Steven M. Goolsby¹, Roger M. Slatt², Neil F. Hurley³

(1) Goolsby Brothers & Associates, Inc, Englewood, CO
(2) University of Oklahoma, Norman, OK
(3) Colorado School of Mines, Golden, CO

ABSTRACT: Core and Borehole Image Log Characterization of Turbidite Sandstones in the Lewis Shale, Green River Basin, Wyoming

The Upper Cretaceous (Maastrichtian) Lewis Shale of the Green River Basin, Wyoming, provides an ideal setting in which to study sandstones deposited in mud-rich shelf, slope, and toe-of-slope depositional settings. To study the wellbore attributes and reservoir characteristics found in these environments, the Colorado School of Mines drilled a 1700 ft deep well in the outcrop belt in 1999.

A full suite of logs has been run in the well, including electrical borehole images and nuclear magnetic resonance (NMR). Approximately 580 ft of this well was cored. Conventional core analyses are available for 170 samples, and minipermeameter results are available for every 0.5 ft of core. Capillary pressure studies are underway for selected core plugs. A detailed core description has been compared to the electrical borehole image log. Core permeabilities match NMR permeabilities over several orders of magnitude. The integration of open hole logs, core information, and outcrop studies in the Lewis have led to new insights in the interpretation of the reservoir characteristics of similar turbidite deposits.

Outcrop studies demonstrate a variety of channel fill lithologies in the Lewis Shale. Some of the channels contain fill that is comprised of stacked high-density turbidite deposits. Differentiating between these channel deposits and unconfined sheet deposits is difficult using cores and image log analysis alone. Amalgamation surfaces appear in borehole image logs in what appears to be massive sandstone in core. Shale-clast conglomerates and slump/dewatering structures are also present in core and logs.

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