Exploring the effects of water content on friction behavior and mechanism of DLC films in oil production environment based on molecular dynamics simulation and first-principles calculations

To provide atomic-level insights for improving the service life of the Sucker Rod Production System (SRPS) in the harsh oil extraction environment, we attempted to investigate the friction and wear behavior of the Fe-Fe model (conventional steel plunger pump barrel) and the DLC-Fe model (DLC-coated plunger pump barrel) in the oil extraction environment through molecular dynamics (MD) simulations and first-principles calculations. The results show that the interaction force between the conventional steel plunger and the light oil chain increases significantly as the crude oil moisture content increases. The shear strain of friction layer is intensified, severely limiting its wear resistance in the harsh oil extraction environment. Interestingly, due to the weaker interaction with the light oil chain, the plunger-pump barrel system coated with DLC films exhibited excellent frictional performance. Further studies showed that the passivation of C-suspension bonds on the films surface in the crude oil effectively improved the shear resistance of the DLC friction layer with the increase of water molecules. The related results provide a theoretical support for the practical engineering application of DLC film on the surface of oil well pump plunger.