Assessment of Naphthalene Deposition in Crude Oil Pipelines and Its Impact on Flow Assurance

Abstract

Naphthalene deposition in crude oil pipelines has emerged as a significant flow assurance challenge, impairing pipeline efficiency, increasing operational costs, and threatening production continuity. This study assesses the formation, behaviour, and impact of naphthalene deposition in crude oil transportation systems using a combined experimental, field-data analysis, and computational simulation approach. A laboratory flow loop was used to replicate pipeline operating conditions, while field data from an operational crude oil pipeline provided real-world performance indicators. Computational fluid dynamics (CFD) simulations were further employed to examine deposition patterns under varying thermal and hydrodynamic conditions. The results show that naphthalene deposition is strongly temperature-dependent, with an onset between 27°C and 29°C and rapid crystallisation below 25°C. Deposition rates increase significantly with decreasing temperature and decreasing flow velocity, while higher flow velocities reduce deposition due to increased shear stress at the pipe wall. Field data indicate that pressure drop increases from 6.5 bar under clean conditions to 14.2 bar under severe deposition, confirming substantial flow restriction. CFD results further reveal that deposition is concentrated in low-velocity and thermally unstable regions of the pipeline system. The study concludes that naphthalene deposition significantly degrades flow assurance by increasing hydraulic resistance and reducing pipeline efficiency. It also highlights the need to integrate aromatic hydrocarbon deposition mechanisms into existing flow assurance models, which are predominantly focused on wax and asphaltene behaviour. The findings provide valuable insights for improving pipeline design, operational strategies, and mitigation techniques in crude oil transportation systems.