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

Abstract

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 °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 °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.