PSVariability in Syn-Rift Structural Style Associated with a Mobile Substrate and Implications for Trap

Definition and Reservoir Distribution in Extensional Basins: A Subsurface Case Study from the South Viking

Graben, Offshore Norway*

Christopher A-L. Jackson1, Karla Kane

1, Eirik Larsen

2, Elisabeth Evrard

1, Gavin Elliott

1, and Rob Gawthorpe

3

Search and Discovery Article #10423 (2012)**

Posted July 16, 2012 *Adapted from poster presentation at AAPG Annual Convention and Exhibition, Long Beach, California, April 22-25, 2012 **AAPG©2012 Serial rights given by author. For all other rights contact author directly. 1Department of Earth Science & Engineering, Imperial College, London, SW7 2BP, UK (c.jackson@imperial.ac.uk) 2Statoil ASA, Sandsliveien 90, Bergen, N5020, Norway 3Department of Earth Science, University of Bergen, N-5020, Bergen, Norway

Abstract

The South Viking Graben (SVG), northern North Sea, hosts many large hydrocarbon accumulations. In the Norwegian sector, the main reservoir-trap pairs are: (i) Middle Jurassic shallow marine sandstones in structural traps, and (ii) Palaeocene Deepwater sandstones in structural or combination traps. Upper Jurassic, syn-rift turbidite sandstones form reservoirs in several fields in the UK sector, but the equivalent succession in the Norwegian sector remains relatively unexplored due to difficulties in predicting reservoir distribution and trapping configurations. These difficulties reflect the control that rift-related normal faults and salt movement has on the deposition of Deepwater reservoir sandstones. In this study we use potential field, 3D seismic and well data to investigate how normal fault growth and movement of the evaporite-dominated Zechstein Supergroup control spatial variations in syn-rift structural style, trapping styles and reservoir distribution in the SVG. In the north of the basin, syn-rift deformation is dominated by listric faults that detach downwards into the underlying evaporites. These faults formed in response to tilting of the hangingwall and break-up of the supra-salt units, and halokinesis in this area is restricted to low-relief salt rollers in the immediate footwalls of the listric faults. In the central part of the basin, rift-related normal faults are basement-involved and only rarely propagated up through the Zechstein Supergroup. In this location fault-propagation folds, which are cored by low-relief salt pillows, developed in the supra-salt cover strata. The southern part of the basin is dominated by a series of ‘minibasins’ developed in response to the collapse of older Triassic-age salt diapirs; normal faulting is rare, and limited to low-displacement structures overlying the crests of salt diapirs and a few basement-involved faults that breach the Zechstein Supergroup. This study demonstrates that the Late Jurassic, syn-rift structural evolution of the SVG varied markedly over relatively short (i.e. <20 km) length-scales. We interpret this variability is related to mobile halite distribution within the Zechstein Supergroup; ‘halite-poor’ parts of the basin

are characterized by supra-salt, gravity-driven faults, whereas minibasins formed in ‘halite-rich’ parts of the basin. We conclude by demonstrating how these variations in structural style control the distribution and geometry of syn-rift reservoirs.

2. Study Area

1. RationaleDeep-water sands within the Upper Jurassic syn-rift succession form the reservoir for several hydrocarbon fields in the UK sector of the South Viking Graben but the equivalent succession in the Norwegian sector remains relatively unexplored (Fig. 1a).

The prediction of syn-rift reservoir distribution requires an understanding of: (1) the control of salt lithology and thickness on normal faulting and folding; (2) the impact of halokinesis and salt-influenced rifting on trap development; and (3) the influence of faulting and halokinesis on syn-rift sediment dispersal during (Fig. 1b).

Variability in Syn-Rift Structural Style Associated with a Mobile Substrate andImplications for Trap Definition and Reservoir Distribution in Extensional Basins:

A Subsurface Case Study from the South Viking Graben, Offshore Norway

Shallow marinesands nucleatingaround salt dome Ponded turbidites

in mini-basins

Major rift-shoulderdrainage system

Coupled basementand cover faulting

De-coupled basementand cover faulting

Sediment-starved high

Rift-axisturbidites

Syn-rift depocentresstrongly influencedby salt

Small footwallcatchments

Complex sedimenttransport acrosscover fault/foldarray

Over-thickenedparasequeces abovesalt weld

Utsira High

FladenGround

Spur

SouthVikingGraben

BerylEmbayment

9 25

NOUK

15 1616

20 km

GudrunArea

SW Utsira High

Sleipner Basin

= shallow marine sandstones

= offshore fine-grained deposits

= subaerially-exposed sediment source areas

= deep-water sandstones/conglomerates

+ w

ater

dep

th

8(& 8A)

