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published September 10, 2012; doi 10.1144/SP374.9 v.374, firstGeological Society, London, Special Publications

K. Ogata, K. Senger, A. Braathen, J. Tveranger and S. Olaussen (Spitsbergen, Arctic Norway)

middle Jurassic Kapp Toscana Group−Triassic storage: a case study of the upper2for potential CO

The importance of natural fractures in a tight reservoir

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The importance of natural fractures in a tight reservoir for potential

CO2 storage: a case study of the upper Triassic–middle Jurassic

Kapp Toscana Group (Spitsbergen, Arctic Norway)

K. OGATA1*, K. SENGER1,2,3, A. BRAATHEN1, J. TVERANGER2 & S. OLAUSSEN1

1University Centre in Svalbard (UNIS), PO Box 56, 9171 Longyearbyen, Norway2Centre for Integrated Petroleum Research (CIPR), Uni Research,

Allegaten 41, 5020 Bergen, Norway3Department of Earth Science, University of Bergen, Allegaten 41, 5020 Bergen, Norway

*Corresponding author (e-mail: [email protected])

Abstract: In the Longyearbyen CO2 laboratory project, it is planned to inject carbon dioxide into aTriassic–Jurassic fractured sandstone–shale succession (Kapp Toscana Group) at a depth of 700–1000 m below the local settlement. The targeted storage sandstones offer moderate secondary por-osity and low permeability (unconventional reservoir), whereas water injection tests evidence goodlateral fluid flow facilitated by extensive fracturing. Therefore, a detailed investigation of fracturesets/discontinuities and their characteristics have been undertaken, concentrating on the upperreservoir interval (670–706 m). Datasets include drill cores and well logs, and observations of out-crops, that mainly show fracturing but also some disaggregation deformation bands in the sand-stones. The fracture distribution has a lithostratigraphical relationship, and can be subdividedinto: (A) massive to laminated shaly intervals, offering abundant lower-angle shear fractures;(B) massive to thin-bedded, heterogeneous, mixed silty–shaly intervals, with a predominance ofnon-systematic, pervasive bed-confined fractures; and (C) massive to laminated, medium- tothick-bedded, fine- to coarse-grained sandstones with a lower frequency of mostly steep fractures.These domains represent pseudo-geomechanical units characterized by specific fracture sets andfracture intensity, with indicated relationships between the bed thickness and fracture intensity,and with domains separated along bedding interfaces. We discuss the impact of these lithostruc-tural domains on the fluid flow pathways in the heterolithic storage unit.

In the Longyearbyen CO2 laboratory project (LYBCO2 lab) the possible depth interval for an injectionof carbon dioxide is a siliciclastic unit located at adepth of 700–1000 m in the subsurface beneaththe High Arctic community of Longyearbyen, Sval-bard (Fig. 1). The project, initiated in 2007 by theUniversity Centre in Svalbard (UNIS), involvespartners from both academia and industry (Braathenet al. 2010; Baelum et al. 2012). The principal aimis to utilize the proximity of suitable reservoir rocksto store CO2 from the local coal-fuelled powerplant. Research focuses on understanding the behav-iour of CO2 in the subsurface while at the same timecontributing to the reduction of local emissions ofCO2. The coal-powered co-generation 10 MW heatand power plant, located only 5 km from the plan-ned injection site, emits approximately 64 000tonnes of CO2 annually, from the combustion ofabout 26 000 tonnes of locally mined coal. The pro-ximity of the energy source (i.e. coal mines), powerplant and injection site, in combination with thefact that Longyearbyen is a nearly closed energysystem, makes it a highly suitable candidate for

demonstrating the complete carbon value chain(Braathen et al. 2010).

In order to investigate the suitability of theplanned sequestration site, the Longyearbyen CO2

lab has drilled and cored four wells during theperiod of 2007–2010 (the drill site locations areshown in Fig. 2), two of which penetrated the reser-voir (Dh2 and Dh4: Fig. 3). The target reservoir hasno mapped closure and it crops out approximately15 km NE of the planned injection site. However,borehole analyses on the Dh4 well recorded morethan 50 bar underpressure at 870 m (Braathen et al.2010) showing the presence of an efficient trap,probably either a stratigraphical or a combinedstratigraphical–structural trap, and supporting thesealing efficiency of the cap rock. Although there isno clear evidence of large faults or major structuralfeatures in the area close to the planned injectionsite, the reservoir interval is vertically sandwichedbetween two main decollement zones. These zonesrelate to the Palaeogene contractional event respon-sible for the development of the transpressional fold-and-thrust belt that characterizes the western part of

From: Spence, G. H., Redfern, J., Aguilera, R., Bevan, T. G., Cosgrove, J. W., Couples, G. D. & Daniel, J.-M. (eds)2012. Advances in the Study of Fractured Reservoirs. Geological Society, London, Special Publications, 374,http://dx.doi.org/10.1144/SP374.9 # The Geological Society of London 2012. Publishing disclaimer:www.geolsoc.org.uk/pub_ethics

10.1144/SP374.9 Geological Society, London, Special Publications published online September 10, 2012 as doi:

Hornsund Fault Zone

150 km

BFZLFZ

SvalbardNORWAY

Franz Josef LandRUSSIA

Sevemaya ZemlyaRUSSIA

NovayaZemlyaRUSSIA

RUSSIA

SWEDEN

NORWAY

ICELAND

GreenlandDENMARK

CANADANorth Pole

Arctic Circle

Arctic Ocean

GreenlandSea

Barents Sea

Western hinterland

Basement-involvedfold-thrust complexThin-skinned fold-thrust beltEastern foreland province

BFZ

BFZ LFZ

LFZ

ISFJORDE

N

BELLSUND

HORNSUND

SØRKAPP

50 km

N

N

Western hinterland

West

50 km

Basement-involvedfold-thrust complex Central Zone Eastern foreland province

EastBFZLFZ

Cp Cp

Cp

CpCp Cp

Ca

T

DD D Ca

Ca

Ca

Tr

Tr

JC JC JC

0 0

A B

A

B

a

b

c

d

LYB CO2

Lab

LYB CO2

Lab

HornsundFault Zone

Fig. 1. Location and tectonic setting of the Svalbard archipelago and position of the Longyearbyen CO2 lab site (LYBCO2 Lab). The planned injection target, the Kapp Toscana Group, is sandwiched between the upper and middledecollement zones associated with the West Spitsbergen fold-thrust belt, a direct result of the Palaeogenetranspressional tectonics. (a) The location of the Svalbard archipelago in the context of the North Atlantic. Thearchipelago lies within the High Arctic, approximately half way between northern Norway and the North Pole. (b) Mainstructural lineaments on Svalbard, aligned predominantly NNW–SSE. (c) Tectonic overview map of Spitsbergen,illustrating the West Spitsbergen fold-and-thrust belt (modified from Bergh et al. 1997). (d) Schematic cross-sectionacross Spitsbergen, emphasizing the LYB CO2 lab targeted reservoir/storage unit. The cross-section’s location ismarked in (c). Figure modified after Bergh et al. (1997). BFZ, Billefjorden Fault Zone; LFZ, Lomfjorden Fault Zone;D, Devonian; Ca, Carboniferous; Cp, Permian; Tr, Triassic; JC, Jurassic–Cretaceous.

