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Efficiencies of expulsion and transport need to be estimated and used to account for inefficiencies in the [[migration]] path. Only part of the oil and gas generated by the [[source rock]] is actually expelled; of the amount that is expelled, only a small amount is trapped. The diagram below summarizes the efficiencies of the expulsion, migration, and entrapment processes.

Efficiencies of expulsion and transport need to be estimated and used to account for inefficiencies in the [[migration]] path. Only part of the oil and gas generated by the [[source rock]] is actually expelled; of the amount that is expelled, only a small amount is trapped. [[:file:migration-of-petroleum_fig7-13.png|Figure 1]] summarizes the efficiencies of the expulsion, migration, and entrapment processes.

[[file:migration-of-petroleum_fig7-13.png|thumb|{{figure number|7-13}}After Magara.<ref name=ch07r5>Magara, K., 1980, Evidences of primary migration: AAPG Bulletin, vol. 64, p. 2108–2117.</ref>]]

 

[[file:migration-of-petroleum_fig7-13.png|left|thumb|{{figure number|1}}After Magara.<ref name=ch07r5>Magara, K., 1980, Evidences of primary migration: AAPG Bulletin, vol. 64, p. 2108–2117.</ref>]]

Typical oil expulsion efficiencies are estimated to be in the 5-10% range, with values in the 15% range uncommon and 30% rarely demonstrated. This efficiency is low because most of the source rock section contains too low a concentration of organic material to participate in the expulsion process. Efficiencies of gas expulsion are estimated to be 50-90%, with values of 75% common. Unfortunately, much of this is gas lost due to solution and does not participate in reservoir charging. For both oil and gas, expulsion efficiencies tend to increase with increasing TOC. Expulsion efficiencies for oil and gas can be as high as 70-80% for very rich, effective [[source rocks]] near preferential [[migration pathways]].

Typical oil expulsion efficiencies are estimated to be in the 5-10% range, with values in the 15% range uncommon and 30% rarely demonstrated. This efficiency is low because most of the source rock section contains too low a concentration of organic material to participate in the expulsion process. Efficiencies of gas expulsion are estimated to be 50-90%, with values of 75% common. Unfortunately, much of this is gas lost due to solution and does not participate in reservoir charging. For both oil and gas, expulsion efficiencies tend to increase with increasing TOC. Expulsion efficiencies for oil and gas can be as high as 70-80% for very rich, effective [[source rocks]] near preferential [[migration pathways]].

==Procedure==

==Procedure==

In migration volumetrics, it is important to estimate the original petroleum potential of the source rock—not just its present measured potential (with increasing [[maturation]], a portion of the original potential will have been realized and is therefore unmeasurable). Estimates of expelled hydrocarbons may be derived by measuring the amount remaining in a source and subtracting that value from the amount that should have been generated from the original assumed kerogen content.

In migration volumetrics, it is important to estimate the original petroleum potential of the source rock—not just its present measured potential (with increasing [[maturation]], a portion of the original potential will have been realized and is therefore unmeasurable). Estimates of expelled hydrocarbons may be derived by measuring the amount remaining in a source and subtracting that value from the amount that should have been generated from the original assumed kerogen content.

==Expulsion diagram==

==Expulsion diagram==

[[:file:migration-of-petroleum_fig7-14.png|Figure 2]] summarizes the procedure for estimating expulsion efficiency.

 

[[file:migration-of-petroleum_fig7-14.png|thumb|{{figure number|7-14}}. Copyright: McDowell (1975); courtesy Oil & Gas Journal.]]

==See also==

==See also==