3

7

3/511/61

2/61

6/515/51

4/615/61

2/51

6/613/61

8/519/51

7/61

8/619/61

8/6116/7

16/1216/13

16/1816/17

16/23

16/316/2

UK NORWAY

X

X’

Y

Y’

study area

Norway

UK Netherlands

Denmark

Germany

SOUTH VIKING GRABEN(Ve sub-basin)

SOUTH VIKING GRABEN(Vilje sub-basin)

UTSIRA HIGH

Regional lines Key wells

Gr a

ben

Bo

und

ary

Faul

t Z

one

Gudrun Fault

Brynhild Fault

Sleipner Fault

GUDRUN TERRACE

SLEIPNER TERRACE

Sleipner Graben

5 km

16/1-8 discovery(late-2007)

Thelma

Larch

S.Brae

C.Brae

N.Brae/ Beinn

Pine

Birch

E.Brae

Miller

Kingfisher

Toni

Tiffany

Elm

FLADEN GROUND

SPUR Gudrun

Upper Jurassic hydrocarbon fields

Fig. 2b

Fig. 2c

2.2. Stratigraphy and Palaeogeography59° 00’

58° 40’

58° 20’

2° 00’15/3

16/116/2

15/616/4

16/715/9

16/8

yawro

NK

U

5 km

Volg

ian

Kim

mer

idgi

anO

xfor

dian

Baj

ocia

n

Draupne

Mid.

Form

atio

n

Auk

Mid-Cimmerian(base-Jurassic)Unconformity

post-rift

syn-rift

Skagerrak

Åsgard

RødbySola

HeatherHugin

Sleipner

SmithBank

Vestland

Rot

lieg-

ende

sZe

chst

ein

Sup

ergr

oup

Heg

reG

roup

Viking

CromerKnoll

Lwr.

Ser

ies

Sys

tem

Cre

t.Ju

rass

icTr

iass

icP

erm

ian

Upr

.

Lwr.

Upr.

Structural and/ortectono-stratigraphic

significance Stra

tal U

nit/

Lith

ostra

tigra

phy

Sta

geB

atho

nian

Cal

lovi

an

M

M

SU2

SU1

M

M

M

E

E

E

E

E

L

L

L

L

L

L

pre-

rift

Dra

upne

Fm

Hea

ther

Fm

Hug

in F

mS

leip

ner F

m

145

150

155

160

175

170

165

Age

(Ma)

SU

1aS

U1b

pre-rift

Evaporite-rich

sub-Zechsteinbasement

BPN8802_22

Y Y’

UK

UTSIRA HIGH LDSLEIPNERTERRACE

SOUTH VIKING GRABENFGS

Cretaceous-Tertiary

Pre-Zechstein Gp ‘basement’

NORWAY

10 km

Triassic-Middle Jurassic

SW Utsira High study area(Panel 2)

Sleipner Basin study area(Panel 3)

sm 005T

WT

Upper Middle to Upper Jurassic

Zechstein Gp

The Graben Boundary Fault Zone (GBFZ) bounds the South Viking Graben to the west (Fig. 2b-c).

The case studies presented here are located on the hangingwall dipslope of the graben (Fig. 2a-c).

The South Viking Graben is a half-graben located along the northern arm of the Late Jurassic North Sea rift (Fig. 2a-c).

The pre-rift succession contains the Upper Permian Zechstein Supergroup evaporites; these influenced the rift structural style (Fig. 2d).

Syn-rift succession subdivided into:SU1: early syn-rift, late Callovian to late Oxfordian, Hugin (shallow-marine sandstone) and Heather (shelf mudstone) formations.SU2: late syn-rift, late Oxfordian to Volgian, Draupne Formation (deep-marine mudstone and turbidite sandstone) (Fig. 2e).

Triassic and early Middle Jurassic units form pre-rift cover strata (Fig. 2d).

