The Johansen formation is a candidate site for large-scale CO 2 storage offshore of the southwestern coast of Norway. An overview of the geology for the Johansen formation and neighboring geological formations is given, together with a discussion of issues for geological and geophysical modelling and integrated fluid flow modelling. We further describe corresponding simulation models. Major issues to consider are capacity estimation and processes that could potentially cause CO 2 to leak out of the Johansen formation and into the formations above. Currently, these issues can only be investigated through numerical simulation. We consider the effect of different boundary conditions, sensitivity with respect to vertical grid refinement and permeability/transmisibility data, and the effect of residual gas saturations, since these strongly affect the CO 2 -plume distribution. The geological study of the Johansen formation is performed based on available seismic and well data. Fluid simulations are performed using a commercial simulator capable of modelling CO 2 flow and transport by simple manipulation of input files and data. We provide details for the data and the model, with a particular focus on geology and geometry for the Johansen formation. The data set is made available for download online.
[1] The ultraslow spreading Knipovich Ridge shows axial topographic highs that are associated with offaxis linear arrays of seamounts that parallel the spreading direction. These linear arrays suggest that the segmentation has been stable for at least 7-8 m.y. Axial topographic highs are marked with distinct gravity anomalies, suggesting that they represent thicker crust and hence volcanic segment centers. Dredging on the northern Knipovich Ridge between 76°30 0 and 77°50 0 N shows that the axial and off-axial seamounts, and the deeper axial rift valley between the segment centers, are composed of volcanic rocks. The basalts are subdivided into high-, intermediate-, and low-FeO groups. Low-FeO basalts, with generally more enriched radiogenic isotope ratios and REE patterns, were only dredged midway between segment centers, whereas dredges close to the segment centers comprised high-and intermediate-FeO basalts. The variations in isotopes and REE patterns suggest that the mantle below the northern Knipovich Ridge is heterogeneous, and the along-axis variations can be explained by higher degrees of melting of this heterogeneous source close to segment centers. The high-and intermediate-FeO basalts define different MgO-FeO liquid lines of descents that may reflect differences in the crystallization pressures or the water contents of the magmas. Similar water contents of the high-and intermediate-FeO basalts suggest that the differences in FeO primarily are a pressure effect and that the intermediate-FeO group fractionated at higher pressure than the high-FeO group. The high-FeO basalts show both low-and high-pressure phenocryst assemblages, suggesting crystallization at high pressures (6-7 kbar) followed by shallow, lowpressure fractionation. On the basis of the new data we propose that magmas at this ultraslow spreading ridge fractionate at mantle depth, except at segment centers where magma productivity occasionally is high enough to sustain shallow level magma reservoirs.
Th e well-preserved extrusive sequence of the Solund-Stavfjord Ophiolite Complex (SSOC) in the West Norwegian Caledonides enables reconstruction of the uppermost oceanic crust that developed in a marginal basin. Basaltic sheet flows, pillow lavas and volcanic breccias are the main components of the extrusive sequence and show stratigraphic and structural evidence for a cyclic development. The first stage in a volcanic cycle is characterized by high extrusion rates yielding sheet flows, commonly with the thickest flow units at the base. Sequences of sheet flows can be correlated laterally for at least 6.5 km. Pillow lavas succeed the sheet flows later in a volcanic cycle with progressively smaller pillows forming at decreasing extrusion rates. Volcanic breccias occur towards the end of a volcanic cycle, but may also occur at lower stratigraphic levels. They are made generally of pillow breccias and hyaloclastites. The extrusive sequence of the SSOC oceanic crust was constructed through seven volcanic cycles that resulted in stratigraphic units with thicknesses ranging from 40 to 225 m. This architecture is comparable to sequences in in situ oceanic crust developed along slow-to intermediate-spreading ridges.
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