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Rollover anticlines (develop above curved normal faults)Ramp anticlines (develop above transition from ramp to flat in thrust faults)

Anticlinal traps:

Example of the Maui Field (New Zealand)

Fault Related traps: The key question is whether or not a fault will be aseal. It partly depends on whether the fault places a

permeable or impermeable unit in contact with thereservoir. In some cases the fault itself can besealing. Faults in extensional settings have a greater chance of being open to migration.

Normal fault traps: Roll over anticlines related to curved faultsTilted fault blocks

Thrust fault traps: Parts of a fold and thrust belt.Faulted anticlines, tilted fault blocks, rampanticlines, drag folds on the footwall

Strike slip traps: Positive and negative flower structuresrelated to bends of the fault.

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What determines whether a fault will be sealing or not? Know how to identify traps if given a cross section or contour map of an area.

Diapirs :Salt is driven upward by buoyancy of the salt after compaction of the surrounding

sedimentsThere can be many traps above, and surrounding a salt diapir.In addition to diapirs there are salt-withdrawal structures (turtle backs)Salt is frequently deposited in restricted basins during the early development of a riftsystem, so they are often associated with extensional tectonic settings.

Progressive developmentof salt diapirs

Seismic image of a saltstructure. Notice itseffect on the sedimentarylayers around it.

Types of traps associatedwith salt diapirs.

Stratigraphic Traps

The main trapping mechanism is a Stratigraphic feature such as anunconformity, a lateral change in facies from reservoir rocks to sealrocks, or a diagenetic change from non-cemented to cemented rock.

Traps related to unconformities: The hydrocarbons can be trapped below the unconformity bytruncation, or above the unconformity when a porous bed onlapsagainst the unconformity surface. Often a structural element such astilting is required, so many of this traps can be consideredcombination traps .Terminology: Onlap, truncation , angular unconformity

Diagenetic traps: This are more common in carbonate reservoirs which are moreeasily affected by cementation, dissolution and dolomitization.

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These post-depositional processes lead to a lateral change inreservoir quality to acts as the trapping mechanism.

Sedimentological traps:

Several depositional systems will produce isolated bodies of porousrock surrounded by impermeable rock. Examples are:• Point bar sands surrounded by flood-plain clays in a fluvial

system.• Distributary channels within deltaic muds.• Reefs within lagoonal and marine shales• Barrier island sands also within lagoonal and marine shales

The picture above corresponds to oil fields in the Golden Lane of theMexican Gulf coast. The oil deposits are a set of Cretaceous reefs,

part of an ancient atoll.

The diagram below is an example of barrier island sands fromKansas. They for long, linear traps surrounded in shale.

Hydrodynamic traps In some rare cases the movement of water can modify the geometry of an oil accumulation (tilted OWC is the most common example), or even trap the oil in a location where it would other wise escape, as incase D in the diagram.