LUTZ, SUSAN J., and DENNIS L. NIELSON, University of Utah Research Institute, Salt Lake City, UT, and DAVID THORN, Schlumberger Well Services, Aurora, CO

ABSTRACT: Utilizing Orientation Data from Formation Imaging Logs: Examples from the Fluvial-Deltaic Ferron Sandstone of Utah

Bedding orientations of sedimentary features have been acquired from two coreholes drilled through the Ferron Sandstone of Utah using Formation Microscanner(TM) logs. The orientation data represent a hierarchical order of bedding and bounding surfaces from the facies to the parasequence scale. Plots of dip and azimuth versus depth are useful in packaging sedimentary facies into genetic units and constructing characteristic vertical sequences.

In forward-stepping parasequences, plots of depth versus azimuth (DVA) for distal-bar facies indicate a narrow range of azimuths that represent the direction of deltaic progradation. DVA plots of distributary mouth-bar facies show a wider, bimodal spread of azimuths that indicate deposition as a result of both wave and fluvial processes. Overlying channelized sandstones exhibit a cyclic pattern; the channels trend northwest at the base and rotate clockwise upsection into the northeastward direction of deltaic progradation. These channels are interpreted as crevasse splays into an adjacent interdistributary bay.

The architecture of the distributary channels in backstepping parasequences is reflected in different vertical azimuthal profiles. Laterally-migrating channels exhibit a clockwise or counterclockwise rotation of azimuths with depth, and radical shifts in orientation across scour surfaces. Downstream-accreting macroforms in overlying channels are unidirectional and exhibit subtle shifts in orientation along multiple reactivation surfaces. The straight-reached channels predictably accrete in the direction of delta progradation, but are volumetrically less important than the underlying, variably-oriented, reservoir-quality sandstones.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.