--> ABSTRACT: Reservoir Ichnology of the Sag River Formation, Prudhoe Bay Field, Alaska: Reservoir Architecture, Depositional Environment and Reservoir Properties Understanding Through Ichnological Analysis of a Fine-Grained Bioturbated Sandstone, by Floyd 'Bo' Henk, S. George Pemberton, Tom Saunders, Rick E. Levinson, and James J. Hickey; #90906(2001)

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Floyd 'Bo' Henk1, S George Pemberton2, Tom Saunders2, Rick E. Levinson3, James J. Hickey4

(1) PhD Candidate Univ of Alberta,Edmonton/ Pachiron Group Consultants, McKinney, Tx, McKinney, TX
(2) University of Alberta, Edmonton
(3) Phillips Petroleum Alaska, Anchorage, AK
(4) Applied Reservoir Petrology, Dallas, TX

ABSTRACT: Reservoir Ichnology of the Sag River Formation, Prudhoe Bay Field, Alaska: Reservoir Architecture, Depositional Environment and Reservoir Properties Understanding Through Ichnological Analysis of a Fine-Grained Bioturbated Sandstone

ARCO Alaska's Prudhoe Bay Geoscience group, in 1998, commisioned a one year Ichnology study of the bioturbated Sag River sandstone. The results of the one-year study have provided the Operating District the information needed to optimize a horizontal and coiled tubing drilling program . The Sag River is a thoroughly bioturbated fine-grained sandstone that has been interpreted as a massive shelf sand body and /or an interdeltaic shoreface. Primary sedimentary structures are virtually non-existent and the understanding of the Ichnology was imperative for layering the system. The Ichnology and sedimentology from conventional core was described for 30 wells, integrated with reservoir properties data to include minipermeameter data and thin-section petrology for a comprehensive understanding of the Sag River reservoir. No fewer than 4 regional Glossifungites firmgrounds, three major flooding events and two shoreface progradational events are correlative on a field-wide scale within this 50 foot thick ( average) reservoir. Miniperm data reveals one foot thick alternating high and low perm layers interpreted as bioturbated lam-scram in the lower shoreface as well as a pseudo-fracture behaving Glossifungites system of Thalassinoides burrows with increased permeability, relative to the matrix, due to dissolution of exotic mineral fill, determined through petrographic examination of large format thin-sections of the Thalassinoides. The reserevoir ichnology study facilitated construction of a five layer model for the reservoir and is being utilized to direct the horizontal/coiled tubing drilling program for this secondary reservoir and it has provided a Glossifungites model for the dual perm pressure depletion profile observed in earlier wells.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado