Multiscale Simulations of Wax Deposition Processes in Petroleum Pipeline Flows

Wax deposition has a significant effect on petroleum pipelines. It severely reduces flow rate and can even cause total blockage if not maintained periodically. There are various techniques for wax removal that involve thermal, chemical or mechanical processes. In order to improve these techniques and designs, a fundamental understanding of the mechanisms of wax deposition and aging is essential. In this paper, we use a channel configuration to depict a slice of pipeline flow in the flow direction with height extended from the wall to the free flow of the pipe. Due to a large range of length scales in the wax deposition process, a multiscale strategy is applied to build a consistent model including mesoscale and microscale. On the mesoscale, we simulate the growth of the porous wax structure in detail, by using the semi-implicit incompressible flow solver NGA coupled to the refined level set grid solver LIT to describe the complex evolution of the petroleum/wax phase interface. On the microscale, we model individual wax crystals in the liquid petroleum using a Lagrangian point particle approach that includes growth of the wax crystals by condensation. Coupling from the micro to the mesoscale is achieved by incorporating the appropriate source terms in the mesoscale flow solver and transferring wax crystals larger than a threshold size from the Lagrangian description to the interface geometry resolved description of the level set solver.