significant extent of uplift and erosion. Density-derived porosity values for the Velkerri and Kyalla Formations are anomalously low for their present-day depths, corroborating a greater palaeo-depth at time of emplacement. The extent of alteration of the host rock surrounding the Derim Derim Dolerite is highly variable, with a small number of occurrences of graphitisation of the organic matter adjacent to intrusions. However, this appears to be highly localised and the detrimental impact of the Derim Derim Dolerite on potential reservoir and/or source rocks appears generally minimal.

The Caswell Sub-basin, situated within the Browse Basin in the North West Shelf constitutes one of Australia’s primary hydrocarbon producing regions, with notable gas-condensate producing fields including Ichthys and Prelude. Jurassic syn-rift sandstones are extensively distributed across the basin and serve as one of the major reservoirs. However, reservoir sequences are typically intensely faulted and exhibit heterogeneity in thickness and lithofacies, with some areas experiencing localised erosion on uplifted fault blocks (e.g. Northern Caswell Sub-basin). Hence, understanding the nature of the 3D fault patterns and their growth history is crucial for evaluating the reservoir characteristics for field development and additional exploration activities. This study, therefore, aims to evaluate the structural framework and the tectonic evolution of the Caswell Sub-basin. Detailed structural interpretation of Paleozoic and younger sequences was conducted using multiple 3D seismic datasets extending over Ichthys, Prelude, Lasseter, and Crown fields. Our study focuses mainly on Mesozoic faulting patterns and kinematics evaluated from interpreted structural maps, thickness changes of each stratigraphic interval and fault throw profiles of major bounding faults. The extensional phase during the Early–Middle Jurassic triggered the development of NE–SW trending faults and the deepening of the Brewster Graben. While, from the Late Jurassic to the Early Cretaceous, the development of E–W trending faults in the north of the Crown and Lasseter fields indicate a shift in the regional stress regime. We highlight the importance of evaluating the structural linkage from basement to cover sequences to achieve a comprehensive understanding of reservoirs and associated petroleum systems.

Abstract Igneous intrusions in sedimentary petroleum basins are often perceived as having a negative impact on the elements of the petroleum system, though the impact of intrusion-related deformation features on petroleum systems and broader geoenergy applications is not well understood. In this study, we use 3D seismic reflection data to document a variety of deformation styles that are spatially and temporally associated late Cenozoic magmatic activity in the Bass Basin, offshore southeastern Australia; three types of normal fault systems (conjugate faults, concentric faults, radial faults) and fluid escape pipes. These deformation features occur in the overburden up to ∼600 m above underlying igneous intrusions, within the Eocene to Miocene Demons Bluff and Torquay formations. The conjugate faults bound graben and are interpreted to have formed in response to underlying dyke intrusions. The radial faults are interpreted to have formed in response to overburden uplift, though the link between these and associated igneous activity is less clear. We identify 101 fluid escape features that show variation in both the morphology of their surficial depressions and of the seismic reflection characteristics of their infilling deposits. These features are interpreted to be hydrothermal or volcanic vents with underlying pipe-like feeders, depending on their spatial association with adjacent or underlying igneous intrusions. The concentric fault systems are associated with surficial depressions, and quantitative analysis of reflection sags within these depressions suggest that they are a result of subsurface subsidence in response to formation of maar-craters. The intrusion-related deformation features documented in this study may have multiple effects on working petroleum systems, such as providing secondary fluid flow pathways that can either reduce seal integrity, or enabling migration of fluids into shallower reservoirs.

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.

Hydrogen gas can provide baseload energy as society decarbonizes through the energy transition. Underground Hydrogen Storage (UHS) will be secure, convenient and scalable to accommodate excess hydrogen production or compensate temporary shortfalls in energy supply. Hydrogen is a gas under all viable subsurface conditions, so is invasive, mobile and low-density. Methane and CO2 are also stored underground but storage parameters differ for each, affecting the balance of geological storage risks. UHS in Australia is most likely to utilise conventional sedimentary reservoir rocks bound by conventional trapping closures. Hydrogen energy density will affect the competitiveness of UHS against purpose-built surface storage or solution-mined salt cavities. This study presents an overview of key considerations when screening for UHS opportunities and evaluates them for five Australian sedimentary basins. A threshold storage depth mapped across them reveals that the most prospective UHS basins will have to function as integrated energy fluid resource systems.

