Pinch-out

A pinch-out or wedge-out[1] is a point where a stratum or other lithologically distinct body of rock thins to a feather edge and disappears, so that the underlying and overlying strata separated by the pinching out stratum come into direct contact. The term also is used in petroleum geology to describe a stratigraphic trap created by a pinch-out. Petroleum migrating through a porous stratum is trapped where the stratum pinches out between impermeable underlying and overlying strata.[2][3]

Diagram illustrating a pinch-out petroleum trap

As of 2019, at least 20 oil fields containing reserves of 6-7 billion barrels of petroleum are thought to be a result of pinch-out of turbidite beds.[4]

A pinch-out is distinct from a shale-out, which is a structural trap formed when a porous bed grades laterally into impermeable shale without the bed actually pinching out.[5]

References
  1. Jackson, Julia A., ed. (1997). "wedge-out". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.
  2. Jackson 1997, "pinch-out".
  3. Nelson, S.A. (19 October 2015). "Energy Resources". Tulane University. Retrieved 3 November 2021.
  4. Amy, Lawrence A. (December 2019). "A review of producing fields inferred to have upslope stratigraphically trapped turbidite reservoirs: Trapping styles (pure and combined), pinch-out formation, and depositional setting". AAPG Bulletin. 103 (12): 2861–2889. doi:10.1306/02251917408. hdl:10197/11533.
  5. Jackson 1997, "shale-out".


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