ABSTRACT: Uni-Log System of Symbolic Logic Makes Possible the Plotting of Detailed Lithofacies Information with Virtually Any Vertically-Profiled Set(s) of Data
JORDAN, C. F., Mobil Research and Development Corp., Dallas, TX, and J. P. ADAMS III, Advanced Logging Technologies, Houston, TX
A Macintosh-based system of data-gathering and composite-log plotting has been developed for combining symbolic lithofacies data (based on core examination and/or thin-section petrology) along with numerous additional data sets that vary as a function of depth: porosity and permeability measurements from core plugs or whole core, mechanical log suites, paleontological determinations, various parameters relating to source-rock geochemistry, and images from thin-section photomicrographs or core photography.
Of all these data, the most difficult data sets to present in a columnar plot are lithofacies data and petrographic images. Yet, the basic reason why rocks produce hydrocarbons or not is a direct function of the type of lithofacies involved, as shown by images. Proper description of rock types (to at least a semi-quantitative level) and an integration of that data with other downhole data are essential to a thorough understanding of reservoir characterization. A system of approximately 450 geologic symbols has been compiled and designed to produce a set of three geological fonts, similar to the symbolic fonts called Zapf Dingbats or Cairo. Lithofacies terms are based on Dunham (1962) and modified by Jordan (1985) to (1) allow a maximum of 5% mud in grainstones, (2) consider mud to be he total of the silt- and clay-size fractions of a sediment or a rock, i.e., mud refers to particles smaller than 62.5 microns in diameter, and (3) consider dolomites or dolomitic rocks as diagenetic overprints of Dunham textural terms and to log them as such. The basic lithofacies (LF) equation used in Uni-Log is LF = (Lithic Descriptors)(Grain Types)(Texture) +/- (Remarks).
The implementation of Uni-Log means speed and self-sufficiency for the geoscientist in producing plots of lithology and related data. Examples of Uni-Log plots are available from several basins, including the Canning and the Carnarvon basins.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)