Changes

Large stratigraphic traps are most common in basins with gentle structural dip, where small hydrocarbon columns can be areally extensive. As structural dip steepens, the need for high-quality seals increases, raising the probability of trap failure.<ref name=ch21r19>Gries, R., Dolson, J., C., Reynolds, R., G., H., 1993, [http://archives.datapages.com/data/specpubs/basinar3/data/a136/a136/0001/0350/0395.htm Structural and stratigraphic evolution and hydrocarbon distribution, Rocky Mountain Foreland], in Macqueen, R., W., Leckie, D., A., eds., Foreland Basins and Fold Belts: [http://store.aapg.org/detail.aspx?id=143 AAPG Memoir 55], p. 395–425.</ref> That is why large stratigraphic traps are most common in basins with gentle structural dip, where small hydrocarbon columns can be areally extensive. [[:file:exploring-for-stratigraphic-traps_fig21-2.png|Figure 2]] illustrates in map view how dip rate affects stratigraphic trap size.

Large stratigraphic traps are most common in basins with gentle structural dip, where small hydrocarbon columns can be areally extensive. As structural dip steepens, the need for high-quality seals increases, raising the probability of trap failure.<ref name=ch21r19>Gries, R., Dolson, J., C., Reynolds, R., G., H., 1993, [http://archives.datapages.com/data/specpubs/basinar3/data/a136/a136/0001/0350/0395.htm Structural and stratigraphic evolution and hydrocarbon distribution, Rocky Mountain Foreland], in Macqueen, R., W., Leckie, D., A., eds., Foreland Basins and Fold Belts: [http://store.aapg.org/detail.aspx?id=143 AAPG Memoir 55], p. 395–425.</ref> That is why large stratigraphic traps are most common in basins with gentle structural dip, where small hydrocarbon columns can be areally extensive. [[:file:exploring-for-stratigraphic-traps_fig21-2.png|Figure 2]] illustrates in map view how dip rate affects stratigraphic trap size.

[[file:exploring-for-stratigraphic-traps_fig21-3.png|left|thumb|{{figure number|3}}See text for explanation.]]

 

[[file:exploring-for-stratigraphic-traps_fig21-3.png|300px|thumb|{{figure number|3}}See text for explanation.]]

Raven Creek field (with 40 million BOE) illustrates the importance of a bottom seal. It is a paleotopographic trap in the Powder River basin of Wyoming. An unconformity overlying the “A” sandstone of the Permian Minnelusa Formation determines the primary trap geometry. This unconformity has paleotopographic relief, and the Opeche Shale red beds are sabkha deposits that infill an erosional valley forming the top and lateral seals to the “A” sandstone reservoir. The dolostone bed separating reservoir sandstones “A” and “B” provides the bottom seal.

Raven Creek field (with 40 million BOE) illustrates the importance of a bottom seal. It is a paleotopographic trap in the Powder River basin of Wyoming. An unconformity overlying the “A” sandstone of the Permian Minnelusa Formation determines the primary trap geometry. This unconformity has paleotopographic relief, and the Opeche Shale red beds are sabkha deposits that infill an erosional valley forming the top and lateral seals to the “A” sandstone reservoir. The dolostone bed separating reservoir sandstones “A” and “B” provides the bottom seal.