Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Evaluating top and fault seal

  | chapter = Evaluating top and fault seal

  | frompg  = 10-1

  | frompg  = 10-80

  | topg    = 10-94

  | topg    = 10-80

  | author  = Grant M. Skerlec

  | author  = Grant M. Skerlec

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm

==How thick is necessary?==

==How thick is necessary?==

There is no simple relationship between seal thickness and the height of the hydrocarbon column. Seals can be extremely thin—less than [[length::1 m]] thick that seal individual hydrocarbon accumulations. There are also examples of traps with thick shale seals that are dry. This difficulty in establishing a relationship between seal thickness and column is especially true since many hydrocarbon columns are controlled by fault-related spill points that are independent of top seal thickness.

There is no simple relationship between [[seal]] thickness and the height of the [[hydrocarbon column]]. Seals can be extremely thin—less than [[length::1 m]] thick that seal individual hydrocarbon [[accumulation]]s. There are also examples of traps with thick shale seals that are [[dry]]. This difficulty in establishing a relationship between seal thickness and column is especially true since many hydrocarbon columns are controlled by [[fault]]-related [[spill point]]s that are independent of top seal thickness.

==Seal thickness studies==

==Seal thickness studies==

Data compiled from fields in California and the Rocky Mountains show no relationship between seal thickness and hydrocarbon column height.<ref name=ch10r98>Zieglar, D., M., 1992, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0004/0000/0501.htm Hydrocarbon columns, buoyancy pressures, and seal efficiency: comparisons of oil and gas accumulations in California and the Rocky Mountain area]: AAPG Bulletin, vol. 76, no. 4, p. 501–508.</ref> Nonetheless, some workers have suggested a correlation between seal thickness and seal capacity.<ref name=ch10r58>Nederlof, M., N., Mohler, H., P., 1981, Quantitative investigation of trapping effect of unfaulted caprock: AAPG Bulletin, vol. 65, no. 6, p. 964.</ref><ref name=ch10r75>Slujik, D., Nederlof, M., H., 1984, Worldwide geological experience as a systematic basis for prospect appraisal, in Demaison, G., Murris, R., J., eds., Petroleum Geochemistry and Basin Evaluation: AAPG Memoir 35, p. 15–26.</ref>

Data compiled from fields in California and the Rocky Mountains show no relationship between seal thickness and hydrocarbon column height.<ref name=ch10r98>Zieglar, D., M., 1992, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0004/0000/0501.htm Hydrocarbon columns, buoyancy pressures, and seal efficiency: comparisons of oil and gas accumulations in California and the Rocky Mountain area]: AAPG Bulletin, vol. 76, no. 4, p. 501–508.</ref> Nonetheless, some workers have suggested a correlation between seal thickness and [[seal capacity]].<ref name=ch10r58>Nederlof, M., N., Mohler, H., P., 1981, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0065/0005/0950/0964c.htm Quantitative investigation of trapping effect of unfaulted caprock]: AAPG Bulletin, vol. 65, no. 5, p. 964.</ref><ref name=ch10r75>Slujik, D., Nederlof, M., H., 1984, [http://archives.datapages.com/data/specpubs/geochem1/data/a028/a028/0001/0000/0015.htm Worldwide geological experience as a systematic basis for prospect appraisal], in Demaison, G., Murris, R., J., eds., Petroleum Geochemistry and Basin Evaluation: AAPG Memoir 35, p. 15–26.</ref>

==Seal continuity and fracturing==

==Seal continuity and fracturing==

Seal thickness is not an independent variable. Thin seals have a higher probability of being laterally discontinuous, of being fractured completely, or of having local variations in fracture intensity or pore throat diameter that provide a leakage pathway. Similarly, thick seals have a higher probability of being laterally continuous, having fractures terminate within the seal, and having at least one shale lamina with a high displacement pressure.

Seal thickness is not an independent variable. Thin seals have a higher probability of being laterally discontinuous, of being [[Fracture|fractured]] completely, or of having local variations in fracture intensity or [[Pore and pore throat sizes|pore throat diameter]] that provide a leakage pathway. Similarly, thick seals have a higher probability of being laterally continuous, having fractures terminate within the seal, and having at least one shale lamina with a high [[displacement pressure]].

==See also==

==See also==

* [[Seal capacity]]

* [[Seal capacity]]

* [[Seal capacity of different rock types]]

* [[Seal capacity of different rock types]]

* [[Variation in seal capacity with depth and hydrocarbon phase]]

* [[Seal capacity variation with depth and hydrocarbon phase]]

* [[Seal capacity and two-phase hydrocarbon columns]]

* [[Seal capacity and two-phase hydrocarbon columns]]

* [[Fault-dependent leak points, continuity, and charge]]

* [[Fault-dependent leak points, continuity, and charge]]

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Evaluating top and fault seal]]

[[Category:Evaluating top and fault seal]]