GF

BF

Gudrun study area(Panel 4)Cretaceous-Tertiary

Upper Middle toUpper Jurassic

Zechstein Gp

Pre-Zechstein Gp Basement

sm 005T

WT5 km

SOUTH VIKING GRABEN

X X’

2.1. Structural Setting

Fig. 2b

Fig. 2c

FladenGround

Spur

GBFZ

GB

FZ

-

+

DEP

TH

Christopher A-L. Jackson1, Karla Kane1*, Eirik Larsen2§, Elisabeth Evrard1,Gavin Elliott1, Rob Gawthorpe3

1Department of Earth Science & Engineering, Imperial College, London, SW7 2BP, UK,2Statoil ASA, Sandsliveien 90, Bergen, N5020, Norway,

3Department of Earth Science, University of Bergen, N-5020, Bergen, Norway*Present address: Statoil (U.K.) Ltd, 1 Kingdom Street, London, W2 6BD, UK,

§Present address: Rocksource ASA, Bergen, N-5808, Norway

email: c.jackson@imperial.ac.uk

Salt-influenced riftNon-salt influenced rift

Fig. 1a

Fig. 2a

Fig. 2d Fig. 2e

Panel 2

Panel 4

Panel 3

UtsiraHigh

GudrunTerrace

SouthVikingGraben

SleipnerTerrace

High subsidence ratesoutpace sediment supplyleading to deepening of basinand slope by-pass

Fault scarp degradationcauses major slidesgenerating basinalmegabreccias

Sediment starved basin

Axial turbidites sourcedfrom intra basin slidesand axial/hangingwalldeltas

Tilting of basin floor generatesvertical stacking of axial turbiditesadjacent to footwall scarp

Fig. 1b

Gawthorpe et al. (unpublished)modified from Gawthorpe and Leeder (2000)

BasinsResearch

Group

3. Thickness and lithology of the Zechstein Supergroup

4. Case Study 1: Minibasins on the SW margin of the Utsira High

16/4-2

16/4-1

16/7-2

16/4-2

16/4-1

16/7-2

NNUTSIRA HIGH

UTSIRA HIGH

The early syn-rift (early Callovian to Late Oxfordian) Hugin and Heather formations were deposited across the slope but were thickest in the basins (Fig. 4b & 4d).

The late syn-rift (Late Oxfordian to Volgian) Draupne Formation were largely restricted to the western slope; thickness variations on the eastern slope are subtle because relief had been filled by early syn-rift deposits (Fig. 4c & 4d).

Topography/bathymetry associated with flow of the ZSG during the Triassic-early Middle Jurassic and later collapse of salt structures during the late Middle and Late Jurassic (Fig. 4e).

16/7-2 UTSIRA HIGHSLEIPNER TERRACE

P

PP

PIP

IP

IP

IP

Lower Cretaceous

Upper Cretaceous

basement-involvednormal faulting

SP

SP

SP

SP

ENEWSW

5 km

500 ms TW

T

Minibasins are developed between the Utsira High and Sleipner Terrace (Fig. 4a & 4d).

Minibasins are cored by thick Triassic successions, and early Middle Jurassic strata and Zechstein Supergroup evaporites are thin (Fig. 4d).

Early syn-rift Hugin and Heather Formations (Early Call-Late Oxf.) thicken within basins

and thin significantly across highs.

Late syn-rift Draupne Formation (Late Oxf.-Volg.) is largely isochronous though

thickness variations are observed in the west.

Thick Triassic-early Middle Jurassic and thin salt

beneath structural highs.

X X’

TMB

(c) Late Triassic-Early Jurassic

EW

WX

2

1

base

-leve

lfa

ll

(a) Early Triassic (b) Late Triassic (d) Middle-Late Jurassic (Syn-rift)

BCUMCU

regionaluplift

TMB TMBJMB

JMBJMB

Initial stage of Triassic minibasin (TMB) development and salt wall formation within the Zechstein Supergroup Minibasin (TMB) deepening and salt wall growth due to

continued sediment loading. Pods in east (W & X) become grounded.

Regional Early Jurassic uplift accompanied by subterranean dissolution of the Zechstein Supergroup and initiation of

Jurassic minibasins (JMB) formation.

Syn-rift filling of minibasins (JMB). Minibasins in the east are filled earliest due to earlier cessation of subsidence related to

TMB grounding and/or higher sediment supply.

