Wax Deposition in Pipelines: Flow-Loop Experiments and Investigations on a Novel Approach

Abstract

Abstract: Models used to predict wax deposits in oil production pipeline are based on thermodynamic properties coupled with several Fick's diffusion mechanisms. These models generally need fitting parameters to match computational results to experimental data, and moreover they do not explain all aspects of this phenomenon. One of these aspects is the "sticking" of the deposit to the wall. In this study, it is demonstrated that the deposit could result from flow patterns caused by rheological factors. Indeed, thermodynamic properties create the onset of wax crystals, and diffusion mechanisms result in the displacement and accumulation of wax in a particular region. This results in rheological changes that modify the flow pattern and create an unyielded region near the wall, namely a wax deposit. To highlight this process, experimental tests of wax deposition were performed on the Lyre loop at IFP-Lyon in Solaize, France. This loop is 140 meter long with a 2 inches internal diameter and is fully temperature-controlled. A wax deposition section consisting of a 7 meter sub-cooled section is integrated in this loop. A one-meter spool piece can be retrieved to observe and sample the wax deposit. Temperature, pressure drops and flow rate were monitored. The wax deposit was observed after 4h, 24h and 72h and was sampled for rheological measurements. The experimental results are presented in this paper. In addition, to analyse this experimental data, a numerical model based on the previously described physical aspects is implemented, and the results show good agreement with experimental data.