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Hydrodynamics: change in configuration (view source)
Revision as of 17:40, 21 January 2014
, 17:40, 21 January 2014Initial import
{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting preservation and destruction of accumulations
| frompg = 11-1
| topg = 11-30
| author = Alton A. Brown
| link = http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
[[Fluid contacts]] can tilt in response to fluid potential gradients in underlying water. If the tilt of the fluid contact exceeds the dip of the reservoir-seal interface on the down-potential (flow downdip) side of the trap, the accumulation will spill downdip. If petroleum is trapped under hydrodynamic conditions on an unclosed structure, decrease in the potential gradient may result in spillage of the petroleum updip.
The figure below shows the effects of hydrodynamics on trapping. During water movement (Hydrodynamic, top figure), oil accumulations are displaced from the structural crest; gas may remain near the crest of the structure (A). Even unclosed structures can be traps, as long as the downdip tilt is steeper than the tilt to the oil-water contact (B).
If water movement stops (Hydrostatic, lower figure), the accumulations quickly return to trapping at the crest of structural closures (C). Some structural closures may have accumulations; nearby closures may not (D).
[[file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|thumb|{{figure number|11-3}}See text for explanation.]]
==Duration of hydrodynamic regimes==
Petroleum distribution adjusts to trapping hydrodynamics much faster than changes in natural hydrodynamic regimes.<ref name=ch11r15>Hubbert, M., K., 1953, Entrapment of petroleum under hydrodynamic conditions: AAPG Bulletin, vol. 37, p. 1954–2026.</ref> In general, hydrodynamic regimes, especially those established by elevation–head differences in recharge, are time-transient events that are much shorter than the theoretical lifetime of accumulations under hydrostatic conditions. If present hydrodynamic flow affects [[fluid contacts]] of reservoirs charged in the past, then spillage and tertiary migration probably have occurred.
==Hydrodynamic mapping==
To evaluate the potential for spillage from hydrodynamic effects, we can construct maps (potentiometric; U, V, Z; hydrodynamic) for the reservoir horizons of interest. U, V, Z mapping determines present oil and gas potential minima (traps) [described by Hubbert<ref name=ch11r15 />) and Dahlberg<ref name=ch11r7>Dahlberg, E., C., 1982, Applied Hydrodynamics in Petroleum Exploration: New York, Springer-Verlag, 161 p.</ref>]. Where data quality is good, hydrodynamic mapping can identify (1) structural closures that have spilled as a result of hydrodynamics and (2) hydrodynamic traps.
==Evaluating ancient spillage==
Ancient hydrodynamic events that have occurred since charging can be identified by evaluating topographic evolution in the area around the basin of interest (evaluate patterns of subsurface salt dissolution, tectonic history, and map unconformities around the basin). Direction and magnitude of flow can be inferred but not quantified. Although petroleum resumes its hydrostatic configuration once hydrodynamic conditions cease, some traps may have essentially all movable petroleum flushed from their structural fetch area if potentiometric gradients were steep (as shown in Figure 11-3, A and B).
==See also==
* [[Spillage]]
* [[Changes in trapping geometry]]
* [[Postaccumulation cementation]]
* [[Consequences of spillage]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting preservation and destruction of accumulations]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting preservation and destruction of accumulations
| frompg = 11-1
| topg = 11-30
| author = Alton A. Brown
| link = http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
[[Fluid contacts]] can tilt in response to fluid potential gradients in underlying water. If the tilt of the fluid contact exceeds the dip of the reservoir-seal interface on the down-potential (flow downdip) side of the trap, the accumulation will spill downdip. If petroleum is trapped under hydrodynamic conditions on an unclosed structure, decrease in the potential gradient may result in spillage of the petroleum updip.
The figure below shows the effects of hydrodynamics on trapping. During water movement (Hydrodynamic, top figure), oil accumulations are displaced from the structural crest; gas may remain near the crest of the structure (A). Even unclosed structures can be traps, as long as the downdip tilt is steeper than the tilt to the oil-water contact (B).
If water movement stops (Hydrostatic, lower figure), the accumulations quickly return to trapping at the crest of structural closures (C). Some structural closures may have accumulations; nearby closures may not (D).
[[file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|thumb|{{figure number|11-3}}See text for explanation.]]
==Duration of hydrodynamic regimes==
Petroleum distribution adjusts to trapping hydrodynamics much faster than changes in natural hydrodynamic regimes.<ref name=ch11r15>Hubbert, M., K., 1953, Entrapment of petroleum under hydrodynamic conditions: AAPG Bulletin, vol. 37, p. 1954–2026.</ref> In general, hydrodynamic regimes, especially those established by elevation–head differences in recharge, are time-transient events that are much shorter than the theoretical lifetime of accumulations under hydrostatic conditions. If present hydrodynamic flow affects [[fluid contacts]] of reservoirs charged in the past, then spillage and tertiary migration probably have occurred.
==Hydrodynamic mapping==
To evaluate the potential for spillage from hydrodynamic effects, we can construct maps (potentiometric; U, V, Z; hydrodynamic) for the reservoir horizons of interest. U, V, Z mapping determines present oil and gas potential minima (traps) [described by Hubbert<ref name=ch11r15 />) and Dahlberg<ref name=ch11r7>Dahlberg, E., C., 1982, Applied Hydrodynamics in Petroleum Exploration: New York, Springer-Verlag, 161 p.</ref>]. Where data quality is good, hydrodynamic mapping can identify (1) structural closures that have spilled as a result of hydrodynamics and (2) hydrodynamic traps.
==Evaluating ancient spillage==
Ancient hydrodynamic events that have occurred since charging can be identified by evaluating topographic evolution in the area around the basin of interest (evaluate patterns of subsurface salt dissolution, tectonic history, and map unconformities around the basin). Direction and magnitude of flow can be inferred but not quantified. Although petroleum resumes its hydrostatic configuration once hydrodynamic conditions cease, some traps may have essentially all movable petroleum flushed from their structural fetch area if potentiometric gradients were steep (as shown in Figure 11-3, A and B).
==See also==
* [[Spillage]]
* [[Changes in trapping geometry]]
* [[Postaccumulation cementation]]
* [[Consequences of spillage]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting preservation and destruction of accumulations]]