Sand remobilization and injection above an active salt diapir: the Tyr sand of the Nini Field,...

Sand remobilizationand injectionaboveanactive saltdiapir: theTyr sandof theNini Field,EasternNorth SeaJohan Byskov Svendsenn, Henrik Juhl Hansenw, Thomas Stærmosen,Michael Kragh Engkilden

nDONGEnergy, Exploration and Production, H�rsholm, DenmarkwSchlumberger, Data & Consulting Services, CopenhagenN, Denmark

ABSTRACT

The Selandien [58Ma (PP3c-d)] Tyr sand in theNini area, Siri Fairway, DanishNorth Sea, is severelyin£uenced by the syn-depositional movement of the Nini Salt Diapir.The sand is faulted andremobilized into a degree where no original depositional signature can be recognized.TheTyr sandis drilled (and cored) by a number of wells, and the sand is never found in the same stratigraphicposition. In some wells, theTyr sand is injected down into the chalk of theDanian Eko¢sk Formation,whereas other wells show theTyr sand embedded in the SelandienVileMember claystone, withvarying degree of remobilization.TheTyr sand is thin (2^7m) and is therefore below seismicresolution and close to seismic detection. Standard re£ection seismic data has proven problematic indetermining the actual thickness and spatial distribution of the thinTyr sand locatedwithin orimmediately above the chalk. A simultaneous AVO (amplitude vs. o¡set) inversion using time-alignedangle stack seismic data, has improved resolution of the thin and complex reservoir, allowing a betterunderstanding of the remobilization processes occurring above the rising salt diapir, and thereby animproved understanding of the reservoir and its performance.Three di¡erent remobilization featuresare described: injection into the chalk, injection up along fault planes and compactional driveninjection.The force for the remobilization spans in orders ofmagnitude frommetre scale phenomena,to injections of100s of metres, moving millions of tons of material and £uids.

INTRODUCTION

Many Paleocene^Eocene hydrocarbon reservoirs of theNorth Sea are characterized by a high degree of injection/remobilization (Jenssen et al., 1993; Timbrell, 1993; Dixonet al., 1995; Lonergan & Cartwright, 1999; MacLeod et al.,1999; Lonergan et al., 2000; Bergslien, 2002; Duranti et al.,2002; Duranti & Hurst, 2004; Hamberg et al., 2007; Huuseet al., 2007). The geological setting for getting signi¢cantpost-depositional movements of sands is often unconsoli-dated sand with signi¢cant water content, trapped belowan impermeable seal, giving an overpressured situation.However, remobilization without impermeable trappingseal is known, e.g. the Leadon Field, UK (Templeton et al.,2002, 2005). It is a general perception, that £uid release,and thereby injection,will occur upwards, although down-ward injection has been documented (Parize&Frie' s, 2003;Friis etal., 2007; Parize etal., 2007). However, the main dri-ver for movement of £uids is the pressure gradients, whichof course in most settings, will guide the £uids in an up-ward direction. But if lower pressures on a local scale areobtained by moving downwards, injections can be seen in-

jecting into the substratum of the host sediment.The low-ered pressure can be generated in numerous ways,spanning from regional events such as earthquakes (Ober-meier,1998;Huuse etal., 2005) to more local events such asadditional £uids (Osborne & Swarbrick, 1997; Lonerganet al., 2000) and local structural/tectonic movements(Davison et al., 2000; Hamberg et al., 2007).

The scope of this paper is to illustrate the signi¢cant re-mobilization taking place above an active salt diapir. Theremobilized nature can be depicted on both cm^m scalein the numerous cores, as well as on 1^10m scale on thethree-dimensional (3D) seismic cubes. In addition, a seis-mic tool [simultaneous AVO (amplitude vs. o¡set) inver-sion] to enhance sub-surface mapping of remobilizedsand is presented.

GEOLOGICAL SETTING

The hydrocarbon bearing reservoirs of the Nini Area inthe Siri Fairway (Fig. 1) are the Bor, Tyr, Idun, Rind andKolga Sands (Fig. 2) and are characterized by glauconite-rich (20^30 vol%) ¢ne-grained well-sorted sand, em-bedded in hemipelagic to pelagic mud and marl stones(Hamberg et al., 2005; Friis et al., 2007; Poulsen et al.,

EAGE

Correspondence: Johan Svendsen, DONG Energy, AgernAlle¤ 24-26, DK-2970 H�rsholm, Denmark. E-mail: [email protected]

BasinResearch (2010) 22, 548–561, doi: 10.1111/j.1365-2117.2010.00480.x

r 2010 The AuthorsJournal Compilationr Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists548

mailto:[email protected]

mailto:[email protected]

