• Outcrop studies of fracture distribution in basaltic lava flows. • Positive correlation between lava flow thickness and fracture spacing. • Fracture orientation is scale invariable. • Fluids are expected to move in the same direction as the large-scale lineaments. • Fractures have a significant effect on the permeability of basaltic lava flows. Mafic lava flows have significant potential as fluid reservoirs, particularly for CO 2 ; however, their highly heterogeneous nature results in variable storage capacity across different locations. A crucial parameter for assessing reservoir potential is injectivity, which is primarily controlled by porosity and permeability. Porosity and permeability in lava flows, typically in the form of vesicles, are high at the lava flow top and base, while the flow core tends to have low permeability. Additionally, secondary fracturing of lava flow units may significantly influence both injectivity and overall storage capacity. Despite the potential positive impact on reservoir properties, there has been a lack of detailed descriptions and quantifications regarding fractures in basalts. Our field-based study presents an area onshore the Faroe Islands, which serves as an analogue for the offshore North Atlantic Igneous Province. We have mapped the spatial distribution of lineaments and fracture network characteristics using digital elevation and outcrop models ranging from km-scale to cm-scale. Permeability was calculated using the software FracPaQ to evaluate the influence of fractures on reservoir potential. We found that (1) fracture spacing increases with lava flow thickness, (2) fractures add significant secondary permeability, and (3) both km-scale and cm-scale fractures exhibit similar east-west preferred orientation, implying a preferential fluid flow in the same east-west orientation. Our study provides vital field evidence of vertical and horizontal fracture distributions in lava flows, forming a foundational basis for initial site characterisation of future CO 2 reservoirs, and highlighting the importance of including fractures in the characterisation of volcanic reservoirs.
Johannesen et al. (Sun,) studied this question.