A Molecular Dynamics Investigation of Wax Crystallization in Crude Oil under Varying Pressures, Temperatures, and CO ₂ Contents

Wax precipitation in crude oil poses a significant flow assurance challenge, leading to a reduced level of production and operational blockages. This study employs molecular dynamics (MD) simulations to investigate the molecular mechanisms of wax crystallization under varying wellbore conditions. A multicomponent crude oil model was constructed based on samples from the Mahu oilfield, and simulations were performed at different depths (0 to 3400 m) and CO₂ concentrations (0% to 50%). The results reveal that wax crystallization, quantified by a decrease in the diffusion coefficient and an increase in cluster size, intensifies as the pressure and temperature decrease with wellbore depth. A complex, dual role of CO₂ was identified, where it not only acts as a light component at high pressures, inhibiting wax formation, but also extracts light components from the oil, promoting aggregation of heavier molecules. This results in the maximum crystallization observed at 30% CO₂ under flash separation conditions. To reconcile discrepancies with field observations, a differential separation ("degas") route was simulated, which demonstrated significantly enhanced crystallization, particularly at 50% CO₂. These findings underscore the importance of the thermodynamic pathway in predicting wax deposition and suggest that maintaining high pressure and temperature and managing the CO₂ concentration are key strategies for mitigation.