Using Microscopy Image Analysis to Calculate the Mineral Brittleness Index in Organic-Rich Shale

Summary The study investigates the factors that influence the mechanical and acoustic properties of shale as a potential top seal for CO2 sequestration, nuclear waste disposal, and oil and gas traps. Using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques on borehole samples from the Norwegian Continental Shelf, we separate shale bulk mineralogy into three major components: hard minerals (quartz, feldspar, pyrite), soft minerals (clays), and kerogen content. These outputs are used for calculating the Mineralogical Brittleness Index (MBI). The separation process utilizes a novel image analysis technique, and then the results are compared with the X-ray diffraction data. From the results, estimates of the mechanical and acoustic properties of the organic-rich Draupne and Hekkingen formation shales as a potential seal are proposed. After validation of the proposed image analysis technique, correlations with Elastic Brittleness Index (EBI) are highlighted as they apply to the acoustic properties of the shale. By separating shale out into three phases, defined by the transition of kerogen into hydrocarbons and the nearly simultaneous smectite-illite transformation, the effect of organic and inorganic components on top seal integrity is investigated during each stage relate to both mechanical and acoustic properties.