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Svalbard (see Fig. 1c, d) (Bergh et al. 1997; Braathenet al. 1999). Based on vitrinite data (Throndsen1982), the reservoir is thought to have experiencedmaximum burial of approximately 4.5 km in depthduring the Eocene, prior to an estimated uplift ofabout 3.5 km in the Oligocene–latest Neogene.However, a number of workers using additionalmethods consider this to be an overestimation (seethe work of Blythe & Kleinspehn 1998 for an exten-sive review). Rapid unroofing during Quaternarytimes is attributed to the widespread glaciations inthe area (Ingolfsson 2011). The deep burial led tomechanical compaction with dense grain packing aswell as extensive quartz cementation (Braathen et al.2010). Matrix permeability in Dh4, as measuredfrom drill core plugs, is typically less than 2 mD(where1 mD ¼ 10215 m2),withporosityvaluesvary-ing from 8 to 18% (Farokhpoor et al. 2010, 2011).Despite these low measured permeabilities, threewater injection tests confirmed the good injectionpotential of the target reservoir. A 5 day injectiontest conducted in August 2010 suggested an aver-age flow capacity of 45 mD . m in the lowermostpart of the reservoir (870–970 m: Braathen et al.2010). The injectivity is thought to be primarilya function of the natural fractures identified bothin the drill cores and in the outcrops. Accordingly,a detailed understanding of the fracture systemsobserved in the reservoir is essential for predictingthe behaviour of CO2 and other fluids in the reservoir.

In this contribution we investigate the upper partof the reservoir succession, presenting a case studyof selected examples from an extensive dataset ofnatural fractures obtained from both borehole andoutcrop data. When fully processed, the data willbe utilized in fluid flow modelling. At this stage,our aim is to highlight the importance of naturalfractures when viewed as potential CO2 storage onSpitsbergen, as well as to illustrate the need for well-constrained and reliable outcrop data as input to thereservoir modelling and simulation.

Geological setting

Tectonic development

The Svalbard archipelago is an uplifted part of theNW margin of the Barents Shelf (Harland 1997).Our study area is situated on the NW margin of theCentral Spitsbergen Basin (CSB), a major synclinalfeature (see Fig. 1c, d). The CSB’s boundaries alignto the predominant NNW–SSE structural grainprevalent on Svalbard (Nøttvedt et al. 1993). Follo-wing the Caledonian Orogeny, assumed Devoniancrustal-scale extension and localized Carboniferousrifting, Svalbard evolved into a stable platformduring the late Carboniferous–Mesozoic time,

drifting northwards during the deposition of theMesozoic succession. The opening of the NorthAtlantic led to dextral movement along the DeGeer Zone (i.e. the Hornsund Fault Zone) betweenSvalbard and East Greenland during the Palaeogene(Eldholm et al. 1987; Braathen et al. 1995; Leeveret al. 2011). This caused oblique compression andthe development of the West Spitsbergen fold-and-thrust belt (WSFB), and the consequent Terti-ary CSB, a foreland to wedge-top basin comprisingan infill of mixed continental and marine clastics(Steel et al. 1985; Braathen et al. 1997; Helland-Hansen 2010). The development of the WSFB dur-ing the Palaeocene–Eocene generated a series ofeastwards-extending thrust sheets soled by decol-lement zones along evaporite and shale intervals(Bergh et al. 1997). This folding and thrusting canbe linked to a significant fracturing. However, LateCretaceous magmatic dyke–sill intrusion (Mina-kov et al. 2012) and Quaternary unroofing anddecompaction probably also added fractures to thesuccession.

Stratigraphical development

The targeted storage unit is an aquifer made up of asiliciclastic succession belonging to the upper Trias-sic–middle Jurassic Kapp Toscana Group. It com-prises the De Geerdalen Formation and elementsof the overlying Wilhelmøya Subgroup (Figs 2 &3) (Worsley 1973, 2008; Knarud 1980; Mørk et al.1982; Harland & Geddes 1997; Mørk & Worsley2006). The 270 m-thick drilled section of the DeGeerdalen Formation includes shales, siltstonesand sandstones deposited in a near-shore, paralic(lagoonal–delta plain) environment with net sand-stone of approximate 30% (net/gross (N/G) ratioof c. 0.3). Most palaeogeographical reconstructionssuggest a NW-prograding deltaic system (Mørket al. 1982; Steel & Worsley 1984; Riis et al. 2008;Glørstad-Clark et al. 2010). The overlying 20 m-thick Norian–Bathonian Knorringfjellet Formationof the Wilhelmøya Subgroup is interpreted as a con-densed siliciclastic unit (i.e. remanie), probably alag resulting from coastal reworking of deltaic sedi-ments (Mørk et al. 1982; Harland & Geddes 1997;Nagy et al. 2011). These units are overlain by a250 m-thick shale unit of the middle–upper Juras-sic Agardhfjellet Formation and the 200 m-thick,predominantly shaly, Lower Cretaceous RurikfjelletFormation: together these two units form the caprock of the reservoir/storage unit (i.e. ‘lower aqui-fer’) (Fig. 3). The Upper Jurassic Agardhfjellet For-mation is widespread regionally and its time-equivalent stratigraphical interval represents themajor source, and commonly the main cap rock,of many of the oil and gas fields on the Norwegiancontinental shelf (Spencer et al. 2008). Above the

NATURAL FRACTURES AND CO2 STORAGE10.1144/SP374.9




cap rock, an approximately 60 m-thick deltaic unit,the Barremian Helvetiafjellet Formation, comprisesan ‘upper aquifer’. Above this, the 120 m-thick over-burden consists of a 60 m-thick, Aptian–Albian,mixed sandstone–shale unit of shallow-marineto inner-shelf affinity belonging to the Carolinefjel-let Formation, and a 60 m-thick interval of Quatern-ary and Holocene fluvial sand/gravel and marineclay. The thickness of the permafrost in the areais estimated to be approximately 100 m (Humlumet al. 2003).