2007). High-density bottom currents, formed by halinewater shed out from the coast line, formed con¢ned ero-sional features. The mass £ow sands of the Siri Fairwayare shed from the Stavanger Platform in the northeastand are deposited in the previously mentioned erosionalgullies formed by dense water. In theNini area, signi¢canterosion occurred in the time between the deposition of thechalk of theEko¢skFm. (Danian) and the deposition of theclayeyVileMb and theTyr sandMb (Selandien), which re-sulted in the removal of some of the chalk and the entirelowerSelandianV�le marl.Consequently, theVile claystoneandTyr sand unconformably overlies the chalk of the Eko-¢sk Fm (Fig. 2).This erosional hiatus is most likely gener-ated by sub-sea erosion by dense water currents as well asslumping, caused by the rising diapir, as also describedfrom the UKCentral Graben byDavison et al. (2000).TheTyr sand is never seen in the same stratigraphic position(Fig. 3). For the wells at the foot of the diapir, the sand ispresent within the chalk, whereas for the wells on the dia-pir, the sand is located stratigraphically higher, either im-mediately above the chalk (Nini-2) or with some Vileclaystone between the chalk and the Tyr sand (Nini-1A).In addition to this diverse stratigraphic setting of the sand,some clearly discordant sand^claystone interfaces as wellas a number of angular intraformational claystone frag-

ments are present within the main sand intervals (Fig. 4).Furthermore, orientated bands of angular intraforma-tional claystone fragments (rip-up clasts) are seen in somecores (Fig. 4), a remobilization phenomenon also recog-nized by Kawakami & Kawamura (2002). These observa-tions suggest that the majority of the sand is injected,rather than found in its original depositional position.Any indication of the primary sedimentary agent has beendestroyed by the massive remobilization and injection.

Nini Tyr FIELD HISTORY

The Nini Tyr Field is located above a salt diapir in thenortheastern part of the Siri Fairway, Danish North Sea(Fig. 1). It is the stratigraphically oldest (Thanetian) ¢eldsegment in theNiniMainArea (Fig. 2).TheTyr sand reser-voir in the Nini Field has been drilled by a number ofwells, such as Nini-1, -1A, -2 and -4, and NA-2B, NA-7P,NA-7A (Fig. 1). All wells proved a chaotic nature of theTyr sand (Fig. 3). A 24-h production test was carried outin Nini-1A (in 2000). The results of the test were not en-couraging, as pressure declined more rapid than expectedand the well performed at lower rates than anticipated.The chaotic nature of the reservoir presence and the test

58°

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Top Ty Depth Map

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Nini Salt Diapir57°

Fig.1. Location map of the Nini Salt Diapir.The wells used in the paper are shown on the three-dimensional map of the diapir.Thedegree ofwell control is high, with penetration on virtually all sides, and both at the base (Nini-1, -4 andNA-2B) and £anks (Nini-1A,NA-7Pand -8) of the diapir, as well as in the central collapse graben (Nini-2).TheNiniDiapir is approximately 3 kmwide. For distancesbetweenwells, see Fig. 3.Vertical exaggeration of10 times.

r 2010 DONG EnergyJournal Compilationr Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 549

Remobilization above an active salt diapir

EarlyEocene

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Lithostratigraphy Actual Appearanceat Nini Salt Diapir

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Fig. 2. Litho- and biostratigraphiccompilation of the Palaeocene^Eocenesuccession in the Siri Fairway.Modi¢edfromSchi�ler etal. (2007). Dinocyst eventsfromHarland et al. (1992). Absolute age(Ma) shown as guide, and should not beused as exact measures.

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Fig. 3. Log panel of the Nini Tyr key-wells. Inset map shows location ofwells. Notice the very uniform thickness of sand in all thecentral wells; Nini-1, -1A, -2 andNA-7P. All wells are datumed toTop Eko¢sk.

r 2010 DONG EnergyJournal Compilationr Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists550

J. B. Svendsenet al.

results formed the basis for not developing the Tyraccumulationwhen the remainingNini areawas developedin 2003.

The fact that oil was found in most of the wells, andespecially the very good sands observed in NA-7P (drilledin 2005), made it apparent that an attempt to produce theTyr sand reservoir could be economically viable. It wasdecided to develop theTyr reservoir in two phases, wherephase 1 consisted of one production well and phase 2 ofup to two more wells depending on the outcome of theproduction performance of the ¢rst well.

The ¢rst well, NA-8, was drilled, completed and put onproduction during July/August 2007.The well was drilledas a long (�1000m) horizontal well to traverse as manyfaults as possible, thereby minimizing the e¡ect of poten-tial reservoir compartmentalization caused by faults. Bymid-October 2008, the well has produced approximately330 000Sm3, far exceeding expectations.The main reasonfor the better reservoir performance is a signi¢cantly bet-ter reservoir connectivity, compared with the pre-drillmodels. This enhanced connectivity is mainly caused by

the remobilization and injection of theTyr sand, which in-terconnects the entire sand body.

GEOPHYSICAL CHARACTERISTICS

The limited thickness of theTyr sand relative to the fre-quency content of seismic data implies that theTyr sandis close to or below the limit of seismic resolution (similarproblems are discussed by Huuse et al., 2007). Resolutioncriteria like the Ricker criterium (Kallweit & Wood, 1982)indicates that the available re£ection seismic data alone isable to resolve thicknesses down to 8m and detectthicknesses down to 2m (Fig. 5), where characteristicthicknesses for theTyr sand are 2^7m. Seismic character-istics are: frequency range: �8 to �100Hz, dominantfrequency: �50Hz, sandstone velocity: 2250m s�1.

TheTyr sand has a lower acoustic impedance (AI) thanthe overlyingVile shale. As a result, the topTyr appears as astrong negative amplitude on seismic lines (Fig. 6). In ad-dition, the oil- ¢lledTyr sand has a lowPoisson’s ratio (PR)

(c)(b) (d)

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B

C

DFig.4. Core photos of theTyr sand inNini-1 andNini-1A (deviatedwell, 241).Letters in yellow circles in upper partshow location of zooms shown in lowerpart. Chalk is white,Tyr sand is brownishgreen (or light green/greyish greenwhencemented) and Vile shale is multicolouredlight to dark grey. (a) EntireTyr sandsection as seen in Nini-1, where all Tyrsand is embedded in the chalk.Furthermore, chalkmaterial is seenwithintheTyr sand. (b) Zoom from lower part ofTyr sand, where the £uidization hasgenerated sorting of glauconite grains(darker grains), in a complex network.(c) Angular chalk fragment in theTyr sand.(d) Light greyish brown sand injectedinto slighter darker greyish brown sand.(e) EntireTyr sand section fromNini-1A,consisting of a lower massive part(between red solid lines) and an upperheterolithic part (between green dashedlines), all embedded inVile shale.Lowermost 2m are chalk, with grey chert.The well is deviated approximately 201.(f) Zoom of oriented layers of rip-up clastsfrom the uppermost part of the massiveTyr sand. (g) Zoom of protruding sandinjected into theVile shale. Section fromthe lower part of the heterolithicTyr sand.(h)Water escape pipeswithin theTyr sand,generating cross-cutting lamination.(i) Orientated layer of rip-up clasts, and aprotruding sand in progress of rippingadditional shale into the sand.



relative to the overlying rocks. Consequently, the topTyrre£ection exhibits an increase in amplitude with o¡setwhen theTyr sand is oil- ¢lled.The immediate location ofTopTyr above the pronounced hard kick from the interfacebetween the Tyr sand and the underlying chalk of theEko¢sk Fm results in severe interference between the twoseismic events. As a result, the imprint of theTopTyr re-£ection in the seismic data is not a direct measure of theactual TopTyr. For this reason, it is virtually impossible touse re£ection seismic alone to map the actual Tyr sandbodies.

In an attempt to improve the resolution of theTyr sandbodies, a seismic simultaneous AVO inversion was carriedout using the ISIS approach (Rasmussen et al., 2004). Si-milar approach was used by �zdemir (2002), to improvethe seismic resolution of some North Sea Paleocene^Eocene sands.The deconvolution element of the seismicinversion signi¢cantly limits the interference betweenseismic events by removal of the embedded wavelet. Thedegree of improvement in resolution depends mainly onthe accuracy of the estimated wavelet and the noise levelin the seismic data.The simultaneousAVO inversion algo-rithm inverts partial stacks directly for physical propertiessuch as AI and PR.The partial stacks are inverted simulta-neously using wavelets estimated independently for each

(e) F

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(g)(f) (h) (i)

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Fig. 5. Amplitude spectrum for the reservoir interval of the101^151 angle stack.The dashed blue lines mark the readings used inthe calculation of the Ricker’s resolution criterion (bottom).Thedetection limit is de¢ned as half the resolution limit.



partial stack. As a result, the estimated PR will containhigher frequencies than the far o¡set seismic data.

The above characteristics make simultaneous AVO in-version an ideal tool for improving the imaging of theTyrsand. Ten angle stacks, accurately time aligned for exactamplitude vs. angle information, were used as input forthe inversion.Wavelets for each angle stack targeted thePa-leocene interval in order to match the amplitude, fre-quency and phase characteristics of the reservoir interval.An e¡ort was made in the low-frequency model buildingto limit chalk AI and PR values from propagating into theoverlying target interval. The inversion work£ow is out-lined in Fig. 7.

Evaluation of the AI and PR inversion results at the welllocations indicate an overall resolution of thicknessesdown to 6m and detection of thicknesses down to 3m.

Furthermore, the low PR values characteristic for oil-¢lled Tyr sand are resolved from the seismic amplitudevs. angle information.When the low PR is extracted fromTyr interval of the inversion result PR cube and draped ontoTopTyr, it shows a very good matchwith the well obser-vations (compare Figs 3 and 8).The results of the inversionnot only images the oil- ¢lled sand, but have furthermoreimproved the resolution, especially of the injected sands.From the comparison in Fig. 9, it is clear that the invertedcubes give a signi¢cantly di¡erent perception of the sanddistribution than the re£ection seismic data alone. Bycomparing the results withwell data (e.g. Nini-2 in Fig.9),it becomes clear that the inverted data are much closer to

the truth. In a few places, where the geological setting and/or structural con¢guration is complex and away fromwellcontrol, the simultaneous AVO inversion is somewhat dif-ferent from the re£ection seismic data. This is the casefor the ‘scooped-out’ feature (right-hand side of diapir inFig. 9) described below. In cases where only the amplitudecube has been used to produce geological interpretation,the knowledge fromFig.9 has been used to estimate thick-nesses and spatial distribution of theTyr sand.

