INVESTIGATING THE FRICTIONAL PROPERTIES OF CONSTITUENT MINERALS OF SHALE FROM THE NANOSCALE TO MICROSCALE USING ATOMIC FORCE MICROSCOPY (AFM)

Hydraulic fractures (HFs) and natural fractures (NFs) interaction play a significant role in different aspects of geology, including hydraulic fracturing efficiency, induced seismicity, and the efficiency of carbon sequestration operations. Therefore, understanding the mechanical behavior of shales has been highly important in investigating the HFs and NFs interaction, and the frictional behavior of shales is an indispensable part of this investigation. Even though understanding the stiffness properties of shales in the nanoscale has been a subject of much previous research, there have been a few research about understanding the frictional stability of shales in nanoscale. To understand the frictional characteristics of shales, the frictional experiments were conducted on the quartz, clay minerals (kaolinite, montmorillonite), which are important constituent minerals of shale, in the nanoscale using the atomic force microscopy (AFM), and the possibility of having a stick-slip behavior in the nanoscale was investigated. The samples from pure standard minerals were cut and polished. The scan area of lateral force microscopy was from tens of squared nanometer to squared micrometer, and the range of normal force was in the tens of nano-newton. In this procedure, the range of tip velocity that causes a stick-slip behavior in those minerals were determined. Also, the importance of frictional anisotropy and heterogeneity was also investigated using AFM. It was shown that the amount of lateral force drop is a function of normal force and load point velocity. This research can also lead to the other characterization method for identifying the organic material in the kerogen-rich shales.