--> Abstract: Description, Correlation, and Modeling of Shales and Their Effect on Reservoir Performance, Prudhoe Bay Field, North Slope, Alaska, by E. R. Gustason, D. A. Bodnar, S. Begg, and G. Geehan; #91012 (1992).

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ABSTRACT: Description, Correlation, and Modeling of Shales and Their Effect on Reservoir Performance, Prudhoe Bay Field, North Slope, Alaska

GUSTASON, EDMUND R., DIRK A. BODNAR, and STEVE BEGG, BP Exploration (Alaska) Anchorage, AK, and GREG GEEHAN, BP Research, London, U.K.

The Triassic Ivishak Formation, which forms the major hydrocarbon reservoir in Prudhoe Bay field, North Slope Alaska, consists of a fluvio-deltaic complex overlain by high net/gross fluvial deposits. Continuous and discontinuous shales comprise up to 10% of the total thickness and their frequency, distribution, and continuity are the major heterogeneity controlling fluid flow in the reservoir.

Continuous shales can be mapped over areas of up to 50 sq. miles. They are interpreted as floodplain/lacustrine deposits that developed following major fluvial channel-belt avulsion. Discontinuous shales are interpreted as either drapes that formed on bars or large in-channel dunes during waning flow conditions, abandoned channel fill, or scour lag deposits (mudchip conglomerates).

Continuous shales divide the oil column into hydraulically isolated units, prevent rapid gas and water coning, aid in waterflood and EOR miscible gas sweep efficiency, and allow hydraulic fracture containment. Continuous shales impact reservoir performance by the formation of pressure anomalies that result in gas underrunning and reduced productivity of wells, the formation of trapped oil lenses in the expanded gas cap, and aquifer reducing recovery efficiency. Discontinuous shales constitute only 3% of the reservoir but have significant impact on vertical permeability by increasing the tortuos- ity of fluid flow. They provide barriers to upward segregation of gas and downward drainage of oil or water. Continuous shales are mapped and modeled as permeability barriers (Kv/Kh = 0), wher as discontinuous shales are modeled statistically, their thickness and frequency determined from core and well logs, and their lateral extent and dimensions estimated from outcrop analogs.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)