REMOBILIZATION FEATURES

The main scope of this paper is to illustrate the injection/remobilization features in the Nini Tyr Field. A dynamicmodel for the remobilization is proposed, showing how re-mobilization processes can severely modify the originaldepositional setup.

The following injection/remobilization features will beillustrated:

� ‘Scooped-out’ feature,� Injectedwings,� Intra-chalk sands,� Fault-guided injectites.

Location of the features, and the seismic lines used to il-lustrate them, is shown in Fig.10.

‘Scooped-out’ feature

When looking at theTopTyr map, a pronounced scoop-shaped feature is present on the southern part of the dia-pir, corresponding to the hanging wall block (Figs1and 8).The feature looks at ¢rst glance as a slump scar.However, acloser examination reveals a very complex nature of thefeature, as the material ‘scooped-out’ is not presentdown-dip of the feature. The seismic signature of thefeature (a succession of peaks and troughs indicating suc-cessive increase/decreases of impedance downwards) indi-cates that a soft body is sandwiched in between two hardevents (Figs 9 and 11).The lowermost hard event is clearlythe chalk of the Eko¢sk Fm., whereas the upper seems tobe a large raft of chalk. A seismic section and geosectionshowing the seismic setting and the assumed geologicalcon¢guration is shown onFig.11c.The size of the chalk raftis 0.23 km2, and the assumed thickness (based on seismicinterpretation) is approximately 12^15m, giving the chalkraft a minimumweight when it was elevated of at least 2^3million tons, and probably signi¢cantly more. Similarchalk rafts elevated by remobilization at this scale are alsofound by Wild and Briedis (2010) (this volume).The sandin the ‘scooped-out’ feature has a thickness of 6^18m, giv-ing an approximate volume of sand of 3million m3 of sand.

Injected wings

Protruding upward and out of the down-dip part of the‘scooped-out’ feature are steep re£ections, extendingsome 20^30m up into the overlying shale (Fig. 12). Thesebodies are interpreted as injected sands protruding out of

Fig. 6. Synthetic seismic tie of the Nini-2 well.The actual TopTyr is marked by green line, whereas theTopTyr proxy (soft kickon the seismic ^ yellow line) is seen some 4^6m above.



Fig.7. Simultaneous amplitude vs. o¡set (AVO) inversionwork£ow. Left: Key steps in the work£ow. Right from top to bottom: Anglestack decomposition:The10 angle stacks cover angles of incidence from 0 to 50. Here the10^15 and 30^35 angle stacks are highlighted.Time alignment: Angle stack gather at a single location before and after time alignment.The £attened angle stack gather indicates thatthe angle stacks are well aligned.Wavelet estimation: Estimatedwavelets for the10 angle stacks.The wavelets are consistent. Low-frequency model building: Separate models are built for the intervals above and belowTop chalk and then combined in order to avoidleakage of the chalk interval into the reservoir interval. Here the acoustic impedance model is shown. Simultaneous AVO inversion:Acoustic impedance (left) and Poisson’s ratio (right) inversion results.The seismic and the inversion result sections are from the sameline crossing the Nini main structure.



A: Nini-1 B: Nini-1A C: Nini-2 D: Nini-4 E: NA-2B F: NA-7P G :NA-7A H: NA-8

: Area with low Poison’s ratio above Top Chalk : Area with high Poison’s ratio above Top Chalk

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Fig. 8. Poisson’s ratio (PR) draped on theTopTyr depth structure map.The four di¡erent views show the appearance around the NiniSalt Diapir.Warm colours indicate low PR, and thereby the presence of oil- ¢lled Tyr sand (see discussion in text).The Nini Diapir isapproximately 3 kmwide. For distances betweenwells, see Fig. 3.Vertical exaggeration of10 times.

Nini-2 Nini-2

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Acoustic Impedance Geosection based on Inversion Cubes

Difference between the twoGeosection approaches

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Fig.9. Seismic sections andgeosection generated from the re£ection seismic (upper row)and from the inverted cubes (lower row). It is clear thatthe inverted cubes bring much more detail into the interpretation.Upper right shows comparison between the geosection generated by the twodi¡erent data sets, with the geosection shown being the one from the inverted cubes, and the re£ection seismic generated shown in red lines.



the thick sand body in the ‘scooped-out’ feature, duringcompaction at shallow depth.Thus, the wings are injectedbodies from already remobilized sand.The expected sandy

nature of these is based on the high amplitude (soft event)seen in the bodies. Similar wing-like features are docu-mented from numerous remobilized settings (Surlyk,1987; MacLeod et al., 1999; Lonergan et al., 2000; Surlyk &Noe-Nygaard, 2001; Duranti et al., 2002; Jackson, 2007;Hubbard et al., 2007; Huuse et al., 2007). The uppermostpart of the of the injection ends with a kink to a strata-par-allel setting, as also documented by Lonergan et al. (2000),Jonk et al. (2005) and Jackson (2007).The wings are there-fore seen to disturb only the lower part of the Paleocene^Eocene package, giving a good timing of the protrudingevent, expected to be lower-middle Lista Fm time[57^53Ma (PP4-PP5a)]. However, a younger age of theinjection cannot be excluded, as the injection could havetaken place without disturbing the younger strata.

