Flow separation characteristics of non-Newtonian oil and polymer solution fluids in T-junctions of offshore production platforms

Currently, offshore oil exploitation widely uses polymer flooding techniques, which result in the produced fluid exhibiting non-Newtonian characteristics. This creates an urgent need for efficient and compact separators for oil–water separation in polymer-containing produced fluids. This study establishes a numerical model for T-junctions based on the Euler–Euler multiphase flow model, Reynolds stress turbulence model, and a non-Newtonian force model. It explores the effects of various operational parameters (such as inlet oil content, inlet velocity, split ratio, and oil phase density) and structural parameters (such as branch pipe angle and number of branches) on the separation efficiency of non-Newtonian oil and polymer solution two-phase flow in T-junctions. The results indicate that reducing the inlet velocity and decreasing the branch pipe angle can significantly lower the turbulence intensity within the main pipe, promote fluid stratification, and improve separation efficiency. Particularly, at a flow split ratio of 0.5, the separation efficiency peaks. Furthermore, a comparison between heavy oil–water two-phase flow and non-Newtonian oil and polymer solution two-phase flow disclose that the former achieves a maximum separation efficiency of approximately 87% under six branch conditions, while the latter shows poorer stratification and separation efficiency in the front section of the main pipe. By investigating the key factors affecting separation performance, this study provides theoretical support for the design and development of separation devices tailored to non-Newtonian polymer-containing produced fluids.