TMB

4.2. Tectono-stratigraphic evolution

ca. 10 km

NNE

IP

IPIP

IP

IP

IP

IP

IP

IP

Utsira High

Sleipner TerraceDep

th (m

s TW

TT)

1980

3150

X’

X

time structure map = top Triassic

Reflection terminations= erosional truncation= onlap= apparent downlap(rotated onlap)

SP = Salt PillowP = PodIP = Interpod

GBFZ

10 km

Utsira HighSouth Viking Graben

NW

Base TertiaryunconformityKey Base Cretaceous

unconformity Top Triassic Top Zechstein Base Zechstein

15/5-3(projection: 630 m)

16/4-1(projection: 810 m)

0.5

sec

Zone

4

Zone

3

Zone

2

Zone

1

Zone 1

Zone 1 (No halite)31 km 35 km

Anhydrite Halite Carnallite Carbonate Silt-Silstone Shale

Key for stratigraphic correlation

3900

4000

4100

4200

4300

4400

4500

4600

4700

4800

2500

2600

16/4-1MD

GR RHOB DT-130 700 1.4 3.8 40 120

15/9-9MD

GR RHOB DT-130 700 1.4 3.8 40 120

30002980

15/5-3MD

GR RHOB DT-130 700 1.4 3.8 40 120

Top Zechstein

Base Zechstein

15/5-3 - SVG 16/4-1 - Utsira High 15/9-9 - Sleipner TerraceZone 4 (98% halite) Zone 1 (No halite)

6% 1%

49%

35%16% 12%

88%

93%

The ZSG is dominated by halite, anhydrite and carbonates (Fig. 3a).

At the basin margins, the ZSG is relatively thick and dominated by anhydrite and carbonate; towards the basin centre the unit is relatively thick and halite-dominated (Fig. 3a-b).

Based on halite proportion, four depositional zones are identified (Fig. 3a).

Fig. 3a

Fig. 3b

Fig. 4a (see Fig. 2a for location)

Fig. 4b Fig. 4c

Fig. 4d

Fig. 4e

4.1. Structural Style

UK

NO

RW

AY

20 km

58º

59º

1º 2º 3º 4º

NORWAY

Stavanger

LingGraben

ÅstaGraben

Witch GroundGraben

EgersundBasin

StavangerPlatform

FladenGround

Spur

SeleHigh

SouthVikingGraben

UtsiraHigh

SU1: Early Syn-Rift SU2: Late Syn-Rift

ZSG Lithology Distribution

Tectono-stratigraphic model for Case Study I

Thic

knes

s (m

s TW

T)0

200

Thic

knes

s (m

s TW

T)0

240

Basement faultSelected well control

Zechstein depositional zones:Zone 1=<10%Zone 2=10-50% haliteZone 3=50-90% haliteZone 4=>90% halite

Limit of ZechsteinKey to map

5. Case Study 2: Salt-influenced fault-related folding in the Sleipner Basin

Seismic isochron mapping (Fig. 5d & 5e) provide insights into the temporal and spatial development of the SFZ and the Sleipner Graben and these allow proposal of a tectono-stratigraphic model (Fig. 5f).

The Sleipner Basin is bound to the east by a segmented extensional fault (Sleipner Fault Zone - SFZ) and to the west by a large salt-cored high (Fig. 5a & 5b).

Fault-Perpendicular Folds - Three fault-perpendicular, salt-cored anticlines or intra-basin highs (IBH) compartmentalise the basin into four sub-basins (X-X’ in Fig. 5a & 5b). These intra-basin highs are located adjacent to areas of fault segment overlap.

Fault-Parallel Fold - A fault-parallel monocline underlain by thickened salt is identified in the immediate hangingwall of the SFZ (W-W’ in Fig. 5a & 5b). This structure is interpreted as a fault-propagation fold (extensional forced fold) which formed through the inhibited growth of the Sleipner Fault within the ductile Zechstein Group (Fig. 5a & 5b).

Fault and salt-related fold structures are identified in the basin:

15/6-8 S

15/6-7

15/6-5

15/6-6

15/6-4

1

23

4

1-4 = Sub-Basins2 km

N

Sleipner Fault Zone

26243428 TWT (msec)

Fault-Parallel Fold

Fault-Perpendicular Fold (IBHB)

Fault-Perpendicular Fold (IBHC)

X’

X

W

W’

time structure map =top Sleipner Fm. (top pre-rift)

2500

3000

3500

4000

Mid. VolgianLate Volgian

SLEIPNER FAULT

TWT

(mse

c)

Triassic-Middle Jurassic-aged salt-cored high

Syn-rift depocentre offset from SFZ by

fault-propagation fold

Fault-propagation fold related to inhibited growth of SFZ within evaporite-rich Zechstein Gp.