Intra-chalk sands

In a few places around theNini Salt Diapir, signi¢cant softkicks are present below theTop Eko¢sk. Figure 13 showstwo seismic lines crossing one of these areas. Mappingsuggests that that the soft-kick body pinches out in all di-rections, and that the event seems to be initiated from theupper part of the ‘scooped-out’ feature (Fig. 13).The softevent is interpreted to be thin, Tyr sands (2^5m) injected¢rst down into the chalk as dykes, and then evolving intoa sill located in the uppermost part of the chalk. The in-tra-chalk sands are believed to be the stage before the

Fig.10. Location map of the remobilized features and theseismic lines used to illustrate them. Numbers in circles refer tothe ¢gures showing the features in more detail.

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Injected wings above intra-chalk sand limitation

Intra-chalk sand

km-scale chalk raftlifted by injected sand

Sand relict after majority ofsand has been remobilized

Sand relict after majority ofsand has been remobilized

Fig.11. Illustration of the ‘scooped-out’feature. Light blue horizon isTop Eko¢sk.(a) Regional line, (b) zoom (from yellowbox) of ‘scooped-out’ features, (c)geosection generated by using severalseismic lines, both from the amplitudeand inverted cubes.



chalk fragment is completely detached from the parentchalk body.

Faulting

Signi¢cant faulting is seen in theTyr sand. Most promi-nent are the two curved graben faults, caused by the apicalcollapse of the diapir (Figs 1 and 8). In conjunction withthese major faults, a number of minor fault systems exist,three of which should be mentioned here

(1) En-echelon intra-graben faults.(2) Radial faults.(3) Secondary collapse faults.

This type of faulting is classical around rising salt diapirs(Davison et al., 2000). Low AI and PR bodies on the rockphysics cubes, as well as negative re£ections on the ampli-tude cube, are seen along many of the fault planes, and of-ten protruding up into the overburden (Fig. 14). Theoverpressured sandmade itsway out of the reservoir, using

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Fig.12. Illustration of the wing-likefeature. Light blue horizon isTop Eko¢sk.(a) Regional line, showing that no majorfaulting or tectonic has a¡ected thegeneration of the injectedwings.Theapparent striping below the ‘scooped-out’feature, is believed to be seismic artefactfrom the soft sand. (b) Zoom of the wingarea, (c) zoom (fromyellow box) of‘scooped-out’ features. (d) Geosectiongenerated by using several seismic lines,both from re£ection seismic and invertedcubes.

(a) (b)

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Fig.13. Illustration of the intra-chalksand feature. (a) The NE-SW seismic lineand (b) the NW-SE seismic line. (c and d)Geosections generated by using numbersof seismic lines, both from re£ectionseismic and inverted cubes.



the pressure chimneys generated by the faults. However,the sand was plugging the chimney (as also described byJolly & Lonergan, 2002), and was not able to completelyleave the main body, hence it is seen oil- ¢lled today. Com-parable £uid escapes have been reported by Mazzini et al.(2003).

REMOBILIZATION PROCESSES

Signi¢cant injection/remobilization is seen around theNini Diapir. Timing referred to in this chapter relates tothe stratigraphic nomenclature presented in Fig. 2. Themovement of the diapir is never seen to a¡ect the overlyingKolga sand in the Sele Fm of PP5b age (53Ma) (Fig. 2).The

Tyr sand itself is of late PP3 [most likely PP3c (59Ma)] age,giving a fairly narrow time span for the remobilizationprocess.The remobilization is interpreted to take place inPP3d-PP5a time (58^53Ma), during deposition of the Lis-ta Fm. Structural movement of the Nini Diapir is knownto take place in this time interval, as the Kolga sand(PP5b age) never passed over the central part of the struc-ture, indicating that a signi¢cant structure was present atthe sea bed in PP5b time.The internal timing within theremobilization is di⁄cult to estimate. However, based onthe internal relation, it is likely that the early remobiliza-tion moved Tyr sand originally deposited at the lower partof the diapir into the chalk, re-using old weakness zones,e.g. slump scars and interfaces between hard grounds andsofter chalk (Fig.15).This suggests that weakness zones in

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Fig.14. Illustration of the fault-guidedinjectites. Light blue horizon isTopEko¢sk. (a) Regional line, (b) zoom (fromyellow box) of fault-guided injectites.TopEko¢sk is not shown as interpretation, toavoid much noise. (c) Geosectiongenerated by using numbers of seismiclines, both from re£ection seismic andinverted cubes.



Intra-chalk sand isguided by weak zones

Faulted and foldedchalk due to slump



Collapse faultson top of structure

No Pelagic carbonateproduction occurs

Formation of hardgroundand phosphorous nodulesduring non-deposition


Slumped outmaterial

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Intra-stratal collapseand faulting due toremoval of sand

Fault guidedinjected sand

Sand is guidedby weak zones

Deposition ofKolga sand

Minor remobilization of Tyr sandduring compaction of Kolga sand

Intra-stratal faults willfocus the injected sand

Deposition of Tyr Sandin local depressions

Deposition ofLower Vile

Deposition of UpperVile, Ve and Bue Mb.

