Molecular Dynamics Simulations of the Tribology of Diamond-Like Carbon Films in CO₂ Fracturing Fluid Environments

Surface wear of fracturing pump plungers seriously diminishes the efficiency of oil and gas production, while diamond-like carbon (DLC) film is considered to be a promising material for reducing friction and wear of oil and gas equipment due to its excellent comprehensive properties. However, the lubricating performance of DLC films is influenced by various factors, and the impact of CO2 content on their microscopic tribological behavior and mechanism under CO2 fracturing environment remains unexplored. This study employs reactive molecular dynamics simulations to investigate the tribological properties of two distinct systems under different CO2 contents in fracturing fluid environments. The results indicate that the reduction of average friction force primarily relies on the increase of CO2 content, and the increase in CO2 content enhances the mobility of medium molecules while also retarding the transformation of atomic lattice and the consumption of medium molecules. Although DLC film is encapsulated by atomic transfer layers at the later stages of sliding, atomic passivation still contributes to the reduction of friction force. Nevertheless, the application of DLC film directly and effectively diminishes the transformation of atomic lattice and shear strain, thereby reducing wear and deformation of the friction pairs. Concurrently, it significantly lowers the average temperature of the system. The findings suggest that enhancing CO2 content on the basis of applying DLC films significantly contributes to extending the service life of plungers.