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Conceptual 3D representation of the identified LSUs and SUs and related fracture patterns, showing their possible 
influence on fluidflow migration. Stereonets (poles to planes, equal-area, lower hemisphere, 1% area contour) sum-
marise all the collected fracture data for each LSU and SU (colour code as for each LSU).From Ogata et al. (2014).

Schematic cartoon summarizing the 
inferred tectonic evolution phases 
responsible for the development of 
the observed structural discontinu-
ities in the Upper Triassic–Jurassic 
succession of Central Spitsbergen.

Fracture systems in the subsurface of the Longyearbyen CO2 Lab





        - Ogata et al. 2014

This study analyzes systematic fracture patterns within the Mesozoic succession of central Spitsbergen to charac-
terize the reservoir-caprock system explored for geological CO2 storage by the Longyearbyen CO2 Lab project. We 
carried out and integrated structural and stratigraphic analyses of outcrop and borehole data, subdividing the in-
vestigated sedimentary interval into five litho-structural units (LSUs): A) massive to laminated shales characterized 
by predominant low-angle fractures, B) heterogeneous, fine-grained intervals with both low- and high-angled frac-
tures, C) massive, coarse-grained intervals dominated by high-angle fractures, D) igneous intrusions characterized 
by syn- and post-emplacement fractures and veins, and E) carbonate beds dominated by high-angle fractures and 
veins. LSUs are identified on the basis of their fracture associations, lithologies and dominant sedimentary facies, 
and thus implicitly include information on the primary porosity and permeability. In general two main, sub-vertical 
extensional fracture sets are recognized:  (i) a principal fracture set trending approximately NE–SW to ENE–WSW 
(J1) and (ii) a subordinate fracture set trending about NNW–SSE to NNE–SSW (J2). Conjugate shear fractures (S1) 
are trending roughly NE–SW and NW–SE in the coarser-grained and more cemented lithologies. A low-angle fracture 
set (S2) striking approximately NNW–SSE to WNW–ESE is also observed. Variations in fracture patterns suggest 
that the LSUs are pseudo-mechanical units, which are able to steer, baffle or impede horizontal and vertical fluid 
migration due to their primary matrix (i.e., grain size and mineralogy) and fracture network properties. At a larger 
scale, the resultant stratigraphic and structural architecture controls the hydrogeological regime of the investigat-
ed reservoir-caprock succession, providing: 1) fracture-related secondary porosity and permeability, 2) enhanced 
micro-fracturing matrix connectivity, and 3) preferential directions of subsurface fluid flow pathways. We conclude 
that, given the present-day stress field, subsurface fluid flow would be augmented in an ENE–WSW direction, with 
possible additional NE–SW communication.