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Introduction

The ultimate aim of the Longyearbyen CO2 Lab project is to develop an onshore, pilot-scale (c. 60,000 of CO2 tons yr-1; Lokalstyre, 2011) site for geological sequestration of CO2 in a tight, siliciclastic unit located at 700–1000 m depth on Spitsbergen, Svalbard (Braathen et al., 2012; Fig. 1). In the 2007–2013 pilot project, a total of eight slimline boreholes have been drilled and fully cored at two drill sites, four of which penetrate the targeted reservoir

sandstone successions of Late Triassic to Mid Jurassic age (De Geerdalen and Knorringfjellet formations; Figs. 2, 3). The reservoir conforms to a gentle regional monocline tilting the stratification toward the SW and thus reaches the surface c. 15 km NE of the drill sites, allowing direct observations of the exhumed reservoir-caprock section.

At the drill sites (see Figs. 2A, 3), sub-hydrostatic pressure recorded in the boreholes Dh4 (at 853 m) and Dh7A (at 655 m) shows that the near-well reservoir is contained

Ogata, K., Senger, K., Braathen, A., Tveranger, J. & Olaussen, S.: Fracture systems and mesoscale structural patterns in the siliciclastic Mesozoic reservoir-caprock succession of the Longyearbyen CO2 Lab project: Implications for geological CO2 sequestration in Central Spitsbergen, Svalbard. Norwegian Journal of Geology, Vol 94, pp. 121–154. Trondheim 2014, ISSN 029-196X.

In unconventional, naturally fractured reservoirs, networks of structural discontinuities largely control fluid flow. In this study, we mapped and analysed systematic fracture patterns within the Mesozoic succession of Central Spitsbergen to characterise 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 investigated sedimentary interval into five litho-structural units (LSUs): (A) massive to laminated shales characteri-sed by predominant low-angle fractures, (B) heterogeneous, fine-grained intervals with both low- and high-angled fractures, (C) massive, coarse-grained intervals dominated by high-angle fractures, (D) igneous intrusions characterised 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 domi-nant sedimentary facies, and thus implicitly include information on the primary porosity and permeability. In general, two main, subvertical exten-sional fracture sets are recognised: (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 investigated reservoir-caprock succession, providing: (1) fracture-related secondary porosity and permeability, (2) enhanced microfracturing 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 trend, with possible additional NE–SW com-munication.

Kei Ogata, Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway. Present address: Dipartimento di Fisica e Scienze della Terra ‘Macedonio Melloni’, Università degli Studi di Parma, Campus Universitario – Parco Area delle Scienze 157/A, I–43124 Parma, Italy. Kim Senger, Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway. Centre for Integra-ted Petroleum Research (Uni CIPR), Uni Research, Allégaten 41, 5007 Bergen, Norway. Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway. Alvar Braathen, Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway. Present address: Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern 0316 Oslo, Norway. Jan Tveranger, Centre for Integrated Petroleum Research (Uni CIPR), Uni Research, Allégaten 41, 5007 Bergen, Norway. Snorre Olaussen, Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway.

E-mail corresponding author (Kei Ogata): [email protected]; [email protected]

Published December 24. 2014.

Kei Ogata, Kim Senger, Alvar Braathen, Jan Tveranger & Snorre Olaussen

Fracture systems and mesoscale structural patterns in the siliciclastic Mesozoic reservoir-caprock succession of the Longyearbyen CO2 Lab project: Implications for geological CO2 sequestration in Central Spitsbergen, Svalbard

NORWEGIAN JOURNAL OF GEOLOGY Fracture systems and structural patterns in the reservoir-caprock succession, Longyearbyen CO2 Lab

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within an isolated pressure cell, suggesting lateral compartmentalisation by structural or stratigraphic seals (Braathen et al. 2012; Ogata et al., 2012). Matrix permeability of less than 2 mD was measured on drillcore plugs, with porosity varying from 6 to 18% (Braathen et al., 2012; Farokhpoor et al., 2013; Mørk, 2013). The bulk of the present matrix porosity consists of non-connected pores (i.e., secondary porosity) with an effective porosity likely to be below 10% (Mørk, 2013). Despite this, water injection tests show an average flow capacity of 45 mD m-1 in the lowermost part of the reservoir (i.e., 870–970 m), thought to be primarily due to the natural

fracture network (Ogata et al., 2012). The upper part of the reservoir, from 672–700 m in Dh4, exhibits better petrophysical parameters with a matrix permeability of up to 2 mD (Braathen et al., 2012), and recent water injection tests suggest a radial matrix-dominated response in this part of the succession (Larsen, 2012; Senger et al., 2013a).

The target formations are vertically sandwiched between two main detachment zones (i.e., subhorizontal décollement zones) related to the development of the Palaeogene West Spitsbergen fold-and-thrust belt (Bergh et al., 1997; Braathen et al., 1999). Subsequent

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Figure 1. Simplified geological map showing the main structural features of central Spitsbergen, with location of the Longyearbyen CO2 Lab project site (black box represents the area of the map shown in Fig. 2). A regional cross-section and explanation are also provided. Abbreviations: BFZ – Billefjorden Fault Zone; LFZ – Lomfjorden Fault Zone; D – Devonian; Ca – Carboniferous; Cp – Permian; Tr – Triassic; JC – Jurassic–Cretaceous. Modified after Ogata et al. (2012), with schematic cross-section based on Bergh et al. (1997).

123NORWEGIAN JOURNAL OF GEOLOGY Fracture systems and structural patterns in the reservoir-caprock succession, Longyearbyen CO2 Lab

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Figure 2. (A) Geological map of the area between Sassendalen and Longyearbyen, with explanations and cross-section. Location of the drill sites 1 (Dh1 and Dh2) and 2 (Dh3 to Dh8) are labelled (redrawn and modified from Major et al., 2001). (B) Close-up of A showing the Deltaneset–Hat-ten fieldwork area with location of the stratigraphic section depicted in D. Formation names are labeled. (C) Panoramic view of the Deltaneset–Hatten area looking approximately toward the south (location shown in (A)). Formation names, main structures and toponyms are labelled. (D) Composite stratigraphic log of the upper De Geerdalen and Knorringfjellet formations. Palaeocurrent data from different sedimentary structures collected throughout the sandstone bodies recognised in the sections are represented in rose diagrams (red lines represent the relative reference bed-ding).

124 K. Ogata et al.

tectonic-sedimentary burial in a foreland basin setting down to c. 4.5 km during the Eocene caused mechanical compaction and quartz cementation, reducing the matrix permeability considerably (e.g., Michelsen & Khorasani, 1991; Mørk, 2013).

Uncertain parameters such as the presence of an unknown amount of natural gas in the cap-rock shale (i.e., top seal) immediately above the reservoir unit has added an operational challenge to evaluate the storage potential (see Senger et al., 2013a). Furthermore, the sub-hydrostatic pressure regime, the emplacement of igneous intrusions and possible sub-seismic steep extensional faults and low-angle thrusts introduce additional complexities for the reservoir description, all with consequences for reservoir modelling and subsequent flow simulations.

In this contribution, we present the structural characterisation of the natural fractures occurring in the reservoir-caprock section, integrating mesoscale, structural-stratigraphic analyses performed on both borehole and outcrop datasets. The derived semi-quantitative results are recommended for the reservoir modelling efforts, which are not directly addressed in this paper. Accordingly, the

processed data were directly used as input parameters in the development of a static geological model of the reservoir unit as presented by Senger et al. (2013a).

Geological outlineThe Svalbard archipelago is part of the emergent, uplifted, northwestern margin of the Barents Shelf. The uplifted strata yield information on a geological record of the (i) Caledonian Orogeny and older events, (ii) inferred Devonian crustal-scale extension followed by some contraction, (iii) localised Carboniferous rifting, (iv) relatively stable, long-term platform sedimentation from Permian to Mesozoic, (v) intrusion of mafic dykes and sills in the Late Cretaceous, and eventually (vi) establishment of a Cenozoic transform plate margin (e.g., Harland, 1997). Due to the opening of the North Atlantic, a dextral transform fault zone known as De Geer Zone (i.e., palaeo Hornsund Fault Zone) developed between Svalbard and East Greenland during the Palaeogene (Eldholm et al., 1987; Braathen et al., 1995; Leever et al., 2011). The consequent oblique convergence or transpression led to the development of the West Spitsbergen fold-and-thrust

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Figure 3. Correlation panel of the drilled wells (Longyearbyen CO2 Lab) showing the main lithology types and the interpreted depositional envi-ronments. Location of the igneous intrusions, marker beds, and water injection test (step-rate, shut-in and leak-off tests; LOTs) intervals are also labelled.


Hekkingen Fm., Draupne Fm.) represent a major source rock and the primary top seal of many oil and gas fields on the Norwegian continental shelf (Spencer et al., 2008).

The drilled succession of Adventdalen (see Fig. 3) continues with a 120 m-thick overburden consisting of an approximately 60 m-thick fluvial to deltaic unit, the Barremian Helvetiafjellet Fm. (Midtkandal et al., 2007). Above this there is the 60 m-thick, Aptian to Albian, mixed sandstone-shale unit of shallow-marine to inner shelf sediments belonging to the Carolinefjellet Fm. (Mørk et al., 1999). The uppermost 60 m-thick interval is made up of Quaternary and Holocene fluvial sand/gravel and marine clay. The average thickness of the permafrost is estimated to approximately 100–150 m in the valley floors (Humlum et al., 2003), but is expected to be thinning towards the coast and disappears beneath the marine realm (Fig. 3).

MethodsDetailed (1:10 scale) structural logging was undertaken on a database of nearly 4500 m of drillcores, gathered by the Longyearbyen CO2 Lab during eight full-coring drilling campaigns (see Fig. 3). High-resolution logging was performed on the drillcores from the Dh4, Dh5R and Dh7A boreholes (c. 380 m in total) to describe the physical characteristics and frequency distribution of natural discontinuities (as defined by Schultz & Fossen, 2008), primarily distinguishing between closed (e.g., veins) and open (e.g., fractures) ones.

Complementary fieldwork was conducted on the target reservoir-caprock analogues on the outcrops exposed in the Deltaneset–Hatten locations (see Fig. 2), where scan-lines (i.e., line-intersection method; Singhal & Gupta, 2010) have been measured to provide horizontal fracture frequency plots along individual intervals. Stratigraphic logging (1:50 scale) was also carried out in order to correlate outcrop and borehole successions, and to organise fracture data in comparable litho-structural units (LSUs).

The characterisation of the encountered mesoscale fractures has been performed both in cores and in the field using the following standard parameters (Singhal & Gupta, 2010): (1) orientation (i.e., strike and dip); (2) stratigraphic position (i.e., middle point depth in cores); (3) spacing (i.e., vertical in cores, horizontal in outcrops); (4) length/persistence (i.e., cross-core vs. core-confined in cores, bed-confined vs. through-going in outcrop); (5) linear density/frequency (i.e., vertical in cores, horizontal in outcrops); (6) connectivity (e.g., characteristics of structural intersections); (7) surface asperity (i.e., character of the roughness/smoothness of the fracture walls); (8) wall coatings and infillings (e.g., sealed and/or healed fractures). Due to the high degree of decompaction in drillcores and the heavily altered

belt (WSFB) and the Palaeogene Central Spitsbergen Basin (CSB), a foredeep to wedge-top basin filled with mixed continental and marine clastics (Steel et al., 1985; Braathen et al., 1999; Helland-Hansen, 2010). The Paleocene–Eocene evolution of the WSFB generated a series of eastward-transported thrust sheets rooted in detachment zones along weak evaporite and shale intervals (Bergh et al., 1997). This compression and related folding likely contributed to the bulk of the brittle fracturing of the Spitsbergen sedimentary succession as explored in this study.

Summarising, the overall structural framework represents the combined product of the emplacement of mafic dyke and sill intrusions during the Early Cretaceous (Nejbert et al., 2011; Minakov et al., 2012; Corfu et al., 2013; Senger et al., 2014), uplift and unroofing in the north during the Cretaceous, development of the WSFB, uplift and unroofing in the west during the Oligocene, and eventually the rapid, isostatic-related, Quaternary unroofing and consequent decompaction of the whole sedimentary succession related to glaciations (Fig. 1).

