Sample Analysis: Wilcox Shale And Pottsville Reploye Example

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Wilcox shale and Pottsville shale samples are tested with the indentation method in this experiment. Both samples are quartz rich and silty shales which contain about 45 to 50% of quartz, 40 to 45% of clays and about 5% of plagioclase. Wilcox shale sample is from Louisiana and formed in upper Cretaceous while Pottsville shale samples are from Alabama and formed in upper Pennsylvanian. These two type of shale rocks are chosen because they are “local” rocks which was abundant and available in the lab, also they have very similar mineralogical compositions.

Both of the shale samples are provide by the SEER lab (Abiola). Before the tests, samples are cut into piece from the core with thickness about 1 in, and polished to
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When compare with the reference of Woodford and Wolfcamp shale, it shows that generally higher hardness sample yields higher Young’s Modulus. Although both Pottsville and Wilcox have very similar mineralogical compositions, their mechanical properties are significantly different. Both of them have about 40 to 45% of clays but the types of clays in both samples are different. Wilcox shale had a significant amount of montmorillonite, which is a well-known swelling clay. Figure below is a Scanning Electron Microscopy micrograph of montmorillonite, this type of clay has a poorly crystallize layer structure. The layers are crumbled and showing an overall “rose-like” texture. When contact with water, the layers can be expanded to accommodate extra water between the layers. The present of swelling clay results in soft texture on adsorption of water and ultimate weakening of the material. On the other hand, the Pottsville shale is swelling clay free, which does not experienced this weakening …show more content…
Which means in order to calculate Young’s modulus, we need to know the Poisson ratio of the material. In this experiment the Poisson ratio is assumed to be constant for all samples as 0.3, which is approximate value for shale rock and may not represent the real values and have impact on the final results. So calculation of Young’s modulus was also done with assumption of Poisson ratio equals to 0.2. The results differ slightly. Considering the error bar, this result should represent the right range of the real

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