salt tectonics, associated sedimentary structures and hydrocarbon traps msc exploration geophysics...
TRANSCRIPT
Salt Tectonics, Associated sedimentary Salt Tectonics, Associated sedimentary structures and hydrocarbon Trapsstructures and hydrocarbon Traps
MSc Exploration GeophysicsSchool of Earth and Environment
University of Leeds, LeedsLS2 9JT
presented by:presented by:
Adeniyi Sanyaolu, Dan Sopher,Adeniyi Sanyaolu, Dan Sopher,Nick Shane & Cormac O’ReillyNick Shane & Cormac O’Reilly
Topics to be coveredTopics to be covered
Depositional environments of EvaporitesDepositional environments of Evaporites Physical properties of saltPhysical properties of salt Salt related structuresSalt related structures Sedimentary structures associated with Sedimentary structures associated with
saltsalt Role of salt in generation of hydrocarbonsRole of salt in generation of hydrocarbons Salt related hydrocarbon trapsSalt related hydrocarbon traps Case study: Persian GulfCase study: Persian Gulf
What are Evaporites?What are Evaporites?
How are Evaporites How are Evaporites DepositedDeposited
Two principle modes ofTwo principle modes ofDeposition:Deposition:
Subaqueous PrecipitationSubaqueous Precipitation Shallow to deep waterShallow to deep water Evaporating dish processEvaporating dish process Periodic replenishmentPeriodic replenishment
Subaerial PrecipitationSubaerial Precipitation SubkhasSubkhas Sediments around salt Sediments around salt
lakeslakes OasesOases
Evaporite minerals include Evaporite minerals include gypsum, sylvite, polyhalite, gypsum, sylvite, polyhalite, anhydrite, etc.anhydrite, etc.
Where are Evaporites Where are Evaporites Deposited?Deposited?
After Tucker ,1991
Physical Properties of Physical Properties of SaltSalt
Denisty: Denisty: 0.00215Kg/cm0.00215Kg/cm33
Hardness: 2.5 Hardness: 2.5 (Moh’s)(Moh’s)
Colour: clear to whiteColour: clear to white Soluble in waterSoluble in water High DuctilityHigh Ductility High Thermal High Thermal
conductivityconductivity Flows easily under Flows easily under
pressure and at pressure and at geological geological timescales by either:timescales by either: Pressure solutionPressure solution Dislocation CreepDislocation Creep
SALT TECTONICSSALT TECTONICS Salt, which is weak and buoyant is found in Salt, which is weak and buoyant is found in
many sedimentary basins where it occur as a many sedimentary basins where it occur as a weak layer between other lithologies, as such weak layer between other lithologies, as such it behaves like a pressured viscous fluid it behaves like a pressured viscous fluid during deformation and tends to flow.during deformation and tends to flow.
Key factors in salt tectonics are:Key factors in salt tectonics are:
Buoyancy (density contrast)Buoyancy (density contrast) Differential LoadingDifferential Loading Regional TiltRegional Tilt The weakness of salt The weakness of salt
SALT FLOWSALT FLOW
A tabular layer of salt can deform either A tabular layer of salt can deform either by poiseuille flow or couette flow.by poiseuille flow or couette flow.
Poiseulli flow involves the vertical Poiseulli flow involves the vertical thinning of overburden and the lateral thinning of overburden and the lateral extrusion of salt from under sediment extrusion of salt from under sediment depocenters.depocenters.
Couette flow on the other hand Couette flow on the other hand corresponds to layer parallel simple shear corresponds to layer parallel simple shear as overlying sediments translate seawardas overlying sediments translate seaward
Extrusion of SaltExtrusion of Salt
SALT STRUCTURESSALT STRUCTURESSalt flow or movement results in the formation of Salt flow or movement results in the formation of structures. Salt forms two main types of structures:structures. Salt forms two main types of structures:
Salt pillows: here the movement of salt results in Salt pillows: here the movement of salt results in the uplift of overlying lithologies.the uplift of overlying lithologies.
Salt diapirs: here the overlying sediments are Salt diapirs: here the overlying sediments are pierced by the moving salt and diarpirs can be of pierced by the moving salt and diarpirs can be of different shapes (Walls, columns, bulbs and different shapes (Walls, columns, bulbs and mushrooms).mushrooms).
The geometry of salt structures is dependent on the The geometry of salt structures is dependent on the rate of sedimentation and the rate at which the salt rate of sedimentation and the rate at which the salt flows.flows.
