ROBISON, VAUGHN D., LOU M. LIRO, JOHN W. RUSSO, and WILLIAM C. DAWSON, Texaco, Inc., Houston, TX

ABSTRACT: Integrated Geochemical and Sequence Stratigraphic Analysis of the Triassic Shublik Formation, Tenneco Phoenix #1 Well, North Slope, Alaska

The Triassic Shublik Formation is an important source of North Slope Alaska crude oil. Organic facies within the Shublik are highly variable, however, and not all the formation is of source quality. This variability is dependent on stratigraphic position and is predictable in a sequence stratigraphic framework. The Phoenix #1 well recovered continuous core throughout the Shublik Formation. The lower portion of this Shublik core represents part of a transgressive systems tract and is characterized by alternating intervals of bioturbated and well-laminated shales. A pronounced condensed section occurs at the top of this interval. The upper portion of the Shublik is interpreted to represent initial deposits of a highstand systems tract. This interval contains siltstones and is more biotu bated than the base of the unit.

Detailed geochemical analyses reveal the distinction between the transgressive and regressive portions of the Shublik. The transgressive, lower portion of the Shublik contains all of the oil-prone portions of the section, while the upper, regressive Shublik contains gas-prone to non-source intervals. These observations directly affect resource assessment, where the effective source rock thickness used for volumetrics calculations cannot typically be determined from cuttings samples collected over 30' intervals. Well-laminated, organic-rich, oil-prone intervals in the Phoenix core correspond to uranium anomalies on the spectral gamma

ray log. This relationship is observed in other wells across the North Slope and can be used to refine estimates of effective source rock thickness for volumetric considerations in those areas.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.