Investigating the frictional properties of shale organic matter with atomic force microscopy

The interaction of hydraulic fractures (HFs) and natural fractures (NFs) of low-permeability media plays a significant role in different aspects of subsurface energy studies, including hydraulic fracturing efficiency, induced seismicity, and enhanced carbon sequestration operations. Therefore, understanding the mechanical behavior of shales, especially the frictional behavior of shales, has been attracting much attention. Organic matter may be the spot of fracture initiation or HFs/NFs interaction; however, even though understanding the stiffness properties of organic matter in the nanoscale has been a subject of some previous research, there have been few studies about understanding the frictional behavior of organic matter in nanoscale. In this work, the frictional experiments were conducted on the organic matter at the nanoscale using the Atomic Force Microscopy (AFM), and the possibility of having a stick-slip behavior in the nanoscale was investigated. The shale samples were cut and polished before the analyses. The Scanning Electron Microscopy and Energy Dispersive Spectroscopy were used to identify the organic matter on the surface of each shale sample prior to conducting the friction experiments by AFM for frictional anisotropy and heterogeneity. It was shown that the amount of lateral force is a function of normal force and load point velocity. This research can shed a light on the frictional characteristics of the organic matter within the organic-rich shales. Acknowledgements: This project was completed with funding provided by the Nuclear Energy University Program of Office of Nuclear Energy at the U.S. Department of Energy (award number DE-NE0008797).