Evolution of frictional slip behavior on shale surface using friction reducers

The shale-on-shale COF was measured in a pin-on-disk tribometer for dry and fluid (DI water, polymer-based anionic commercial oilfield friction reducer, and carbon nanodots solution) saturated conditions under a constant load of 15 N and at varying sliding speeds. Shear strengthening behavior was observed at the initial slip stage where the solid-solid contact mechanics were dominant. But no consistent trend was observed for the early COF. Steady-state friction is achieved after prolonged sliding, with the carbon nanodots requiring the shortest time for stability and showcasing the lowest COF. The DI water exhibits velocity weakening behavior while the friction reducer and carbon nanodots exhibit the velocity strengthening behavior. Sommerfeld analysis shows that fluid films govern the lubricating behavior over longer durations.