Salt Dome Growth Stages
Salt Dome Growth StagesSalt Dome Growth Stages Seni & Jackson (1984)Seni & Jackson (1984)
Seni & Jackson (1984)
A number of processes are known to thin or A number of processes are known to thin or weaken overburden thereby creating paths or weaken overburden thereby creating paths or spaces for salts to move into. These processes spaces for salts to move into. These processes include :include :
PASSIVE DIAPIRISMPASSIVE DIAPIRISMMOVEMENT TRIGGERED BY DIFFERENTIAL MOVEMENT TRIGGERED BY DIFFERENTIAL LOADINGLOADINGMOVEMENT TRIGERRED BY EXTENSIONMOVEMENT TRIGERRED BY EXTENSIONMOVEMENT TRIGERRED BY CONTRACTIONMOVEMENT TRIGERRED BY CONTRACTIONMOVEMENT CAUSED BY STRIKE-SLIP FAULTINGMOVEMENT CAUSED BY STRIKE-SLIP FAULTINGNEAR DIAPIR DEFORMATIONNEAR DIAPIR DEFORMATIONALLOCHTHONOUS SALTALLOCHTHONOUS SALT
Other processes that enhance salt flow
Salt diapirs in seismic Salt diapirs in seismic sectionsection
Associated Sedimentary Associated Sedimentary StructuresStructures
Peripheral SinksPeripheral Sinks Basins developed due to flow of salt Basins developed due to flow of salt
layer.layer. Primary Peripheral sink generated far Primary Peripheral sink generated far
from diapir early in development.from diapir early in development. Secondary Peripheral sink generated on Secondary Peripheral sink generated on
penetration of the upper layerspenetration of the upper layers
After Halbouty, 1967
TurtlesTurtles Form Between two adjacent Salt diapirsForm Between two adjacent Salt diapirs Salt flow generates accommodation in the Salt flow generates accommodation in the
centre of the basincentre of the basin Continued salt flow leaves anticlinal Continued salt flow leaves anticlinal
structures that pinch out towards the diapirs structures that pinch out towards the diapirs “Turtles”.“Turtles”.
After Ordling, 2005
Unconformities and lateral Unconformities and lateral changeschanges
After Allen ,1992
Effects of salt on h/c maturationEffects of salt on h/c maturation
• Geothermal heat flow is the product of 2 factors:
(1) Thermal gradient
(2) Thermal conductivity variation with depth
• Thermal conductivity of salt is 3 to 4 times greater than that of other sedimentary rocks.
• Salt body will funnel geothermal heat and cause a higher temperature anomaly in the surrounding rocks.
• Anomaly can be up to 2 to 3 times greater than what would normally be expected.
Effects of salt on h/c maturationEffects of salt on h/c maturation
Geothermal gradients created by salt structures may move Geothermal gradients created by salt structures may move surrounding rocks into the maturation window.surrounding rocks into the maturation window.
Factors which effect the geothermal gradient of salt are:Factors which effect the geothermal gradient of salt are:
(1) size of the salt structure(1) size of the salt structure
(2) geometrical shape of the salt structure(2) geometrical shape of the salt structure
(3) depth of burial(3) depth of burial Salt structures can produce both positive and negative anomalies.Salt structures can produce both positive and negative anomalies. Oil maturation window : Temperatures of 80 Oil maturation window : Temperatures of 80 °c - 120°c - 120 °c°c
Gas maturation window : Temperatures of 120 Gas maturation window : Temperatures of 120 °c - 150°c - 150 °c°c
If heat flow anomaly is characterised in detail, this can help to If heat flow anomaly is characterised in detail, this can help to
better define the geometry of the salt body better define the geometry of the salt body
Positive and negative anomaliesPositive and negative anomalies
Salt diapirs were the first diapiric structures to be recognised and best understood due to their economic importance.
The upturned sediments, truncated against the impermeable salts, provide excellent traps for hydrocarbons.
Hydrocarbon Traps in Salt Hydrocarbon Traps in Salt ProvincesProvinces
Doming
Graben
Pinch out
Walling
Walling
Unconformity
Cap rock
Flank Fault
sFlank Fault
s
Figure from Allen & Allen (1992)
Widespread in USA, Mexico, SW Russia, West Central Africa and Canadian Arctic…
Boutique provinceBoutique province
U.S. province that is ranked among the world priority provincesU.S. province that is ranked among the world priority provinces
Priority provincePriority province
Case Study – Persian GulfCase Study – Persian Gulf
Case Study – Persian GulfCase Study – Persian Gulf
The dark circular patches represent the surface expression of salt domes that have risen diapirically from the Cambrian Hormuz salt horizon through the younger sediments to reach the surface.
Only in a hot arid environment such as that of the Gulf can the soluble salt escape rapid erosion.
Source: Landsat 7, NASA (2002)
Case Study – Persian GulfCase Study – Persian Gulf
• Extensional rifting of Arabic Plate > basin development > evaporites deposited up to 2.5km thick (Hormuz Series) and up to 4km (Oman Salt Basin)
• Diapiric movement initiated by extensional and strike slip movements of Precambrian basement block
• Pathways for salt movement:
- basement faults cut overlying seds` (doming + walls)
- pull apart from wrench fault deflections
- reactivation of extensional grabens with salt deposits
- instability of thick salt beds at the foot of tilt blocks (gravity glides)
Pillows.. Rim anticlines.. Turtlebacks..
