1. trapping and movement of petroleum

8/4/2019 1. Trapping and Movement of Petroleum

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THIRUSHKA T.GOVENDER208500558

AHISTHA CHANERIKA207511828

TRAPPING ANDMOVEMENT OF

PETROLEUM


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PETROLEUM SYSTEMS

Five elements constitute thepetroleum system :v Source Rockv Carrier bedsv Trapv Reservoirv Seal


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4/14/12 Diagram of a Typical Petroleum System


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MIGRATION OF PETROLEUMPetroleum migration refers to theseries of processes by which

petroleum is transported from thesite of generation, the source rock, to

the trap.

There are two major sub-divisions:v Primary Migrationv Secondary Migration


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PRIMARY MIGRATION

The movement of petroleum fromwithin the source rock to anadjacent carrier bed

Carrier beds are lithologicallysimilar to reservoir rocks i.e.sandstones, limestones, orfractured rocks

The driving force that moves thefluid phase (crude oil and natural

gas) from the source to the trap isbuo anc


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PRIMARY MIGRATION

The crude oil and natural gas inthe deep subsurface havedensities in the range of 500 800 kg/m3

Waters in sediments havedensities of over 1000kg/m3

The solid kerogen (organicmaterial formed from organicsediments) phase converts to a

fluid phase which bears part ofthe load reviousl carried b


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Thus fluid pressures in source rock risedriving fluid phase out of the source rockthrough:

v fractures formed by overpressuring,v pore system of the source rock and

v partly in solution in remainingkerogen matrix.


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SECONDARY MIGRATION

The movement of petroleumfrom the carrier bed contact tothe trap

Petroleum moves updip in acarrier bed due to bouyancy(has lower density thansurrounding formation waters)

Petroleums in subsurface havedensities in the range of 500 -800 kg/m3 for oils and aminimum of 100kg/m3 for


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Vertical and Hori zontal Movement of Petroleum into Trap


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WHAT IS A TRAP ? A geometric arrangement of rock,

regardless of origin, that permitssignificant accumulation of oil orgas, or both in the subsurface

The critical components of the trap

are :v Reservoir

v Seal


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Reservoir Rock Adequate porosity is required within

the reservoir interval

Must supply enough volume toaccommodate a significant amount of

fluids

Must be capable of transmitting andexchanging fluids therefore it

requires sufficient permeability withinboth the :

v Reservoir intervalv Migration conduit which connects

the reservoir with the active sourcerock


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Seal Without an effective seal

hydrocarbons will migrate out of thereservoir rock with time causing thetrap to lack viability

Most effective seals are usuallyformed by relatively thick, laterallycontinuous, ductile rocks with highcapillary entry pressures

Best seals: gas hydrates, evaporites(salt), organic rich shales, clay richshales, tight carbonates


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TYPES OF TRAPS Structural Traps: Have an upper boundary which

is concave, as viewed from below, due to localdeformation, such as folding or faulting or both, ofthe reservoir rock. Structural traps are subdividedinto: Fault related, Fold related and Diapirs

Stratigraphic Traps: chief trap-making element issome variation in the lithology of the reservoir rock.Egs include: Unconformities, Sedimentological Trapsand Diagenetic traps

Hydrodynamic Traps: Hydrodynamic movement of

waters down the permeable beds will trap oil movingupward provided the hydrodynamic force of thewater is greater than the force due to buoyancy ofthe oil

Combination Traps:Traps formed by acombination of structural and stratigraphic


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FOLD TYPE: ANTICLINAL TRAP An anticline is an upward fold in the layers

of rock, usually as a result of tectonicallyinduced deformation

Petroleum migrates into the highest partof the fold, its escape is prevented by an

overlying bed of impermeable rock


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ANTICLINE TRAP


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FAULT TRAPS A fault trap occurs when the formations

on either side of the fault have beenmoved into a position that preventsfurther migration of petroleum.

FAULT


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DIAPIRS : SALT DOMES Circular or concave down fold Result of sediments atop dome

basement rock or rising diapirs ofclay or salt.

Commonly produce multiple stacked

reservoirs


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SEDIMENTOLOGICAL TRAPS:REEF TRAPS Reefs are carbonate buildups (coral reefsthat become buried undersediment)

High reefal porosity and permeability

Are arguably the most importantstratigraphic trap

Geometry is usually a domal pinnaclewith an elongated anti-formal platform


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DIAGENETIC TRAPS Solution and precipitation of

mineral cements bydiagenesis can form traps

Solution is especiallycommon in carbonates

Migrating oil towardssurface can be oxidized bybacterial degradation andform an impervious tarresidue


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DIAGENETIC TRAPS


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UNCONFORMITIES An interruption of the geologic record

manifest as an erosion surface bounded byrocks which are not immediately

chronologically successive

Hydrocarbons can be trapped below the

unconformity by truncation, or above theunconformity when a porous bed onlaps

against the unconformity surface.

Often a structural element such as tilting is

required


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HYDRODYNAMIC TRAPS Oil attempting to escape to surface up

a reservoir, is held against an un-

eveness of its upper surface by waterflowing in the opposite direction.

No structural or stratigraphic closure Oil-water-contact (OWC) is tilted

downward in the direction of water flow


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COMBINATION TRAPS Structural closures or deformations

in which reservoir rock covers onlypart of the structure

Traps formed by the combination ofstructural and stratigraphic

circumstances Wide range of possibilities

/combinations


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DIFFERENCE BETWEEN THE 3MAJOR TRAP TYPES Structural Traps are formed by tectonic

processes AFTER deposition of thereservoir beds involved

Stratigraphic Traps are created DURINGthe deposition of the reservoir beds

Combination Traps are formed by a

combination of processes present in thesediments DURING the time of depositionof the reservoir beds AND by tectonicactivity that occurred in the reservoir bedsAFTER their deposition .


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DISTRIBUTION OF WORLDSPETROLEUM ACCUMULATIONS


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CONDITIONS OF FINDINGPETROLEUM

Is there a trap to holdpetroleum?

Find a geological feature thatcan act as an accumulator of

oil and gas

Is there a migration path?

Path must exist to allow flowof oil/gas to trap

Is the trap sealed?


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QUESTIONS ???

1. trapping and movement of petroleum

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