The coastal region of southwest Saudi Arabia contains a thick sequence of Late Oligocene basalts in the Jizan Group, which accumulated along the continental rift that preceded the opening of the Red Sea. These basalts are targeted for the disposal of CO2 emitted from industrial sources by subsurface carbon mineralization processes. The disposal potential of the Jizan Group basalts depends on having adequate permeability along fracture networks capable of conducting injected fluids away from the wellbores. The basalts in the Jizan Group generally lack primary permeability due to hydrothermal alteration, but are cross-cut by a dense network of fractures. In this paper, we describe and interpret the structural geology of the area based on field and geophysical data, and characterize the fracture development in the Jizan Group. The Jizan Group in the area comprises a bimodal suite of 30–21 Ma volcanic and volcaniclastic rocks and lacustrine sediments that accumulated in a continental rift valley similar to the East African rift. It consists predominantly of basaltic lavas that were fed by dense swarms of sheeted basalt dikes intruded parallel to the rift axis. Structurally the area is composed of half grabens bounded from the west by antithetic normal faults, and from the east by a megaflexure. Fractures in the Jizan Group were characterized by ground and aerial digital photogrammetry of outcrops. Mean P21 fracture intensities from 12 scattered meter scale outcrops are in the range 5–54 m−1, which demonstrates that the Jizan Group is highly fractured. Fracture directions are multimodal. The dominant fracture trend is 140–160 N, which is parallel to the sheeted dike swarms and normal faults, and therefore parallel to the paleo-rift axis. Additional conjugate and orthogonal fracture sets are also recognized. The presence of pervasive fracture-based permeability in the Jizan Group will facilitate the injection and mineral carbonation of carbon dioxide in the mafic volcanic rocks in this region.

<p>This study aims to characterize fracture permeability in altered Oligocene-Early Miocene basalts of the Jizan Group, which accumulated in half grabens during the continental rift stage of Red Sea evolution. Unlike fresh basalts, the Jizan Group was affected by low temperature hydrothermal metamorphism, which plugged the original matrix porosity in vesicles, breccias, and interflow layers with alteration minerals. On the other hand, the basalts are pervasively shattered by open closely spaced fractures in several directions. Characterization of these fractures is essential to reducing the fracture permeability uncertainty for mineral carbonation by the dissolved CO2 process such as Carbfix.<br>Conventional measurements of fracture orientations and densities were initially taken at outcrops of the Jizan Group to characterize the fracture network. Photogrammetry of drone images covering larger areas were then used to create 3D models of the outcrops using Agisoft Metashape, which were analyzed for fracture geometries using Cloud Compare. The automated analysis of fracture orientations and densities compared well with conventional manual measurements. This gives confidence in semi-automated dronebased fracture characterization techniques in 3D, which are faster and less labor intensive, especially for characterization of large and difficult to reach outcrops.<br>Our fracture characterization will be used to construct 3D fracture permeability models of the Jizan Group for combined physical and chemical simulation of injection of dissolved CO2 from industrial sources into basalts. This will provide essential parameters to mitigate geological risks and to determine depth, spacing, and injection rates in CO2 disposal wells.</p>

The extensive and well-preserved lava fields, "harrats" in Arabic, of western Saudi Arabia stretch for 3000 km south to north and cover an area of more than 120.000 km 2 in total. The alkalic volcanism initiated at ca. 15 Ma has been more or less continuous since [1], with the youngest eruption recorded in 1256 A.D. next to the city of Medina. Recent dike emplacements in 2009 [2] and 1999 [3] indicate that future eruptions may be possible and further highlight the importance of understanding the nature of these volcanoes.The harrats show a broad variety in ages, but also a wide compositional spectrum from mildly alkaline basalt to rhyolite and alkaline basanite to phonolite [1], leading to varying eruptive styles and behaviors. This diverse volcanism can offer a unique insight to the evolution of intraplate volcanic fields. However, many magmatic processes in the upper crust are still poorly constrained which in turn may impede adequate assessment of eruption precursors and volcanic hazards in the area.We have collected an extensive sample suite from harrats of various ages, maturity stage, and composition, covering variations in chemistry and eruptive style from the younger volcanism in Saudi Arabia. This study presents new whole-rock, basaltic glass, and mineral geochemistry, as well as geochemical modelling results, to shed light on the development of intraplate volcanism over time, and to unravel processes such as magma stagnation and crustal underplating.

Underground hydrogen (H2) storage is a prominent technique for enabling H2-based economy via offering a large-scale storage medium. Recently, volcanic basaltic formations have been investigated as a potential medium for gas storage due to their thickness, vast extension, and potential volumetric capacity. Wettability is one of the essential parameters studied to understand the capillary-entrapment of the stored gas in porous media. Therefore, in this study, we evaluate the wettability of rock/H2/brine system of two different saudi basaltic rock samples by measuring the contact angles using relevant reservoir brine (10% NaCl) under storage conditions at temperature of 323K and varying pressures (3 to 28 MPa). The measurements were conducted using the modified sessile drop method and surface roughness was determined to ensure accurate results. The results showed relatively low variation with pressure. Basalt-1 with less Si-O-Si bonding demonstrated better sealing conditions for H2 storage than Basalt-2. Additionally, the pore throat radius has a proportional relationship with 𝑝𝑐𝑒 and ℎ𝑔𝑚𝑎𝑥. Smaller pore-size basaltic rocks are better for safe and secure storage, and a potential effictive capillary entrapment of H2. Introduction Governments and countries worldwide are adapting strict environmental regulations to reduce harmful anthropogenic emissions of greenhouse gases such as carbon dioxide (CO2), attributed mainly to the burning of fossil fuels (Hashemi et al., 2021; IEA, 2018). Alternatively, hydrogen (H2) emerges as a promising clean fuel to support decarbonization by converting energy production from fossil fuels into a more environmental-friendly form and supporting clean energy from renewable resources such as wind turbines and solar power (Pan et al., 2021). However, wide-scale implementation of an H2-based economy requires a medium of Giga to Tera scale storage capacity, which can be theoretically offered by geological formations such as saline aquifers, depleted oil and gas reservoirs, and salt caverns (Heinemann et al., 2021).

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