Traps

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  • Topic: Structural geology, Geology, Fault
  • Pages : 7 (2380 words )
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  • Published : December 29, 2012
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[the british university in egypt]|
[ Petroleum traps ]|
[ Traps classification and examples from El-Hassana dome field trip]| |
Name: Abdelrahman Hamed Elkhayat| ID: 111863Group: A4| Table of Contents

An introduction3
Anticlinal theory of traps3
Traps classification4
1)Structural Traps:5
a)Faults:5
I.Dip slip fault:6
II.Strike slip fault:.6
b)Folds:7
i.Anticline fold7
ii.Syncline fold.7
2)Stratigraphic Traps:7
I.Pinch out trap.8
II.Unconformity trap8
III.Sand lens traps8
3)Combination traps:8
El-Hassana dome9
Location and history9
Examples for petroleum traps with pictures9
Bibliography11

An introduction:
During the exploration phase, an exploration geologist will normally look for three essential components; a source rock, a reservoir rock and a trap. The most important thing among these three components is the trap. It is important to mention that the trap is an important sign for the existence of an oil and/or gas reservoir. In other words, if the trap is big enough, many companies will drill it because of the large reserve potential. Traps are composed of three important features: 1. Reservoir rock: a rock with enough porosity to be capable of storing economic quantities of petroleum and enough permeability, either natural or induced, to be able to transmit the oil to the wellbore. Examples for reservoir rocks are sandstone, limestone and dolomite. 2. Seal: a relatively impermeable rock to prevent the escape of oil by moving upward through rocks. 3. Three-dimensional closure: a kind of a barrier against the base of the seal. Anticlinal theory of traps:

It was recognized very early that oil and gas tend to accumulate in structurally high areas. It became very clear that gas and oil normally accumulate at the top of anticlines, as shown in the figure. The oil is generated within the source rocks such as organic rich shales and evaporites in the subsurface. When these source rocks are compacted, they drive out fluids including water, oil and gas. All these fluids escape into the available pore spaces. And as they migrate through any available permeability, much escapes to the surface. The oil becomes trapped in locations where water can continue onto the surface, but oil and/or gas cannot. In most cases the oil and gas are considered to have been trapped in the top of the anticline by an impermeable seal, such as a shale or evaporite, in the same way by which the upward travelling gas bubbles would be trapped in a reversed bowl in a bathtub full of water. Nowadays, many people think that the seal is not totally impermeable, but it acts as a semipermeable membrane allowing water, but not oil and gas, to pass through. Apart from the permeability of the seal, oil and gas are trapped at the crest of the anticline while water is displaced. All of that is known as the anticlinal theory. In order for an anticline to trap hydrocarbons, the trap must be three-dimensional. In other words, the anticline should form a dome. Therefore, the anticlinal theory is misnomer and it should have been called the domal theory, because the anticline will not necessarily trap oil and it has to be three-dimensional or form a dome to trap oil. Traps classification:

The earth’s crust is part of a dynamic system and movements within the crust are accommodated partly by rock deformation. Like any other material, rocks may react to stress with an elastic, ductile or brittle response, as shown in the stress-strain diagram. As mentioned, there are three types of deformations which are elastic, ductile and brittle. It is well known that the elastic deformations (which occur during earthquakes) are rare to observe since elastic deformations don’t leave any...
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