The North West Australian Margin, which formed as Greater India rifted from Australia during the Jurassic to Early Cretaceous, is recognised as an archetypal magma-rich rifted margin, with records of extensive igneous activity in the Exmouth Plateau and Exmouth Sub-Basin (ESB) of the Northern Carnarvon Basin (NCB). Pre -breakup magmatism is manifested by a large-400 x 150 km intrusive sill complex, emplaced into Triassic and Jurassic strata in the Late Jurassic and Early Cretaceous. An apparent lack of extrusive igneous rocks has caused previous works to describe the region as a large intrusive igneous province. Here, we describe two recently identified Upper Jurassic volcanic centres: the Pyrenees Volcano in the eastern ESB (first reported here), and the Toro Volcanic Complex (TVC), in the western ESB. Although offset by Early Cretaceous normal faulting, the edifice of the Pyrenees Volcano and associated lava flows are well preserved beneath a protective carapace of Upper Jurassic strata below the angular Intra-Hauterivian Unconformity on the Novara Arch. In contrast, a significant proportion of the TVC was peneplaned beneath an intra-Valanginian (Early Cretaceous) unconformity following breakup-related uplift. As Upper Triassic to Lower Cretaceous strata appear to have been eroded over the Ningaloo Arch in the southern ESB, we postulate that Late Jurassic extrusive volcanism may have been more spatially extensive, prior to erosion associated with Early Cretaceous exhumation in the southern NCB. Hence our findings suggest that the NCB was potentially host to significantly more extrusive volcanism than has been preserved within basin fill. Our findings also have broader implications for the conditions required to preserve extrusive igneous material in sedimentary basins within large igneous provinces that have undergone complex histories of rift-related vertical motion.

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.

The Northern Carnarvon Basin (NCB) contains extensive networks of igneous intrusions emplaced during Late Jurassic and Early Cretaceous rifting that led to the breakup of the Greater India from Australia. We present the first basin-wide study of the distribution and morphology of these igneous intrusions through the interpretation of regionally extensive 3D and closely spaced 2D seismic data across the Exmouth Plateau and Exmouth Sub-basin. We observe three dominant intrusion morphologies: (1) Saucer-shaped intrusions up to ~20 × 40 km, but commonly much smaller, present in Jurassic strata of the southern Exmouth Plateau and central Exmouth Sub-basin; (2) Large, stacked, strata parallel, sheet intrusions, often >100 km in length, dominant in Triassic strata in the Exmouth Plateau and southern Exmouth Sub-basin; and (3) Variably sized, predominantly strata parallel and occasionally fault hosted intrusions (ranging in dimension from ~5 × 8 to ~35 × 65 km) present in Jurassic rocks in the Exmouth Sub-basin, and uppermost Triassic rocks in the Exmouth Plateau. We suggest that the morphologies of intrusions in the NCB are predominantly controlled the mechanical properties of their host rocks.

Mafic volcanic rocks, typically basalts of mainly late Cretaceous age, have been intersected by Gippsland Basin wells. Intersections of volcanic rocks primarily occur along the basin-bounding Rosedale Fault System in the northern part of the basin, where they exhibit a close spatial correspondence with high-CO2 content gas accumulations. Though petrographic data indicates that the basalts have been variably altered to clays and carbonates, they provide the top seals to numerous hydrocarbon accumulations, most notably at the Kipper Field. Despite the widespread distribution of these volcanics and their relevance to petroleum systems, they have received only sporadic attention over the past few decades. Here we combine petrophysical, geomechanical, geophysical and geochemical datasets to elucidate the origin of the volcanic record of the Gippsland Basin, and to evaluate their potential role in the decarbonisation of the basin, for example through providing opportunities for intra and sub-basaltic storage of CO2.

The Northern Carnarvon Basin (NCB) hosts an extensive record of Jurassic–Cretaceous rift-related igneous activity, manifested by a >45 000 km2 intrusive complex and series of volcanic centres constrained by seismic mapping. However, there are relatively few well penetrations of these igneous rocks (<1% of ~1500 exploration wells) in comparison to other basins that witness extensive magmatism, and thus, their lithological and petrophysical characteristics are poorly understood. Here, we describe the properties of igneous rocks encountered in nine petroleum exploration wells and scientific boreholes in the NCB and evaluate their impacts on exploration and development issues. Igneous rocks in the NCB are characterised by pervasive alteration, with ramifications for seismic imaging and drilling. For example, low acoustic velocities in mafic lavas altered to clays in Toro-1 were mistaken for overpressure, whilst intrusive rocks in Palta-1 were initially unrecorded and only recognised due to subsequent post-drilling thermal history analysis. The alteration of mafic igneous rocks to clays reduces acoustic impedance contrasts relative to sedimentary host rocks, making their identification prior to drilling more challenging. Whilst the preferential emplacement of intrusive rocks in Triassic strata deeper than reservoir targets is primarily responsible for the paucity of well penetrations, our findings of extensive alteration of igneous rocks in the NCB suggests that additional wells may intersect as yet unrecognised intrusive or extrusive sequences.

