Marija Plahter Rosenqvist

• Rosenqvist, Marija Plahter; Dunkel, Kristina; Nogueira, Liebert Parreiras; Planke, Sverre; Polteau, Stephane & Ardit, M. [Vis alle 8 forfattere av denne artikkelen] (2026). Natural CO<inf>2</inf>sequestration: mechanisms and conditions of carbonate precipitation in basalt. Geochimica et Cosmochimica Acta. ISSN 0016-7037. 427, s. 381–402. doi: 10.1016/j.gca.2026.07.013. Fulltekst i vitenarkiv
• Polteau, Stéphane; Smalley, P. Craig; Devegowda, Vani N.; Johansen, Ingar; Millett, John & Rosenqvist, Marija Plahter [Vis alle 8 forfattere av denne artikkelen] (2026). Well-connected basalt sequences as potential reservoirs for large-scale carbon sequestration revealed by strontium isotopes. Communications Earth & Environment. 7(1). doi: 10.1038/s43247-025-03020-7. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Permanent storage of gigatons of carbon in basalt requires thick, uncompartmentalized sequences that allow lateral dissipation of CO 2 away from injection sites. Here we assess the presence of flow barriers by evaluating the variations in 87 Sr/ 86 Sr patterns in pore water, a method used extensively in sedimentary successions. Present-day pore water 87 Sr/ 86 Sr was measured from residual salts in core samples, while past water compositions were reconstructed from carbonate cements of different ages. We reveal smooth and uninterrupted trends in strontium isotopes through a 100 m thick basalt section indicating a common fluid reservoir unaffected by low-permeability massive lava flow interiors. The data further indicate that unconsolidated overburden sediments act as a good seal preventing seawater to mix with in situ pore water, and buoyant supercritical CO 2 to leak. Finally, basaltic sequences form viable targets for CO 2 storage and suggests that fractures may bypass low-permeability units to create a well-connected reservoir system.

• Betlem, Peter; Rosenqvist, Marija Plahter; Millett, John; Griffiths, Luke; Filina, Irina & Park, Joonsang [Vis alle 9 forfattere av denne artikkelen] (2025). Fluid flow behaviour in vesicular basalt samples from the Skoll High, Vøring Margin. Geomechanics and Geophysics for Geo-Energy and Geo-Resources. ISSN 2363-8419. 12(1). doi: 10.1007/s40948-025-01080-9. Fulltekst i vitenarkiv Vis sammendrag

  Abstract This study presents the fluid flow testing results of 32 lava flow samples recovered from IODP Sites U1571/U1572 (145–315 mbsf) on the Skoll High, Vøring Margin. Few past studies have investigated the mid-Norwegian margin’s basalt reservoir and flow properties. Even fewer implement subsurface-like conditions to explore in-situ fluid flow and the possible response to changing pore fluids during injection. These aspects are critical for large-scale carbon sequestration. In this study, hydraulic properties including porosity and permeability were measured at ambient conditions for all samples along with multi-stress, multi-fluid core flooding experiments on a representative sample enclosed in an X-ray µCT scanner. Petrographic observations reveal varying degrees of alteration with secondary clays, including smectite, commonly lining pores and vesicles. He-porosities (4.2–45.6%) fall mostly below the theoretical percolation threshold of ~ 30% for randomly distributed spherical pores. Klinkenberg-corrected nitrogen-gas permeability (0.0038–361.9 mD) shows weak correlation to porosity and no apparent depth dependence. Further, brine permeability is four orders of magnitude lower than gas permeability, with no notable flow reduction during injection of CO 2 . Rather than being stress-dependent, we argue that brine-induced swelling significantly reduced the accessibility of microstructural elements to fluids. The findings urge caution when using literature-reported, ambient gas measurements for basalts with similar levels of alteration as they may not accurately reflect in-situ fluid flow properties. Low matrix permeability of the moderately to highly altered vesicular basalts and prevalence of swelling clays may, without major contributions from fractures, limit the injectivity potential into the basaltic lava flows on the Skoll High, Vøring Margin.