Our study area is situated on the NE margin of the CSB (see Figs. 1, 2), whose boundaries align with the predominant NNW–SSE structural arrangement prevalent on Svalbard (Nøttvedt et al., 1993). The targeted siliciclastic storage unit belongs to the Upper Triassic to Middle Jurassic Kapp Toscana Group (Figs. 2, 3). It comprises the sandstone-dominated De Geerdalen Formation (Fm.) and the overlying Wilhelmøya Subgroup (i.e., Knorringfjellet Fm.; e.g., Worsley, 1973, 2008; Knarud, 1980; Mørk et al., 1982; Harland & Geddes, 1997; Mørk & Worsley, 2006; Mørk, 2013). The 270 m-thick section of De Geerdalen Fm., as drilled by the Longyearbyen CO2 Lab in Adventdalen, includes shales, siltstones and sandstones deposited in a near-shore, paralic (e.g., lagoonal to delta plain) environment with approximately 30% net sandstone (N/G ≈ 0.3). Palaeogeographic reconstructions based on seismic data and stratigraphic logging suggest an overall northwestward prograding deltaic system, mainly fed from the southeast (Mørk et al., 1982; Steel & Worsley, 1984; Riis et al., 2008; Glørstad-Clark et al., 2010; Anell et al., 2013), though southwestward progradation with a northeasterly source cannot be ruled out (Worsley, 2008). The overlying 20 m-thick, Norian to Bathonian Knorringfjellet Fm. is interpreted as a condensed, generally coarse-grained unit, representing a lag due to coastal reworking of deltaic sediments (Mørk et al., 1982; Harland & Geddes, 1997; Nagy et al., 2011). These units are capped by a 450 m-thick, shale-dominated succession belonging to the Middle to Upper Jurassic Agardhfjellet Fm. and the Lower Cretaceous Rurikfjellet Fm. (Dypvik et al., 1991), which represent the regional caprock and top seal of the targeted reservoir/storage unit. It is important to note that the dark mudstones of the Agardhfjellet Fm. are widespread across the Barents Sea, and its time-equivalent stratigraphic intervals (e.g.,

126 K. Ogata et al.

outcrop conditions (e.g., weathering, frost-thaw cycles, etc.), the relative aperture has not been considered as a reliable parameter that can be quantified accurately.

The identification of drilling-induced fractures (excluded from the final count) was performed by taking the following into account: (1) the overall appearance (e.g., fresh vs. weathered), (2) their continuity across the core (e.g., through-going vs. core-confined, point of origin/termination within vs. outside the core), (3) the occurrence of mineralisation/coatings, (4) anomalous trends (e.g., abrupt hooking toward pre-existing fractures and core boundaries), and (5) the matching/mismatching of the fracture sides (Kulander et al., 1977).

Optical televiewer data were acquired in two of the boreholes to characterise the caprock and the upper part of the reservoir: the interval 440–710 m TVD (i.e., true vertical depth) in the Dh4, and the intervals 138–359 m and 459–644 m TVD in Dh5R. Unfortunately, the narrow drillhole diameter (i.e., 46 mm in the lower part of Dh4) prevented data acquisition from deeper levels (Elvebakk, 2010). Since the retrieved drillcores were not oriented, information on azimuth and dip direction of bedding and fracture surfaces is only available from televiewer data. Nonetheless, such data have been used to compare and integrate the direct observations. The projected reservoir interval (i.e., storage unit) in the Knorringfjellet Fm. was fully logged using wireline tools recording gamma ray, resistivity, temperature, compressional velocity, as well as acoustic televiewer (Elvebakk, 2010). This allows correlation of the fractures registered by the televiewer and the manual count, indicating some agreement of the fracture intensity and orientation with the stratigraphic position (i.e., on the vertical axis), particularly within the uppermost part of the De Geerdalen Fm. (Ogata et al., 2012).

In outcrops, representative stratigraphic intervals within a range of lithologies were analysed in order to capture variations in the fracture character with respect to stratigraphy. The orientation of each fracture was measured, using either a geological compass or a GeoClino digital clinometer. Strike data were corrected for a magnetic declination of 6° east of true north. As for cores, individual natural fractures were classified based on their mesoscale characteristics (see above), including in this case observations on their outcrop-scale vertical continuity (bed-confined vs. through-going). Furthermore, stratigraphic logging (1:50 scale) was conducted throughout the Knorringfjellet Fm. and the upper third of the De Geerdalen Fm. in order to correlate the outcrop data with the borehole data (see Fig. 2). Wherever possible scan-lines were measured with two perpendicular orientations, approximately E–W along the coast and N–S along the valleys, to minimise the directional bias and maximise the recognition of the different fracture sets. A total of 105 scan-lines were collected, totalling about 1400 m with 7672 individual fracture measurements (Table 1).

ResultsIn the following sections we separate the description and analyses of the results from drillcore and outcrop data.

Borehole data

The cored reservoir interval exhibits relatively high frequencies of vertical and horizontal, sharp and tabular structural discontinuities, which have been primarily distinguished as closed and open, as shown in Figs. 4 & 5, respectively. These results, which represent a follow up of the preliminary work presented by Ogata et al. (2012), are listed below.

Closed structural discontinuitiesTabular and closed (i.e., sealed) discontinuities bearing evidence of shearing (e.g., millimetres- to centimetres-displaced and drag-folded laminae) are recognisable within coarser-grained lithologies. These features include hairline microfaults (mostly with normal movement), with a very fine-grained material infill, identifiable as pseudo-disaggregation deformation bands (Fossen et al., 2007; Fossen, 2010) showing a phyllosilicate core and displaying shiny, polished and slightly striated walls when split. The latter suggest secondary microfracturing along the walls of these bands, otherwise formed by granular flow. These disaggregation-deformation bands constitute up to 30% of counted discontinuities in fine- to medium- and coarse-grained sandstones (Fig. 4A–C). Mineralised fractures (mainly high-angle, calcite- and pyrite-filled veins) concentrate in coarse-grained lithologies, especially within and around doleritic intrusions (Senger et al., 2013b) and carbonate-rich beds such as bioclastites or limestones (Fig. 4E–G). Some lines of evidence

Figure 4. Examples of closed structural discontinuities in drillcores. (A) Non-systematic, dendritic array of subvertical disaggregation deformation bands each showing displacements of millimetres- to cen-timetres (De Geerdalen Fm., DH4 depth 766.55 m). (B) Deformation bands (red arrows) in massive, fine- to medium-grained sandstone (De Geerdalen Fm., DH4 depth 766.35 m). (C) Closely spaced network of systematic disaggregation deformation bands (red arrows) charac-terised by normal movement and c. 1 cm displacement (De Geerdalen Fm., DH4 depth 769.11 m). (D) Ductile-plastic, c. 6 cm-thick shear zone characterised by plastic deformation and incipient asymmetric boudinage (Knorringfjellet Fm., DH4 depth 695.90 m). (E) Locali-sed cm-thick calcite veins within well-cemented massive shales in the lower contact aureole of a dolerite intrusion, c. 1.5 m below the contact (De Geerdalen Fm., DH4 depth 953.50 m). (F) Hairline calcite vein just above a dolerite intrusion (within its contact aureole). Note the glassy, greenish layer at the base of the core representing the upper chil-led margin of the dolerite intrusion (De Geerdalen Fm., DH4 depth 949.80 m). (G) Hairline calcite vein in heterogeneous, bioturbated silt-stone located c. 2 m below a thin (c. 10 cm) fine-grained dolerite intru-sion (De Geerdalen Fm., DH4 depth 841.76 m). (H) Midpoint fracture depth vs. dip angle diagram of the closed structural discontinuities log-ged in the DH4 well, compared with the lithology.

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Table 1. List of all the measured scan-lines and relative characteristics.

Scanline ID Easting Northing Scanline type Thickness (cm)

Scanline orientation (bearing)

Length (m)

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Average F/m

TG/ Continuous

BC/Discon-tinuous Lithology LSU Formation

BC_KS_1 523268 8698310 scanline 330 SW-NE 13 134 10,3 38 96 fine-grained dolerite D Diabasodden SuiteBC_KS_2 523268 8698310 scanline 50 SW-NE 13 63 4,8 17 46 siltstone, contact zone D De Geerdalen FmBC_KS_3 523287 8698308 scanline 330 SW-NE 6 103 17,2 33 70 fine-grained dolerite D De Geerdalen FmBC_KS_4 523651 8698705 scanline 300 SW-NE 16 188 11,8 57 131 medium grained dyke and sill D Diabasodden SuiteBC_KS_5 523604 8698840 scanline 300 NW-SE 11 99 9,0 29 70 medium grained dyke and sill D Diabasodden SuiteBC_KS_6 523313 8698312 scanline 70 E-W 4 44 11,0 4 40 fine-grained dolerite dyke + hostrock D De Geerdalen FmBC_KS_7 523815 8698534 scanline 300 N-S 7 112 16,0 16 96 medium grained dyke and sill D Diabasodden SuiteCD_KA_1 521151 8696942 scanline 300 S-N 35 144 4,1 60 84 shale-silt interbeds B De Geerdalen FmCD_KA_2 521184 8697157 scanline 50 S-N 24 124 5,2 31 93 highly bioturbated white fine sand B De Geerdalen FmCD_KA_3 521186 8696982 scanline 50 S-N 8,5 54 6,4 12 42 highly bioturbated white fine sand B De Geerdalen FmCD_KA_4 521199 8696898 scanline 50 S-N 26 147 5,7 65 82 highly bioturbated white fine sand B De Geerdalen FmCD_KA_5 521259 8696755 scanline 200 SSE-NNW 26 76 2,9 29 47 medium-coarse sand bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_6 521252 8696752 scanline 150 SSE-NNW 10 85 8,5 23 62 shale A Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_7 521260 8696665 scanline 90 S-N 16,5 76 4,6 31 45 conglomerate, Brentskardhaugen Bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_8 521172 8696850 scanline 90 S-N 6 39 6,5 8 31 conglomerate, Brentskardhaugen Bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_9 521062 8696876 scanline 100 S-N 17,5 105 6,0 36 69 well-cemented, yellowish, cliff-forming cemented shale/silt (authigenic carbonate?) A Agardhfjellet Fm

CD_KA_10 521082 8696932 scanline 300 S-N 9,5 85 8,9 27 58 flaky shales in upper Criocerosdalen A Agardhfjellet FmDD_KA_1 532011 8693939 scanline 500 W-E 16 167 10,4 40 127 dolerite dyke D Diabasodden SuiteBA_KAL_1 520377 8697720 scanline 500 E-W 10 33 3,3 21 12 silty-shaly interval B De GeerdalenBB_KAL_1 521057 8697966 scanline 150 E-W 24 35 1,5 14 21 fine-medium sst bedset C De Geerdalen FormationGSF_KA_1 527296 8697643 scanline 3000 NW-SE 6,5 43 6,6 9 34 dolerite D Diabasodden SuiteJF_KA_1 518535 8695247 scanline 130 E-W 16 62 3,9 27 35 very fine sandstone C Helvetiafjellet Fm (?)JF_KA_2 519117 8695647 scanline 100 SSE-NNW 6 20 3,3 2 18 medium-grained sandstone C Helvetiafjellet Fm (?)JF_KA_2a 519117 8695647 scanline 100 SSE-NNW 2,5 17 6,8 2 15 medium-grained sandstone C Helvetiafjellet Fm (?)

KD_E_110m 520234 8696584 orientations only N/A NW-SE N/A 36 N/A 14 22 siltstone-shale A Agardhfjellet FmKD_E_122m 520245 8696575 scanline 50 NW-SE 4,5 26 5,8 10 16 Silt to very fine sand B Agardhfjellet FmKD_E_131m 520265 8696669 orientations only 260 SE-NW N/A 34 N/A 5 29 Shale-silt sequence A Agardhfjellet FmKD_E_98m 520208 8696588 scanline 250 NW-SE 6 46 7,7 10 36 siltstone-shale A Agardhfjellet Fm

KD_W_144m 519773 8696111 orientations only 60 N/A N/A 30 N/A 17 13 silty layer within black shales, lensoid B Agardhfjellet FmKD_W_170m 519712 8696083 orientations only 20 N/A N/A 33 N/A 15 18 silt/very fine sand B Agardhfjellet Fm

CD_KD_1 521174 8697326 scanline 20 S-N (350) 30 221 7,4 106 115 bioclastic, well cemented bedset E De Geerdalen FmCD_KD_2 521174 8697326 scanline 200 S-N (350-335) 25 317 12,7 147 170 finely laminated silty shale interval A De Geerdalen FmCD_KD_3 521174 8697326 scanline 70 S-N 9,25 74 8,0 38 36 oxidized sst bedset, ledge forming C De Geerdalen FmCD_KD_4 521174 8697326 scanline 150 S-N (340) 30 192 6,4 107 85 medium-coarse sand bed, Slottet bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KD_5 521174 8697326 scanline 200 S-N (320) 30 144 4,8 88 56 conglomerate, Brentskardhaugen Bed C Wilhelmøya Subgroup, Knorringfjellet Fm.

