Quantitative Analysis of Geologic Samples with Chromastratigraphy: Applications to Conventional and Unconventional Resources
The use of color as a descriptive tool for geologic samples has traditionally relied upon qualifying modifiers such as “light” or “dark” to describe the varied range of rock Values and Hues. Attempts at more systematic methods have introduced complex descriptive systems, such as Munsell Soil Color Charts. While these efforts represent improvements, they remain highly qualitative and fail to remove the primary source of poor accuracy and precision: human error. Moreover, these descriptors are not readily converted into a useful tool for visual interpretation and analysis (e.g., well logs). Here we present Chromastratigraphy™, a quantitative technique for the rapid, reproducible characterization, and correlation of chromatic data in well log format and demonstrate its application to conventional and unconventional resource plays.
Using proper protocols, quantitative chromatic data can be rapidly and reproducibly gathered from rock cuttings (interval samples), core, or outcrop (spot) samples from any region and age. Saturated slurries of pulverized sample and distilled water are photographed under tightly controlled conditions. Raw color data is extracted from each sample via software and used to calculate an average color for that depth or interval, and can be equally collected in the laboratory setting or at the rig site for near real-time results. Here we focus on the RGB and HSV color systems, though others remain suitable. Color data can be displayed in color-component form (e.g., Red, Value) to identify absolute deviations, or relative changes through component ratios [e.g., Red/Blue, Red/(Red + Green + Blue)]. When plotted in well log format, these curves form systematic and predictable changes that can be interpreted and correlated, as with wireline data. A key component of the ChromaLog™ is a graphical display of the reconstructed color from the measured samples, similar to viewing a core or outcrop. This powerful image allows for the immediate recognition of facies and formation changes, especially in well studied settings. When integrated with a suite of independent data, a robust chromastratigraphic framework can be developed allowing the ChromaLog™ profile to be confidently utilized as an interpretative tool. For example, combining chromatic data with stratigraphic markers (e.g., biostratigraphy), Chromastratigraphy™ can be used to confirm lithostratigraphic correlations and, under certain circumstances, create chronostratigraphic tie-lines.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California