Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Surface geochemical exploration for petroleum

  | chapter = Surface geochemical exploration for petroleum

  | frompg  = 18-1

  | frompg  = 18-8

  | topg    = 18-27

  | topg    = 18-8

  | author  = Dietmar Schumacher

  | author  = Dietmar Schumacher

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch18/ch18.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch18/ch18.htm

Areas where subsurface hydrocarbons are not actively seeping are referred to as characterized by '''passive seepage'''. Such seeps usually contain low-molecular-weight hydrocarbons and volatile high-molecular-weight hydrocarbons above background levels. Acoustic anomalies may be present, but water column anomalies are rare. Anomalous levels of hydrocarbon seepage may only be detectable near major leak points or below the zone of maximum disturbance.

Areas where subsurface hydrocarbons are not actively seeping are referred to as characterized by '''passive seepage'''. Such seeps usually contain low-molecular-weight hydrocarbons and volatile high-molecular-weight hydrocarbons above background levels. Acoustic anomalies may be present, but water column anomalies are rare. Anomalous levels of hydrocarbon seepage may only be detectable near major leak points or below the zone of maximum disturbance.

[[file:surface-geochemical-exploration-for-petroleum_fig18-2.png|thumb|{{figure number|1}}.]]

[[file:surface-geochemical-exploration-for-petroleum_fig18-2.png|300px|thumb|{{figure number|1}}Zone of maximum disturbance in shallow marine sediments. From Abrams;<ref name=ch18r2 /> courtesy AAPG.]]

==Zone of maximum disturbance==

==Zone of maximum disturbance==

The '''zone of maximum disturbance''', defined by Abrams,<ref name=ch18r1 /> <ref name=ch18r2 /> is a near-surface zone of variable depth and thickness in which sedimentary and biological processes alter or destroy volatile hydrocarbons. Anomalous concentrations of hydrocarbons may not be detectable if samples are not obtained from below the zone of maximum disturbance. [[:file:surface-geochemical-exploration-for-petroleum_fig18-2.png|Figure 1]] illustrates the zone of maximum disturbance in shallow marine sediments. Deeper sampling may be required in areas of passive seepage.

The '''zone of maximum disturbance''', defined by Abrams<ref name=ch18r1 /><ref name=ch18r2 /> is a near-surface zone of variable depth and thickness in which sedimentary and biological processes alter or destroy volatile hydrocarbons. Anomalous concentrations of hydrocarbons may not be detectable if samples are not obtained from below the zone of maximum disturbance. [[:file:surface-geochemical-exploration-for-petroleum_fig18-2.png|Figure 1]] illustrates the zone of maximum disturbance in shallow marine sediments. Deeper sampling may be required in areas of passive seepage.

==See also==

==See also==

* [[Principles of surface geochemical exploration]]

* [[Principles of surface geochemical exploration]]

* [[Assumptions of surface geochemical exploration]]

* [[Assumptions of surface geochemical exploration]]

* [[Limitations and uncertainties]]

* [[Limitations and uncertainties of surficial gechemistry]]

* [[Macroseepage vs. Microseepage]]

* [[Macroseepage vs. microseepage in surficial geochemistry]]

* [[Surface expression]]

* [[Geochemical surface expression]]

==References==

==References==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Surface geochemical exploration for petroleum]]

[[Category:Surface geochemical exploration for petroleum]]