INVESTIGATING THE EFFECT OF MOISTURE CONTENT ON THE USE OF COLOR AS A KEY LITHOLOGIC PARAMETER

Geologic logging of borehole samples and drill cuttings, combined with borehole geophysics and laboratory analyses, provide some of the primary datasets for interpretation of lithofacies and their sequence stratigraphic relationships. The color of these samples and drill cuttings is one of the key parameters recorded by well site geologists (i.e., its Munsell soil color). However, these samples often have variable moisture content depending on subsurface moisture conditions and/or the use of fluids during drilling. This has made it difficult to directly compare the observed colors from one sample to another.

The moisture content of a soil sample is known to affect its perceived color. Thus, we planned to investigate the effect of moisture content on the color of selected sediment samples, and to evaluate possible mechanisms to promote the use of soil color (irrespective of moisture content) as a key lithologic parameter. We used both qualitative visual analysis and semi-quantitative digital image processing to analyze the color of three different sediment samples at nine different moisture contents (up to about 32 weight percent).

Results showed that at low to moderate moisture contents (below about 10-12 weight percent), the Munsell color value and chroma were moderately to strongly inversely correlated with moisture content. However, there was no correlation between the hue and moisture content. We found the color value (i.e., lightness) dropped 2-4 units with an increase from 0 weight percent moisture to 10-12 weight percent, while the chroma (i.e., color saturation) dropped by an average of 2 units. At higher moisture contents (above about 10-12 weight percent), we observed virtually no correlation between the moisture content and color value or chroma. To confirm there was no correlation between the hue (i.e., its relation to red, green, and blue) and moisture content, we used the histogram tool in Adobe® Photoshop® to determine the red, green, and blue (RGB) values from digital photographs of the samples. We found virtually no change in the ratios of the red, green, and blue color components relative to moisture content. Thus, it appears that hue (particularly the color components such as red, green, and blue) could be used as a key lithologic parameter, independent of moisture content.