Probing the Synergistic Lubrication Mechanism between Graphene Nanoparticles and Diamond-Like Carbon Films at Drill Pipe Joints: A Molecular Simulation Study

Wear between drill pipe joints and casings can seriously affect the extraction efficiency of oil and gas resources, and diamond-like carbon (DLC) films have great prospects for reducing this wear by virtue of their high hardness, ultralow coefficient of friction, and high chemical inertness. This paper investigates the impact of graphene nanoparticles (GNP) and DLC films on the friction behavior at the drill pipe connections under water-based drilling fluid environments based on molecular dynamics. By analyzing changes in the physical structure of the friction interface, atomic-level stress, and combining these with the motion laws of the friction medium, the lubrication mechanism is elucidated. The results indicate that the drill pipe joint model coated with the DLC film can significantly reduce friction. However, the addition of GNP on this basis deteriorates the frictional wear behavior. The DLC film can protect friction pairs while achieving low friction behavior by changing the shape of the rock chip particles. And due to the change of the relative position of the rock chip particles to the GNP, different nanostructures are formed. The horizontal nanostructure can effectively improve the lubrication performance, while the vertical nanostructure can cause abrasive wear between friction interfaces.