• Millett, John M.; Rossetti, Lucas; Bischoff, Alan; Rossetti, Marcos; Rosenqvist, Marija Plahter & Avseth, Per Åge [Vis alle 11 forfattere av denne artikkelen] (2024). Lava flow-hosted reservoirs: a review. Geological Society Special Publication. ISSN 0305-8719. 547(1), s. 357–387. doi: 10.1144/SP547-2023-102. Fulltekst i vitenarkiv Vis sammendrag

  Lava flows form important fluid reservoirs and have been extensively exploited for water aquifers, geothermal energy, hydrocarbon production and, more recently, for carbon storage. Effusive subaerial mafic to intermediate lava flows account for vast rock volumes globally, and form reservoirs with properties dictated by well-known lava flow facies ranging from pāhoehoe through several transitional forms to ‘a’ā lava. These variations in flow type lead to critical differences in the pore structure, distribution, connectivity, strength and fracturing of individual lava flows, which, alongside lava flow package architectures, determine primary reservoir potential. Lava flow margins with vesicular, fracture and often autobreccia-hosted pore structures can have porosities commonly exceeding 40% and matrix permeabilities over 10−11 m2 (>10 D) separated by much lower porosity and permeability flow interiors. Secondary post-emplacement physicochemical changes related to fracturing, meteoric, diagenetic and hydrothermal alteration can significantly modify reservoir potential through a complex interplay of mineral transformation, pore-clogging secondary minerals and dissolution, which must be carefully characterized and assessed during exploration and appraisal. Within this contribution, a review of selected global lava flow-hosted reservoir occurrences is presented, followed by a discussion of the factors that influence lava flow reservoir potential.

• Rosenqvist, Marija Plahter; Millett, John M.; Planke, Sverre; Johannesen, Rakul Maria Ingunardóttir; Passey, Simon R. & Sørensen, Erik V. [Vis alle 8 forfattere av denne artikkelen] (2024). The architecture of basalt reservoirs in the North Atlantic Igneous Province with implications for basalt carbon sequestration. Geological Society Special Publication. ISSN 0305-8719. 547(1), s. 389–413. doi: 10.1144/SP547-2023-96. Fulltekst i vitenarkiv Vis sammendrag

  Offshore CO2 sequestration in basaltic formations of the North Atlantic Igneous Province may allow permanent storage of large volumes of CO2 through rapid carbonate mineralization. Characterizing the internal architecture of such reservoirs is key to assessing the storage potential. In this study, six photogrammetry models and three boreholes on the Faroe Islands have been used to characterize the internal lava sequence architectures as a direct analogue to potential offshore North Atlantic Igneous Province storage sites. The studied formations are dominated by c. 5 to 50 m thick simple and compound lava flows, with drill core observations documenting a transition from pāhoehoe moving towards ‘a’ā lava flow types interbedded with thin (<5 m thick) volcaniclastic rock units. The identification of flow margin breccias is potentially important as these units form excellent reservoirs in several other localities globally. Stacked, thick simple flows may present sealing units associated with dense flow interiors. Connected porous and permeable lava flow crusts present potential reservoirs; however, the degree of secondary mineralization and alteration can alter initially good reservoir units to impermeable barriers for fluid flow. Large-scale reservoir volumes may be present mainly within both vesicular, fractured pāhoehoe and brecciated flow margins of transitional simple lava flows.

• Rosenqvist, Marija Plahter; Meakins, Max William John; Planke, Sverre; Millett, John M.; Kjøll, Hans Jørgen & Voigt, Martin J. [Vis alle 7 forfattere av denne artikkelen] (2023). Reservoir properties and reactivity of the Faroe Islands Basalt Group: Investigating the potential for CO<inf>2</inf> storage in the North Atlantic Igneous Province. International Journal of Greenhouse Gas Control. ISSN 1750-5836. 123. doi: 10.1016/j.ijggc.2023.103838. Fulltekst i vitenarkiv Vis sammendrag

  Offshore injection of CO2 into volcanic sequences of the North Atlantic Igneous Province may present a large-scale, permanent storage option through carbonate mineralization. To investigate this potential, onshore studies of reservoir properties and reactivity of the subaerially erupted Faroe Islands Basalt Group have been conducted. Outcrop and borehole samples reveal that the lava flow crusts commonly contain vesicles that have been filled with secondary minerals due to hydrothermal fluid circulation, however, unmineralized and highly porous layers do occur. Bulk density measurements, micro-computed tomography (µ-CT) image analysis, and microscope studies of samples from onshore boreholes give present-day porosities ranging from 0.5% to 36.2% in the volcanic sequences. The unmineralized brecciated lava flow crusts contain the largest estimated porosity and simulated absolute permeability (reaching up to 10−12 m2). µ-CT studies of the mineralized, brecciated flow crusts indicate initial porosities reaching up to 45%, before clogging. Kinetic experiments of rock dissolution show that the reactivity of the basalt and volcaniclastic sediments depends on the alteration state with more altered basalt being less reactive. However, the presence of reactive, high porosity, and high permeability flow crusts prior to clogging indicate the existence of promising and very large CO2 reservoirs in less altered offshore sequences.

