Date post: | 27-Dec-2015 |
Category: |
Documents |
Upload: | pham-minh-khanh |
View: | 13 times |
Download: | 0 times |
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 ([email protected]) 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: [email protected]
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).
latest Oxfordian
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
16/7-2
atadfoegde
edge of the main Utsira High
16/4-1
16/4-2
UTSIRA HIGH(exposed)
he main
atadfoegde
16/4-2
edge of tUtsira High
16/4-1
UTSIRA HIGH(exposed)
KEY
= predicted shoreface sandstones
= predicted deep-water sandstones
= exposed
= turbidite pathway
shoreface
16/7-2
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
latest Oxfordianlatest Oxfordian
Kimm.-Volg.
Fig. 6a
Fig. 7a