Thickened salt

West East

X-X

’ in

ters

ect

North South

2 KM

500

MS

TW

T

2 KM

500

MS

TW

T

1 2 43

IBHC

4

IBHB

2500

3000

3500

4000

TWT

(mse

c)

4 = Sub-Basins of Sleipner Graben

Fault-perpendicular salt-cored intra-basin highs

Significant thinning of early syn-rift Hugin & Heather Fm (Early Callovian to Late Oxfordian) across intra-basin highs W

-W’

inte

rsec

t

Y Y’

Late syn-rift (SU2) - diminished influence of fault-perpendicular folds and formation of a larger, linked depocentre; eventual breaching of fault-parallel fold (Fig. 5b-c and e).

Z Z’

Early syn-rift (SU1) - growth of fault-perpendicular (IBH) and fault-parallel folds formed a compartmentalised depocentre and influenced syn-rift sediment distribution (Fig. 5b-d).

Thickness (ms TW

T)420

0

N

SB2 SB

3

SB4

IBHB IBHC

SF1SF2 SF3 VFZ

1 km

Sleipner Terrace15/6-8S

15/6-515/6-6

Coalesced depocentres suggest decreased IBH activity

Thinning towards fault-propagation fold

SB2 SB

3

SB4

IBHB IBHC

SF1SF2 SF3 VFZ

Thickness (ms TW

T)340

0

N

1 km

15/6-8S

15/6-515/6-6

Sleipner Terrace

Thinning towards fault-propagation fold

Thickest sediment within isolated depocentres.

Salt distribution

Salt distribution

Structural style cross-section

Structural style cross-sectionSupra-salt depocentre geometry

N~ 2 km

Linked SFZ

SF3SF2SF1

IBHB IBHC

Fault growth monocline

Normal fault Salt movement Fault-perpendicular fold

Zechstein Sgp evaporites

SB2 SB3 SB4

SB2 Sub-basins

IBHB Intra-basin highs

X X’

Y’

Y

X X’

Z’

Z

X X’W W’

early

syn

-rift

(late

st O

xfor

dian

)la

test

syn

-rift

(Vol

gian

)

Key

Supra-salt depocentre geometry

5.2. Tectono-stratigraphic evolution

5.1. Structural Style

SU1: Early Syn-Rift SU2: Late Syn-Rift

Fig. 5a (see Fig. 2a for location)

Fig. 5b Fig. 5c

Fig. 5eFig. 5d

Fig. 5g

Fig. 5f

6. Case Study 3: Thin-skinned gravity-driven extension in the Gudrun area

SU1b: Middle Syn-Rift (Fig. 5e)SU1a: Early Syn-Rift (Fig. 5d) SU2: Late Syn-Rift (Fig. 5f)

2 km

200 ms

(TWT)

hangingwallrotation

X

hangingwallrotation

GF

BFN

hangingwallrotation

15/3-3

15/3-715/3-1S

15/3-5

15/3-4

0

366

thic

knes

s (T

WT)

Lateral propagation of Gudrun fault

North Brynhild fault segment &

hangingwall array active

SU1b - late Early Callovian to Late Oxfordian

Brynhild South active

5 km

?

X

5 km

Brynhild north segment

Brynhild south segment

Gudrun Fault

0

979

thic

knes

s (T

WT)

15/3-3

15/3-715/3-1S

15/3-5

15/3-4

SU2 - Late Oxfordian to Mid VolgianLocalisation onto

Brynhild fault (hangingwall faults

inactive)

Northward propagation of Brynhild South

Central Gudrun fault

active

5 km

Brynhild fault

Gudrun fault

GF

BFN

GF

15/3-3

15/3-7

15/3-5

15/3-4

Brynhild fault inactive

0

153

thic

knes

s (T

WT)

SU1a - Early Callovian

Central Gudrun fault active

15/3-1S

5 km

Gudrun fault

Salt-controlled depocentres

Minor thickening of SU1a across Gudrun Fault

Minor thickness variations across

salt-cored structural high

Thickening of SU1b across Gudrun Fault

Thickening of SU1b across Brynhild Fault

Brynhild Fault active until mid-SU2 times

The central part of the Gudrun Fault active and the Brynhild Fault inactive.

