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Beverly A. Burns1, Liangmiao (Scott) Ye2, Jim Hickey2, Rick Levinson3
(1) ARCO Alaska, Anchorage, AK
(2) ARCO, Plano, Texas
(3) ARCO, Anchorage, Alaska

Abstract: Genetic Facies and Systems Tract Architecture of the Tango Interval, Ivishak Sandstone, North Slope, Alaska: A Reinterpretation

A multidisciplinary reservoir description has shed new light on the Triassic Tango interval of the Prudhoe Bay field, North Slope of Alaska. An integrated approach resulted in the identification of new facies and a proper subdivision of the reservoir both laterally and vertically. Recent work has shown the influence of marine processes on the previously interpreted nonmarine sequence. Two principal system tracts have been defined within the Tango interval: Regressive and Transgressive. The Regressive tract is composed of two facies associations: axial fluvial and off-axis fluvial. The Transgressive systems tract comprises several different facies associations: wet floodplain/lacustrine, interdistributary bay, and fluvial/estuarine channel. Field wide stratigraphic and sedimentologic analysis has resulted in the definition of three transgressive and regressive cycles within the Tango interval. The level of marine influence varies systematically: decreasing northward through the field and upwards through the Tango. The Transgressive facies are dominated by nonreservoir strata and therefore represent significant barriers to fluid flow. Axial fluvial sediments consist principally of stacked amalgamated channel deposits and are characterized by a very high net:gross ratio. Off-axis fluvial deposits consist of channel and floodplain deposits and have a lower net:gross ratio. However, the best sandstone porosity and permeability is associated with the off-axis facies. Poorer sorting and a higher percentage of chert clasts reduce reservoir quality in the coarser-grained axial fluvial deposits. New insights on the distribution of fluvial and paralic facies in the Prudhoe Bay Field has greatly improved our reservoir description and provided a robust database for reservoir modeling and well targeting.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana