Characterization of the elastic properties of Bakken Shales using nanoindentation and homogenization methods

Shale rocks are hydrocarbon source rocks and reservoir-source rocks that have formed in a variety of environment and have undergone different evolution processes. Organic-rich shales such as Bakken Shales contain abundant presence of nano- and micro-pores mostly located in the kerogen which decreases the overall response of the elastic properties no matter which fluid is filling those pores. In this paper, we modeled and characterized the behavior and the elastic properties of organic matter in the shale matrix using nanoindentation measurements. In the first step, we evaluated the rock composition and distribution of two Bakken Shale samples at different maturity, using X-Ray Diffraction (XRD) analysis. Secondly, we analyzed our samples using scanning electron microscope (SEM) imaging where the major mineral elements and organic matter are identified. Then, we performed nanoindentation test estimating local mechanical properties using deconvolution method. Finally, we combined the obtained result for the prediction of upscaled mechanical properties using micro-mechanical modeling. From the analyses cited above, we derived the mineral and organic matter distribution and confirmed the presence of the dominant minerals in the studied samples. The presented result showed that factors such as rock heterogeneity and maturity significantly influence the overall mechanical response. The results from homogenization showed that Youngs modulus for immature was found around 13 GPa which is lower than in the mature sample estimated around 19 GPa. The findings of this work contribute to the comprehension of the microstructural and elastic properties of source rocks useful for seismic interpretation and geological models. From the method described in this study, we may conclude that more investigations are encouraged to unveil how organic content and maturity affect geophysical properties in source rocks.