Methods

Borehole analyses

An optical televiewer was used to characterizethe fractures between 442 and 706 m, whereas thenarrow drill hole diameter (46 mm) in the deeperparts of the borehole prevented data acquisitionfrom deeper levels (Elvebakk 2010).

Detailed (1:10 scale) structural logging of thereservoir section (668–970 m) in the drill cores ofDh4 was carried out to describe the physical char-acteristics and frequency distribution of natural dis-continuities (as defined by Schultz & Fossen 2008),primarily distinguishing between closed and openones, with a focus on fractures/cracks. The recog-nition of true pre-coring features has not been easybecause of the high degree of decompaction anddrilling-induced stresses deforming the cores. Thecharacterization of discontinuities includes the fol-lowing standard parameters (see Singhal & Gupta2010 and references therein):

† orientation – spatial attitude and geometricalfeatures (e.g. strike, dip-angle);

† mid-point depth – vertical position of the dis-continuity half-way point within the well;

† spacing – perpendicular distance between adja-cent discontinuities of the same set;

† persistence – minimum relative length of thediscontinuity trace;

† linear density – number of discontinuities perunit length;

† connectivity – intersection and terminationcharacteristics of discontinuities;

† relative aperture – relative perpendicular distancebetween the two margins of the discontinuity;

† asperity – wall-rock morphology along the dis-continuity surface;

† wall coatings and infillings – solid materialoccurring as coatings or filling along the discon-tinuity surface.

The differentiation between natural and drilling-induced fractures (excluded from the final count)was performed taking into account: (1) the overallappearance (e.g. fresh v. weathered); (2) their conti-nuity across the core (e.g. through-going v. core-confined, point of origin/termination within v.outside the core); (3) the occurrence of mineraliz-ation/coatings; (4) anomalous trends (e.g. abrupthooking toward pre-existing fractures and coreboundaries; and (5) the matching/mismatching ofthe fracture sides (Kulander et al. 1977). As theretrieved cores were not oriented, azimuth infor-mation is only available from televiewer data inthe uppermost 39 m of the reservoir interval (667–706 m total depth (TD)).

Outcrop analyses

To complement the borehole information, fieldworkwas conducted at Deltaneset in Central Spitsber-gen, where the reservoir interval reaches the surface(for the location see Fig. 2). Natural fractures werecounted along scanlines, allowing the constructionof frequency plots along individual intervals. Theorientation of each fracture was measured, usingboth a geological compass and a GeoClino digitalclinometer. As for the cores, natural fractures wereclassified based on their mesoscale characteristics(see earlier), including in this case observations oftheir outcrop-scale vertical continuity (bed-confinedv. through-going). Furthermore, stratigraphical log-ging (1:50 scale) was conducted throughout theKnorringfjellet Formation and the upper third ofthe De Geerdalen Formation in order to correlatethe outcrop data to the borehole data. Scanlines weresurveyed along various stratigraphical intervals andwithin a range of different lithologies in order tocapture potential variations in the fracture characterrelated to stratigraphy. Strike data are corrected for amagnetic declination of 68 east of true north.

A total of 59 scanlines were collected during thefield campaign. In the present paper, 13 representa-tive scanlines for the three major lithostructural

Fig. 2. Location of the study area within the context of the regional geology of Central Spitsbergen. The inset mapshows the study area at Deltaneset and the location (circled) of the stratigraphical log presented in Figure 7; theapproximate grid co-ordinates of the stratigraphical log tying the various scanlines are: 0521174 East, 8697326 North(UTM Zone 33X, projection ED50). The cross-section illustrates the open nature of the reservoir succession, which risesto the surface in the NE, as well as the relationship of the drill site (Dh4) with the Deltaneset outcrop locality. Redrawnand modified after Major et al. (2001). Shapefiles of the geological units from the NPI-Geonet project are used.



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associations (LSAs) are presented (Table 1). Theselithostructural domains or units are primarilydefined on the basis of the considered lithologicalinterval: (A) massive to laminated shaly intervals:(B) massive to thin-bedded, heterogeneous, mixedsilty–shaly intervals; and (C) massive to laminated,medium- to thick-bedded, fine- to coarse-grainedsandstones and conglomerates. Each domain is fur-ther characterized by a distinct occurrence of preva-lent systematic and non-systematic fracture sets,sedimentary facies, bed thicknesses and degree ofcementation. These units are regularly distributedthroughout the sedimentary succession and reflectcontrasting rheological behaviour, forming distinctintervals characterized by a specific type of fractur-ing and, thus, inferred to represent proxies of geo-mechanical units (Shackleton et al. 2005).

Apart from the generalized scree/soil coverageof the outcrops, we also took the frost–defrostcycles and glacier dynamics-related slope unloadinginto account as possible factors influencing fracturepatterns and apertures.

Fracture characterization

Borehole data

The reservoir interval in Dh4, from 672 to 970 m,exhibits relatively high frequencies of both verticaland horizontal sharp and tabular discontinuities(Schultz & Fossen 2008), particularly fractures anddeformation bands. Manual counting identified 870individual, predominantly low-angled, and subordi-nately high-angled, open fractures in this interval(Fig. 4). In the upper part of the reservoir (between672 and 706 m TD) the acoustic televiewer iden-tified 35 fractures, whereas for the same intervalthe manual logging revealed at least 108 fractures(Fig. 5). This incongruity is probably related to thepredominance of discontinuities below the instru-ment resolution that are, instead, highlighted on thedirect observation by the high decompaction of retri-eved cores (e.g. strong preferential splitting of coresalong bedding surfaces, laminae and structural dis-continuities), which is probably supported by theunderpressure recorded in the reservoir. For thereservoir succession the N/G ratio is only around25–30%, defined on the total sand thickness.

