Experimental investigation on the tribological behavior and surface damage due to embedment of ceramic proppant – analog mudrock composite systems

The analysis of interface problems involving proppants and rocks is of major interest in unconventional reservoir exploitation and modeling as well as in geophysics, mining engineering and rock mechanics. Despite the significant progresses that have been reported in hydraulic fracturing, there has been given less attention in the fundamental understanding of the interactions between proppants and rocks, which can provide enhanced input parameters in computational-based analyses involving complex multi-phase processes. In this study, the tribological behavior of three types of contacts including ceramic-ceramic (analog) proppants, kaolinite-kaolinite blocks (analog mudrock) and ceramic-kaolinite composite interfaces was investigated performing laboratory tests using a custom-developed loading apparatus and the experiments involved force and displacement measurements by the application of high-precision transducers. Based on a series of normal loading tests, it was observed that the ceramic beads exhibited a completely elastic behavior, whereas the kaolinite blocks showed a softer response with, predominantly, plastic deformations. The results of the shearing tests indicated that for the ceramic-kaolinite composite contacts, the arrangement of the clay microfabric significantly affected the shearing load-displacement response in terms of the post-peak softening behavior, the development of the microslip regime as well as the dynamic friction. It was also shown that even though the interface friction was controlled, predominantly, by the softer kaolinite block, the interface tangential stiffness had different involved mechanisms, in which case the kaolinite blocks showed the highest stiffness specifically at greater magnitudes of normal load, whereas the ceramic-kaolinite composite interfaces had the lowest values of stiffness.