Blocking characteristics of high water-cut crude oil in low-temperature gathering and transportation pipeline

High-pour point and high-viscosity crude oil can be gathered and transported below the pour point during a high water-cut period. However, oil under these conditions can easily aggregate, thereby blocking the pipeline. In this study, a comprehensive field experimental pipeline system (368 m long and 64 mm internal diameter (ID)) was developed to investigate the pipeline blockage mechanism. The changes in the pressure, temperature, and oil-water morphology during cooling experiments were studied. The pipe flow regime under different flow rates of water-blending conditions was divided into blockage, transition, and safe operation modes. The blocking mode was divided into stable development, rising volatility, and fast congestion periods. The rheological change of non-Newtonian crude oil during the cooling process was the dominant mechanism of blockage that caused successive decreases in the oil-water interface until the water phase channel was blocked, finally causing a surge in the flow resistance and pressure drop. The correlation equation of the single well temperature limits as functions of fluid flow rate and water-cut was established, and the error between the prediction results and experiments was between 0.12-0.20 degrees C. The prediction method for the minimum water-blending flow rate was combined with heat transfer analysis, and the corresponding temperature limit was less than the pour point of crude oil at approximately 1-10 degrees C (liquid flow rate: 5-30 m3/d, water-cut: 80%-90%). The investigations conducted in this study further ascertained the crucial impact of non-isothermal and non-Newtonian characteristics on the low-temperature oil-water two-phase flow. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study investigated the pipeline blockage mechanism under different flow rates and water-blending conditions, and found that the rheological change of non-Newtonian crude oil during the cooling process was the dominant mechanism of blockage. A correlation equation of the single well temperature limits as functions of fluid flow rate and water-cut was established to predict the minimum water-blending flow rate.