Successions of mudstone and shale, ranging inthickness from metres to tens of metres, host themajority of fractures. Fractures preferentially occurwithin fine-grained lithologies (massive to lami-nated and interbedded shales and siltstones) and,among these, low-angle (08–458), usually slicken-sided and non-mineralized fractures predominate.High-angle (.458) fractures and veins preferablyoccur within coarser-grained units (fine to coarsesandstones). The other closed (with infillings) preva-lent discontinuity types recognizable within coarser-grained lithologies are sharp hairline microfaults(mostly normal) with very-fine-grained material andcalcite fillings, and disaggregation deformationbands (Fossen et al. 2007; Fossen 2010), usuallybearing a phyllosilicate core. The fine-grained, infill-ing material can be interpreted as a shale gouge ormembrane, possibly also related to the localizeddissolution of the cataclastic material into clay min-erals. Some of these features are millimetre- tocentimetre-thick, tabular deformation zones charac-terized by granular flow (no grain breakage), takenas evidence of soft-sediment deformation (e.g. foldedlaminae, fluidal structures). Deformation bandscomprise up to 30% of counted discontinuities inmedium-coarse sandstones. Mineralized fractures(mainly high-angle, calcite- and pyrite-filled veins)seem to concentrate in coarse-grained lithologies,especially within and around crystalline rocks (e.g.doleritic intrusions) and carbonate-rich beds (e.g.bioclastites). Open fractures predominantly displaydip angles of less than 458 and are mostly hosted infine-grained lithologies. Less than 30% of open frac-tures exhibit steep (.458) dips. These are concen-trated in coarse-grained lithologies.

In general terms, high-angle fractures are predo-minantly represented by Mode I fractures (i.e. joints),whereas low-angle ones belong to Mode II and IIIfractures (i.e. shears/tears), with some evidence ofmixed modes. Zones with high fracture frequenciesobserved within the Janusfjellet Subgroup (i.e. partof the lower Adventdalen Group) cap rock are asso-ciated with the upper main decollement zone,appearing as centimetre- to metre-thick zones ofunconsolidated, ‘crushed’ shales (shale gouge), sur-rounded by a dense network of generally conjugate,low-angle shear surfaces. Other minor peaks in frac-ture frequencies are found within the reservoir

Fig. 3. Overview of the stratigraphy penetrated by the LYB CO2 lab project drilling campaign from 2007 to 2010in Adventdalen, Spitsbergen. Boreholes Dh1 and Dh3 cored the cap-rock succession, whereas the Dh2 borehole coredthe upper part of the target storage unit. The Dh4 borehole penetrated nearly the whole reservoir section. The blackrectangle indicates the proposed injection target, which is further analysed in this paper, and the stratigraphicalportion covered by analyses of cores. The red rectangle highlights the portion of the stratigraphical section investigatedin the field (see Fig. 7 for correlation). Several igneous intrusions, up to 2 m thick, are penetrated by Dh4, and areillustrated in green. Please note that Dh1 and Dh2 are drilled at drill site 1 close to the airport, while Dh3 and Dh4 aredrilled at drill site 2 in Adventdalen (see Fig. 2 for the exact locations).



Table 1. Summary of the selected scanlines used in this contribution

TotalNo. offractures

No. ofTG

fractures

No.of BC

fractures

Fractures/m(average)

Fractures/m(maximum)

TGfractures/m(average)

BCfractures/m(average)

Fractures/m(average)length-

normalized

TGfractures/m

(average)length-

normalized

BCfractures/m(average)length-

normalized

Lithology Consideredthickness

(cm)

Lithostructuralassociation

(LSA)

221 106 115 7.4 15 3.5 3.8 6.3 3 3.2 Fine- tomedium-grainedbioclastic bedset

20 C

317 147 170 12.7 18 5.8 6.8 9 4.1 4.8 Finely laminatedsilty–shaleinterval

200 A

74 38 36 8.0 10 4.1 3.9 2.1 1.1 1 Medium-grainedsandstone bedset

30 C

192 107 85 6.4 13 3.5 2.8 5.4 3 2.4 Medium- tocoarse-grainedsandstone bed

150 C

144 88 56 4.8 12 2.9 1.8 4.1 2.5 1.5 Medium-grainedsand-supportedconglomerate

200 C

144 60 84 4.1 7 1.7 2.4 4.1 1.7 2.4 Thin-beddedshale–siltstoneinterval

300 B

124 31 93 5.2 9 1.3 3.8 3.5 0.9 2.6 Highly bioturbatedfine-grainedsandstone

50 B


50 B


50 B

76 29 47 2.9 7 1.1 1.8 2 0.8 1.3 Fine- tomedium-grainedsandstone bed

200 C

85 23 62 8.5 10 2.3 6.2 2.4 0.6 1.7 Massive shaleinterval

150 A


90 C


90 C

The scanlines are collected across the stratigraphy of the upper reservoir section (for the location, see Fig. 7). See the text for an explanation of the shown parameters.

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TOP

TOP

TOP

TOP

OPEN DISCONTINUITIES

TOP

TOP

CLOSED DISCONTINUITIES

162 107 98 118 74 73 70 60 109 380 290 98 54 7 2 2 36 3

a

b c

d

e

f

TOP

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TOP

g h

i

I. II.

Lithologies

Fig. 4. Synthesis of fracture information gathered from the drillcores of Dh4. (a) Weathered (oxidized) fracture. KnorringfjelletFormation, depth 676.56–676.83 m. (b) Hairline weathered(oxidized) fracture. De Geerdalen Formation, depth 698.17–698.34 m. (c) Hairline fresh fractures. De Geerdalen Formation,depth 716.77–716.91 m. (d) Highly fractured interval. DeGeerdalen Formation, depth 753.00–753.36 m. (e) Disaggregationdeformation band, with phyllosilicate membrane andapproximately 1 cm displacement. Knorringfjellet Formation,depth 679.71–679.86 m. (f) Disaggregation deformation band.Knorringfjellet Formation, 0.8 cm displacement, depth 678.54–678.64 m. (g) Calcite veins in sandstone. De Geerdalen Formation,depth 920.75–920.96 m. (h) Calcite veins in shale. De GeerdalenFormation, depth 966.42–966.48 m. (i) Mixed calcite–pyrite,thick vein in shale. De Geerdalen Formation, depth 955.61–955.70 m. The graphs indicate the relative fractions of the open andclosed types for different dip angles (to the left; diagram I) and indifferent host lithologies (to the right; diagram II). The absolutenumber of discontinuities within each category is given at the topof each bar.

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section related to specific stratigraphical intervals(see Fig. 5).

The projected reservoir interval (storage unit) inthe Knorringfjellet Formation was fully loggedusing wireline tools recording gamma ray, resistiv-ity and temperature readings, as well as an acousticteleviewer (Elvebakk 2010). This allows correla-tion of the fractures registered by the televiewerand the manual count (see Fig. 5). As the drill coreswere not oriented during recovery, the azimuthalinformation cannot be compared. The stratigraphi-cal fracture intensity (i.e. on the vertical axis), how-ever, indicates some agreement, particularly withinthe uppermost part of the De Geerdalen Forma-tion. The fracture frequency is clearly highest forthe 08–308 dip angle category; this is generally con-centrated within the finer-grained lithologies, as

discussed earlier. Furthermore, closed discontinu-ities generally occur only within coarser-grainedunits, especially in the upper third of the Knorringf-jellet Formation, peaking at approximately 678 m.