Initiation of the Gudrun Fault associated with activity on the GBFZ, westward tilting of the hangingwall, and extension of Triassic to Lower Middle Jurassic units above the Zechstein Gp.

Lateral growth of the Gudrun Fault and initiation of activity on the Brynhild North and South fault segments.

Reduced activity and death of the Gudrun Fault and lateral propagation and overlap of the Brynhild Fault segments. Upslope migration of strain is interpreted to reflect progressive “unbuttressing” and extensional faulting of supra-salt strata.Eventual fault death during the latest Jurassic

Formation of a rollover anticline due to the listric geometry of the Brynhild Fault.Salt migration and formation of salt rollers in fault footwalls.

X X’ Y Y’ Z Z’

500 ms

(TWT)

2 km

GF

SU2

SU1b

SU1a

15/3-7(projected)

15/3-1S

X

uppe

rD

raup

ne F

mlo

wer

Dra

upne

Fm

Hea

ther

Fm

pre-

rift

syn-

rift

post

-rift

(syn

-inve

rsio

n)

15/3-1 S 15/3-7 15/3-515/3-415/3-3

Bry

nhild

Fau

lt

Gud

run

Faul

t

Hug

in F

mS

leip

ner

Fm

early Middle Volgian(147.7 Ma)

top Bathonian(164.5 Ma)

late Early Callovian(162.2)

early Late Oxfordian(155.2 Ma)

GR (API)2067

GR (API)2067

GR (API)2067

GR (API)2067

GR (API)2067

400

m

Skagerrak Fm(and older)

1.8 km 4.5 km 9.6 km 5 km

Skagerrak Fm(and older)

?

?

?

??

ENE

Brynhild Fault

Gudrun Fault

East Braesub-basin

15/3-1S

15/3-3

15/3-4

15/3-5

15/3-7

5 km

N

2420

4791

dept

h (m

s TW

T)

top Hugin Fm time-structure map

BFN

BFS

GF

T

V

V’

W’

W

V

V’

SU2

SU1b

SU1a

V V’

W’W

BFN

The Gudrun Fault is 17 km long, planar in cross-section and dips steeply to the NW. The fault tips out downwards into the ZSG and upwards into the lower part of the Draupne Fm (SU2) (Fig. 5a & 5b).

Biostratigraphically-constrained stratigraphic correlations (Fig. 5c) and seismic isochron mapping (Fig. 5d-f) document the temporal and spatial evolution of the Gudrun fault array (Fig. 5gi-iii).

In the Gudrun area the ZSG formed a detachment for a thin-skinned fault array that developed due to progressive westward hangingwall tilting towards the GBFZ (Fig. 5a & 5b)

The Brynhild Fault occurs 5 km to the NE (i.e. up the hangingwall dipslope) of the Gudrun Fault. It is 15 km long and is divided into a southern (BFS) and northern (BFN) segment. Both are listric in geometry, detaching at a shallow angle into the Zechstein Gp and tipping out steeply upwards into SU2. A rollover anticline is developed in its hangingwall (Fig. 5a & 5b).

Steeply dipping Gudrun Fault detaching downwards into Zechstein Gp and upwards into the lower part of SU2

Listric Brynhild Fault detaching at a shallow angle

into Zechstein Gp and steeply upwards into middle SU2

?

??

?

time-structure map = top early syn-rift (Hugin Fm)

datum = Base Cretaceous Unconformity (BCU)

N N N

5 km 5 km5 km

Fig. 5c

Fig. 5bFig. 5a (see Fig. 2a for location)

X Y

X’ Y’ Z’

Z

turbiditereservoir

sandstone

turbiditereservoir

sandstone

turbiditereservoir

sandstone

6.1. Structural Style

6.2. Tectono-Stratigraphic Evolution

15/3-315/3-1S 15/3-7

ca. 2 km

6. Summary of salt-influenced rift structural styles

7. Implications for reservoir distribution in salt-influenced rift basins

8. References

EARLY SYN-RIFTKEY POINTS

LATE SYN-RIFTM

INIB

ASI

NS

(e.g

. Uts

ira H

igh

SW m

argi

n)FA

ULT

-REL

ATED

FO

LDS

(e.g

. Sle

ipne

r Gra

ben)

GR

AVIT

Y-D

RIV

EN F

AU

LTS

(e.g

. Gud

run

faul

t arr

ay)

rift evolution

decr

easi

ng th

ickn

ess

and/

or s

alt m

obili

ty

hangingwallrotation

hangingwallrotation

X

Syn-Rift: (Early Call-Late Oxf)PP

IP IP

PP

IP IP

Where salt is relatively thick and halite-rich, a minibasins may develop.

