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Some petroleum accumulations are likely to persist for hundreds of millions of years with relatively little alteration or dilution. Other accumulations, however, may be destroyed. Several processes deplete or destroy hydrocarbon accumulations. In many prospects it is not enough just to know that a trap is present in a basin where hydrocarbons were [[Petroleum generation|generated]] and migrated. We also must know that the trap was preserved over time. It is imperative that explorationists know destructive processes and how to determine the age of an accumulation.

Some petroleum [[accumulation]]s are likely to persist for hundreds of millions of years with relatively little alteration or dilution. Other accumulations, however, may be destroyed. Several processes deplete or destroy hydrocarbon accumulations. In many prospects it is not enough just to know that a trap is present in a basin where hydrocarbons were [[Petroleum generation|generated]] and migrated. We also must know that the trap was preserved over time. It is imperative that explorationists know destructive processes and how to determine the age of an accumulation.

==The problem==

==The problem==

Petroleum may have accumulated at a prospect sometime in the past but may not be preserved in economic quantities, even where trapping geometry is still intact. Or a trap may still contain petroleum, but the [[Oil as an energy source|oil]] and/or [[natural gas|gas]] has been diluted or altered so that accumulations are no longer economic.

Petroleum may have accumulated at a prospect sometime in the past but may not be preserved in economic quantities, even where trapping geometry is still intact. Or a trap may still contain petroleum, but the [[Oil as an energy source|oil]] and/or [[natural gas|gas]] has been diluted or altered so that [[accumulation]]s are no longer economic.

From an explorationist's point of view, these accumulations are destroyed. The problem is to determine where destruction of accumulations is likely and what mechanisms are likely to lead to destruction of accumulations in different geological settings.

From an explorationist's point of view, these accumulations are destroyed. The problem is to determine where destruction of accumulations is likely and what mechanisms are likely to lead to destruction of accumulations in different geological settings.

==Determining age of accumulations==

==Determining age of accumulations==

Accumulations should be dated to evaluate the potential importance of accumulation destruction in an area of interest. Leakage, spillage, petroleum destruction, and cementation are more likely to alter the size and quality of old accumulations than young accumulations. Young accumulations with active petroleum charge are more likely to be affected by displacement of oil by later gas charge. Accumulation preservation is a function of tectonic setting, trap type, depth of burial, and seal type.<ref name=ch11r24>Mcgregor, D., S., 1996, Factors controlling the destruction or preservation of giant light oilfields: Petroleum Geoscience, vol. 2, p. 197–217., 10., 1144/petgeo., 2., 3., 197</ref>

[[Accumulation]]s should be dated to evaluate the potential importance of accumulation destruction in an area of interest. Leakage, spillage, petroleum destruction, and cementation are more likely to alter the size and quality of old accumulations than young accumulations. Young accumulations with active petroleum charge are more likely to be affected by displacement of oil by later gas charge. Accumulation preservation is a function of tectonic setting, trap type, depth of burial, and seal type.<ref name=ch11r24>Mcgregor, D., S., 1996, Factors controlling the destruction or preservation of giant light oilfields: Petroleum Geoscience, vol. 2, p. 197–217., 10., 1144/petgeo., 2., 3., 197</ref>

Three methods help us determine the age of accumulations.

Three methods help us determine the age of accumulations.