Middle - Upper Selandian

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Upper Selandian

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Lower - Middle DanianLower - Middle Danian

Middle - Upper Selandian Upper Selandian - Thanetian

Upper Selandian - Thanetian Upper Thanetian - Lower Yppresian

Lower Ypresian Present Day - Seismic (time)

Pelagic carbonateproduction Tectonic activity

at Nini DomeFaulted and foldedchalk due to slump

Deposition of Tyr Sandin local depressions

Fault guidedinjected sand

Intra-chalk sand isguided by weak zones


Fig.15. Schematic illustration of the remobilization/injection processes, and their expected timing.The section is partly conceptual, toillustrate all the four di¡erent remobilization features. It has not been possible to ¢nd a single line that encompassed all. See text formore details explain the di¡erent phenomena.



the chalk were less competent than the overlying Vile Mbclaystone. Alternatively, if the chalk was at hydrostaticpressure, (not overpressured), the overpressured Tyr sandcould be injected into the bulk chalk package, and no pre-de¢nedweakness zoneswould be required,however, if pre-sent these would be preferably exploited. Such a normalcompaction setting for the chalk could be formed by thelong period (approximately1Myr) of low/no deposition be-fore deposition of the Vile Mb claystone and Tyr sand. Inboth scenarios, sand is injected into chalk, giving rise to acomplex lithological setting.

The subsequent compaction and structural movement[57^54Ma (PP4-PP5a)] of the Nini Diapir generated ex-tensional faults which acted as conduits for the overpres-sured sand. The compaction of the large chalk rafts aswell as the sand beneath it resulted in generation of in-jected wings, which reach intra-strata equilibrium at ornear the surface, resulting in a sub-horizontal shape inthe uppermost part of the injection. Furthermore, this re-sulted in a complex web of injected sands, near the termi-nation of the sand bodies. The remobilization of theTyrsand ceased completely in PP5b time, when deposition ofthe Sele shale and Kolga sand took place. The post-Selemovement of the Nini Diapir generated numerous faults,but none of thesewere able to reactivate the remobilizationof theTyr sand, most likely because theTyr sand had reacha normal compaction scenarios.

CONCLUSION

The thin (2^7m) Tyr sand (Selandian age) at the Nini SaltDiapir is found in a number of stratigraphic settings,clearly showing the injected nature of the sand, as the sandis found both within the chalk, immediately above thechalk, and several metres above the chalk. The injectednature is supported bya number of non-conformable rela-tions and rip-up clasts, which often are orientated in thinlayers.The proximity to the top of the chalk makes seismicinterpretation of theTyr sand di⁄cult, as the sand is belowseismic resolution and often close to seismic detection. Si-multaneous AVO inversion has proven e¡ective for resol-ving the thin Tyr sand, and it plays a crucial role indelineating the sand in a very complex reservoir.

In addition to the highly complex setting observed inthe cores and the high-quality 3D seismic volumes, the si-multaneous AVO inversion has assisted in de¢ning threedi¡erent remobilization features:

� Injection of sand into the underlying chalk, generatinglarge (up to 0.23 km2) rip-up rafts, as well as continu-ous (100^200m) sand units within the chalk.

� Injected wings protruding out of the main sand bodydescribed above, and terminating as strata-parallelsand units.

� Fault-guided injected sands, occasionally protruding20^40m into the overburden.

The decision to develop the thin and complex reservoirtook 7 years, mainly due to the expected low connectivity

of the reservoir. However, when the ¢rst producer wasdrilled, it performed signi¢cantly better than initially an-ticipated. The main reason for this productivity is a highdegree of connectivity within the reservoir, caused by theinterconnectedness of the injected and remobilized sand.

ACKNOWLEDGEMENTS

The authorswould like to thank the partnership ofLicence4/95 (DONG Energy, Noreco and RWE Dea) for allowingthe publication of this paper. Ideas and models presentedhere are those of the authors, and not necessarily those ofthe partnership ofLicence 4/95. Erik Skolem andLarsVes-tergaard made constructive comments to the study andearlier versions of the paper. Ideas andmodels in the paperbene¢tted greatly from the constructive and inspiring re-view comments from Mads Huuse, Patrice Imbert, JohnWild andGerhardTempletonwho are all thanked for theircontributions.

REFERENCES

Bergslien, D. (2002) Balder and Jotun; two sides of the samecoin? A comparison of two tertiary oil ¢elds in the NorwegianNorth Sea. Petrol. Geosci., 8, 349^363.

Davison, I., Alsopb, I., Birchc, P., Eldersa, C., Evansd, N.,Nicholsone,H.,Rorisonf, P.,Wadeg,D.,Woodwardh, J.&Young,M. (2000) Geometry and late-stage structural evo-lution of Central Graben salt diapirs, North Sea. Mar. Petrol.Geol., 17, 499^522.

Dixon, R.J., Schofield,K., Anderton, R., Reynolds, A.D.,Alexander, R.W.S.,Williams,M.C. &Davies,K.G. (1995)Sandstone diapirism and clastic intrusion in theTertiary sub-marine fans of the Bruce Beryl Embayment, Quadrant 9,UKCS. In: Characterisation of Deep-Marine Clastic Systems (Ed.by A.J. Hartley & D.J. Prosser), Geol. Soc., London, Spec. Publ.,94, 77^94.