The Upper Cretaceous Paaratte Formation, Otway Basin, Austra-lia, is a deltaic reservoir-seal succession and currently the target for field-scale CO2 injection research experiments of the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) (now CO2CRC Ltd.) Otway Project. A relatively homogeneous ,s,7-m-thick injection interval was identified for stage 2 CO2 injec-tion experiments by analysis of wire-line and core log data. Core from above, below, and through the injection zone was sampled to quantify the effects of CO2 storage on physical and chemical heter-ogeneities to determine storage efficiency. The injection interval consists of two distinct yet related facies associations of a marine tract of an upper-deltaic, depo-sitional environment. They exhibit broadly similar bulk petro-physical reservoir properties, though their mineralogy and fine-scale sedimentary fabrics differ. A dolomitic horizon above the reservoir constitutes an intraformational barrier. Early diagenetic alterations (ca. 80 Ma) occurred within dis-tributary delta channel and mouth-bar sandstones. These altera-tions include formation of early authigenic clays that inhibited quartz overgrowth development while simultaneously preserving intergranular porosity. Primary dolomitic cement was precipitated from anoxic organic fluids passing through proximal, mouth-bar sandstones, along with processes such as quartz dissolution and minor kaolin precipitation until maximum burial (ca. 40 Ma). Mineralogical markers con-strained the position (proximal-to-distal and lateral) within the deltaic depositional tract, and low-resolution sedimentation rates derived from palynological dating provided information to esti-mate the spatial scale of delta facies. Clarification of the lithologi-cal heterogeneity within the injection zone has helped to determine CO2 storage efficiency by establishing an in-depth assessment of sequence stratigraphic and depositional facies architecture.

Generative Adversarial Networks (GAN) have shown great potential in not only producing acceptable realizations of geologically complex models but also successfully reparametrizing them. Training GANs is quite challenging. One such challenge is mode collapse. When generating realizations of spatial property, mode collapse causes reduction in variability, compared to the input training dataset, and thus, the realizations become spatially biased at specific locations. To address this issue, we developed a new GAN architecture where a regularization term is introduced to maintain the variability and reduce mode collapse. This is achieved by using a probability map to evaluate variability and spatial bias of generated realizations and modifying the GAN loss function to minimize this bias. We applied the new architecture to a binary channelized permeability distribution and compared the results with those generated by Deep Convolutional GAN (DCGAN) and Wasserstein GAN with gradient penalty (WGAN-GP). Our results show that the proposed architecture significantly enhances variability and reduces the spatial bias induced by mode collapse, outperforming both DCGAN and WGAN-GP in the application of generating subsurface property distributions.

Australia contains rich natural gas resources, but many of Australia’s currently producing and undeveloped gas fields contain relatively high CO2 contents; if not captured and stored, the venting of co-produced CO2 could hinder efforts to meet Australia’s emission reduction targets. The most mature technology for isolating produced CO2 from the atmosphere is by containing it in deep sedimentary formations (e.g. saline aquifers or depleted oil and gas reservoirs). The effectiveness of this approach is dependent on factors such as reservoir capacity, the presence of low-permeability seals that physically impede vertical migration of injected CO2, the chemical reactivity of both reservoir and seal minerals, the risk for leakage, and a gas-entrapping structure. An alternative and attractive mechanism for permanent storage of CO2 is geochemical or mineral trapping, which involves long-term reactions of CO2 with host rocks and the formation of stable carbonate minerals that fill the porosity of the host rock reservoir. Natural mineral carbonation is most efficient in mafic and ultramafic igneous rocks, due to their high reactivity with CO2. Here we review the outcomes from a series of recent pilot projects in Iceland and the United States that have demonstrated high potential for rapid, permanent storage of CO2 in basalt reservoirs, and explore the practicalities of geochemical trapping of CO2 in deeply buried basaltic volcanoes and lava fields, which are found in many basins along the southern (e.g. Gippsland Basin) and northwestern (e.g. Browse Basin) Australian margins, often in close proximity to natural gas fields with high CO2 content.