Existence of a critical carbon number in the aging of a wax‐oil gel

A fundamental study was carried out to understand the aging (or hardening) of the wax‐oil gels formed in the subsea pipelines during the flow of crude oil from offshore wells to shore. The aging process is a counterdiffusion phenomenon where there exists a critical carbon number (CCN), and wax molecules with carbon numbers greater than the CCN diffuse into the gel matrices and vice versa. Using a careful analysis of carbon number distributions of gel deposits, collected from a cold finger after various deposition time intervals, the CCN for the wax‐oil system was obtained. A mathematical model, based on a modified version of UNIQUAC model, was developed to predict the CCN for wax‐oil systems. The size of the interaction units for n‐alkanes in the solid‐phase UNIQUAC model was found to be a strong function of the mean carbon number in the solid phase.