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8/12/2019 Hydrocarbon Formation
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Formation of Oil and Gas, Sources,
Reservoirs and Traps
• Origin of Oil and Gas
• Sources – what are good source conditions?
• Migration – how does hydrocarbon migrate and whatinfluences migration?
• Reservoirs – what makes for good storage potential?
• Traps – how is hydrocarbon trapped?
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Formation of Oil and Gas
• Decay of algae andbacteria
• Burial
• Cooking (temp+press)
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Formation of Hydrocarbon
Favourable Preservation Conditions
•High organic production (over 10%)
•Anaerobic depositional systems
•Moderate to low rate of sedimentation
Lake (thermal stratification)ocean strat.
Barred basinSalinity contrast
Continental shelfupwelling
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Hydrocarbon type
Gas
(e.g. S. North Sea,Carboniferous)
CoalPlants
Gas
(e.g. N. North Sea,Jurassic)
OilAlgae and Bacteria
Deep burialShallow burialMaterial
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Changes on Burial
Diagenesis (up to 50ºC)
• Biological
• Chemical
• PhysicalCatagenesis (50-200ºC)
Metagenesis (200-250ºC)
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Formation of Oil and Gas
Fats, waxes, oils Kerogen
Cellulose, woodWoodyKerogen
HEAT +PRESSURE
HeavyOil
Coal
Light
oil
Gas
Gas
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8/12/2019 Hydrocarbon Formation
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The Oil Window
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Hydrocarbon Needs
Source Rock
Reservoir Rock
Trapping Mechanism
Timing
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North Sea
Oil – 3.5-5kmGas –4-6km
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Migration
• Physical Compaction - burial
• Oil and gas formation (chemical)
Kerogen expansion
Increase in pressure
Expulsion
Factors controlling migration?
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Migration
• Porosity
• Permeability – primary and secondary
High Low
Connected Unconnected
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Migration
Differentiation of
Water, oil and gas
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Hydrocarbon Traps
Types of Trap
• Structural• Stratigraphic
• Diagenetic
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Trap type
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North Sea – Key Hydrocarbon Events
• Mesozoic extension and rifting, Jurassic-Cretaceous highorganic input to rift valley
• Permian (Pangaea) basin formation (crustal subsidence) onVariscan folding
• Variscan Orogeny – Southern North Sea• Crustal Extension – Carboniferous, equatorial swamps, highorganic content
• Caledonian Orogeny – closing of Iapetus, volcanic activity inback-arc basin, land of lakes (Devonian ORS)
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North Sea Examples –Salt Gas Traps, Southern North Sea
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North Sea Examples –Salt Gas Traps, Southern NorthSea
High organic inputCarboniferous Coal
Permian desert lakebordered by vast sand dunes
Rotliegend Sandstone
Deposition of salt layer
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North Sea Examples –Salt Gas Traps, Southern North Sea
Indefatigable and Leman Fields in Rotliegend Sand
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North Sea Examples – Salt Movement and Basin Inversion
Salt flow through Permian e.g. Fulmar and Gannet Fields
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North Sea Examples – Deep (Permian) Basins
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North Sea Examples – Deep (Permian) Basins
Half-graben“trap-door mechanism
e.g. Faeroe-Shetland Basin,giant Morecambe field
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North Sea Examples – Mesozoic Rift Valleys & Extension
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North Sea Examples – Rift
Valleys & Extension
Rifting for 100MYMost active in JurassicJurassic - highest source potentialKimmeridge Clay (140Ma) sourceKimmeridge (Brent) delta sands reservoirfrom upland volcanic centre
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North Sea Examples – Rift Valleys & Extension
Source – slow subsidence and large accumulationMaturation still in progress today
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North Sea Examples – Rift Valleys & Extension
Reservoir in delta sands off active rivers e.g. Brent Field
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North Sea Examples – Rift Valleys & Extension
150ma (Jurassic-Cretaceous)•Rapid subsidence and slumping –•Large low relief deposits ofsheet-like sandse.g. Brae, Galley,Claymore and Magnus fields
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