Changes

[[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 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).

[[: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 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 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.]]

 

[[file:predicting-preservation-and-destruction-of-accumulations_fig11-3.png|thumb|{{figure number|1}}See text for explanation.]]

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.

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.