Wax deposition modeling in oil-water stratified pipe flow

Abstract

Wax deposition in oil-water stratified flow is commonly encountered onshore and offshore oil production pipe systems, and typically reduces transportation capacity of oil. The accurate predicted model of wax deposition has becomes an indispensable approach to design effective remediation strategies. However, a reliable mechanistic model for wax deposition prediction in oil-water two-phase stratified pipe flow is lacking to validate the deposition process. In this work, a three-dimensional (axial, radial, and angular) robust wax deposit model for oil-water stratified circular pipe flow was developed. The model of formation of a gel deposit based on the first principles of rheology was developed, associated with the results obtained from hydrodynamics and heat/mass transfer simulations. The predictions for wax deposition are found to compare satisfactorily with experimental data with two different oils for single phase and four different water cuts for oil-water stratified pipe flow. It can be seen from the wax gelation mechanism that an increase in water cut can help to reduce the wall/oil-deposit interface shear stress, thereby leading to an increase in the degree of gelation as well as the deposit rate. Furthermore, a local deposit analysis in the circumferential direction was conducted, for water cut 75% and total flow rate 5 m 3 /h, which provided insights to understand that the thickness on pipe wall was roughly uniformly distributed locates near the top of the pipe and the nearer the position gets close to two points, where the oil-water interface contacts the inner wall, the deposition thickness quickly dropped to 0. It was attributed to the fact that a roughly uniformly thickness far away from the oil-water interface contact the inner wall resulted in the slowly changes temperature along the circumferential pipe wall wetted by oil.