|Exploring for Oil and Gas Traps|
|Series||Treatise in Petroleum Geology|
|Part||Predicting the occurrence of oil and gas traps|
|Chapter||Evaluating top and fault seal|
|Author||Grant M. Skerlec|
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 1 m3.281 ft
39.37 in 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.
Seal thickness studies
Data compiled from fields in California and the Rocky Mountains show no relationship between seal thickness and hydrocarbon column height. Nonetheless, some workers have suggested a correlation between seal thickness and seal capacity.
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 capacity
- Seal capacity of different rock types
- Seal capacity variation with depth and hydrocarbon phase
- Seal capacity and two-phase hydrocarbon columns
- Fault-dependent leak points, continuity, and charge
- Zieglar, D., M., 1992, 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.
- Nederlof, M., N., Mohler, H., P., 1981, Quantitative investigation of trapping effect of unfaulted caprock: AAPG Bulletin, vol. 65, no. 5, p. 964.
- 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.