--> Abstract: Using Detailed Gamma-Ray Log Correlations To Understand Depositional Patterns Of A Fluvial-Deltaic Lacustrine Reservoir, by C. D. Morgan; #90928 (1999).

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MORGAN, CRAIG D.
Utah Geological Survey, Salt Lake City, UT

Abstract: Using Detailed Gamma-Ray Log Correlations to Understand Depositional Patterns of a Fluvial-Deltaic Lacustrine Reservoir

Detailed gamma-ray cross-sections were constructed to better understand the depositional patterns of lacustrine sediments that have no analogous outcrops and only a few hundred feet of core. The cross sections allow correlations of depositional packages across distances of tens of miles and individual beds across several miles, and identification of numerous shoaling-upward sequences.

In the Uinta Basin, Utah, oil and gas are produced mainly from the Tertiary-aged, lacustrine Green River Formation with lesser production from the intertonguing, fluvial Colton Formation. Throughout the Uinta Basin the Tertiary reservoirs have been classified as fluvial-dominated deltaic reservoirs (FDDRs) based on outcrops in Nine Mile Canyon along the south rim (south shore of Tertiary Lake Uinta) and at Raven Ridge on the northeast rim (northeast shore of Lake Uinta).

The gamma-ray log pattern typical of a distributary-mouth bar and channel common in FDDRs has not been recognized. The lateral continuity is more typical of storm- and wave-dominated shoreface reservoirs. Recently, other workers reinterpreted outcrop data at Raven Ridge and subsurface data in the neighboring Red Wash field as primarily indicating storm-dominated shoreface and gravity-flow deposits with no evidence of fluvial-dominated deltaic influences.

Based on interpretation of the gamma-ray curves, the Bluebell field might best be described as a storm- and wave-dominated shoreface reservoir (Green River) with an intertonguing alluvial and fan-delta reservoir (Colton). Additional core and outcrop data are needed to verify this new interpretation.

This study was funded in part by the U.S. Dept. of Energy under the Class I Reservoir Demonstration Program.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas