Work

Fault permeability in carbonate-marl multilayers: implications for faulted CO2 storage site assessment

Year: 2025

Type: article

Abstract: This study investigates the petrophysical and structural properties of faulted marl-carbonate multilayers to better understand their potential as barriers or conduits to fluid migration. The research focuses on the potential Smeaheia CO2 storage site in the Norwegian North Sea, complemented by analogues from the Gubbio and Mt. Gorzano fault zones in Italy. Utilizing petrophysical measurements, optical microscopy, and structural analysis, we evaluate the deformation mechanisms and their impact on fault rock permeability. Our findings reveal significant variability in fault rock permeability, governed by lithological heterogeneity. Marl-rich fault rocks exhibit permeability that is lower in comparison to that measured within the undeformed host rock, due to clay-rich pressure solution seams and veining, enhancing their sealing capacity. Conversely, carbonate-rich units display increased permeability, associated with brecciation, cataclasis, and open fracturing, which may compromise sealing integrity. Carbonate-marl mixed scenarios show intense brecciation, cementation, veining and pressure solution that results in an average permeability that is similar to that measured within the undeformed host rock, despite the variety of deformation microstructures. At Smeaheia, the dominance of marl within the overburden suggests a potential for effective containment when juxtaposed against the reservoir unit. Transmissibility analyses indicate scenarios where fault cores may act as barriers or pathways for fluids, depending on the dominance of marl or carbonate layers. By refining our understanding of fault-sealing mechanisms in carbonate-marl multilayers, these insights are useful for site selection and risk assessment for CO2 storage where these lithologies are common in the subsurface, contributing to global efforts in carbon management.

Source: International journal of greenhouse gas control

DOI: 10.1016/j.ijggc.2025.104427

Authors: E.A.H. Michie, F. Agosta, L. Smeraglia, S.L. Allshorn