Outcrop data

The presented scanlines dataset was primarily col-lected in a valley located about 1 km east of Konus-dalen (for the location see Fig. 2). The valley haspreviously been studied for biostratigraphical pur-poses (Wierzbowski et al. 1981; Chlebowski &Wierzbowski 1983; Wierzbowski 1989), and is cur-rently being investigated for its Jurassic marinereptiles and hydrocarbon seeps (Hammer et al.2011). Outcrops are often scree-covered and scan-lines are, therefore, correspondingly short due to

Fig. 5. Wireline logs and fracture measurements for the target reservoir interval in the upper part of the De GeerdalenFormation and the Knorringfjellet Formation, as cored by Dh4. The wireline tools record the gamma ray, resistivityand temperature logs (Elvebakk 2010). Major changes in the resistivity and calculated geothermal gradient logsgenerally line up with heavily fractured intervals, possibly suggesting enhanced fluid flow. The fracture intensity plotsare subdivided into three dip angle categories, as well as into open and closed fracture intensity curves. GR, gamma ray;Res, resistivity (ohm . m); Temp, temperature (8C); TV int, televiewer intensity; f/m, number of fractures per metre.



limited exposure (Fig. 6). Nonetheless, the valleyprovides full exposure of the Knorringfjellet For-mation, as well as the uppermost 57 m of the DeGeerdalen Formation, and thus serves well for com-piling a representative stratigraphical log for corre-lation to the Dh4 borehole, approximately 20 kmaway (Fig. 7).

Also in this case, the high-angle fractures are pre-dominant and are mainly represented by Mode I frac-tures (i.e. joints), while the subordinate low-angleones are expressed by Mode II and III fractures(i.e. shears/tears), preferentially occurring withincoarse-grained and fine-grained intervals, respect-ively. These structures have been distinguished intwo main populations, through-going (TG) or bed-confined (BC), on the basis of their persistence withinthe considered lithostratigraphical interval (e.g.bed, bedset, lithological unit), their cross-cuttingrelationships with the host lithologies and, wherepossible, their continuity at the outcrop scale. Inthis framework, compared to BC fractures, TG frac-tures are defined by sets that are more homogeneous.

Localized high dispersions of structural orien-tations are observed within the laminated to thin-bedded, heterogeneous intervals (i.e. lithostructuraldomain B), while the massive, generally homo-geneous rocks are characterized by relatively moreeven and clear distributions (i.e. lithostructuraldomains A and C).

In general, the high-angle fractures seem to beorganized into two main sets, trending approxi-mately east–west and NNE–SSW, and two subor-dinate and less defined NW–SE and NE–SW sets.The low-angle fractures, prevailing within the fine-grained, massive to laminated intervals (i.e. litho-structural domain A), are, instead, represented bytwo principal sets striking approximately WNW–ESE and NNE–SSW (Fig. 8).

The above-described fracture sets are expresseddifferently within the investigated section, with evi-dent strike rotations of the main trends. In the lowerpart of the exposed De Gerdaleen Formation, themain fracture set trends approximately east–west,with a subordinate set trending NNE–SSW; whilethe upper part of this formation is, instead, charac-terized by WNW–ESE and ENE–WSW sets,with minor occurrence of the east–west and theNNE–SSW sets. The fracture sets of the Knorring-fjellet Formation are represented by three mainENE–WSW, NE–SW and NW–SE sets, with thesecondary occurrence of the NNE–SSW set, definingin places a single broad fan of fractures (see Fig. 7).

Systematic high-angle fractures do not showclear terminations within specific lithologies, ran-domly tipping out into each defined lithostructuraldomain, while low-angle ones seems to preferen-tially die out at well-defined lithological boundaries(e.g. master bedding surfaces and abrupt lithological

contacts), sometimes showing deflections wherethey propagate across different lithologies.

It should be noted that the fracture sets character-izing the conglomerate beds of the KnorringfjelletFormation display evidence of generalized shear-ing, with a relatively high frequency of striated(i.e. slickensided) walls and, sometimes, other kin-ematic indicators (e.g. calcite steps, en echelonveins). Such structures are distributed in both high-angle and low-angle fractures, exhibiting preferen-tial strike-slip and dip-slip movements, respectively(Fig. 9).

Throughout the investigated section, some evi-dence of calcite and quartz veining and cementationwas observed within carbonate layers (e.g. lime-stones, bioclastites) and medium- to thick-beddedsandstones and conglomerates, respectively. Enhan-ced, localized calcite cementation occurs within andaround fossiliferous carbonate beds and limestones,especially in the upper part of the De GeerdalenFormation; whereas the Knorringfjellet Forma-tion is generally characterized by quartz-cemented,coarse-grained beds. Enhanced cementation andveining was also observed within and around deci-metre- to metre-sized dolerite dykes and sills in thelower–middle part of the De Geerdalen Formation.Localized oxide-cemented parts are also observedthroughout the section, especially in the upper-most De Geerdalen Formation and RurikfjelletFormation.

Iron and manganese oxides forming dark,reddish- to purplish-coloured coatings on fracturewalls are widely distributed, especially on most con-tinuous open cracks and on weathered surfaces.

Discussion and conclusions

The structural characterization of the reservoir sec-tion was performed on the upper 100 m of the KappToscana Group, from which borehole and outcropdata were available and thus comparable in the data-base. Utilizing both data sources, we discuss thegenesis and the evolution of the investigated struc-tures, their lithostratigraphical distribution andtheir possible implications for subsurface fluid flowin the reservoir and the cap rock.

Tectonic events and related structures

Based on cross-cutting relationships and the phys-ical/geometrical characteristics of the investigatedstructural discontinuities, we propose the followingchronological subdivision from oldest to youngest(Fig. 10):

† High-angle disaggregation deformation bands(clay-filled microfaults) affecting coarse-grainedbeds. These are attributed to the early phases



CD_KD_1CD_KD_2

CD_KD_3~ S ~ N

CD Strat. Log

CD_KD_4CD_KD_5

De Geerdalen Fm.

