ABSTRACT: Cyclicity, Facies, and Diagenesis of Wahoo Formation, Prudhoe Bay, Alaska

Jeremy Jameson

Extensive development drilling in the Lisburne oil field has provided new data on the geological setting and processes of porosity development in the Pennsylvanian Wahoo Formation. The Wahoo productive interval was deposited as a mosaic of lagoonal and shoal facies in a platform interior setting. Sixteen upward-shoaling depositional cycles are present. The thickness and bathymetric range of cycles decrease upward, suggesting shallowing through time.

Wahoo Formation porosity is diagenetic, associated with three separate episodes of dissolution and dolomitization. Earliest porosity formed during the Pennsylvanian as the tops of some cycles were exposed subaerially. Regional subaerial exposure, development of a regional mixing zone, and dolomitization followed during the Permian-Triassic. Intercrystalline porosity formed during subsequent burial by expulsion of fluids from shales and neomorphism of early dolomite.

The youngest stage of porosity is Cretaceous/Tertiary, associated with deep burial and hydrocarbon maturation. Extensive dissolution resulted in moldic and micromoldic porosity on the eastern side of the field. The interaction between early and late processes accounts for the observed range in reservoir properties and pore types throughout the Lisburne field. Most porosity is of burial origin and likely to be found in similar geological settings elsewhere. Although burial processes generally are perceived as being destructive to porosity in carbonates, the Lisburne field is an example where late processes combine to enhance reservoir quality.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990