• Bellwald, Benjamin; Batchelor, Christine L.; Garcia, Aurora Machado; Barrett, Rachel; Rosenqvist, Marija Plahter & Planke, Sverre [Vis alle 9 forfattere av denne artikkelen] (2022). Contourites of the Northern North Sea, North Sea Fan, and Mid-Norwegian Margin, 83rd EAGE Annual Conference & Exhibition 2022. European Association of Geoscientists and Engineers (EAGE). ISSN 9789073834125. doi: 10.3997/2214-4609.202210247. Fulltekst i vitenarkiv Vis sammendrag

  Contourites contribute to the shaping and building of continental margins, and have an economic importance for the offshore-energy sector by acting both as reservoir and seal rock. Here we study the different contourites of the northern North Sea, North Sea Fan and mid-Norwegian margin formed in the Neogene and Quaternary, which are unconventional targets in the region. Based on extensive 3D reflection seismic data combined with borehole data, we suggest that fine-grained drifts form regionally large and thick accumulations, while relatively coarse-grained sediment deposits develop locally. Sourced from the East Shetland Platform and the northern North Sea, the contour currents transported the available sediments northwards, where the regional physiography enhanced the ocean currents and hosted contouritic deposition. The Pliocene to early-Quaternary contourites are characterized by continuously laminated sediments, and most likely contain gas-charged sands in selected locations. Trapped by megaslide escarpments, the late-Quaternary contourites have a transparent facies, most likely representing fine-grained muds. The contourites to the north of the North Sea Fan are further sealed by a bottom-simulating reflection, indicating the presence of a gas-hydrate barrier. Contourites are thus a promising unconventional play model in the region, but caution is required when interpreting the sedimentologic characteristics of these deposits.

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• Polteau, Stephane; Smalley, P. Craig; Devegowda, Vani; Millett, John; Rosenqvist, Marija Plahter & Abdelmalak, Mohamed Mansour [Vis alle 8 forfattere av denne artikkelen] (2026). Well-connected basalt sequences as potential reservoirs for large-scale carbon sequestration revealed by strontium isotopes. doi: https:/www.egu26.eu/. Fulltekst i vitenarkiv Vis sammendrag

  Basalt complexes can cover hundreds to thousands of km2 and be several km thick; with an estimated global capacity of 40 Tt for carbon storage, they represent a solution for the large-scale injection of CO2 to reach the 2050 emission targets. However, the hydraulic conductivity of basalt sequences is difficult to predict because it has never been the focus in basalt research. In this contribution, we evaluate for the first time the vertical fluid connectivity of a basalt sequence using the Sr isotope composition of pore waters, sampled using the strontium residual salt analysis (SrRSA) method. Thirty seven samples were collected in the U1571A borehole (IODP Expedition 396 on the Skoll High, offshore Mid-Norway). Sampling of the well targeted the most representative lithologies in the core, and hence included vesicular and tight basalt. The SrRSA method measures the 87Sr/86Sr ratio in the salt residue that precipitated in the pores of core samples after the pore water evaporated, and the value measured in the laboratory should accurately reflect that of the in situ pore water. However, since the well was drilled using seawater with barite and sepiolite additives, each sample was washed in de-ionized water to reduce potential contamination. The samples were subsequently dried, crushed, the salts were leached, the leachate filtered, and the strontium analyzed using a MC-ICPS. The results show that the Sr concentrations are very low: 1-35 ppb in vesicular basalt samples and up to 2 ppb in tight basalt samples. The 87Sr/86Sr ratio of the vesicular basalt varies little away from the average value of 0.7085, while the values of tight basalts show more variability with an average of 0.7093. The SrRSA pattern vs. depth for the vesicular basalt samples is smooth, indicating limited contamination from drilling fluids, and further suggesting a good vertical connectivity. On the other hand, the pattern of the tight basalts is shifted towards heavier values similar to modern seawater, suggesting the SrRSA for these samples to be contaminated by the drilling fluids. In addition to the residual salts, we are currently analyzing the 87Sr/86Sr in carbonate vesicles and in basalt, which together represent the three main reservoirs of strontium in the samples. These additional results should help us constrain the source of the strontium in the pore system (i.e.: external, flowing or diffusing through the sequence). These results further show that the fluid connectivity of basalt sequences can be characterized using the SrRSA method by focusing the analyses on vesicular basalt samples. Finaly, this study will provide additional constrains to follow-up numerical models simulating the injectivity and capacity of intra- and inter-basalt reservoir units.

