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[[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.

[[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 [[Fluid_contacts#Hydrodynamic_gradients|potential gradient]] may result in spillage of the petroleum updip.

[[:file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|Figure 1]] 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 [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water%20contact oil-water contact] (B).

[[:file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|Figure 1]] 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 [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water%20contact 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).

If water movement stops (Hydrostatic, lower figure), the accumulations quickly return to trapping at the crest of structural [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=closure closures] (C). Some structural closures may have accumulations; nearby closures may not (D).

==Duration of hydrodynamic regimes==

==Duration of hydrodynamic regimes==

[[file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|300px|thumb|{{figure number|1}}Effects of hydrodynamics on trapping.]]

[[file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|300px|thumb|{{figure number|1}}Effects of hydrodynamics on trapping.]]

Petroleum distribution adjusts to trapping hydrodynamics much faster than changes in natural hydrodynamic regimes.<ref name=ch11r15>Hubbert, M., K., 1953, [http://archives.datapages.com/data/bulletns/1953-56/data/pg/0037/0008/1950/1954.htm 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 [[accumulation]]s under hydrostatic conditions. If present hydrodynamic flow affects [[fluid contacts]] of reservoirs charged in the past, then spillage and tertiary migration probably have occurred.

Petroleum distribution adjusts to trapping hydrodynamics much faster than changes in natural hydrodynamic regimes.<ref name=ch11r15>Hubbert, M., K., 1953, [http://archives.datapages.com/data/bulletns/1953-56/data/pg/0037/0008/1950/1954.htm Entrapment of petroleum under hydrodynamic conditions]: AAPG Bulletin, vol. 37, p. 1954–2026.</ref> In general, hydrodynamic regimes, especially those established by elevation–[[Wikipedia:Hydrogeology#Hydraulic_head|head]] differences in recharge, are time-transient events that are much shorter than the theoretical lifetime of [[accumulation]]s 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==

==Hydrodynamic mapping==

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 [[Unconformity|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 [[:file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|Figure 1 A and B]]).

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 [[Unconformity|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 [[:file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|Figure 1 A and B]]).

==See also==

==See also==\* [[Hydrodynamics]]

* [[Trap spillage]]

* [[Trap spillage]]

* [[Changes in trapping geometry]]

* [[Changes in trapping geometry]]