Duranti, D. & Hurst, A. (2004) Fluidisation and injection inthe deep-water sandstones of the Eocene Alba Formation(UK North Sea). Sedimentology, 51, 503^529.

Duranti, D., Hurst, A., Bell, C., Goves, S. & Hanson, R.(2002) Injected and remobilised sands from theAlba ¢eld (Eo-cene, UKCS): core and wireline log characteristics. Petrol.Geosci., 8, 99^107.

Friis, H., Poulsen, M.L.K., Svendsen, J.B. & Hamberg, L.(2007) Geochemical discrimination between density £ow de-posits within a narrow submarineCanyon, Palaeogene,DanishNorth Sea ^ implications for subtle provenance di¡erentia-tion.Mar. Petrol. Geol., 24, 221^235.

Hamberg, L., Dam, G., Wilhelmson, C. & Ottesen, T.G.

(2005) Paleocene deep-marine sandstone plays in the SiriCanyon, o¡shore Denmark^southern Norway. In: PetroleumGeology: North-West Europe and Global Perspectives - Proceedings ofthe 6th PetroleumGeology Conference (Ed. by A.G. Dore¤ & B.Vin-ing), Petrol. Geol. Conf. Ltd., Geol. Soc., pp.1185^1198.

Hamberg,L., Jepsen,A.-M.,ter Borch,N.,Engkilde,M.K.

& Svendsen, J.B. (2007) Mounded structures of injectedsandstones in deep-marine Paleocene reservoirs, Cecilie ¢eld,Denmark. In: Sand Injectites: Implications for Hydrocarbon Ex-ploration and Production (Ed. by A. Hurst & J. Cartwright),AAPGMem., 87, 69^79.



Harland, R.,Hine,N.M. &Wilkinson, I.P. (1992) Paleogenebiostratigraphic markers. In: Paleogene of the Central and North-ern North-Sea (Ed. by R.W.O.B. Knox & S. Holloway), BritishGeological Survey, pp. A1^A5.

Hubbard,S.M.,Romans,B.W.&Graham,S.A. (2007) An out-crop example of large-scale conglomeratic intrusions sourcedfrom deep-water channel deposits, Cerro Toro formation,Magallanes basin, southern Chile. In: Sand Injectites: Implica-tions for Hydrocarbon Exploration and Production (Ed. by A. Hurst& J. Cartwright),AAPGMem., 87, 199^207.

Huuse, M., Cartwright, J.A., Gras, R. & Hurst, A. (2005)Kilometre-scale sandstone intrusions in the Eocene of theOuter Moray Firth (UK North Sea): migration paths, reser-voirs and potential drilling hazards. In: Petroleum Geology:North-West Europe and Global Perspectives - Proceedings of the 6thPetroleum Geology Conference (Ed. by A.G. Dore¤ & B. Vining),Petrol. Geol. Conf. Ltd., Geol. Soc., pp.1577^1594.

Huuse, M., Cartwright, J., Hurst, A. & Steinsland, N.(2007) Seismic characterization of large-scale sandstone in-trusions. In: Sand Injectites: Implications for Hydrocarbon Explora-tion and Production (Ed. by A. Hurst & J. Cartwright), AAPGMem., 87, 21^35.

Jackson,C.A.-L. (2007) The geometry, distribution, and devel-opment of clastic injections in slope systems: seismic examplesfrom the upper Cretaceous Kyrre Formation, M�l�y slope,Norwegian margin. In: Sand Injectites: Implications for Hydrocar-bon Exploration and Production (Ed. byA.Hurst & J. Cartwright),AAPGMem., 87, 37^48.

Jenssen, A.I., Bergslian,D., Rye-Larsen,M. & Lindholm,R.M. (1993) Origin of complex mound geometry of Paleocenesubmarine-fan sandstone reservoirs, Balder Field,Norway. In:Petroleum Geology of Northwest Europe: Proceedings of the 4th Con-ference (Ed. by J.R. Parker),Geol. Soc., 135^143.

Jolly, R.J.H. & Lonergan, L. (2002) Mechanisms and con-trols on the formation of sand intrusions. J. Geol. Soc., 159,605^617.

Jonk, R.,Hurst, A.,Duranti,D., Parnell, J.,Mazzini, A. &Fallick,A.E. (2005) Orgin and timing of sand injection, pet-roleum migration, and diagenesis of Tertiary reservoirs, southViking Graben, North Sea.AAPGBulletin, 89, 329^357.

Kallweit,R.S.&Wood,L.C. (1982)The limits of resolution ofzero-phase wavelets.Geophysics, 47, 1035^1046.

Kawakami,G. &Kawamura,M. (2002) Sediment £ow and de-formation (SFD) layers: evidence for intrastratal £ow in lami-nated muddy sediments of the Triassic Osawa Formation,northeast Japan. J. Sediment. Res., 72, 171^181.

Lonergan, L. & Cartwright, J. (1999) Polygonal faults andtheir in£uence on deep-water sandstone reservoir geometries,Alba Field, United Kingdom Central North Sea. AAPGBull.,83, 410^432.