CD_KD_1

CD_KD_2

CD_KD_3

CD_KD_4

CD_KD_5 ca. 2 m

ca. 2 m

ca. 1 m

ca. 1 m

ca. 1 m

ca. 10 m

Knorringfjellet Fm.

scanline pathbed-confined fracturethrough-going fracture

ca. 50 cm

a

b

c

d

A

B

C

D

considered interval

Fig. 6. Overview of the investigated section (location informally defined as Criocerasdalen, approximately 1 km east ofKonusdalen), illustrating the location of the some selected scanlines (traces and scanline identities are labelled in red) aswell as the stratigraphical log (yellow dashed line). For scanline descriptions see Table 1. The location of the



of deformation, within basically unconsolidatedrocks.Calcite-filledveinsmaydevelop in thecon-tact zones of igneous intrusions due to expansionand shrinkage during the heating–cooling cycle,and possibly related aureole metasomatism andhydrothermal circulation.

† Predominant low-angle fractures affecting fine-grained horizons. These relate to layer-parallelslip caused by a near-horizontal compression,probably associated with the crustal shorteningduring the Tertiary episode of transpression. Thecompetence contrast between layers could faci-litate bedding-parallel slip along weak (fine-grained) layers and subsequent strain accommo-dation-induced fracturing in intercalated, stifferbeds (e.g. coarse grained), probably reactivat-ing the older high-angle discontinuities. Layer-parallel shearing is evidenced by the predomi-nance of low-angle slickensided fractures andtheir apparent arrangement in conjugate systems.Moreover, high- and low-angle, strike-slip anddip-slip shear fractures in the thick conglomeratebeds of the Knorringfjellet Formation reflect anapproximately NE–SW-oriented compression,as is also recorded in the western fold-and-thrustbelt (Bergh et al. 1997; Braathen et al. 1997). Thegeneral lack of sealed fractures in fine-grainedlithologies may be attributed to the compartmen-talization of mineralizing fluids provided bylayer-parallel discontinuities in shaly layers (i.e.permeability anisotropy) with restricted com-munication between fine-grained beds and sand-stone layers. Considering the general inferredpatterns of intersection between these differ-ent fracture sets, it is possible to argue for anenhanced and generalized vertical connectivity,with three main trends of lateral connectivitydirected approximately NNE–SSW, NW–SEand east–west. In this framework, highly minera-lizing permeating fluids (such as those resultingfrom the water–rock interactions with carbon-ate-rich and igneous lithologies) could causeenhanced cementation of fractures within coarse-grained beds and in the nearby host rocks (seebelow).

† The most continuous, non-mineralized and wea-thered open fractures could be interpreted as

unloading joints (Engelder 1987), newly createdor, most probably, developed through the reacti-vation and interconnection of earlier discontinu-ities resulting from the generalized extensioncaused by Pliocene and Quaternary uplift andsubsequent unroofing. Oxide coatings on thewalls often characterize such open cracks, whichindicates subsequent circulation of fluids.

Lithostructural domains and fracture density

The fracture sets characterizing the studied strati-graphical section have been subdivided into threemain lithostructural domains (A, B and C). Theclassification is based on lithology, compositions(e.g. sand/mud ratio, coarse- v. fine-grained popu-lations), texture (homogenerous v. heterogeneous)and sedimentary structures (e.g. massive v. lami-nated). By combining these lithostructural associ-ations with the considered thicknesses and thefracture densities (i.e. fractures per metre (frac-tures/m)), based in this preliminary analysis, thefollowing pattern emerges (Fig. 11):

† a positive distribution for domain A – fracturedensities increase with increasing intervalthicknesses;

† a slightly negative distribution for domain B – amoderate decrease of fracture densities withincreasing interval thickness;

† a negative distribution for domain C – frac-ture densities decrease with increasing intervalthickness.

Whereas an increase in fracturing is expectedwithin stiffer and thinner beds (Lorenz et al. 2002;Shackleton et al. 2005 and references therein), anopposite trend can be discerned for the shaly inter-vals of domain A. Although only a part of the fulldataset has been included here, on-going analysessuggest this pattern to be consistent for the wholedatabase.

This observation may be explained by anenhanced strain concentration within the metre-thick, homogeneous, massive to laminated shalyintervals caused by predominantly generalized layer-parallel shearing. The high content of organicmaterial, the general lamination and the compaction

Fig. 6. (Continued) stratigraphical log is illustrated in Figure. 2. In addition, five photo-mosaics with relativeinterpretations of the represented scanlines are shown. Through-going (red) and bed-confined (black) fractures arelabelled in the interpretations. Stereoplots and fracture frequency histograms for these scanlines are shown in Figure 7.The red circle in CD_KD_1 and CD_KD_2 indicates the 20 cm-long measuring handle for scale. Locations of close-upphotographs (lens cap for scale; 6.7 cm in diameter) are marked in the photo-mosaics: (a) high-angle fracture network inan approximately 2 m-thick, coarse-grained layer (i.e. Slottet Bed of the lowermost Knorringfjellet Formation);(b) jigsaw erosional relief of a medium- to coarse-grained sandstone bedset highlighted by tens of centimetre-spaced,high-angle, through-going fractures; (c) high- and low-angle fracture network within a metre-thick shaly interval;(d) detail of the closely spaced high-angle fractures within a centimetre-thick, well-cemented carbonate bed.



foliation (i.e. pseudo-bedding) of these lithologiesmay have contributed to the development of thelow-angle shear fractures.

In this framework, a strain decoupling due to fric-tional slip and interface opening at the main litho-logical boundaries (e.g. master bedding planes,

Fig. 7. Correlation of the Dh4 with the measured section at the Deltaneset field locality. The CD stratigraphical log (forlocation see Fig. 6) correlates fairly well the Knorringfjellet Formation, and the upper third of the De GeerdalenFormation with the upper part of the reservoir in the Dh4 (sedimentary log from Dh4 is compiled by Atle Mørk: seeBraathen et al. 2010). Stereoplots and histograms showing the fracture distribution of each scanline are representedbeside the stratigraphical log in correlation with the labelled scanline location to highlight their relationships with theconsidered lithostratigraphical intervals. In the histograms, through-going (red) and bed-confined (grey) fractures aredistinguished, while the sedimentary succession is subdivided into three lithostructural associations (LSA), A, B and C,on the basis of their sedimentary facies, lithology and fracture patterns (see the text for an explanation).



Equal Angle

Great Circle: N = 17 ; first plane = 1 ; last plane = 17 Pattern = solid

WILHELMØYA SUBGROUPKnorringfjellet Fm.

