The Lisburne field at Prudhoe Bay, Alaska, produces from shelfal carbonates in the Pennsylvanian Wahoo formation. Four major factors control reservoir behavior: (1) depositional stratification, (2) a fractured, permeable subunconformity alteration zone (SAZ), (3) multiple episodes of porosity formation, and (4) faulting. This paper is the first written description of facies, cyclicity, and diagenetic processes as they apply to porosity formation and reservoir modeling in the Lisburne field.

Successive depositional cycles in the Wahoo formation pass from ooid/skeletal grainstones deposited in shoal complexes to oncolitic packstones and skeletal/peloidal wackestones formed in restricted lagoonal environments. Geochemical data and crosscutting relationships between porosity and unconformities, pressure solution features, fractures, and faults provide evidence of three distinct episodes of porosity formation. Earliest porosity is probably due to periodic, localized exposure during the Pennsylvanian. A second stage of porosity is associated with shallow-burial dolomitization that probably began during Permian-Triassic subaerial exposure. Reservoir quality in dolomites varies with the degree of neomorphic recrystallization. The third stage began in the Cretaceous and lasted in o the Tertiary, and is associated with final burial and hydrocarbon maturation. This burial dissolution event also opened existing fault systems, creating a complex reservoir. Most Lisburne field effective porosity is of late-burial origin due to either dolomitization or dissolution.

Faults and the SAZ act as giant collectors of oil from low-permeability matrix, and they have reduced the number of wells needed for field development. Faults also complicate waterflood implementation and maintenance of uniform reservoir pressure. Field studies such as these demonstrate the importance understanding the diagenetic history of a reservoir can have for field management and development planning.