Interaction between extensional faulting and salt mobility causes fault-propagation folding and the development of fault-perpendicular folds.

Fault-propagation folding influences depocentre development for much of the rift phase; fault-perpendicular folds largely active during the early syn-rift.

In areas where salt is relatively thin and/or immobile, a gravity-driven, thin-skinned extensional faulting may develop in response to basement tilting.

Extensional fault activity may migrate in response to ongoing basement tilting and progressive ‘unbuttressing’ of the cover strata located further up the hangingwall dipslope.

The initial post-salt succession thickest in minibasins adjacent to diapirs; syn-rift succession thickest in the later minibasins that develop above collapsed diapirs.

Minibasin relief fills during the rift event; later depocentres more less localised than early depocentres.

It is critical to integrate seismic and well data to determine the tectono-stratigraphic evolution of salt-influenced rift basins.

Variations in structural style occur over relatively short length-scales (i.e. <10 km)Spatial variations in structural style are broadly related to the thickness and/or mobility of the ZSG salt (see Section 3).

Reservoir distribution in salt-influenced rifts is more complex then that predicted by existing tectono-stratigraphic models (Fig. 7a).

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Axially transported deep-water sandstones offset from basin margin by fault-propagation fold

Axially transported deep-water sandstones deposited in immediate hangingwall of fault after fold breaching

Deepwater sandstones deposition in conduits and minibasins across entire width of slope

Deepwater sandstones deposition in conduits and minibasins on western slope only

early

syn

-rift

late

syn

-rift

Minibasins:thick and/or mobile (halite) salt

Thick-skinned faulting:salt mobility and thickness variable

Thin-skinned faulting:thin and/or immobile (anhydrite) salt

3

4

5

78

1S

BFN

BFS

GF

X

XX

X

X

X

BFN

BFS

3

4

5

7

8

1S

Deep-water sandstones restricted to the hangingwall of growth

faults

Deep-water sandstones ‘track’ thin-skinned deformation and

extend updip into hangingwall of landward growth fault

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atadfoegde

edge of the main Utsira High

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UTSIRA HIGH(exposed)

he main

atadfoegde

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edge of tUtsira High

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UTSIRA HIGH(exposed)

KEY

= predicted shoreface sandstones

= predicted deep-water sandstones

= exposed

= turbidite pathway

shoreface

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Volgian Kimmeridgian

Jackson, C.A-L. et al., (2011) “Structurally-controlled syn-rift turbidite deposition on the hangingwall dipslope of the South Viking Graben, North Sea Rift System”. AAPG Bull., 95, 1557-1587.Jackson, C.A-L., et al., (2010) “Structural evolution of minibasins on the Utsira High, northern North Sea; implications for Jurassic sediment dispersal and reservoir distribution”. Pet. Geosci., 16, 105-120..Kane, K.E., et al., (2010) “Normal fault growth and fault-related folding in a salt-influenced rift basin: South Viking Graben, offshore Norway”. J. Struc. Geol., 32, 490-506.Kieft, R.L., et al., (2010) “Sedimentology and sequence stratigraphy of the Hugin Formation, Quadrant 15, Norwegian sector, South Viking Graben”. In: Petroleum Geology: From Mature Basins to New Frontiers Jackson, C.A-L. and Larsen, E., (2009) “Temporal and spatial development of a gravity-driven normal fault array: Middle–Upper Jurassic, South Viking Graben, northern North Sea”. J. Struc. Geol., 31, 388–402.Jackson, C.A-L. and Larsen, E., (2008) “Timing basin inversion using 3D seismic data: a case study from the South Viking Graben, offshore Norway”. Basin Res., 20, 397-417.

shoreface

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Kimm.-Volg.

Fig. 6a

Fig. 7a