DBB_KD_1 521783 8697979 scanline 100 E-W (115) 30,23 108 3,6 35 73 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmDBB_KD_2 521783 8697979 scanline 100 N-S (170) 3,8 21 5,5 12 9 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmDBB_KD_3 521783 8697979 scanline 100 N-S (175) 2,75 20 7,3 11 9 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmDBB_KD_4 521783 8697979 scanline 100 N-S (170) 3,68 35 9,5 14 21 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmGS_KD_1 527264 8697655 scanline 5000 NNW-SSE (320) 5,35 41 7,7 27 14 dolerite D Diabasodden SuiteGS_KD_2 527264 8697655 scanline 5000 E-W (250) 14,97 54 3,6 18 36 dolerite D Diabasodden SuiteJF_KD_1 518528 8695207 scanline 170 S-N 19,9 14 0,7 10 4 whitish medium to coarse sst bedset with scattered pebbles C Firkanten Formation (early Paleocene)JF_KD_2 519032 869550 scanline 150 S-N (310) 7,81 55 7,0 11 44 yellowish-reddisch medium-to coarse-sst bedset with HCS, bioturbation and cherty mudstone in between C Carolinefjellet Formation (Cretaceous)

KD_GEC_1 519569 8697203 scanline 30 SE-NW 25,7 98 3,8 47 51 fine to medium sst bed in silty interbeds C De Geerdalen FmKD_KD_2 519569 8697203 scanline 20 S-N (334) 8,96 51 5,7 25 26 sst bed C De Geerdalen FmKD_KD_3 519569 8697203 scanline 60 S-N (334) 9,06 49 5,4 11 38 shale interval A De Geerdalen FmKD_KD_4 519569 8697203 scanline 30 S-N (330) 10,59 37 3,5 22 15 sst bed comprised within shale-silt interbeds C De Geerdalen FmDD_KD_1 532011 8693939 scanline 500 E-W (290) 11,98 294 24,5 74 220 dolerite dyke D Diabasodden SuiteBB_KD_1 521057 8697966 scanline 150 E-W (260) 12,33 65 5,3 9 56 heterolitologic silty-shaly interval, finely bedded (1-10 c, sst beds), tidal wavy and flaser bedding A De Geerdalen FmBB_KD_2 521200 8697967 scanline 100 E-W (275) 17,8 23 1,3 13 10 sandy bar with sigmoids, pinch and swell C De Geerdalen FmBB_KD_3 521317 8697956 scanline 200 E-W (270) 17 56 3,3 25 31 shale A De Geerdalen FmBB_KD_4 521783 8697979 scanline 200 E-W (270) 31 58 1,9 16 42 carbonate bed, laminated limestone E De Geerdalen Fm


Table 1. List of all the measured scan-lines and relative characteristics.



Length (m)

Number of fractures

Average F/m

TG/ Continuous


BC_KS_1 523268 8698310 scanline 330 SW-NE 13 134 10,3 38 96 fine-grained dolerite D Diabasodden SuiteBC_KS_2 523268 8698310 scanline 50 SW-NE 13 63 4,8 17 46 siltstone, contact zone D De Geerdalen FmBC_KS_3 523287 8698308 scanline 330 SW-NE 6 103 17,2 33 70 fine-grained dolerite D De Geerdalen FmBC_KS_4 523651 8698705 scanline 300 SW-NE 16 188 11,8 57 131 medium grained dyke and sill D Diabasodden SuiteBC_KS_5 523604 8698840 scanline 300 NW-SE 11 99 9,0 29 70 medium grained dyke and sill D Diabasodden SuiteBC_KS_6 523313 8698312 scanline 70 E-W 4 44 11,0 4 40 fine-grained dolerite dyke + hostrock D De Geerdalen FmBC_KS_7 523815 8698534 scanline 300 N-S 7 112 16,0 16 96 medium grained dyke and sill D Diabasodden SuiteCD_KA_1 521151 8696942 scanline 300 S-N 35 144 4,1 60 84 shale-silt interbeds B De Geerdalen FmCD_KA_2 521184 8697157 scanline 50 S-N 24 124 5,2 31 93 highly bioturbated white fine sand B De Geerdalen FmCD_KA_3 521186 8696982 scanline 50 S-N 8,5 54 6,4 12 42 highly bioturbated white fine sand B De Geerdalen FmCD_KA_4 521199 8696898 scanline 50 S-N 26 147 5,7 65 82 highly bioturbated white fine sand B De Geerdalen FmCD_KA_5 521259 8696755 scanline 200 SSE-NNW 26 76 2,9 29 47 medium-coarse sand bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_6 521252 8696752 scanline 150 SSE-NNW 10 85 8,5 23 62 shale A Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_7 521260 8696665 scanline 90 S-N 16,5 76 4,6 31 45 conglomerate, Brentskardhaugen Bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_8 521172 8696850 scanline 90 S-N 6 39 6,5 8 31 conglomerate, Brentskardhaugen Bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KA_9 521062 8696876 scanline 100 S-N 17,5 105 6,0 36 69 well-cemented, yellowish, cliff-forming cemented shale/silt (authigenic carbonate?) A Agardhfjellet Fm

CD_KA_10 521082 8696932 scanline 300 S-N 9,5 85 8,9 27 58 flaky shales in upper Criocerosdalen A Agardhfjellet FmDD_KA_1 532011 8693939 scanline 500 W-E 16 167 10,4 40 127 dolerite dyke D Diabasodden SuiteBA_KAL_1 520377 8697720 scanline 500 E-W 10 33 3,3 21 12 silty-shaly interval B De GeerdalenBB_KAL_1 521057 8697966 scanline 150 E-W 24 35 1,5 14 21 fine-medium sst bedset C De Geerdalen FormationGSF_KA_1 527296 8697643 scanline 3000 NW-SE 6,5 43 6,6 9 34 dolerite D Diabasodden SuiteJF_KA_1 518535 8695247 scanline 130 E-W 16 62 3,9 27 35 very fine sandstone C Helvetiafjellet Fm (?)JF_KA_2 519117 8695647 scanline 100 SSE-NNW 6 20 3,3 2 18 medium-grained sandstone C Helvetiafjellet Fm (?)JF_KA_2a 519117 8695647 scanline 100 SSE-NNW 2,5 17 6,8 2 15 medium-grained sandstone C Helvetiafjellet Fm (?)

KD_E_110m 520234 8696584 orientations only N/A NW-SE N/A 36 N/A 14 22 siltstone-shale A Agardhfjellet FmKD_E_122m 520245 8696575 scanline 50 NW-SE 4,5 26 5,8 10 16 Silt to very fine sand B Agardhfjellet FmKD_E_131m 520265 8696669 orientations only 260 SE-NW N/A 34 N/A 5 29 Shale-silt sequence A Agardhfjellet FmKD_E_98m 520208 8696588 scanline 250 NW-SE 6 46 7,7 10 36 siltstone-shale A Agardhfjellet Fm

KD_W_144m 519773 8696111 orientations only 60 N/A N/A 30 N/A 17 13 silty layer within black shales, lensoid B Agardhfjellet FmKD_W_170m 519712 8696083 orientations only 20 N/A N/A 33 N/A 15 18 silt/very fine sand B Agardhfjellet Fm

CD_KD_1 521174 8697326 scanline 20 S-N (350) 30 221 7,4 106 115 bioclastic, well cemented bedset E De Geerdalen FmCD_KD_2 521174 8697326 scanline 200 S-N (350-335) 25 317 12,7 147 170 finely laminated silty shale interval A De Geerdalen FmCD_KD_3 521174 8697326 scanline 70 S-N 9,25 74 8,0 38 36 oxidized sst bedset, ledge forming C De Geerdalen FmCD_KD_4 521174 8697326 scanline 150 S-N (340) 30 192 6,4 107 85 medium-coarse sand bed, Slottet bed C Wilhelmøya Subgroup, Knorringfjellet Fm.CD_KD_5 521174 8697326 scanline 200 S-N (320) 30 144 4,8 88 56 conglomerate, Brentskardhaugen Bed C Wilhelmøya Subgroup, Knorringfjellet Fm.

DBB_KD_1 521783 8697979 scanline 100 E-W (115) 30,23 108 3,6 35 73 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmDBB_KD_2 521783 8697979 scanline 100 N-S (170) 3,8 21 5,5 12 9 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmDBB_KD_3 521783 8697979 scanline 100 N-S (175) 2,75 20 7,3 11 9 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmDBB_KD_4 521783 8697979 scanline 100 N-S (170) 3,68 35 9,5 14 21 Well cemented carbonate/bioclastic bed (bluish layer, pavement) E De Geerdalen FmGS_KD_1 527264 8697655 scanline 5000 NNW-SSE (320) 5,35 41 7,7 27 14 dolerite D Diabasodden SuiteGS_KD_2 527264 8697655 scanline 5000 E-W (250) 14,97 54 3,6 18 36 dolerite D Diabasodden SuiteJF_KD_1 518528 8695207 scanline 170 S-N 19,9 14 0,7 10 4 whitish medium to coarse sst bedset with scattered pebbles C Firkanten Formation (early Paleocene)JF_KD_2 519032 869550 scanline 150 S-N (310) 7,81 55 7,0 11 44 yellowish-reddisch medium-to coarse-sst bedset with HCS, bioturbation and cherty mudstone in between C Carolinefjellet Formation (Cretaceous)

KD_GEC_1 519569 8697203 scanline 30 SE-NW 25,7 98 3,8 47 51 fine to medium sst bed in silty interbeds C De Geerdalen FmKD_KD_2 519569 8697203 scanline 20 S-N (334) 8,96 51 5,7 25 26 sst bed C De Geerdalen FmKD_KD_3 519569 8697203 scanline 60 S-N (334) 9,06 49 5,4 11 38 shale interval A De Geerdalen FmKD_KD_4 519569 8697203 scanline 30 S-N (330) 10,59 37 3,5 22 15 sst bed comprised within shale-silt interbeds C De Geerdalen FmDD_KD_1 532011 8693939 scanline 500 E-W (290) 11,98 294 24,5 74 220 dolerite dyke D Diabasodden SuiteBB_KD_1 521057 8697966 scanline 150 E-W (260) 12,33 65 5,3 9 56 heterolitologic silty-shaly interval, finely bedded (1-10 c, sst beds), tidal wavy and flaser bedding A De Geerdalen FmBB_KD_2 521200 8697967 scanline 100 E-W (275) 17,8 23 1,3 13 10 sandy bar with sigmoids, pinch and swell C De Geerdalen FmBB_KD_3 521317 8697956 scanline 200 E-W (270) 17 56 3,3 25 31 shale A De Geerdalen FmBB_KD_4 521783 8697979 scanline 200 E-W (270) 31 58 1,9 16 42 carbonate bed, laminated limestone E De Geerdalen Fm

130 K. Ogata et al.



Length (m)

