Abstract:

At present, water injection is often used to extract oil, but CO₂ corrosion often occurs in water?bearing pipelines. Therefore, Computational Fluid Dynamics (CFD) was used to study the distribution of oil and water in straight pipes and bends at different water content (volume) and flow rates, to determine the conditions for the occurrence of CO₂ corrosion in oil pipelines, and the effect of flow rate and water content on the wall shear force was analyzed. The results show that the occurrence of CO₂ corrosion depends on the water content and flow rate in the pipeline. When the water content increases, oil infiltration in the inner wall of the pipe to prevent corrosion; when the water content decreases, the amount of water accumulation increases, resulting in serious CO₂ corrosion. When the flow rate increases, turbulence occurs in the pipeline, so it is difficult to form water accumulation, reducing the risk of corrosion. However, an increase in flow rate will lead to an increase in wall shear, which will destroy the corrosion product film and further accelerate the corrosion rate. In downward elbows, under the action of gravity, water often does not occur in the pipeline, and the risk of corrosion is low; in upward elbows, water is most likely to occur, and the risk of corrosion is high; affected by scouring, the elbow end is corroded seriously. The elbow end is susceptible to the interaction of corrosion and mechanics, so corrosion is serious. The research results have certain guiding significance for the safe operation of oilfield gathering pipelines.

Key words: Oil pipeline, Oil?water two?phase flow, Wall shear stress, Flow rate, Water content, CO₂ corrosion

摘要：

目前常采用注水方式开采石油，但是含水输油管道中常发生CO₂腐蚀现象，因此采用计算流体力学方法（Computational Fluid Dynamics，CFD），研究了不同含水率、不同流速下的直管和弯管中油水分布情况，确定了输油管道CO₂腐蚀的发生条件，并分析了流速及含水率对壁面剪切力的影响。结果表明，CO₂腐蚀的发生取决于管道内的含水率和流速。当含水率升高时，油品浸润在管道内壁阻止腐蚀的发生；当含水率降低时，积水量增加，导致CO₂腐蚀严重。当流速增大时，管道内发生湍流，因此难以形成积水，降低腐蚀风险。但是，流速增大时会导致壁面剪切力增加，破坏腐蚀产物膜，进而进一步加快腐蚀速率。向下倾斜弯管在重力作用下往往不会发生积水，腐蚀风险低；向上倾斜弯管最容易发生积水，腐蚀风险高；受冲刷作用的影响，弯头端的腐蚀严重。弯头处容易受腐蚀和力学的交互作用，因此腐蚀严重。研究结果对油田集输管道的安全运行具有一定的指导意义。

关键词: 输油管道, 油水两相流, 壁面剪切力, 流速, 含水率, CO₂腐蚀