• Polteau, Stephane; Smalley, P. Craig; Devegowda, Vani; Johansen, Ingar; Millett, John & Rosenqvist, Marija Plahter [Vis alle 8 forfattere av denne artikkelen] (2026). Fluid connectivity and evolution of pore water in breakup basalt offshore mid-Norway with implications for CO2 storage. doi: https:/ngwm2026.fi/. Fulltekst i vitenarkiv Vis sammendrag

  Basalt complexes can cover thousands of square kilometres and be several kilometres thick. With an estimated global carbon storage capacity of 40 Tt they represent a possible solution to reach the 2050 emission targets. However, the injection of gigatons of CO2 into basaltic formations requires a thick reservoir system lacking barriers to lateral fluid flow for the CO2 to dissipate away from injection points. In this contribution, we evaluate for the first time the vertical fluid connectivity of a basalt sequence using the Sr isotope composition of pore waters, sampled using the strontium residual salt analysis (SrRSA) method. Thirty-seven samples were collected in the U1571A borehole (IODP Expedition 396 on the Skoll High, offshore mid-Norway). Sampling of the well targeted the most representative lithologies and hence included vesicular basalt and massive flow interiors. The SrRSA method measures the 87Sr/86Sr ratio in the salt residue that precipitated in the pores of core samples after the pore water evaporated, and the value measured in the laboratory should accurately reflect that of the in-situ pore water. In addition to present-day pore water from the residual salts, the 87Sr/86Sr of past water compositions were reconstructed from carbonate cements of different ages. We reveal smooth and uninterrupted trends in strontium isotopes through a 100 m thick basalt section indicating a common fluid reservoir unaffected by the low-permeability massive lava flow interiors. The data further indicate that the unconsolidated overburden sediments act as a good seal preventing seawater to mix with in situ porewater and may prevent CO2 leakage to the surface for buoyant supercritical CO2 injection scenarios. This study supports the premise that basaltic sequences form viable targets for CO2 storage and suggests that fractures may bypass low-permeability units to create a well-connected reservoir system. Finally, the 87Sr/86Sr method is demonstrably useful in basalts, and warrants being included routinely in evaluating thick basalt sequences for large-scale CO2 storage.

• Polteau, Stephane; Smalley, P. Craig; Devegowda, Vani N.; Johansen, Ingar; Millett, John & Rosenqvist, Marija Plahter [Vis alle 8 forfattere av denne artikkelen] (2026). Fluid connectivity and evolution of pore water in breakup basalt offshore mid-Norway with implications for CO2 storage. doi: https:/ngwm2026.fi/conference-programme. Fulltekst i vitenarkiv
• Millett, John; Planke, Sverre; Jolley, David; Berndt, Christian; Betlem, Peter & Rosenqvist, Marija Plahter [Vis alle 9 forfattere av denne artikkelen] (2025). Characterizing lava flows in offshore North Atlantic boreholes: a review with implications for basalt carbon storage. doi: 10.5194/egusphere-egu24-12383. Fulltekst i vitenarkiv Vis sammendrag

  Widespread and large-scale volcanism associated with the North Atlantic Igneous Province (NAIP) erupted during the Paleocene and Early Eocene and covers vast regions of the conjugate North Atlantic rifted margins. The majority of the preserved volume occurs in the offshore sequences of the continental shelves of Greenland, the Faroe Islands, UK, and Norway. These vast mafic igneous rock volumes in the offshore NAIP have been proposed as a potential area for permanent CO2 storage. However, a wide range of factors influence the suitability of mafic rock masses to act as fluid reservoirs including perhaps most importantly the volcanic facies (and associated pore structure, permeability, and distribution), along with alteration state, fracturing, and reactivity. In this contribution we focus on assessing the nature, distribution, and reservoir potential of sub-aerial lava flows from available borehole data across the NAIP. Lava flows are chosen for focus as they represent the most favorable reservoir target identified to date whilst also often constituting the dominant facies within much of the accessible NAIP offshore sequences.Over 50 offshore boreholes have penetrated the lava sequences of the NAIP including both industry and scientific boreholes drilled from the 1970&#8217;s onwards. Boreholes have encountered anything from a single lava flow through to several 10&#8217;s of lava flows in volcanic sequences reaching over 2 km in cumulative thickness in the deepest industry wells such as Brugdan (6104/21-1) and Lagavulin (217/15-1z) in the Faroese and UK sectors respectively.A summary of the lava flow nature (simple, compound, thickness, core-crust ratios) and physical property ranges (P-wave velocity, density, resistivity) of the penetrated lava flow sequences is presented utilizing available core, sidewall core, wireline and drill cuttings data to support the facies appraisal.Borehole data and the level of possible interpretation vary significantly depending on the age, purpose, and importantly the drilling operations of the individual boreholes. Some of the most robust and complete datasets are represented by modern hydrocarbon industry boreholes, for example those from the Rosebank Field in the UK sector, and cored boreholes from recent IODP Expedition 396 drilling Mid-Norway. Results from Expedition 396 are presented to highlight formation evaluation approaches for NAIP lava flow sequences including assessing the effects of different lava flow facies on Net to Gross calculations and the impact of alteration and secondary alteration on wireline log responses.This study presents important new constraints on the nature, variability, and distribution of NAIP lava flows from extensive available borehole ground truth data forming a foundational study for the development of reservoir appraisal techniques in the province going forward.

