Changes

  | part    = Traps, trap types, and the petroleum system

  | part    = Traps, trap types, and the petroleum system

  | chapter = Classification of exploration traps

  | chapter = Classification of exploration traps

  | frompg  = 2-1

  | frompg  = 2-41

  | topg    = 2-42

  | topg    = 2-41

  | author  = Richard R. Vincelette, Edward A. Beaumont, Norman H. Foster

  | author  = Richard R. Vincelette, Edward A. Beaumont, Norman H. Foster

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch02/ch02.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch02/ch02.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

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.

Fluid-composition traps are controlled by the physical or chemical properties of the trapped fluids themselves. The [[Wikipedia:Solubility|insolubility]], [[Wikipedia:Miscibility|immiscibility]], and [[Wikipedia:Density|density]] contrasts between [[hydrocarbon]]s 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==

==Classes and families==

The outline below presents the hierarchy and definitions for fluid-composition traps.

The outline below presents the hierarchy and definitions for fluid-composition traps.

'''Regime:''' Fluid-composition traps

 

Result from a chemical property of the trapped oil or gas.

! Regime || Class || Subclass || Family

 

* '''Class:''' Viscosity traps

| rowspan = 4 | ''Fluid-composition traps''; Result from a chemical property of the trapped oil or gas. || rowspan = 3 | ''[[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]].

* Petroleum can be trapped by the presence of barriers created by highly viscous oil (asphalt, tar) or solid hydrocarbons (albertite, gilsonite, or grahamite).

|-

 

| colspan = 2 | ''Disseminated;'' Tar or asphalt fills the pores of [[shale]]s, [[sandstone]]s, or [[carbonate]]s. These traps are often called [[tar sands]], [[oil shale]]s, bituminous sandstones, or bituminous limestones.

<list-item>'''Subclass:''' Tar seals

|-

 

| colspan = 2 | ''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.

<list-item>'''Family:''' Bacterial degradation</list-item><list-item>Updip tar seal created by bacteria degradation of the hydrocarbons, preferentially removing the lighter fractions.</list-item></list-item><list-item>'''Subclass:''' Disseminated</list-item><list-item>Tar or asphalt fills the pores of shales, sands, or carbonates. These traps are often called tar sands, oil shales, bituminous sandstones, or bituminous limestones.</list-item><list-item>'''Subclass:''' Veins</list-item><list-item>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.</list-item>

|-

* '''Class:''' Coal-bed methane

| colspan = 3 | ''[[Coal bed methane]];'' [[Coal]] beds trap large volumes of [[Wikipedia:Methane|methane]], where most is [[Wikipedia:Adsorption|adsorbed]] onto internal surfaces of [[micropore]]s or along [[cleat face]]s. [[Coalification]] generates methane along with water, [[Wikipedia:Carbon dioxide|carbon dioxide]], and [[Wikipedia:Carbon monoxide|carbon monoxide]].

* 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.

==See also==

==See also==

[[Category:Traps, trap types, and the petroleum system]]  

[[Category:Traps, trap types, and the petroleum system]]  

[[Category:Classification of exploration traps]]

[[Category:Classification of exploration traps]]