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  = 18-9

  | topg    = 18-27

  | topg    = 18-9

  | 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

==Macroseeps==

==Macroseeps==

There is a seepage continuum from the smallest detectable levels to visible oil and gas seeps. The term '''macroseepage''' refers to visible oil and gas seeps. Macroseeps are very localized areas containing large concentrations of light hydrocarbons as well as, if available, high-molecular-weight hydrocarbons. They are localized at the termination of faults, fractures, and outcropping unconformities or carrier beds. These visible seeps have led to the discovery of many of the world's important oil and gas producing areas.<ref name=ch18r21>Link, W., K., 1952, [http://archives.datapages.com/data/bulletns/1949-52/data/pg/0036/0008/1500/1505.htm Significance of oil and gas seeps in world oil exploration]: AAPG Bulletin, vol. 36, p. 1505–1541.</ref><ref name=ch18r23>Macgregor, D., S., 1993, Relationships between seepage, tectonics, and subsurface petroleum reserves: Marine and Petroleum Geology, vol. 10, p. 606–619., 10., 1016/0264-8172(93)90063-X</ref>

There is a seepage continuum from the smallest detectable levels to visible oil and gas seeps. The term '''macroseepage''' refers to visible oil and gas seeps. Macroseeps are very localized areas containing large concentrations of light hydrocarbons as well as, if available, high-molecular-weight hydrocarbons. They are localized at the termination of faults, fractures, and outcropping [[Unconformity|unconformities]] or carrier beds. These visible seeps have led to the discovery of many of the world's important oil and gas producing areas.<ref name=ch18r21>Link, W. K., 1952, [http://archives.datapages.com/data/bulletns/1949-52/data/pg/0036/0008/1500/1505.htm Significance of oil and gas seeps in world oil exploration]: AAPG Bulletin, vol. 36, p. 1505–1541.</ref><ref name=ch18r23>Macgregor, D. S., 1993, Relationships between seepage, tectonics, and subsurface petroleum reserves: Marine and Petroleum Geology, vol. 10, p. 606–619., 10., 1016/0264-8172(93)90063-X</ref>

==Microseeps==

==Microseeps==

==Microseepage evidence==

==Microseepage evidence==

The existence of microseepage is supported by a large body of empirical evidence.<ref name=ch18r30>Price, L. C., 1986, A critical overview and proposed working model of surface geochemical exploration, in Davidson, M. J., ed., Unconventional Methods in Exploration for Petroleum and Natural Gas IV: Dallas, Texas, Southern Methodist Univ. Press, p. 81–129.</ref><ref name=ch18r18>Klusman, R., W., 1993, Soil gas and related methods for natural resource exploration: New York, John Wiley & Sons, 483 pp.</ref><ref name=ch18r19>Klusman, R., W., Saeed, M., A., 1996, Comparison of light hydrocarbon microseepage mechanisms, in Schumacher, D., Abrams, M. A., eds., Hydrocarbon Migration and Its Near-Surface Expression: AAPG Memoir 66, p. 157–168.</ref><ref name=ch18r25>Matthews, M., D., 1996a, Migration a view from the top, in Schumacher, D., Abrams, M. A., eds., Hydrocarbon Migration and Its Near-Surface Expression: AAPG Memoir 66, p. 139–155.</ref> This includes the following:

The existence of microseepage is supported by a large body of empirical evidence.<ref name=ch18r30>Price, L. C., 1986, A critical overview and proposed working model of surface geochemical exploration, in Davidson, M. J., ed., Unconventional Methods in Exploration for Petroleum and Natural Gas IV: Dallas, Texas, Southern Methodist Univ. Press, p. 81–129.</ref><ref name=ch18r18>Klusman, R. W., 1993, Soil gas and related methods for natural resource exploration: New York, John Wiley & Sons, 483 pp.</ref><ref name=ch18r19>Klusman, R. W., and M. A. Saeed, 1996, [http://archives.datapages.com/data/specpubs/memoir66/12/0157.htm Comparison of light hydrocarbon microseepage mechanisms], in D. Schumacher, and M. A. Abrams, eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 157–168.</ref><ref name=ch18r25>Matthews, M. D., 1996a, [http://archives.datapages.com/data/specpubs/memoir66/11/0139.htm Migration a view from the top], in D. Schumacher, and M. A. Abrams, eds., Hydrocarbon Migration and Its Near-Surface Expression:[http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 139–155.</ref> This includes the following:

* Increased concentration of light hydrocarbons and hydrocarbon-oxidizing microbes in soils and sediments above hydrocarbon reservoirs.

* Increased concentration of light hydrocarbons and hydrocarbon-oxidizing microbes in soils and sediments above hydrocarbon reservoirs.

* Increased key light hydrocarbon ratios in soil gas over oil and gas reservoirs.

* Increased key light hydrocarbon ratios in soil gas over oil and gas reservoirs.

* Sharp lateral changes in these concentrations and ratios at the edges of the surface projections of these reservoirs.

* Sharp [[lateral]] changes in these concentrations and ratios at the edges of the surface projections of these reservoirs.

* Similarity of stable carbon isotopic ratios for methane and other light hydrocarbons in soil gases to those found in underlying reservoirs.

* Similarity of stable carbon isotopic ratios for methane and other light hydrocarbons in soil gases to those found in underlying reservoirs.

* The disappearance and reappearance of soil gas and microbial anomalies in response to reservoir depletion and repressuring.

* The disappearance and reappearance of soil gas and microbial anomalies in response to reservoir depletion and repressuring.

==Microseep migration==

==Microseep migration==

Research and field studies suggest that the dominant migration medium is as a continuous-phase, buoyancy-driven gas flow within carrier and reservoir rocks and capillary imbibition in the transition from sources and seals into carrier rocks. Hydrocarbon microseepage is predominantly vertical and is dynamic; migration rates range from less than 1 meter per day to tens of meters per day.<ref name=ch18r4>Arp, G., K., 1992, Effusive microseepage: a first approximation model for light hydrocarbon movement in the subsurface: Assoc. Petroleum Geochemical Explorationists Bulletin, vol. 8, p. 1–17.</ref><ref name=ch18r1>Abrams, M., A., 1992, Geophysical and geochemical evidence for subsurface hydrocarbon leakage in the Bering Sea, Alaska: Marine and Petroleum Geology Bulletin, vol. 9, p. 208–221., 10., 1016/0264-8172(92)90092-S</ref><ref name=ch18r1 />

Research and field studies suggest that the dominant migration medium is as a continuous-phase, buoyancy-driven gas flow within carrier and reservoir rocks and capillary imbibition in the transition from sources and seals into carrier rocks. Hydrocarbon microseepage is predominantly vertical and is dynamic; migration rates range from less than 1 meter per day to tens of meters per day.<ref name=ch18r4>Arp, G. K., 1992, Effusive microseepage: a first approximation model for light hydrocarbon movement in the subsurface: Assoc. Petroleum Geochemical Explorationists Bulletin, vol. 8, p. 1–17.</ref><ref name=ch18r1>Abrams, M. A., 1992, Geophysical and geochemical evidence for subsurface hydrocarbon leakage in the Bering Sea, Alaska: Marine and Petroleum Geology Bulletin, vol. 9, p. 208–221., 10., 1016/0264-8172(92)90092-S</ref>

==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]]

* [[Seepage activity]]

* [[Seepage activity and 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]]