Wax Deposition Experiment with Highly Paraffinic Crude Oil in Laminar Single-Phase Flow Unpredictable by Molecular Diffusion Mechanism

Wax deposition data for a Brazilian crude oil was investigated using a facility designed to study flow assurance problems related to waxy crude oils. This work reports the preliminary efforts behind validating the pressure drop methods in place for identifying deposition, i.e., isothermal and nonisothermal flows were evaluated, to confirm whether it was possible to differentiate between temperature gradient effects, and wax deposition. Additionally, deposition experiments show a phenomenon that is not commonly reported in the literature. Once the oil's temperature was below the wax appearance temperature and the water temperature at 5 degrees C, the deposit did not start to build up immediately; it only began after a period of time. Under some conditions the pressure drop only began increasing after 1 day. These results show that, at least for highly paraffinic crudes, models based on molecular diffusion alone cannot predict when and where the deposit will form, which is a major concern in the industry. We believe that other mechanisms such as shear dispersion, Brownian diffusion, and the non-Newtonian behavior of waxy crudes at low temperatures should be considered. In this experimental setup two different ways were used to measure deposit thickness: (1) pressure drop and (2) weight of the deposit.