• Rosenqvist, Marija Plahter; Dunkel, Kristina; Planke, Sverre; Nogueira, Liebert Parreiras; Polteau, Stephane & Menegon, Luca (2025). Porosity structures and local compositional variations associated with natural CO2 sequestration in basalts offshore Norway. doi: 10.5194/egusphere-egu25-11073. Fulltekst i vitenarkiv Vis sammendrag

  Permanent storage of CO2 as carbonates in basalt deposits utilises natural weathering reactions between silicate minerals and carbonic water. By studying how CO2-enriched water has altered basalt in 43 samples from the V&#248;ring Margin, offshore Norway, we demonstrate the pathways and reactions of CO2 within a basalt reservoir.The pore spaces occupied by carbonates in the samples were studied through &#956;-CT (computer tomography) studies on three minicores and detailed microanalyses on 32 thin sections via scanning electron microscopy (SEM), electron microprobe analysis, and electron backscatter diffraction (EBSD). Single crystal X-ray diffraction on 15 samples determined the type of carbonate minerals and precipitation ages were determined for two samples through U/Pb-radiomeric dating. &#948;18O and &#948;13C-isotope analyses were used to determine the fluid origin in 11 samples.Three types of carbonate precipitation were characterised based on the pore structures they fill and the associated mineralogy. Type I carbonates, seen in 18 thin sections, fills vesicles, mainly along lava flow margins. SEM analyses showed that all vesicles are initially coated with a smectite layer which incorporates most of the Mg2+ and Fe2+ from dissolving silicate minerals. As pH and Ca concentrations increase, calcite precipitates in some vesicles. The secondary mineral assemblage and precipitation order fit with low-temperature alteration of basalt with pore water and atmospherically balanced CO2 levels (pH&#8805;8). Type II carbonates appear in seven thin sections as

• Lebedeva-Ivanova, Nina N.; Bünz, Stefan; Berndt, Christian; Millett, John; Betlem, Peter & Zastrozhnov, Dmitry [Vis alle 9 forfattere av denne artikkelen] (2025). High-resolution 2D and 3D seismic imaging and core-log-seismic integration of seaward dipping reflectors on the Vøring volcanic rifted margin. doi: 10.5194/egusphere-egu25-12935. Fulltekst i vitenarkiv Vis sammendrag

