| Exploring for Oil and Gas Traps
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| Series
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Treatise in Petroleum Geology
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| Part
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Traps, trap types, and the petroleum system
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| Chapter
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Classification of exploration traps
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| Author
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Richard R. Vincelette, Edward A. Beaumont, Norman H. Foster
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| Link
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Web page
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| Store
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AAPG Store
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Fluid-composition traps are controlled by the physical or chemical properties of the trapped fluids themselves. The insolubility, immiscibility, and density contrasts between hydrocarbons and water are major factors that allow hydrocarbons to concentrate into subsurface accumulations. Therefore, in its purest sense, all hydrocarbon accumulations have fluid-composition trapping elements. However, for classification purposes, fluid-composition traps are those in which unique properties of the hydrocarbons provide trapping mechanisms.
Classes and families
The outline below presents the hierarchy and definitions for fluid-composition traps.
| Regime |
Class |
Subclass |
Family
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| Fluid-composition traps; Result from a chemical property of the trapped oil or gas. |
Viscosity traps; Petroleum can be trapped by the presence of barriers created by highly viscous oil (asphalt, tar) or solid hydrocarbons (albertite, gilsonite, or grahamite). |
Tar Seals |
Bacterial degradation; Updip tar seal created by bacteria degradation of the hydrocarbons, preferentially removing the lighter fractions.
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| Disseminated; Tar or asphalt fills the pores of shales, sandstones, or carbonates. These traps are often called tar sands, oil shales, bituminous sandstones, or bituminous limestones.
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| Veins; The solid, essentially infusible form of petroleum is called pyrobitumen. It occurs in veins length::1 mm to length::8 m across and appears to have been injected or is a dead seepage.
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| Coal bed methane; Coal beds trap large volumes of methane, where most is adsorbed onto internal surfaces of micropores or along cleat faces. Coalification generates methane along with water, carbon dioxide, and carbon monoxide.
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See also
External links
find literature about
Fluid-composition trap regime
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