Number of fractures

Average F/m

TG/ Continuous


BB_KD_5 521839 8697958 scanline 100 E-W (275) 19,56 24 1,2 14 10 greenish sst bedset (5-10 cm beds), fine silty/muddy intervals above and below C De Geerdalen FmBB_KD_6 521855 8697956 scanline 100 E-W (275) 10 31 3,1 3 28 heterolitologic facies (fine sand, silt, mud), highly bioturbated B De Geerdalen FmBB_KD_7 522153 8698014 scanline 200 NE-SW (230) 5 58 11,6 12 46 shale A De Geerdalen FmCD_KD_6 521096 8696983 scanline 350 S-N (355) 10 180 18,0 49 131 shale A Agardhfjellet FmBW_KK_1 530518 8696907 scanline 1000 W-E 30 677 22,6 59 618 dolerite D Diabasodden Suite in Bothneia Fm.BB_KO_1 521810 8697956 vertical scanline N/A N/A 2 30 15,0 11 22 across thin fine-grained dolerite sill and host rock D De Geerdalen FmCCIP_1 521062 8696876 scanline N/A S-N 335) 6,8 43 6,3 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet FmCCIP_2 521062 8696876 scanline N/A S-N 335) 7,6 19 2,5 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet FmCCIP_3 521062 8696876 scanline N/A S-N 335) 6,2 32 5,2 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet FmCCIP_4 521062 8696876 vertical scanline N/A N/A 6,6 6 0,9 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet Fm

JF_Detach 519262 8695920 orientations only N/A N/A N/A 41 N/A N/A N/A structural data collection from shales N/A Agardhfjellet FmKK_Diapir 519569 8697203 orientations only N/A N/A N/A 35 N/A N/A N/A structural data collection from shales N/A Agardhfjellet FmAF_KM_01 518965 8696368 scanline 80 NW-SE (305) 43 111 2,6 38 73 shale A Agardhfjellet FmBA_KM_01 520496 8697776 scanline 52 NE-SW (235) 7 14 2,0 4 10 sand C De Geerdalen FmBA_KM_02 520414 8697736 scanline 62 NE-SW (228) 9 32 3,6 19 13 limestone E De Geerdalen FmBB_KIM_01 522179 8698028 scanline 300 N-S (008) 20 53 2,7 5 48 shale/silt A De Geerdalen FmBB_KIM_02 521963 8697966 scanline 73 W-E (282) 20 26 1,3 7 19 sand C De Geerdalen FmBB_KM_03 521532 8697959 scanline 130 E-W (250) 8 22 2,8 5 17 siltstone B De Geerdalen FmBB_KM_04 521096 8697972 scanline 15 NW-SE (314) 1 15 15,0 15 0 carbonate bed within shale E De Geerdalen FmBC_KIM_01 523192 8698256 scanline 1000 NE-SW (250) 13 51 3,9 12 39 silty-shaly interval B De Geerdalen FmBC_KIM_02 523014 8698179 scanline 200 W-E (290) 18 28 1,6 7 21 siltstone B De Geerdalen FmBC_KIM_03 522986 8698173 scanline 150 W-E (260) 31 80 2,6 7 73 siltstone B De Geerdalen FmBC_KIM_04 522938 8698168 scanline 150 W-E (280) 31 75 2,4 15 60 siltstone B De Geerdalen FmMF_KM_01 483167 8713852 scanline 5000 N-S (207) 7,5 61 8,1 19 42 dolerite dyke D Diabasodden SuiteMF_KM_02 483167 8713852 scanline 5000 N-S (207) 17,5 85 4,9 21 64 dolerite dyke D Diabasodden SuiteBH_KM_01 531363 8694845 scanline 150 W-E (084) 10 69 6,9 35 34 dolerite D Diabasodden SuiteKF_KM_01 521296 8695464 scanline 300 NW-SE (325) 13,5 30 2,2 16 14 sandstone C Helvetiafjellet FmKF_KM_02 521296 8695464 scanline 300 NW-SE (325) 8 37 4,6 6 31 siltstone B Helvetiafjellet FmKF_KM_03 521286 8695457 scanline 30 NW-SE (325) 8 34 4,3 15 19 reddish laminated med sst C Helvetiafjellet FmKF_KM_04/AF_KM_03

520888 8696353 scanline 100 E-W (110) 7 52 7,4 12 40 shale A Agardhfjellet Fm

AF_KM_02 519578 8696855 scanline 800 NW-SE (315) 20 53 2,7 19 34 shale (black paper shales) A Agardhfjellet FmAF_KM_03V 519575 8696860 vertical scanline N/A N-S (190) 26,5 78 2,9 22 56 shale (black paper shales) A Agardhfjellet FmAF_KM_04V 519556 8696864 vertical scanline N/A N-S (182) 9,5 37 3,9 12 25 shale (black paper shales) A Agardhfjellet FmAF_KM_05V 519527 8696872 vertical scanline N/A S-N (353) 6,5 19 2,9 6 13 shale (black paper shales) A Agardhfjellet FmDV_KM_01 523800 8697596 scanline 200 S-N (345) 19,5 75 3,8 31 44 fine sand with minor silt/shale laminae, coarser sand at top C De Geerdalen FmDV_KM_02 523796 8697590 scanline 200 S-N (330) 28 150 5,4 42 108 shale (black shales) A De Geerdalen FmKO_AB_1 523208 8658567 scanline 60 S-N (310) 8 42 5,3 7 35 cgl layer, Brentskardhaugen bed C Wilhelmøya Subgroup, Knorringfjeller Fm.KO_AB_2 523208 8658567 scanline 300 S-N (305) 7 71 10,1 71 0 silty shale interval A Agardhfjellet FmKO_AB_3 500000 8658369 scanline 180 S-N (315) 23 33 1,4 13 20 paper shales interval A Agardhfjellet FmKO_AB_4 500000 8658369 scanline 180 S-N (312) 20 49 2,5 16 33 paper shales interval A Agardhfjellet Fm

KO_AB_4b 500000 8658369 scanline 180 E-W (215) 7 22 3,1 7 15 paper shales interval A Agardhfjellet FmKO_AB_5 500000 8658369 scanline 150 E-W (280) 24 114 4,8 27 87 paper shales interval A Agardhfjellet FmKO_AB_6 500000 8658369 scanline 100 N-S (200) 3 26 8,7 26 0 cemented siltstone B De Geerdalen FmKO_AB_7 500000 8658369 scanline 250 S-N (345) 4 76 19,0 76 0 silty shale interval A De Geerdalen FmKO_AB_8 500000 8658369 scanline 40 E-W (248) 6 29 4,8 12 17 fine sst bed C De Geerdalen FmKO_AB_9 500000 8658369 scanline 40 E-W (240) 8 46 5,8 31 15 limestone bed, shell debris, yellowish alteration, gray in fresh cut E De Geerdalen Fm

Table 1 Continued




Length (m)

Number of fractures

Average F/m

TG/ Continuous


BB_KD_5 521839 8697958 scanline 100 E-W (275) 19,56 24 1,2 14 10 greenish sst bedset (5-10 cm beds), fine silty/muddy intervals above and below C De Geerdalen FmBB_KD_6 521855 8697956 scanline 100 E-W (275) 10 31 3,1 3 28 heterolitologic facies (fine sand, silt, mud), highly bioturbated B De Geerdalen FmBB_KD_7 522153 8698014 scanline 200 NE-SW (230) 5 58 11,6 12 46 shale A De Geerdalen FmCD_KD_6 521096 8696983 scanline 350 S-N (355) 10 180 18,0 49 131 shale A Agardhfjellet FmBW_KK_1 530518 8696907 scanline 1000 W-E 30 677 22,6 59 618 dolerite D Diabasodden Suite in Bothneia Fm.BB_KO_1 521810 8697956 vertical scanline N/A N/A 2 30 15,0 11 22 across thin fine-grained dolerite sill and host rock D De Geerdalen FmCCIP_1 521062 8696876 scanline N/A S-N 335) 6,8 43 6,3 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet FmCCIP_2 521062 8696876 scanline N/A S-N 335) 7,6 19 2,5 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet FmCCIP_3 521062 8696876 scanline N/A S-N 335) 6,2 32 5,2 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet FmCCIP_4 521062 8696876 vertical scanline N/A N/A 6,6 6 0,9 N/A N/A Cgl-sst injection/pipe N/A Agardhfjellet Fm

JF_Detach 519262 8695920 orientations only N/A N/A N/A 41 N/A N/A N/A structural data collection from shales N/A Agardhfjellet FmKK_Diapir 519569 8697203 orientations only N/A N/A N/A 35 N/A N/A N/A structural data collection from shales N/A Agardhfjellet FmAF_KM_01 518965 8696368 scanline 80 NW-SE (305) 43 111 2,6 38 73 shale A Agardhfjellet FmBA_KM_01 520496 8697776 scanline 52 NE-SW (235) 7 14 2,0 4 10 sand C De Geerdalen FmBA_KM_02 520414 8697736 scanline 62 NE-SW (228) 9 32 3,6 19 13 limestone E De Geerdalen FmBB_KIM_01 522179 8698028 scanline 300 N-S (008) 20 53 2,7 5 48 shale/silt A De Geerdalen FmBB_KIM_02 521963 8697966 scanline 73 W-E (282) 20 26 1,3 7 19 sand C De Geerdalen FmBB_KM_03 521532 8697959 scanline 130 E-W (250) 8 22 2,8 5 17 siltstone B De Geerdalen FmBB_KM_04 521096 8697972 scanline 15 NW-SE (314) 1 15 15,0 15 0 carbonate bed within shale E De Geerdalen FmBC_KIM_01 523192 8698256 scanline 1000 NE-SW (250) 13 51 3,9 12 39 silty-shaly interval B De Geerdalen FmBC_KIM_02 523014 8698179 scanline 200 W-E (290) 18 28 1,6 7 21 siltstone B De Geerdalen FmBC_KIM_03 522986 8698173 scanline 150 W-E (260) 31 80 2,6 7 73 siltstone B De Geerdalen FmBC_KIM_04 522938 8698168 scanline 150 W-E (280) 31 75 2,4 15 60 siltstone B De Geerdalen FmMF_KM_01 483167 8713852 scanline 5000 N-S (207) 7,5 61 8,1 19 42 dolerite dyke D Diabasodden SuiteMF_KM_02 483167 8713852 scanline 5000 N-S (207) 17,5 85 4,9 21 64 dolerite dyke D Diabasodden SuiteBH_KM_01 531363 8694845 scanline 150 W-E (084) 10 69 6,9 35 34 dolerite D Diabasodden SuiteKF_KM_01 521296 8695464 scanline 300 NW-SE (325) 13,5 30 2,2 16 14 sandstone C Helvetiafjellet FmKF_KM_02 521296 8695464 scanline 300 NW-SE (325) 8 37 4,6 6 31 siltstone B Helvetiafjellet FmKF_KM_03 521286 8695457 scanline 30 NW-SE (325) 8 34 4,3 15 19 reddish laminated med sst C Helvetiafjellet FmKF_KM_04/AF_KM_03

520888 8696353 scanline 100 E-W (110) 7 52 7,4 12 40 shale A Agardhfjellet Fm

AF_KM_02 519578 8696855 scanline 800 NW-SE (315) 20 53 2,7 19 34 shale (black paper shales) A Agardhfjellet FmAF_KM_03V 519575 8696860 vertical scanline N/A N-S (190) 26,5 78 2,9 22 56 shale (black paper shales) A Agardhfjellet FmAF_KM_04V 519556 8696864 vertical scanline N/A N-S (182) 9,5 37 3,9 12 25 shale (black paper shales) A Agardhfjellet FmAF_KM_05V 519527 8696872 vertical scanline N/A S-N (353) 6,5 19 2,9 6 13 shale (black paper shales) A Agardhfjellet FmDV_KM_01 523800 8697596 scanline 200 S-N (345) 19,5 75 3,8 31 44 fine sand with minor silt/shale laminae, coarser sand at top C De Geerdalen FmDV_KM_02 523796 8697590 scanline 200 S-N (330) 28 150 5,4 42 108 shale (black shales) A De Geerdalen FmKO_AB_1 523208 8658567 scanline 60 S-N (310) 8 42 5,3 7 35 cgl layer, Brentskardhaugen bed C Wilhelmøya Subgroup, Knorringfjeller Fm.KO_AB_2 523208 8658567 scanline 300 S-N (305) 7 71 10,1 71 0 silty shale interval A Agardhfjellet FmKO_AB_3 500000 8658369 scanline 180 S-N (315) 23 33 1,4 13 20 paper shales interval A Agardhfjellet FmKO_AB_4 500000 8658369 scanline 180 S-N (312) 20 49 2,5 16 33 paper shales interval A Agardhfjellet Fm

KO_AB_4b 500000 8658369 scanline 180 E-W (215) 7 22 3,1 7 15 paper shales interval A Agardhfjellet FmKO_AB_5 500000 8658369 scanline 150 E-W (280) 24 114 4,8 27 87 paper shales interval A Agardhfjellet FmKO_AB_6 500000 8658369 scanline 100 N-S (200) 3 26 8,7 26 0 cemented siltstone B De Geerdalen FmKO_AB_7 500000 8658369 scanline 250 S-N (345) 4 76 19,0 76 0 silty shale interval A De Geerdalen FmKO_AB_8 500000 8658369 scanline 40 E-W (248) 6 29 4,8 12 17 fine sst bed C De Geerdalen FmKO_AB_9 500000 8658369 scanline 40 E-W (240) 8 46 5,8 31 15 limestone bed, shell debris, yellowish alteration, gray in fresh cut E De Geerdalen Fm

132 K. Ogata et al.

suggesting ductile/plastic shearing deformation are observed to affect centimetres- to tens of centimetres-thick zones characterised by asymmetrically folded and boudined thin beds and laminae, and pseudonodules (see Fig. 4D). The disaggregation deformation bands typically occur in the more sand-dominated part of the De Geerdalen Fm. and the upper third of the Knorringfjellet Fm., peaking at approximately 775 and 678 m, respectively, whereas the mineralised veins show their maximum clustering at c. 950 m, in line with the position of the thicker dolerite intrusion (Fig. 4H).