Lonergan,L.,Lee,N., Johnson,H.D., Jolly,R.J.H.&Cart-

wright, J. (2000) Remobilisation and injection in deepwaterdepositional systems - implications for reservoir architectureand prediction. In: Deepwater Reservoirs of the World (Ed. byP. Weimer, R.M. Slatt, J. Coleman, N.C. Rosen, H. Nellson,A.H. Bouma,M.J. Styzen&D.T. Lawrence),GCS-SEPMFoun-dation, 20th Annual Bob F. Perkins Research Conference, pp. 515^532.

MacLeod, M.K., Hanson, R.A., Bell, C.R. & McHugo, S.(1999) The Alba ¢eld ocean bottom cable seismic survey: im-pact on development.The Leading Edge, 18, 1306^1312.

Mazzini,A.,Duranti,D., Jonk,R.,Parnell, J.,Cronin,B.T.,Hurst, A. & Quine,M. (2003) Palaeo-carbonate seep struc-

tures above an oil reservoir, Gryphon ¢eld, Tertiary, NorthSea.Geo-Mar. Lett., 23, 323^339.

Obermeier, S.F. (1998) Liquefaction evidence for strong earth-quakes of Holocene and latest Pleistocene ages in the states ofIndiana and Illinois, USA. Eng. Geol., 50, 227^254.

Osborne,M.J.& Swarbrick,R.E. (1997)Mechanisms for gen-erating overpressure in sedimentary basins: a reevaluation.AAPGBull., 81, 1023^1041.

�zdemir, H. (2002) Reservoir delineation using joint prestackinversion of multicomponent seismic data. EAGE/SEG Re-searchWorkshop, Pau, France, September 5^8, 2005.

Parize, O., Beaudoin, B., Champanhet, J.-M., Frie' s,G., Im-bert, P., Labourdette, R., Paternoster, B., Rubino, J.-L.& Schneider,F. (2007) A methodological approach to clasticinjectites: from ¢eld analysis to seismic modeling ^ examplesof the Vocontian Aptian and Albian injectites (southeastFrance). In: Sand Injectites: Implications for Hydrocarbon Explora-tion and Production (Ed. by A. Hurst & J. Cartwright), AAPGMem., 87, 173^183.

Parize, O. & Frie' s, G. (2003) The Vocontian clastic dykes andsills: a geometric model. In: Subsurface Sediment Mobilization(Ed. by P.Van Rensbergen, R.R. Hills, A.J. Maltman & C.K.Morley),Geol. Soc., Lond., Spec. Publ., 216, 51^71.

Poulsen, M.L.K., Friis, H., Svendsen, J.B., Jensen, C.B. &Bruhn,R. (2007) The application of bulk geochemistry to re-veal heavy mineral sorting and £ow units in thick massivegravity £ow deposits, Siri Canyon Palaeocene sandstones,Danish North Sea. In:HeavyMinerals inUse (Ed. byM.Mange&D.Wright),Dev. Sedimentol. 58, 1099^1121.

Rasmussen,K.B., Bruun, A. & Pedersen, J.M. (2004) Simul-taneous seismic inversion. EAGE 66th Conference & Exhibi-tion, Paris, France, June 7^10, 2004.

Schi�ler, P., Andsbjerg, J., Clausen, O.R.,Dam,G.,Dybk-

j�r,K.,Hamberg,L.,Heilmann-Clausen,C., Johanne-sen, E.P., Kristensen, L.E., Prince, I. & Rasmussen, J.A.(2007) Lithostratigraphy of the Palaeogene^lower Neogenesuccession of the Danish North Sea. Geol. Surv. DenmarkGreenl. Bull., 12, 1^77.

Surlyk, F. (1987) Slope and deep shelf gully sandstones, UpperJurassic, East Greenland.AAPGBull., 71, 464^475.

Surlyk,F.&Noe-Nygaard,N. (2001) Sand remobilization andintrusion in the Upper Jurassic Hareelv Formation of EastGreenland.Bull. Geol. Soc. Denmark, 48, 169^188.

Templeton,G.,King, P. & Reeder,M. (2002) Leadon Field ^Description of Frigg Reservoir Sand Injection Structures.EAGE 64th Conference & Exhibition, Florence, Italy, May27^30, 2002.

Templeton, G., Mcinally, A., Melvin., A. & Batchelor,T.(2005)Comparison ofLeadon andGryphonFieldsSand Injec-tites: occurrence and performance. EAGE 68th Conference &Exhibition,Vienna, Austria, June12^15, 2006.

Timbrell, G. (1993) Sandstone architecture of the BalderFormation depositional system, UK Quadrant 9 and ad-jacent areas. In: Petroleum Geology of Northwest Europe:Proceedings of the 4th Conference (Ed. by J.R. Parker), Geol. Soc.,135^143.

Wild, J. & Briedis, N. (2010) Structural and stratigraphic rela-tionships of the Palaeocene mounds of the Utsira High. BasinResearch, 22, DOI: 10.1111/j.1365-2117.2010.00479.x.

Manuscript received 14 January 2009; Manuscript accepted6 April 2010.



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Sand remobilization and injection above an active salt diapir: the Tyr sand of the Nini Field,...

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