Abstract: To address the problems such as reduced heating efficiency and excessive load on the downstream treatment system caused by the high viscosity,difficult transportation of ultra-heavy oil,a subsea pipeline liquid separation process for ultra-heavy oil based on gravity settlement was designed. Through simulation experiments and field industrial experiments,the separation law of free water in ultra-heavy oil during pipeline transportation with water blending is obtained,and an improved scheme for separating and discharging free water before it enters the next-stage equipment is proposed. This liquid separation process reduces the water content of ultra-heavy oil from 80% to 72% before it enters the heater and increases the heating temperature of the heater by 7 °C. Meanwhile,the advanced separation of free water reduces the treatment capacity of subsequent processes by 33.3%,which significantly alleviates the treatment pressure of subsequent processes,decreases the water content of exported oil,effectively lightens the treatment burden of onshore terminals,and saves the sewage treatment cost by 450,000 CNY/year. It provides reliable technical support for the economical and efficient development of offshore ultra-heavy oil.

Key words: ultra-heavy oil, subsea pipeline liquid separation, reduction in water content, process optimization, gravity settlement