CD_KD_4CD_KD_5

Strike slipslickenlines

Dip slipslickenlines

Slickenlinestrend/plunge

a

b

Fig. 9. Stereoplot of the shear fractures and the kinematic indicators recognized within the coarse-grained,thick-bedded and well-cemented beds of the Knorringfjellet Formation in the investigated section: for a descriptionof the considered scanlines see Table 1 (locations are shown in Figs 6 & 7). These shear systems suggest an overallNE–SW-oriented axis of horizontal contraction (red arrows). (a) An example of strike-slip slickenlines in a high-angleshear fracture (compass used for scale); and (b) an example of dip-slip slickenlines in a low-angle shear fracture(lens cap used for scale).

Fig. 8. Summary stereoplots showing the entire dataset from the selected scanlines (for a description of each scanlinesee Table 1, and for locations see Figs 6 & 7): (a) planes to poles; and (b) 1% area contours density plot.



erosional surfaces, diagenetic horizons) may haveplayed a major role in the structural segmentationof the stratigraphical section (Cooke & Underwood2001 and references therein).

Implications for fluid flow

Given the abundance of both vertical and horizontalopen fractures observed in the drill cores and in out-crops, and very low matrix permeability, fractur-ing appears to be relevant for fluid circulation.This is supported by borehole water injection testsand results obtained from the wireline logs, particu-larly the resistivity and temperature logs (see Fig. 5).

The block diagram in Figure 12 shows a sche-matic representation of the three-dimensional frac-ture network within the individual lithostructuraldomains A, B and C. Considering the abundance oflower-angle fractures within the finer-grained units,and reiterating that fluid flow in the tight reservoir isessentially a function of the fracture network, theseare thought to represent zones of enhanced lateralconnectivity. Even if such fractures could be sealedby elastic strain due to vertical stress, they are

thought to be prone to opening when subjected toeven relatively small pressure increments, especiallyif the reservoir underpressure is considered. Coarser-grained sandstone intervals, however, are thought toenhance the vertical communication. Silty intervals,defined by the lithostructural domain B, are charac-terized by the predominance of non-systematic,pervasive bed-confined fractures, and represent acombination of both diffused and baffled lateraland vertical flow between the two proposed endmembers.

The interconnectivity of fracture clusters atmechanical interfaces is critical to allow the verti-cal migration of fluids through a layered medium(Gudmundsson et al. 2010; Larsen & Gudmundsson2010). Fracture length and lateral connectivitybetween vertical, open fractures are also key factorsfor horizontal fluid migration (Odling et al. 1999),since they are expected to cause a pronounced per-meability anisotropy that steers the fluid flow in aspecific direction. In the discussed case, besides ageneralized vertical connectivity, the main lateralspreading of the flow is assumed to be directedroughly WSW–ENE, according to fracture set

MES

OZO

ICPA

LEO

GEN

EN

EOG

ENE

CAUSES ANDMECHANISMS

Gravity anddifferentialcompaction

Unroofingand uplift

Tectonic/sedimentaryburial and horizontal

compression

Disaggregationdeformation bands (HA)

Ductile micro-faults (HA)

Diffused soft sedimentdeformation structures

Ductile shear zones(HA and LA)

Reworking (opening) ofpreceding fractures

Activation, reactivationof early structures

Deformation bands (HA)+ hairline fractures (HA)

Slickensided, polished,conjugate fractures (LA)

STRUCTURALPRODUCTS

Brittle micro-faults (HA)

Calcite mineralizationPyrite mineralization

A

B C

HA: High AngleLA: Low Angle

A

Sandy/medium-thick beddedB

C

Shaly/massive-laminatedSilty/thin-bedded

NOT TO SCALE

layer-parallel shearingcaused by crustal

shortening

decompaction andgeneralized extension

igneous intrusions

Fig. 10. Proposed model for the evolution of the investigated structural discontinuities within the differentlithostructural domains and their relationships with the main regional tectonic events.



intersections and the mean strike of the measuredsubvertical fractures (see Figs 8 & 12).

Significance of fractures in the overburden

Fractured cap rocks, such as in the Snorre Field(Caillet 1993), may cause leakage of CO2 and/or

hydrocarbons. The storage of CO2 in depletedhydrocarbon fields is tempting, since the loweredpressure allows more CO2 to be injected beforethe capillary entry pressure of the cap rock isexceeded. However, owing to the lower interfacialtension in the CO2–brine system compared to thehydrocarbon–water system, the cap-rock sealing

Fig. 11. (a) Cross (X–Y ) plot showing the relationships between the different lithostructural domains, average fracturedensities and considered bed thicknesses. Note the opposite trends shown by lithostructural association A with respect toB and C. (b) Whisker-plot showing a summary of the fracture frequency distributions and fluctuations for each scanline(see a for a colour-code explanation). In each box, min–max lower and upper quartile, and median are displayed.



pressure must be determined prior to injection(Li et al. 2006). The increase in pressure related tothe potential CO2 injection furthermore may leadto the reactivation of faults within the overburden(Chiaramonte et al. 2008). Considering the poten-tial storage of CO2 within the coarser-grained inter-vals of the Knorringfjellet Formation, we must alsoconsider possible leakage pathways from theseunits.

On Spitsbergen, even though the JanusfjelletSubgroup cap rock is highly fractured, the differen-tial pressure in the target reservoir and the overbur-den affirms the efficient sealing potential of the unit.Reactivation and opening of the predominantlylow-angle fractures may lead to enhanced lateralmigration at the base and/or within the cap-rocksuccession but, owing to the low vertical connec-tivity, the cap rock is deemed to be sealing. Thisview has recently been corroborated by water injec-tion tests.

Local enhanced sealing processes and

reservoir segmentation

Localized veining and enhanced cementation occurswithin and around beds or intervals characterized byspecific compositions and sedimentary features:increased calcite and quartz precipitation relate tothe diagenesis of carbonate, crystalline and thick-bedded, coarse-grained layers, respectively. Suchdiagenetic horizons may represent intervals with abaffled connectivity due to fracture sealing and,thus, possibly contribute to vertical compartmentali-zation of the reservoir/storage unit.