Open structural discontinuitiesSharp, open cracks show different geometric arrangements depending on the host lithology: high-angle (>45°) fractures (Fig. 5A–B), representing less than 30% of open fractures, typically occur within coarser-grained units (e.g., fine- to coarse-grained sandstones). Low-angle (0–45°) fractures, commonly characterised by shiny-polished, slickensided and non-mineralised surfaces, predominate (Fig. 5C–E). The fracture frequency is highest for the low-angle fracture set concentrated within the finer-grained intervals of the succession, while subordinate clusters of high-angle fractures characterise the coarser ones (Fig. 5F). In general terms, high-angle fractures are predominantly represented by Mode I fractures (i.e., joints) whereas low-angle ones belong to Mode II and III fractures (i.e., shears/tears), with some evidence of mixed modes. Zones with high fracture frequencies observed within the overlying Janusfjellet Subgroup (i.e., part of the lower Adventdalen Group) are associated with the upper main detachment zone, the damage zone of which has a calculated thickness of up to 180 m, with localised peaks in fracture frequencies reaching 60–80 fractures per metre in its inner part (Braathen et al., 2012). These secondary highly fractured zones appear as centimetre- to metre-thick zones of unconsolidated, ‘crushed’ shales (i.e., breccia and shale gouge), surrounded by a dense network of generally conjugate shear fractures, characterised by low-angle slip surfaces, as testified by the striated walls (see above). Other minor peaks in low-angle fracture frequencies are found within the reservoir section related to specific stratigraphic levels characterised by lithological boundaries (i.e., contacts between sand- and shale-dominated units, margins of igneous intrusions) and major shaly intervals (Fig. 5F).

Outcrop data

The observed fractures have been primarily distinguished in two main groups, through-going (TG) or bed-confined (BC), on the basis of their persistence within the considered litho-stratigraphic interval (e.g., bed, bedset, lithological unit), their cross-cutting relationships with the host lithologies and, where possible, their continuity at the outcrop scale. In this framework, non-stratabound TG fractures are defined by more homogeneous and systematic sets compared to

stratabound BC ones. As a general rule, systematic high-angle TG fractures do not show clear terminations within specific lithologies, randomly tipping out into each defined litho-structural domain. Low-angle fractures preferentially die out at well-defined lithological boundaries (e.g., master bedding surfaces and abrupt lithological boundaries), showing deflections where they propagate across different lithologies (Fig. 6).

The resultant intervals, vertically bounded by mechanical layers, coincide with recurrent lithostratigraphic-structural domains characterised by specific dominant lithologies, overall composition, grain-size populations and sedimentary facies, which in turn control the degree of cementation and the characterising fracture patterns. These litho-structural units (LSUs hereafter), defined on the basis of field mapping and the observed fracture characteristics, can be summarised as follows (Fig. 6A–E): (1) massive to laminated shale intervals (LSU A), (2) laminated to heterogeneous, thin-bedded, fine- to medium-grained intervals (LSU B), (3) massive to laminated, thick-bedded, medium- to coarse-grained intervals (LSU C), (4) massive, fine- to coarse-grained dolerite intrusions (i.e., dykes and sills; LSU D), and (5) carbonate-cemented intervals (e.g., limestones, bioclastites; LSU E).

Whatever their persistence, the high-angle fractures, showing little or no displacement and smooth fracture walls, sometimes with evidence of plumose patterns, are accordingly interpreted as Mode I fractures (i.e., joints). Some low-angle joints can also be observed, mainly in shale intervals and dolerite intrusions (see Fig. 6). Other high-angle and low-angle fractures, the latter occurring mostly in fine-grained intervals and dolerite intrusions (see Fig. 6A, D), are characterised by flat-ramp weathered surfaces, sometimes bearing striations on the fracture walls and millimetre- to centimetre-thick, very fine-grained, oxidised material, and, where recognisable, by displacements of

Figure 5. Examples of open structural discontinuities in drillcores. (A) Hairline open fracture (red arrows) developed along a pre-existing deformation band in fine-grained sandstones (upper De Geerdalen Fm., DH4 depth 703.05 m). (B) Continuous, subvertical, hairline open fracture (i.e., joint; red arrows) developed in fine-grained sandstone (Knorringfjellet Fm., DH4 depth 691.48 m). Note the drilling-induced fracture deflected by the pre-existing joint. (C) Example of highly frac-tured shear zone in a shale interval (e.g., crushed horizons), shattered by low-angle, conjugate shear fractures characterised by shiny, polished and striated surfaces (De Geerdalen Fm., DH4 depth 752.80 m). The two dashed lines indicate the two different attitudes of the conjugate systems. (D) Slickensided and polished surface of a high-angle shear fracture in silty shale (Knorringfjellet Fm., DH4 depth 689.08 m). (E) Striated and polished surface of a low-angle shear fracture in black shale (Knorringfjellet Fm., DH4 depth 682.44 m). (F) Midpoint frac-ture depth vs. dip angle diagram of the open structural discontinuities logged in the DH4 well, compared with the lithology

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134 K. Ogata et al.

1 % Area ContoursC.I. = 1.0 % / 1 % area

Equal AreaLower Hemisphere

N = 513

1 % AreaContours

C.I. = 1.0 % / 1 % area

EqualArea

LowerHemisphere

N = 551



N = 264





N = 657





N = 1084



N = 437



N = 299



N = 259

Bed-Con�ned Through-GoingM

assi

ve to

lam

inat

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ale-

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inat

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terv

als

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inat

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het

erog

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N = 546

20 c

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,th

ick-

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oars

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tes)

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N = 898

S2BC

TG

TGBC

BC

TG

TG

BC

TGBC

Figure 6. Outcrop examples of the recurrent lithostratigraphic units recognised throughout the investigated reservoir-caprock section and relative stereonets (poles to planes; 1% area contours; lower hemisphere; equal-area net) showing the spatial distribution of the measured fractures, distin-guished on the basis of their bed-confined or through-going attitude. In outcrop photos, fractures are labelled with white dashed lines, thin for bed-confined ones (BC) and thick for through-going ones (TG)


ShearsAt least two additional high-angle fracture sets bearing evidence of strike-slip movements (i.e., strike-parallel striations with no shear sense indicators) are identified as S1a and S1b, striking approximately NE–SW and NW–SE. The mostly dip-slip, shear-dominated fracture sets identified as S2a and S2b, are ESE–WNW- to SE–NW- and SSE–NNW-striking, respectively, and generally dip at a low angle (<45°) to the mean stratification. Systematic shear fractures have been documented within some metre-thick dolerite sills, appearing as sigmoidal, flat-ramp striated surfaces at the outcrop scale. These structures seem to systematically cut the subvertical (i.e., columnar) joints typical of the dolerite sills with a low but appreciable displacement (up to a few centimetres), becoming nearly bed-parallel at their margins and ramping in the middle of the intrusion (see Fig. 6D). A synthesis of the analysed shear fractures subdivided for each LSU is provided in Fig. 8A. Due to the general lack of kinematic indicators other than striations on the fracture walls, only the trend is provided without reference to the shear sense (Fig. 8B–C). Only a statistically inconsistent number of slickenfibres, calcite steps and displaced veins/fractures have been observed, nonetheless indicating a comparable occurrence of generally oblique sinistral and

centimetres to tens of centimetres. Due to these lines of evidence we interpret these structures as Mode II and III fractures (i.e., shears/tears; Anderson, 2005).

JointsNotwithstanding their persistence (i.e., bed-confined vs. through-going), high-angle fractures seem to be commonly organised in a principal joint set trending approximately ENE–WSW and identified as J1, and two subordinate joints sets J2a and J2b, striking about NNW–SSE and NNE–SSW, respectively. A summary of the statistical analyses performed on these fractures for each LSU is provided in Fig. 7. For some lithologies, the main trends of these sets are characterised by a narrow bimodal distribution defined by secondary peaks in the strike azimuth frequencies. When recognised, these counterparts of the main sets are identified as J1s, J2as and J2bs (see Fig. 7). A relatively small number of low-angle joint sets have also been observed, especially in the shale intervals and dolerite intrusions (see Fig. 7A, D), and identified as J3a and J3b, respectively. Even if their strike trend data seem to overlap with the main trends of the other high-angle joint sets (mainly J1–J1s), some bias is expected in their strike estimation due to the very low-angle attitude of these fractures (usually less than 15°).

Circle = 20 %

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Bed-Con�ned Through-GoingAzimuth Dip Azimuth Dip

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Figure 7. Statistical analysis of the spatial and geometric attitude of bed-confined and through-going fractures for the different litho-structural units shown in Fig. 6. The main recognised fracture sets are labelled in the rose diagrams and shown in the related azimuth and dip angle frequ-ency histograms (see text for discussion).

136 K. Ogata et al.



N = 48

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Striations’ directions

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Veins and weathered fracturesCalcite and subordinate quartz veins and fracture wall coatings have been observed within and in close proximity to carbonate layers (e.g., limestones, bioclastites) and medium- to thick-bedded sandstones and conglomerates. Increased mineralisation in the form of thick and continuous calcite veins was also observed within and around decimetre- to metre-sized dolerite dykes and sills in the lower-middle part of the reservoir section (Fig. 10A–C). Two main vein sets, V1 and V2, striking approximately ENE–WSW and WNW–ESE have been recognised in all the lithologies along with a secondary vein set, V3, oriented c. NE–SW. The latter is apparently missing in the carbonate lithologies (i.e., LSU E). In the dolerites, a subordinate low-angle vein set, V4, striking about NNW–SSE has also been recorded.

dextral strike-slip, and normal and reverse movements (Fig. 8E–F). The overall shearing/compression direction has therefore been interpreted mainly on the basis of the spatial arrangement of the fractures compared to other local to regional observations. The relative statistical analyses are summarised in Fig. 9.

LSU CShears

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Figure 7. Statistical analysis of the spatial and geometric attitude of bed-confined and through-going fractures for the different litho-structural units shown in Fig. 6. The main recognised fracture sets are labelled in the rose diagrams and shown in the related azimuth and dip angle frequency histograms (see text for discussion).

Figure 8. Outcrop examples of the shear fractures and kinematic indicators recognised in outcrop. (A) Contoured stereonets (poles to planes, equal-area, lower hemisphere, 1% contour interval) of the shear fractures identified in each litho-structural unit. No shear fractures have been recorded for the litho-structural units B and E. (B) Example of striations on low-angle (<45°) shear fracture (S2b set; see text for discussion) showing dip-slip movement (striation direction labelled with white dashed line) with no univocal indications on the shear sense (labelled with double arrow); Knor-ringfjellet Fm. (C) and (D) Examples of striations on high-angle (>45°) fractures (S1b and S1a sets, respectively; see text for discussion) showing strike-slip movements (striation directions labelled with white dashed lines) with no univocal indications on the shear sense (labelled with double arrows); Knorringfjellet Fm. The included rose diagram shows the direction (trend/plunge) of the striation trends collected for these types of frac-tures. (E) Slickenfibres (white dashed line) and calcite steps defining a normal dip-slip movement (white arrow) on a low-angle shear fracture (S2a set) in the Knorringfjellet Fm. (F) Two superimposed sets of slickenfibres (white dashed lines) and calcite steps defining a reverse dip-slip movement (white arrow) in a low-angle shear fracture (S2b set) found within a dolerite sill (lower-middle De Geerdalen Fm.). (G) Slickenfibres (white dashed line) and calcite steps defining a sinistral strike-slip movement (white arrows) on a high-angle fracture (S1b set) found in the Helvetiafjellet Fm. (H) Subhorizontal brittle shear zone in a shale interval of the lower-middle De Geerdalen Fm. defined by two low-angle shear fractures (S2a set; thick dashed lines) bounding closely spaced en-échelon fractures (thin dashed lines), which give indication on the overall shear sense.