  Offshore basalt flow sequences represent potential permanent CO2 sequestration sites along volcanic rifted margins. The International Ocean Discovery Program (IODP) Expedition 396 drilled six basement sites on the V&#248;ring volcanic margin in 2021, recovering more than 350 m of basaltic basement cores and 15 m of granite cores. The cores have been extensively analyzed following the IODP shipboard procedures (e.g., velocity, density, porosity, and magnetic susceptibility measurements). In addition, shore-based petrographic, geochemical, CT scanning, and multi-fluid permeability and flow measurements (nitrogen, brine, liquid and gaseous CO2) have been performed to assess reservoir properties. A standard suite of conventional wireline logs along with borehole image (acoustic and resistivity) logs were acquired in four holes. High-resolution 2D and locally 3D seismic reflection data have been acquired across all sites during three surveys (2020, 2022, and 2024) using R/V Helmer Hansen. In total, four HR3D P-Cable cubes with a total areal extent of 62 km2 and c. 2700 km of HR2D data have been collected. The seismic data are interpreted using the concepts of seismic volcanostratigraphy and igneous seismic geomorphology combined with conventional horizon interpretation and core-log-seismic integration. On the Skoll High, the igneous seismic geomorphology of the Top Basalt horizon reveals two distinct domains: a pitted surface in the west, and a faulted surface in the east. Cross-cutting faults and fracture systems are well imaged in borehole data and the 3D seismic data. Borehole data show that the Inner Seaward Dipping Reflectors (SDR) were emplaced in subaerial and coastal environments, including vesicular flow tops and deposition of inter-basalt volcaniclastic sedimentary horizons. Vesicles are observed to be both open or filled with carbonates and clay minerals within different layers, however, laboratory measured matrix permeability of mini-core plugs is typically low and in the milli to micro-darcy range; brine permeability measurements are indicating even lower. Multiple scales of fracturing are identified within the cores and image logs, and Strontium residual salt analysis revealed that they have an important impact on permeability by enhancing fluid communication between flows. In conclusion, the integrated interpretation suggests that the V&#248;ring Margin basalt sequences may have reservoir potential in fractured intervals and flow tops, but reservoir-scale injection testing linked to fracture network parameterization is required for large-scale assessment.

• Polteau, Stephane; Smalley, Craig; Millett, John; Planke, Sverre; Rosenqvist, Marija Plahter & Devegowda, Vani [Vis alle 7 forfattere av denne artikkelen] (2025). Vertical fluid connectivity of basalt sequence assessed using strontium isotopes in pore waters. Fulltekst i vitenarkiv
• Polteau, Stephane; Craig, Smalley,; Millett, John; Planke, Sverre; Rosenqvist, Marija Plahter & V., Devegowda, [Vis alle 7 forfattere av denne artikkelen] (2025). The fluid connectivity of continental margin basalt sequences for CO2 storage revealed by strontium isotopes. Fulltekst i vitenarkiv
• Rosenqvist, Marija Plahter (2026). Multiscale flow pathways in basalts of the North Atlantic Igneous Province Implications for CO2 storage. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Global warming caused by greenhouse gas emissions from human activities is likely to negatively affect the climate, ecosystems, and human health unless action is taken. CO2 emissions are the largest contributor to the rising temperatures, and suggested solutions therefore include capturing the gas and storing it in the subsurface. Injecting captured CO2 into basalts offers many advantages, including safe storage as the gas reacts with the rock and mineralises into carbonate. The large global availability of basalts also suggests extremely large storage potentials. However, we still don’t fully understand how fluids move through basalt reservoirs and which pore structures CO2 can react with and precipitate carbonates. This PhD thesis offers a multiscale characterisation of potential fluid-flow pathways in basaltic sequences of the North Atlantic Igneous Province (NAIP) in the North-east Atlantic Ocean. Furthermore, the natural interactions between pore structures in the rock and CO2-driven reactions are also documented. On the Faroe Islands, we can study exposed flood basalt sequences of the NAIP. Our research suggests that lava flows comprising several internal flow lobes with relatively thick, porous crusts make for likely good reservoirs if the pores are not clogged by secondary mineralisation. In contrast, packages of thick lava flows with massive interiors may serve as seals or barriers to CO2 migration. While pores in the basalts exposed on the Faroe Islands are typically clogged by secondary minerals, offshore basalt sequences along the NAIP may contain less-altered, more porous and more permeable units. Samples collected from the Skoll High on the Vøring Margin, mid-Norwegian continental shelf, by IODP Expedition 396 were used to study natural alteration and cm- to nm-scale fluid-flow properties. Our research shows that these basalts were altered in contact with CO2-bearing fluids at low temperatures (<100˚C) and precipitated clay and carbonate. Carbonate occurs in macroscale pores and in the microporous volume of the basalt rock, where it has replaced primary basalt minerals. This emphasises that the large reactive potential of basalts does not depend solely on macroporosity. Our research also documents significant porosity below the resolution of normal core-scale micro-computed tomography (resolution ca. >50 μm), and we conclude that fluids may have migrated through localised pathways within this micro- or nanoscale pore network. Our results indicate ca. 3–11% additional porosity may be provided through micro- and nanoscale pore entryways in an engineered CO2 injection scenario. Overall, this thesis contributes to a better understanding of potential fluid migration pathways in flood basalt sequences in the NAIP, from the km-scale to the nm-scale, and how these relate to alteration history. The results presented in this thesis may be used for further injection and fluid-flow modelling studies and to evaluate the potential for CO2 storage in the NAIP.

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