NESW
Neoproterozoic Evaporite Basins Develop
Zagros Reverse FaultPrecambrian Basement
Overburden thickens, basement block movements rejuvenated
Sedimentation continuous + Upper Jurassic evaporite deposits
Diapirism + Upper Jurassic + Miocene Cap rocks + faulting and folding
Case Study - Persian GulfCase Study - Persian Gulf
TIM
E
Turtleback Structures in the Persian Turtleback Structures in the Persian GulfGulf
Marmul Field, South Oman Salt Basin – formed by initial salt withdrawal and shallow dissolution.
Near surface and subsurface meteoric waters caused dissolution, evidenced by unconformities
Ara Pillow dissolution
Structural inversion after shallow dissolution
Reasons for Prolific HydrocarbonsReasons for Prolific Hydrocarbons
• Uplift of the Zagros ranges in the Pliocene
• Thick sedimentary sequence (>18000m) with occasional anaerobic intervals, and large basin
• Rich source rocks at several levels (Neoproterozoic, Palaeozoic, Jurassic, Lower Cretaceous and Lower Tertiary.
• Excellent carbonate (faulted) and sandstone reservoir rocks with high permeability and porosity
• Cap rocks of salt, anhydrite and shale sealing the reservoirs; providing multiple stacked reservoirs
• Continuous structural growth of growth of major folds, due to salt diapirism or basement block uplift
• Deep seated diapirism, providing 60% of oil field structures in the Basin
ConclusionsConclusions• Salts deform as a viscous fluid with little or no ultimate stress and will flow if subjected to minimal shear stress. Flow of salt imposes strain on other lithologies they are associated with forming different structures
• Different salt styles control trap styles in supra- and subsalt environments and have varying effects on sediment transport, deposition, and on hydrocarbon generation and migration. Better predictive models for reservoirs will be based on improved knowledge of mechanisms of salt
• The presence of salt also effects the maturation process of hydrocarbons due to its very high thermal conductivity.
• Some 60% of the ultimate recoverable oil reserves of the Persian Gulf Basin originate from Salt tectonism, and 40% of the known world oil reserves are due to salt diapirism in this basin
ReferencesReferences Alsop, G. I., Blundell, D. J. & Davidson, I. (eds), Salt Tectonics, Alsop, G. I., Blundell, D. J. & Davidson, I. (eds), Salt Tectonics,
Geological Society Special Publications No. 100, 129-151 Geological Society Special Publications No. 100, 129-151 (1996)(1996)
Jackson, M. P .A & Talbot, C. J., Advances in Salt Tectonics. In: Jackson, M. P .A & Talbot, C. J., Advances in Salt Tectonics. In: Continental Deformation (Edited by Hancock, P. L.), Pergamon Continental Deformation (Edited by Hancock, P. L.), Pergamon Press, 159-179, (1994)Press, 159-179, (1994)
Allen, P. A., & Allen, J. R., Basin Analysis, Blackwell (1992)Allen, P. A., & Allen, J. R., Basin Analysis, Blackwell (1992) Tucker, M. E., Sedimentary Petrology, Geoscience Texts (1991)Tucker, M. E., Sedimentary Petrology, Geoscience Texts (1991) Halbouty, M. T., Salt Domes, Gulf publishing company (1967)Halbouty, M. T., Salt Domes, Gulf publishing company (1967) Odling, N., EARS5131 course notes, University of Leeds, MSC Odling, N., EARS5131 course notes, University of Leeds, MSC
Exploration Geophysics (2005)Exploration Geophysics (2005) Nagihara, S., Application of marine heat flow data important in Nagihara, S., Application of marine heat flow data important in
oil and gas exploration, (2005)oil and gas exploration, (2005) Shaker, S.S., Geopressure compartmentilization in salt basins: Shaker, S.S., Geopressure compartmentilization in salt basins:
their assessement for hydrocarbon entrapment in the gulf of their assessement for hydrocarbon entrapment in the gulf of Mexico, Geopressure Analysis Services (2004)Mexico, Geopressure Analysis Services (2004)
Letouzey, J., Salt movement, tectonic events, and structural Letouzey, J., Salt movement, tectonic events, and structural style in the central Zagros fold and thrust belt. Institut style in the central Zagros fold and thrust belt. Institut Francais du petrole.(2004)Francais du petrole.(2004)
Nagihara, S., Regional synthesis of the sedimentary thermal Nagihara, S., Regional synthesis of the sedimentary thermal history and hydrocarbon maturation in the deepwater Gulf of history and hydrocarbon maturation in the deepwater Gulf of Mexico. Department of Geosciences, Texas State University Mexico. Department of Geosciences, Texas State University (2003)(2003)
Mello, U.T., The role of salt in restraining the maturation of Mello, U.T., The role of salt in restraining the maturation of subsalt source rocks (2000) subsalt source rocks (2000)