Understanding pore heterogeneity can enable us to obtain a deeper insight into the flow and transport processes in any porous medium. In this study, multifractal analysis was employed to analyze gas adsorption isotherms (CO2 and N2) for pore structure characterization in both a source (Upper-Lower Bakken) and a reservoir rock (Middle Bakken). For this purpose, detected micropores from CO2 adsorption isotherms and meso-macropores from N2 adsorption isotherms were analyzed separately. The results showed that the generalized dimensions derived from CO2 and the N2 adsorption isotherms decrease as q increases, demonstrating a multifractal behavior followed by f(α) curves of all pores exhibiting a very strong asymmetry shape. Samples from the Middle Bakken demonstrated the smallest average H value and largest average α10-α10+ for micropores while samples from the Upper Bakken depicted the highest average α10-α10+ for the meso-macropores. This indicated that the Middle Bakken and the Upper Bakken have the largest micropore and meso-macropore heterogeneity, respectively. The impact of rock composition on pore structures showed that organic matter could increase the micropore connectivity and reduce micropore heterogeneity. Also, organic matter will reduce meso-macropore connectivity and increase mesomacropore heterogeneity. We were not able to establish a robust relationship between maturity and pore heterogeneity of the source rock samples from the Bakken.

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In order to study the mechanical properties of shale samples from Bakken Formation, nanoindentation method, an imaging technique borrowed from other engineering disciplines, was used. Different types of nanoindentation curves were analyzed and the applicability of the nanoindentation theories to study mechanical properties of shale samples at nanoscale was demonstrated. Elastic modulus and Hardness of different samples were calculated, compared and related to their mineral compositions and microstructures which are detected by 2D XRD and FESEM methods, respectively. Results showed that samples with more clay minerals (mainly composed of illite) and larger pore structures have less Young's modulus. In addition, based on the energy analysis method, the fracture toughness at nanoscale was estimated and its relationships with Young's modulus was quantified. It was observed that fracture toughness increases linearly with Young's modulus. This paper presents the results and major findings of this study.