"Calculating Mineral Facies and Organic Matter Trends in the Austin Chalk by Integrating Large Geochemical Datasets with Multivariate Statistics"
Dr. Toti Larson, Research Associate
Bureau of Economic Geology
The Austin Chalk Group is an Upper Cretaceous calcareous mudrock deposited across the Comanche Platform along the north rim of the proto-Gulf of Mexico. It consists of alternating layers of lime packstone (chalk) and laminated argillaceous calcareous mudstones, and is currently being explored for oil and gas production in Louisiana and across Texas.
To more accurately assess any unconventional oil and gas resource it is important to constrain stratigraphic and lateral distributions of mineral facies and organic matter-rich layers and identify correlations between them. Here, high-resolution (i.e., 2” spacing) elemental concentrations measured using portable X-ray fluorescence (pXRF) are compared to a limited set of low resolution (10’s of meters) mineralogical (X-ray diffraction) and total organic carbon (TOC) measurements in the Robert Todd core from Western Louisiana. Multivariate statistics including principal component analysis (PCA) is used to identify correlations within these large geochemical datasets that are collected at different scales, and to calculate high-resolution mineralogy and TOC trends along the core. Finally, these calculations are expanded to geochemical data from eight additional cores across the Comanche Platform to build an internally consistent mineralogical model for the Austin Chalk. Results from these eight cores are compared to total gamma ray logs to demonstrate how these core characterizations can be used to calibrate wireline logs, providing a means to upscale these observations to the inter-well scale. Collectively, this effort uses multivariate statistics to bridge important scales of measurement (inch to 100’s of meters) to better constrain geologic heterogeneities that affect the development of unconventional hydrocarbon resources.