‹

138 K. Ogata et al.

In the lowermost 100 m of the Agardhfjellet Fm. shales some of the most continuous fractures are characterised by a highly weathered appearance, showing millimetre- to centimetre-thick cores filled with pale-grey, loose, homogenised material that appears slightly siltier compared to the country rock (Fig. 10C, D).

Localised oxide-cemented coatings are also sometimes observed on fracture walls, especially in the uppermost De Geerdalen and Knorringfjellet formations. There, we observed iron- and manganese-oxides forming dark, reddish- to purplish-mineralised coatings on most continuous open cracks and on weathered surfaces.

Due to their importance as geodynamic indicators influencing the subsurface fluid conductivity, calcite veins have also been analysed separately. Their spatial attributes and statistical analyses are presented in Fig. 11.

Mesoscale faultsMesoscale normal fault systems were locally observed in the uppermost 50 m of the De Geerdalen Fm. (i.e., Konusdalen locality). These faults are characterised by displacements up to a few metres, striking roughly NE–SW and dipping generally toward the NW, with the

occurrence of a few, associated antithetic counterparts (Fig. 12A–C). Peaks in the fracture frequency characterise the interval of the sedimentary succession hosting these faults, either in the faults’ damage zones or outside. These structural associations, defined as fracture corridors, comprise closely spaced (generally less than 10 cm) through-going fractures, which are observed to cut several lithostratigraphic units without any preferred termination within specific lithologies or structures.

Similar structures defining an overall localised mesoscale ‘horst-and-graben’ pattern were also observed in the lowermost 30 m of the Agardhfjellet Fm. (i.e., Unnamed Valley/Criocerasdalen). This tectonised zone is characterised by striking greenish-yellow alteration colours and localised preferential cementation compared to the surrounding black shales, with the occurrence of displaced, lenticular, metre-sized carbonate concretions and cemented beds (see Fig. 12D).

Sedimentary injectionsAmong the other investigated structural discontinuities, subvertical veins of sedimentary material and other mesoscale fluid-escape features, such as neptunian dykes and pebbly-sandy injectites, were observed in one

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Figure 9. Statistical analysis of the spatial and geometric attitude of the shear fractures as illustrated in Fig. 8. The main recognised fracture sets (see Fig. 7) are labelled in the rose diagrams and the relative azimuth and shown in the related dip angle frequency histograms (see text for discus-sion).


A

SSEE

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Figure 10. Outcrop examples of sealed and healed fractures. (A) Bed-confined, 1–2 mm-thick calcite veins in a limestone bed (De Geerdalen Fm.). (B) Continuous 1–2 cm-thick calcite vein cutting a dolerite dyke at Botneheia (Tschermakfjellet Fm.). (C) Subvertical, through-going, 5 mm-thick calcite vein (right-hand side of the photo) crossing a c. 1 m-thick ‘baked’ sedimentary interval (i.e., laminated, wavy to lenticular, sandstone-silt-stone interbeds) sandwiched between two 2–3 m-thick dolerite dykes (lower De Geerdalen Fm.). (D) Subvertical healed fracture in black paper shales (Agardhfjellet Fm.); location shown in Fig. E. Fracture boundaries are labelled by red arrows. Note the fine-grained altered material forming the cores of such healed fractures. (E) Outcrop view of the healed fracture networks observed within the lower Agardhfjellet Fm. Some displace-ment can be observed from the position of local markers (e.g., oxidised layers). Photographic distortion due to wide-angle lenses.

140 K. Ogata et al.

location (i.e., Unnamed Valley/Criocerasdalen). Notably, this zone is located almost at the same stratigraphic level as the tectonised zone shown in Fig. 12D.

These features, also documented by Wierzbowski & Zieminska-Tworzydle (1984) and Hammer & Nakrem (2010), characterise the lower 30 m of the Agardhfjellet Fm. shales, developing pipe-like structures of coarse-grained material (most likely fed by the pebbly sandstones of the Knorringfjellet Fm.) surrounded by an aureole of reddish-yellow alteration colours (Fig. 13C–E). Notably, these sedimentary injection structures are usually associated with localised zones of increased cementation of the shales, characterised by high erosional relief, and are pervasively bioturbated (Fig. 13F). These metre-sized lenticular bodies are roughly aligned along the same stratigraphic levels and share an evident yellowish alteration colour (see above).

Fractures related to dolerite intrusionsStructural associations such as contacts of dolerite intrusions, fault zones and fracture corridors (see above) are unrelated to specific lithostratigraphic intervals. For instance, fractures around dolerite dykes and sills (i.e., contained within the contact aureole) locally show increased frequencies and preferred orientation parallel

to the boundaries of the igneous body, thus being subhorizontal in the case of sills and inclined to subvertical in the case of dykes. These fractures do not affect the dolerite body itself as they are localised in the host rock, forming fracture corridors (up to 1 m wide depending on the size of the igneous body) parallel to the boundaries of the intrusion (Senger et al., 2014a). Due to the different orientations of the dolerite intrusions, these fractures

LSU DVeins

N = 307

Circle = 27 %

LSU EVeins

N = 46

Circle = 15 %

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02468

1012141618202224262830

Azimuth Dip0 45 90 135 180 225 270 315 360 0 10 20 30 40 50 60 70 80 90

0 45 90 135 180 225 270 315 360 0 10 20 30 40 50 60 70 80 90

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CFigure 11. Statistical analysis of the spatial and geometric attitude of the recognised calcite veins. The main calcite vein sets (see Fig. 10A–C) are labelled in the rose diagrams and the relative azimuth and shown in the related dip-angle frequency histograms (see text for discussion).

Figure 12. Outcrop examples of the recognised mesoscale fault systems. (A) Overview of the mesoscale normal fault system (horst-and-gra-ben-type) affecting the uppermost part of the De Geerdalen Fm. (c. 15 m below the contact with the Knorringfjellet Fm.) as observed at the Konusdalen locality (see Fig. 2), with labelling of the main fault traces and scan-lines’ paths. (B) Combined stereonets and fracture fre-quency diagrams (with relative explanation) of the scan-lines collected across the mesoscale faults (locations shown in (A)) with identification of fault damage zones and fracture corridors. (C) Summary stereonet (poles to planes) of the all the fractures (i.e., joints and shears) cha-racterising the recognised non-stratabound units (i.e., fault damage zones and fracture corridors). (D) Another horst-and-graben-type, mesoscale normal fault system observed in the shales of the lower Agardhfjellet Fm. (approximately 100 m above the top of the measu-red stratigraphic log; see Fig.2B–D). Note the localised, more cemented and greenish-yellowish appearance in contrast with the surrounding weathered black shales.

‹


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KD_KD_4c

N = 43

ca. 50 cmo�set

ca. 150 cmo�set

Ft core shaly gouge

ca. 2 cm wide

1

2

1 2a

a ca. 5 cmo�set

b

b ca. 10 cmo�set

c

c ca. 3 cmo�set

d

d ca. 1 cmo�set

3

ca. 500 cmo�set

0

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KD_GEC_1

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33

ca. 500 cmo�set

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m F

t. D

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ca. 150 cmo�set

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jk

ca. 40 cmo�set

lkl

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Fracture frequency peaks(fracture corridors)

N = 102

Scanline ID

Distance (m)

Fracture N.

through-goingbed-con�ned

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Small-scale faults(< 50 cm throw)dip-slip component

Small-scale faults(< 50 cm throw)strike-slip component

Through-goingfractures (Joints)

Bed-con�nedfractures (Joints)


Stereonet explanationB

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N = 281

Main faultplane

Shear fracture (Dip-slip)Shear fracture (Strike-slip)

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Equal Area

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142 K. Ogata et al.

A

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Pebbly sandstone

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EFigure 13. Examples of sedimentary injections and associated products. (A) Overview of the yellowish, carbonate-cemented parts characterising the lowermost Agardhfjellet Fm. (c. 30–40 m above the reservoir top). The white dashed line highlights a 4–5 cm-thick sand dyke. (B) Close-up of (A) showing the appearance of the pebbly sandstone infilling of the sedimentary dyke. (C) Side view of the outcrop depicted in (A), showing the len-ticular, localised appearance of the carbonate-cemented parts and the altered, reddish haloes around sedimentary dykes piercing the black shales. (D) Close-up of( C) showing a c. 50 cm-thick, branching sedimentary dyke and the surrounding aureole of alteration. (E) Close-up of (C) showing the highly bioturbated appearance (i.e., tubular structures) of the carbonate-cemented parts. (F) Close-up of (D) showing the pebbly sandstone infilling of the sedimentary dyke and its contact with the surrounding weathered black shales.


wide alteration colour haloes and their relationships with localised bioturbated, carbonate-cemented parts (e.g., authigenic carbonate mounds (?); see Fig. 13C, D, F). Similar features have been described and analysed along the same stratigraphic interval in the immediate vicinity of our study area, and interpreted as fossil hydrocarbon seeps (Hammer & Nakrem, 2010; Hammer et al., 2011).

As documented by many observations (see Figs. 5B, C, 13A), both disaggregation deformation bands and injection structures represent marked discontinuities prone to be reworked/reactivated by subsequent defor-mation events. In this context, some local contri bution to the development of these structures could be ascribed to the mechanical deformation of the country rock due to the earliest emplacement phases of the Diabasodden Suite igneous intrusions. Moreover, the orientations of dolerite sills and dykes attest to a NW–SE-directed extension compatible with a NE–SW-directed axis of compression acting during the Early Cretaceous (Senger et al., 2014a, 2014b).

Tectonically generated structuresThe bulk of the brittle deformation, and thus fracturing, is thought to have taken place during Palaeogene time, synchronous with the development of the transpressional WSFB for reasons explained in the following.

The main joint set J1 is consistently aligned ENE–WSW, with its subsets (J1s) defining an arc spanning from NE–SW to E–W, while the subordinate J2 set shows a mean N–S-oriented strike trend, with its subsets (J2a, J2as and J2b, J2bs) spreading along NE–SW to NW–SE trends. High-angle shear fracture sets (S1) comprise two conjugate systems (S1a and S1b) striking about NE–SW and E–W, respectively. Low-angle shear fracture systems (S2) are associated with two main subsets (S2a and S2b) striking about NW–SE and NNW–SSE, respectively. Approximately the same trend of the joint sets has been observed in the mineralised vein sets V1–V3, having strike trends ranging from NE–SW to NW–SE, with an ENE–WSW-oriented cluster. The additional, low-angle vein set V4 shows mostly a NNW–SSE trend.

Assuming that in foreland settings the main regional joint sets are aligned parallel to the maximum regional horizontal palaeostress of the associated fold-and-thrust belt (Engelder & Geiser, 1980), the J1 sets would represent a product of an ENE–WSW horizontal compression. This is also suggested by the rough parallelism of the J1 with the average bisector defined by the coeval, high-angle, strike-slip, conjugate shear fracture sets S1. Contemporaneous layer-parallel shearing developed the low-angle, dip-slip reverse and normal faults arranged in conjugate (resembling Riedel-type P and R shears; see Fig. 5C) systems (S2a and S2b), particularly pervasive and closely spaced within the shaly intervals (i.e., LSU A; see Figs. 4C–F, 6A, 7A, 8A, H, 9A) and dolerite intrusions (i.e., LSU D; see Figs. 6D, 7D, 8A, F, 9C).

do not define spatially and geometrically consistent sets and are thus not clearly recognisable in the summary stereonets and related analyses (see Figs. 6D, 7).

