Complexities of well log interpretation observed through cored samples, Mesaverde Group, Uinta Basin

Abstract

Most natural gas production in the Greater Natural Buttes field in the Uinta Basin, Utah comes from channel deposits within the Mesaverde Group. Within this study area, the 2000 – 2500 ft thick interval is informally subdivided into the Lower Neslen, Upper Neslen, Farrer and Tuscher. The intervals are defined from outcrop descriptions fifty miles to the south and contacts do not correlate well into the subsurface. Subsurface correlations, if done at all, are subjective and cannot be considered reproducible. To accurately create a geocellular model, correlations and intervals must be clearly defined. Understanding the depositional environment through an analysis of facies and facies association provides the foundation for subsurface correlations and geocellular modeling. The purpose of the study is to test the hypothesis that facies associations and associated well log response would provide a foundation for more accurate subsurface correlations, geo-cellular modeling, and ultimately, hydrocarbon recovery. To test this hypothesis, a detailed sedimentological and stratigraphic assessment was conducted using available core data sampled from the Mesaverde Group. Core descriptions allowed for interpretation of facies and facies associations, which were compared to a well log suite. Core samples from the Tuscher, Farrer and Neslen will be shown to display the complexities of identifying channels in logs. Facies, facies associations, mineralogy, and extent of bioturbation are all compared to log motifs and discussed as a possible explanation for the well log complexity. This study addresses the importance of core analysis as it provides sedimentological and stratigraphic information more valuable than outcrop, which may not accurately represent the reservoir.

AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014