Moreover, the presence of dolerite intrusionswithin the reservoir unit is manifested both in Dh4,where a 2 m-thick sill occurs at 950 m, and byseismic data that suggest thicker sills beneath thewell’s total depth of 970 m. Such bodies are alsofound in outcrop: intrusive rocks of the Diabasod-den Suite occur over large parts of the Svalbard

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

LowerHemisphere

N = 402


LowerHemisphere

N = 822


LowerHemisphere

N = 469

Enhanced lateralconnectivity

Enhanced verticalconnectivity

Diffused/baffledlateral and verticalconnectivity

Potential fluidmigration pathways

BC

A

not to scale

A

Sandy/medium-thick beddedB

C

Shaly/massive-laminatedSilty/thin-bedded

Fig. 12. Schematic diagram of the interconnectivity and intensity of fractures within the three lithostructuralassociations: A, B and C (see the text for details). Corresponding stereoplots show the total considered fractures (planeto poles) for each lithostructural association. The finer-grained lithostructural domain A is typically characterized byconjugate, lower-angle shear fractures, leading to enhanced lateral connectivity. The coarser-grained units, however, aretypically dominated by steep fractures, and may thus enhance vertical connectivity. Note also the mixture of steepand lower-angle fractures within the silty interval of lithostructural domain B.



archipelago and are generally thought to be of LateJurassic or Early Cretaceous age (Burov et al.1977; Maher 2001, Nejbert et al. 2011). In outcrop,sills exhibit a thickness ranging from 1 to morethan 30 m, with off-cutting dykes generally minorand localized. An exception is the probable feederdyke at Diabasodden, adjacent to the Deltanesetfield locality. The drilled dolerite in Dh4 shows, on asmall scale, that increased fracturing occurs aroundthe intrusion, probably associated with focusedstrain during Tertiary contractional tectonics. Fur-thermore, millimetre- to centimetre-thick, calcite-filled fractures in the vicinity of this and other, eventhinner, dolerite bodies in Dh4 suggest increasedmineralized fluid circulation, possibly due to syn-emplacement metasomatism and hydrothermalism,and related calcite precipitation, within the contactaureoles, or post-emplacement water–rock interac-tions. The mechanical deformation of the sedimen-tary succession could therefore either be related tothe intrusion phase (e.g. magma flow, bulging andthermal shrinking) and/or to the subsequent tec-tonic- related mechanical decoupling due to rheolo-gical differences between igneous units and the hostrock at the post-intrusive stage.

In this framework, dolerite bodies may play adouble role in controlling the fluid flow: (1) actingas conduits due to along-dyke wall and internal frac-turing; and (2) acting as baffles or barriers for thewall-rock fracture flow due to cemented fracturesin the contact aureole. Depending on their three-dimensional architecture and fracturing-sealingprocesses, dolerite intrusions could serve to com-partmentalize the reservoir into high-conductivityfracture corridors and low-conductivity domains ofcemented fractures. Further work addressing theseissues is currently in progress.

Implications for CO2 storage

The fractured nature of the reservoir, together withits low matrix porosity, complicates the volumetriccalculation of the potential CO2 storage reservoir.Numerical modelling has shown that, dependingon the chemical composition of the fluid, the reser-voir and cap rocks, CO2 may both enhance porositythrough dissolution yet also decrease porosity andpermeability through the precipitation of calcite(Gherardi et al. 2007). In the LYB CO2 lab case,the storage potential of the target aquifer is funda-mentally dependent on the interconnectivity, lengthand aperture of the fracture system. Further, thedynamic interaction between the fractures and thehost-rock matrix represents a substantial source ofuncertainty (Farokhpoor et al. 2010, 2011). At thisstage it is still unclear whether the Kapp ToscanaGroup sediments are, indeed, optimal for storinglarge amounts of CO2, but acquired evidence

suggests that the succession is likely to be suitablefor storing the modest, test-site-scale CO2 emissionsfrom the local power plant.

Concluding remarks

Carbon dioxide may potentially be injected into asiliciclastic succession on Spitsbergen, Svalbard,given the good injectivity of this naturally fracturedtight sandstone–shale reservoir/storage unit. Frac-ture sets have been identified in both drill core andoutcrop data, and three major lithostructuraldomains (A, B and C) can be identified throughoutthe investigated section. In the massive to laminated,shale-dominated unit A, low-angled slickensidedopen fractures dominate and are probably relatedto the regional Tertiary transpression. The other endmember, the massive to laminated, sand-dominatedunit C, is characterized by steeply dipping fractures,probably reworked/reactivated and interconnectedduring the later Quaternary unroofing. The inter-mediate heterogeneous, laminated to thin-bedded,silty unit B displays a predominantly non-systematic,dispersed fracture network, representing a mixedmember in-between. Such fracture associations areconsidered to represent the key factor in control-ling the internal connectivity of the reservoir andthe direction of the fluid flow, by influencing lateraland vertical fluid migration, respectively.

The LYB CO2 Lab project represents a uniquetest site for potential CO2 storage in a naturally frac-tured tight siliciclastic reservoir. The large amountof available data from different methods, coupledwith the possibility of detailed studies on the reser-voir and cap rock directly in outcrop, allow a com-prehensive characterization of the potential storageframework. The future exploitation of unconven-tional reservoirs for subsurface CO2 disposal needsto have the same degree of knowledge developedfor the currently emerging hydrocarbon explorationfor shale gas/oil and enhanced geothermal systems(EGS). This should highlight the importance ofdetailed structural studies, especially for the stimu-lation (i.e. hydrofracturing) of tight reservoirs, theconstruction of datasets gathering key parametersfor the characterization of the vertical–lateral frac-ture connectivity within the reservoir–cap rocksystem and, therefore, the prediction/mitigation ofthe risk of leakage towards the surface.

This work is part of the ‘Geological input to CarbonStorage (GeC)’ project funded by the CLIMIT programmeof the Research Council of Norway, with K. Senger’s field-work supported by an Arctic Field Grant from the SvalbardScience Forum. A. Rittersbacher, D. Richey and L. Farrellare thanked for their assistance in the field. The GeCproject team works in close co-operation with the Long-yearbyen CO2 lab project (http://co2-ccs.unis.no), which



http://co2-ccs.unis.no



is currently funded by Gassnova, ConocoPhillips, Statoil,Statkraft, Store Norske, LNS, Lundin Norway and BakerHughes. Shapefiles from NPI-Geonet have been used toconstruct the geological maps. The North Africa ResearchGroup at the University of Manchester is thanked for orga-nizing the ‘Naturally Fractured Hydrocarbon Reservoirs’workshop where this work was initially presented. Finally,we would like to thank G. Spence and T. Bevan for havingsupported the publication of this work, and R.H. Gabriel-sen and C. Bond for their constructive reviews.

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The importance of natural fractures in a tight reservoir ...co2-ccs.unis.no/Pdf/Ogata etal 2012 - Triassic-Jurassic fractures... · published September 10, 2012; doi 10.1144/SP374.9