DiscussionIn the following section we discuss the origin and the evolution of the observed fracture networks. Our focus is on how the lithological units and fracture associations combine to form a vertical subdivision of the reservoir-caprock succession into pseudo-mechanical units, and their possible implications in terms of subsurface fluid flow.

Structural discontinuities: types and significance

According to their inferred genetic mechanisms and their mutual cross-cutting/abutting relationships (i.e., relative timing), the recorded structures attest to the local tectonic history, representing products of over-lapping and progressive deformation events. These interpretations are summarised in Figs. 14 & 15 and discussed in detail as follows.

Syn- and early post-depositional structuresWe interpret the recognised disaggregation/deformation bands as narrow deformation zones due to microfaulting, suggesting sub-simple shearing in unconsolidated sediments and low confining stress as the generating mechanism, in accordance with common interpretations for this granular flow-related type of structure (Fossen, 2010). Along with the associated folded laminae, fluidal structures and localised ductile/plastic shear zones found within the De Geerdalen and Knorringfjellet fms. (see Fig. 4A–D), these features testify to soft-sediment deformation possibly due to syn-sedimentary tectonism (e.g., seismic shaking, growth faulting) and/or early post-depositional, gravity-induced, differential compaction (e.g., deep-seated slope movements, localised subsidence) occurring during Late Triassic and Jurassic time. Noticeably, growth-fault systems have been described from Eastern Svalbard (Edwards, 1976; Osmundsen et al., in press), and discussed in the light of challenges in seismic imaging (Anell et al., 2013). Considering this, the observed deformation bands could be interpreted as damage zone-related structures of growth faults. These faults, however, are not identified in the seismic sections around the drill site (Bælum et al., 2012), possibly due to poor resolution.

The sedimentary dykes and veins characterising the lower part of the Agardfjellet Fm. (see Fig. 13A, B, D, E) are thought to be fed by liquified coarse-grained material sourced in the thick paraconglomerate beds of the Knorringfjellet Fm. This contrasts with the conclusions of Wierzowski & Zieminska-Tworzydlo (1984) based on palynomorphs, who maintained that at least one clastic dyke in the same area is infilled by material sourced from the Palaeogene Firkanten Fm. The large amount of fluids driven along these structures is testified by the

144 K. Ogata et al.

The large spread of data shown by LSU D is likely due to the intrinsic internal structuring of dolerite dykes and sills such as cooling joints, magma-flow directional features, etc. The cumulative horizontal displacement of these shear zones is interpreted in the order of metres. However, in sum, the S2 shear fracture system yields significant layer-parallel shortening (c. 5–20%), especially in shaly lithologies. In this framework these layer-parallel shear zones found in the reservoir section

seem to be coherent with the deformation recorded within the upper main detachment at the base of the Janusfjellet Subgroup in the caprock section (at the base of the Rurikfjellet Fm.; see Fig. 3). This is supported by unpublished data collected along this detachment during the fieldwork campaign in 2011.

According to this, the analysed vein sets are interpreted to represent fractures developed during an early phase of

Bed-Con�ned Through-Going

A - Massive to laminatedshale-dominated intervals

B - Laminated to heterogeneous,thin-bedded, �ne- to medium-grained intervals

C - Massive to laminated,thick-bedded, medium-to coarse-grained intervals

D - Massive, �ne- to coarse-grained dolerite intrusions(dykes and sills)

E - Carbonate-cementedintervals (limestones,bioclastites)

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Figure 14. Combined summary plots of the mean spatial attitudes of all the investigated structural discontinuities including joints (J1, J1s, J2a, J2as, J2b, J2bs), shear fractures (S1a, S1b, S2a, S2b) and vein (V1, V2, V3, V4) sets, subdivided on the basis of their persistence (bed-confined vs. through-going) and relative LSU. Inferred deformation mechanisms and the consequent stress regime are indicated (black arrows for joint sets, red arrows for shear sets and blue arrows for vein sets). See text for detailed discussion.


zones related to the differential tectonic loading and perturbations of the compressional regime along strike of the WSFB, reworking and reactivating the tectonic discontinuities related to its foreland far-field stress (see above). We suggest that these extensional faults formed nearly parallel to the maximum horizontal stress and shortening axis achieved during eastward-directed folding and thrusting. In this framework, the migration of the foreland bulge and the localised tectonic loading

approximately NE–SW compression and subsequently mineralised. In this context, V2 and V3 sets would correspond to the later S1a and S1b, representing conjugate shear fractures, whereas the V1 set, oriented parallel to the V2–V3 bisector, would represent a former regional joint set.

The roughly ENE–WSW-striking, mesoscale normal faults (see Fig. 12C) are interpreted as local extensional

MES

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CAUSES ANDMECHANISMS

Gravity anddifferentialcompaction

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Figure 15. Schematic cartoon summarising the inferred tectonic evolution phases responsible for the development of the observed structural dis-continuities in the Upper Triassic–Jurassic succession of Central Spitsbergen.

146 K. Ogata et al.

ahead of the local ‘indenter’ that characterises the WSFB deformation front in the inner Isfjorden could play an intriguing role (see Fig. 1). Such E–W normal faults are well documented from coal mines in the basal units of the Palaeogene succession (Goss, 2013), making up the fill of the foreland basin system. In the mines, there is a close link between thrusts and the extensional faults, suggesting a contemporaneous development (M. Jochmann, pers. comm.). The joint sets J2a and J2b, which strike NNW–SSE to NNE–SSW, are oriented approximately parallel to the axes of the major folds of the WSFB (see Braathen et al., 1999). In this scheme, these joint sets may relate to the progressive hangingwall fracturing developed during the migration of gentle detachment folds in the foreland along with thrusting. Reactivation of structures related to earlier systematic deformation such as syn-sedimentary faulting, gravi-tational collapse and differential subsidence/compaction might have played a role in the distribution of these fractures (see above).

In summary, V1–V3 vein sets and J1, S1 and S2 sets together are interpreted to record changes in the eastern foreland far-field stress related to the early and late evolutionary phases of the western transpressional belt, respectively. Accordingly, the different orientations between these structural associations seem to reflect a slight clockwise rotation of the horizontal compression from c. NE–SW to ENE–WSW. Subsequent reworking of the vein networks as tensile and shear fractures can be observed by the marked overlapping relationships between the V1–V3 and the J1 and S1 trends (see Fig. 14). This progressive rotation of the main horizontal stress in the WSFB foreland province would also explain the occurrence of the secondary peaks in the strike azimuths of the main fracture sets, which may represent shear-related en-échelon cross joints due to strike-slip reactivation of older discontinuities. In this scheme, the large number of striations and the relative lack of clear kinematic indicators found on fracture walls may be related to subsequent shearing of already formed joints/cracks without syn-kinematic precipitation of secondary minerals.

This kind of geodynamic situation coincides with the interpretations based on regional analyses of Bergh et al. (1997) and Braathen et al. (1999), and detailed kinematic studies (Braathen & Bergh, 1995; Braathen et al., 1997). Particularly, these authors suggested marked rotations of the palaeostress field from an approximately N–S to a NE–SW compression during an early stage of the WSFB evolution, followed by ENE–WSW compression (see fig. 10 in Braathen et al., 1999), reflecting the main strain-partitioning phase along the transform plate margin.

The different structural trends recorded within the dolerite intrusions are likely due to intrinsic deformation processes typical of intruded igneous bodies (see e.g., Chevallier & Woodford, 1999; Galerne et al., 2011). In

this framework, different generations of calcite veins were observed within the dolerite intrusions and distinguished on the basis of their mineral infill and cross-cutting relationships: a group associated with subordinate pyrite mineralisations which is most likely related to the syn- and early post-emplacement phases of the igneous intrusion (e.g., hydrothermal activity, metasomatism), and a group interpreted as related to precipitation from mineralised enriched fluids charged by in situ enhanced water-rock interaction (i.e., drainage and dissolution of unstable minerals). This latter process is also invoked for the formation of some of the calcite veins found within the carbonate-cemented beds and intervals, and for the oxide smears found within the hematite-cemented deposits of the upper part of the reservoir (i.e., Knorringfjellet Fm.). Due to their occurrence within the lower Agardhfjellet Fm., some of the thicker healed fractures could be interpreted as altered sedimentary dykes with a weathered core. This weathering could be related to the latest phases of the regional exhumation with the consequent general stress release and enhancement of the superficial processes (see Fig. 15).

Lithostratigraphic and structural framework of the reservoir succession

Based on our integration of stratigraphic and structural observations from boreholes and outcrops, the investigated reservoir-caprock succession has been subdivided into five litho-structural units (LSUs) comprising specific systematic and non-systematic fracture sets mainly controlled by dominant lithologies and sedimentary facies. A summary of the stratigraphic-structural correlation between boreholes and outcrops, and the subdivision of the reservoir section into LSUs, is presented in Fig. 16, and can be described as follows: (LSU A) massive to laminated, shale-dominated intervals, characterised by high- and low-angle fractures, with a predominance of the latter; (LSU B) massive- to thin-bedded, heterogeneous, mixed silty-shaly-sandy intervals, characterised by mainly non-systematic BC fractures, both low- and high-angled, and subordinate, high-angled systematic TG fractures; (LSU C) massive to laminated, medium- to thick-bedded, medium- to coarse-grained sandstones and conglomerates, dominated by high-angle systematic BC and TG fractures, with some subordinate low-angle ones, locally showing evidence of strike-slip and dip-slip shearing, respectively; (LSU D) igneous intrusions (i.e., dolerite dykes and sills) characterised by syn- and post-emplacement, TG and BC fractures, and veins subparallel and subperpendicular to the intrusion boundaries; (LSU E) carbonate beds (i.e., limestones, bioclastites), dominated by high-angle TG and BC fractures and calcite veins.

The defined LSUs can be recognised both in the boreholes and in outcrops, and are interpreted to reflect contrasting rheological/mechanical behaviour. They are therefore inferred to represent proxies of


succession with variable intensity. In this sense, the herein defined LSUs and SUs are thought to have specific attributes in terms of fluid conductivity, as summarised in Fig. 18.

The estimation of the true fracture aperture, which is the most important parameter for fracture flow estimates, remains a complicated issue due to the effects of rapid exhumation, such as the high degree of decompaction in drillcores, and the superficial weathering of the outcrops (e.g., frost-thaw cycles, slope unloading). In this context, in situ borehole data would be the most representative, even though the standard resolution of the direct imaging techniques (e.g., down-hole cameras, televiewer) is not high enough to fully characterise the subtle (<1 mm) structural discontinuities. An approximate, qualitative evaluation of the possible apertures is given by the thickness of the associated mineralised veins (generally less than 1 mm), which are too poorly represented and confined within certain lithologies (e.g., dolerites, carbonate beds) to be used as a standard reliable parameter for the rest of the fracture sets. Another option is represented by the CT scanning of drillcores, which gives the best compromise in terms of high-resolution visualisation of the inner fracture networks with a non-destructive approach (Van Stappen, 2013). Such analyses performed on pressurised cores (collected at the formation pressure) would represent the best case study to estimate fracture apertures and interconnections. Further work and analyses are planned to include fracture aperture data in the final database.

On account of its general characteristics, persistence and orientation subparallel to the in situ, present-day, maximum horizontal stress (M. Jochmann, pers. comm.; unpublished data), the fracture set J1 is the most pervasive, systematic and most likely open and conductive to fluid flow. Therefore, to optimise the injectivity by intercepting a maximum of J1 fractures, an inclined well design (horizontal at the reservoir depth) with a NNW–SSE orientation is recommended. For the same reason, at the reservoir level, the injected buoyant CO2 plume is expected to drift mainly towards the E–NE, spreading out horizontally along the finer-grained intervals (e.g., LSUs A) and vertically though the coarser-grained ones (e.g., LSUs B and C). In context with deeper considerations around fluid flow, the fracture orientation data proposed as input parameters for reservoir modelling and fluid-flow simulations have been applied to the development of the reservoir model as presented in Senger et al. (2013b).

Preliminary parameterisation of open-healed-sealed fracture classes

In terms of fluid conductivity, the status of fractures from initiation to sealing and healing with time play a crucial role. With the term ‘sealed’ we mean mineralised fractures (i.e., veins) mostly filled with calcite and, subordinately,

geomechanical units (Shackleton et al., 2005). Lateral and vertical changes in fracture set orientations and fracture frequencies are observed within the LSUs, especially at their boundaries.

