hydrocarbon traps and seals
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Hydrocarbon Traps and Seals
Hydrocarbon Traps and Seals
Revision
What are geological elements of petroleum system?
What are geological processes of petroleum system?
How organic matters is converted into petroleum?
Source Rock - A rock with abundant hydrocarbon-prone organic matter
Reservoir Rock - A rock in which oil and gas accumulates:
- Porosity - space between rock grains in which oil accumulates
- Permeability - passage-ways between pores through which oil and gas moves
Seal Rock - A rock through which oil and gas cannot move effectively (such as mudstone and claystone)
Migration Route - Avenues in rock through which oil and gas moves from source rock to trap
Trap - The structural and stratigraphic configuration that focuses oil and gas into an accumulation
Top of oil window
Top of gas window
Generation
Expulsion
Accumulation
GOC
OWC
Migration
Preservation
The processes
(modified from Tissot and Welte, 1984)
Organic Debris
Kerogen
Carbon
Initial Bitumen
Oil and Gas
Methane
Oil Reservoir
Migration
Thermal Degradation
Cracking
Diagenesis
Catagenesis
Metagenesis
Progressive Burial and Heating
Schematic Representation of the Mechanismof Petroleum Generation and Destruction
i. Diagenesis is chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original mineralogy and texture. There is no sharp boundary between diagenesis and metamorphism, but the latter occurs at higher temperature and pressure than the former.
ii. Catagenesis
Catagenesis is the cracking process which results in the conversion of organic kerogens into hydrocarbons
iii. Metagenesis is the last stage of maturation and conversion of organic matter to hydrocarbons. Metagenesis occurs at temperatures of 150 to 200C. At the end of metagenesis, methane, or dry gas, is evolved along with nonhydrocarbon gases such as CO2, N2, and H2S, as oil molecules are cracked into smaller gas molecules.
What is Trap
A trap is the place where oil and gas are barred from further movement.(Levorsen, 1967)
.
Seals or Cap Rocks
For a trap to have integrity, it must be overlain by an effective seal.
Any rock that is impermeable can act as seal or cap rock but commonly mudstone
Introduction: Oil Traps
Some rocks are permeable
and allow oil and gas to freely
pass through them
Other rocks are impermeable
and block the upward passage
of oil and gas
Where oil and gas rises up
and capped by impermeable rocks it cant escape. This is one type of an Oil Trap.
Impermeable
Permeable
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The permeable rocks than contain oil and gas within the oil trap are known as the Reservoir Rock.
Reservoir rocks have lots of interconnected holes called pores. These allow them to absorb the oil and gas like a sponge.
Earth Science World Image Bank Image #h5innl
This is a highly magnified picture of
a sandy reservoir rock (water-filled
pores are shown in blue)
As oil migrates it fills up the pores
(oil-filled pores shown in black)
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Presenter notes: The permeable rocks than contain oil and gas within the oil trap are known as the Reservoir Rock. Reservoir rocks have lots of interconnected holes called pores. These allow them to absorb the oil and gas like a sponge. The picture on the left shows a good reservoir rock with lots of pore spaces filled with water shown in blue. As we advance the slide, we see the pores gradually fill with oil. This rock can soak up a large amount of oil.
Carbonate as Reservoir
How to find oil: Source rock, reservoir rock, traps
Hydrocarbon Traps
i. Structural traps
Structural traps are caused by structural features. They are usually formed as a result of tectonics.
ii. Stratigraphic traps
Stratigraphic traps are usually caused by changes in rock quality.
iii. Combination traps
Combination traps that combine more than one type of trap are common in petroleum reservoirs.
Other types of traps (such as hydrodynamic traps) are usually less common.
Geology of Petroleum Systems 20
Structural traps are caused by structural features. They are usually formed as a result of tectonics.
Stratigraphic traps are usually caused by changes in rock quality.
Combination traps that combine more than one type of trap are common in petroleum reservoirs.
Other types of traps (such as hydrodynamic traps) are usually less common.
Structural Hydrocarbon Traps
i. Fold
ii. Fault
iii. Salt Dome
Geology of Petroleum Systems 21
Salt flows up as a weak mass
Petroleum trapped in top of dome
Oil and gas trapped on sides of impermeable dome
Rocks above salt dome are bowed up
iii. Salt Dome
Fault Trap
Oil / Gas
Sand
Shale
In this normal fault trap, oil-bearing sandstone is juxtaposed against impervious shale.
Geology of Petroleum Systems 23
In this normal fault trap, oil-bearing sandstone is juxtaposed against impervious shale.
Stratigraphic Hydrocarbon Traps
(modified from Bjorlykke, 1989)
Stratigraphic hydrocarbon traps occur where reservoir facies pinch into impervious rock such as shale, or where they have been truncated by erosion and capped by impervious layers above an unconformity.
Geology of Petroleum Systems 24
Stratigraphic hydrocarbon traps occur where reservoir facies pinch into impervious rock such as shale, or where they have been truncated by erosion and capped by impervious layers above an unconformity.
Asphalt Trap
Hydrodynamic Trap
Water
Meteoric
Water
Biodegraded
Oil/Asphalt
Partly
Biodegraded Oil
Shale
Oil
Water
Hydrostatic
Head
(modified from Bjorlykke, 1989)
Other Traps
In hydrodynamic traps, the hydrocarbon is
trapped by the action
of water movements.
Tilted contacts are
common in this case.
The water usually
comes from a source
such as rain falls or
rivers.
Geology of Petroleum Systems 26
In hydrodynamic traps, the hydrocarbon is trapped by the action of water movements. Tilted contacts are common in this case. The water usually comes from a source such as rain falls or rivers.
Summary
Questions?