Abstract
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 CO(2) 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 CO(2) 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% CO(2) 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% CO(2). These findings underscore the importance of the thermodynamic pathway in predicting wax deposition and suggest that maintaining high pressure and temperature and managing the CO(2) concentration are key strategies for mitigation.