Mesoscale fracture refraction due to the mechanical contrast observed at the lithostratigraphic discontinuities (e.g., bedding planes, lithological/diagenetic boundaries) likely contributes to generating scooped and curved geometries of the fracture surfaces and thus adds to the spread of spatial data. Localised high dispersions of structural orientations are also observed within the laminated to thin-bedded, heterogeneous intervals, whereas the massive, generally homogeneous rocks are characterised by relatively more even and clear distributions.

On the other hand, at a larger scale, there is a striking contrast in fracture orientation between the reservoir and the cap-rock interval (see rose diagrams in Fig. 16). The different trends observed in the fracture systems collected in the overburden, above the upper detachment level (see Figs. 2 & 3), suggest a marked mechanical decoupling of the sedimentary succession likely due to this décollement zone, about 200–250 m above the top of the reservoir.

In terms of fracture spacing, the entire scan-lines dataset shows a negative exponential distribution, with a median value of 0.1 m (Fig. 17A). A bed thickness vs. fracture frequency plot, classified by LSU, suggests a typical direct correlation for the LSUs B, C and E, and a possible inverse relationship for LSU A, testifying to an apparent fracture enhancing in the shale intervals along with the increasing thickness. However, the indicated trends are statistically weak and not significant (R2 <0.5). Fracture data from LSU D have not been analysed in these terms due to the dolerite’s intrusive nature and intrinsic fracturing mechanisms (Fig. 17B).

Further complexity is added to the overall LSU framework by the presence of structural units (SUs) that are not related to specific stratigraphic intervals, such as fracture corridors related to mesoscopic (i.e., sub-seismic) normal faults and the chilled/sheared margins of the dolerite intrusions. Distinct structural associations characterise each LSU and SU, which are inferred to influence subsurface fluid flow by preferentially driving it laterally and/or vertically (see below).

Regional fracture orientation and inferred conductivity

The total dataset of fractures and other discontinuities has been subdivided by: (1) orientation, (2) filling by secondary mineralisation, (3) deformation style (i.e., shear vs. non-shear), and (4) geometric attitude (sharp vs. tabular discontinuities). Noticeably, some of the populations are exclusive to certain lithologies, whereas other populations can be found throughout the studied

148 K. Ogata et al.

CD_KD_5CD_KA_8CD_KA_7CD_KA_5CD_KD_4

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?

Estimated Dh 4 LSU

SubdivisionLog

BrentskardhaugenBed

Slottet Bed

677 m (approx. DH4 depth)

892 m (approx. DH4 depth)

215 m

BC_KS_6

N = 909 Circle 6%

LSU A

N = 815 Circle 7%

LSU B

N = 1052 Circle 6%

LSU C

N = 1521 Circle 4%

LSU D

N = 558 Circle 9%

LSU E

Reservoir

Reservoir

Caprock

BC_KS_1BC_KS_3

BC_KS_2

BB_KO_1

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Sandy/medium-thick bedded

B

CDolerite intrusionsD

CarbonatesE

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Silty/thin-bedded/heterogeneous

LITHO-STRUCTURAL UNITS (LSU)

Top Reservoir

closedopen

closedopen

ca.18 km

Drill Site 2

41.9 %

21.4 %

32.9 %

0.7 % 3.1 %

Boreholes

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24.2 %

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OutcropsLSU A

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y = 0.037x + 1.5111 R = 0.42645

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y = -0.0466x + 10.514 R = 0.32969

Linear (A)

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log LSU thickness (cm)

Mea

n f/

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ulat

ive

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ture

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Figure 16. Lithostratigraphic and structural correlation of the investi-gated reservoir section between boreholes and outcrops. The individual litho-structural units (LSUs) are marked accordingly with the standar-dised colour code, and the measured intervals are indicated with scan-line IDs (see Table 1). Rose diagrams represent fracture-orientation data for each LSU investigated in the reservoir and caprock section. Pie-charts show the relative amount (volume %) of the identified LSUs in boreholes and outcrops.

Figure 17. Cumulative fracture frequency vs. spacing diagram for each collected scan-line (for scan-line IDs see Table 1). (B) Fracture frequ-ency vs. considered LSU thickness (logarithmic scale) for each scan-line. Fit lines and relative data are also represented. LSU D is not con-sidered since dolerites achieve intrinsic fracture systems unrelated to size and thickness of the intrusion (see text for details).

‹

‹

150 K. Ogata et al.

Potential fluidmigration pathwaysnot to scale

A


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Enhanced verticalconnectivity



Diffused/baffled lateral andvertical connectivity.

Enhanced lateral connectivityat unit boundaries



Baffled verticalconnectivity. Enhancedlateral connectivity at

unit boundaries





Enhanced lateralconnectivity

N = 815 N = 1203

N = 1521 N = 5581 % Area ContoursC.I. = 1.0 % / 1 % area


Enhanced verticalconnectivity. Baffledlateral connectivity.

N = 281

B

A

CD

E

Fault core

Fault damagezone

Igneous intrusionchilled margins

Through-goingfracturesBed-con�ned

fractures

Healed fractures(mineralized veins)

N = 1411

Figure 18. Conceptual 3D representation of the identified LSUs and SUs and related fracture patterns, showing their possible influence on fluid-flow migration. Stereonets (poles to planes, equal-area, lower hemisphere, 1% area contour) summarise all the collected fracture data for each LSU and SU (colour code as for each LSU).


the exhumed reservoir-caprock section directly in the field, has allowed the acquisition of an extensive ground-truth database. These calibrated data are thus reliable parameters for geology-based reservoir models, providing a comprehensive characterisation of the potential storage framework. The main achievements of this study are:1. Five major litho-structural units (LSUs) have been

identified in the investigated section: (LSU A) massive to laminated shales characterised by predominant low-angle fractures, (LSU B) heterogeneous, fine-grained intervals with both low- and high-angle fractures, (LSU C) massive, coarse-grained intervals dominated by high-angle fractures, (LSU D) igneous intrusions characterised by syn- and post-emplacement fractures and veins, and (LSU E) carbonate beds dominated by high-angle fractures and veins. Each one is inferred to control lateral and vertical fluid migration in different specific ways. Such structural associations and their intrinsic characteristics represent the key factors in controlling the internal connectivity of the reservoir and the preferred fluid-flow directions.

2. Within the analysed LSUs we identify a main fracture set, J1, comprising systematic joint populations oriented approximately E–W, and a subordinate fracture set, J2, characterised by systematic joint populations oriented approximately N–S. Along with these, a high-angle, conjugate set of shear fractures, S1, trending roughly NE–SW and NW–SE were identified mainly in the coarser-grained and more cemented lithologies, whereas a low-angle, shear fracture set, S2, striking E–W to NW–SE is observed within finer-grained lithologies and some igneous intrusions (S2b).

3. Fracture populations characterising each LSU represent the intrinsic mechanical response to a polyphase and progressive tectonic evolution comprising: (i) synsedimentary deformation, (ii) horizontal compression/transpression, (iii) tectonic loading, and (iv) uplift/unroofing-related decompaction.

4. The localised occurrence of healed and sealed fractures within specific portions of the succession (e.g., dolerite intrusions, carbonate-cemented intervals) is thought to create enough heterogeneous permeability to at least partly compartmentalise the reservoir stratigraphy, forming vertical barriers/baffles where concordant (e.g., beds, bedsets) and lateral ones where discordant (e.g., dykes, carbonate buildups).

5. Preferential fluid-flow pathways represented by high-permeability, fractured zones (e.g., fracture corridors and faults, chilled margins of igneous intrusions, lithological boundaries, mechanical horizons) occur throughout the reservoir section but not in the top seal.

6. Due to the present-day stress regime and the orientation of the most promising fracture systems (i.e., J1) in terms of possible fluid conductivity, we propose a NNW–SSE-oriented horizontal drilling of the injector well at the reservoir level to optimise

pyrite and Fe- and Mn-oxides. The occurrence of these different types of precipitated minerals is confined within (or close to) specific lithologies and structural-stratigraphic positions. On the other hand, with the term ‘healed’ we highlight those fractures which have undergone mechanical compaction, and were later infilled by altered material, usually finer grained and less cemented, as compared to the country rock. For the fractures showing some displacement (i.e., shears, reworked joints), the fine-grained fill can be interpreted as a shale gouge layer or membrane, possibly related to the localised dissolution of the deformed proto-cataclastic material with residual clay minerals (see above).

An attempt at dynamic classification in terms of open-healed-sealed fractures is hereby proposed for a semi-quantitative assessment of the most promising fluid-conductive units. Fracture permeability is a function of the fracture recovery, which is the tendency of the fracture to close again due to mechanical (i.e., healing) and chemical (i.e., sealing) compaction (see above). On this basis, we tentatively introduce the ‘Fracture Permeability Recovery Factor’ (FPRF) as a control parameter for estimating fracture conductivity. The other term of the proposed classification is the ‘Fracture Recovery Mechanism Factor’ (FRMF), which defines the relative contribution from healing vs. sealing processes (e.g., minerals counteracting compaction).

Fractures maintaining the initial aperture unchanged from that achieved during the mechanical failure and opening are obviously the best candidates for driving fluids (FPRF=1), while completely healed (FRMF=0) and sealed (FRMF=1) ones represent instead low-permeability or impermeable barriers (FPRF=0). These three types of ideal fractures represent the end members of the proposed classification, and the analysed case studies fall in between as variable combinations of the three.

In the triangle diagram shown in Fig. 19, a first semi-quantitative assessment of the fracture status classes defined by the FPRFs and FRMFs is proposed. For each investigated LSU and SU, a general FPRF can be inferred from available observations. The plot shows a trend from chiefly sealed fractures of LSUs C and D, to partly healed fractures in LSUs A and F. Accordingly, enhanced flow is forecast for the latter LSUs (i.e., A and F) with a reduced flow capability for the others. Further work is planned to quantitatively define FPRFs and FRMFs and test them as input parameters for numerical reservoir modelling.

ConclusionsThe large amount of available structural and stratigraphic data collected through direct and indirect borehole analyses, along with the detailed studies on

152 K. Ogata et al.

the fracture permeability and to maximise the related fluid flow.

7. In the proposed framework we expect an E–W spreading of the injected buoyant plume with a focused drift towards the E–NE, through horizontal and vertical diffusion within the finer- and coarser-grained intervals, respectively.

8. The moderate injectivity of the tight, naturally fractured reservoir of the Longyearbyen CO2 Lab project affirms that CO2 may potentially be injected and stored, with a major contribution from the regional network of mesoscale fracture sets mapped and analysed in both drillcores and outcrops.

Acknowledgements. This work is part of the ‘Geological input to Carbon Storage (GeC)’ project funded by the CLIMIT program of the Research Council of Norway, with Kim Senger’s fieldwork supported by Arctic Field Grants from the Svalbard Science Forum. Andreas Rittersbacher, Dave Richey, Laura Farrell, Marie Marušková, Gareth S. Lord, Ingrid Anell, Benedikte Jarsto, Berit Husteli, Aleksandra Smyrak-Sikora, Sebastian Sikora and Srikumar Roy are thanked for the fruitful discussions and for their assistance in the field. The GeC project team works in close co-operation with the Longyearbyen CO2 Lab project managed by the UNIS CO2 Lab AS (http://co2-ccs.unis.no) and the SUCCESS center. Shapefiles from NPI–Geonet have been used to construct the geological maps. Finally, we would like to thank the editor Trond Slagstad, and the reviewers Haakon Fossen and Steffen G. Bergh for their constructive assessment of the paper.

Initial openingunchanged

Sealing(chemical)

Healing(mechanical)

Non-stratabound unit(faults/fracture corridors)

A


C

Dolerite intrusionD

Carbonate layerE

F


0 0.2 0.4 0.6 0.8 1

1

0

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1

0

Frac

ture

Per

mea

bilit

y Re

cove

ry F

acto

r (FP

RF)

Fracture Recovery Mechanism Factor (FRMF)

Figure 19. Triangular diagram suggesting fracture status classes by semi-quantitative plotting of each LSU and SU (stars with colour code as for each LSU) in terms of Fracture Permeability Recovery Factor (FPRF) and Fracture Recovery Mechanism Factor (FRMF). See text for discussion.


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