CO2吞吐井套管腐蚀规律及极限吞吐轮次研究

部分老油田进入高含水开发后期，为提高采收率，在注水开发中陆续配套实施了二氧化碳吞吐工艺，使得采出液中二氧化碳含量升高，对井筒管柱造成严重腐蚀，引起管柱强度降低，腐蚀穿孔甚至管柱断裂事故时有发生。为此，基于电化学腐蚀的热、动力学原理和管柱力学相关理论，结合现场实际工况，考虑温度、压力、含水率、CO₂分压、流速、井斜角、pH值等因素的影响，采用腐蚀预测模型计算得到了二氧化碳吞吐井不同阶段的腐蚀速度。建立了腐蚀后剩余强度计算方法及极限吞吐轮次计算方法，开展了大量模拟计算，得到了在该吞吐井腐蚀条件下注气、焖井、放压和生产4个阶段的套管腐蚀规律、剩余壁厚及该井的极限吞吐轮次。

Study of the Patterns of Well Casing Corrosion by the CO2 Huff-and-puff Process and the Maximum Number of Huff-and-puff Cycles

In certain mature oilfields that have entered the late high water cut stage, the CO₂ huff-and-puff process can be implemented as a supplementary measure during waterflooding for enhanced oil recovery. This process has led to an increased CO₂ content in the produced water, which can cause severe corrosion in wellbore columns. Thus, the strength of wellbore and casing columns is reduced, leading to pitting corrosion or even column fractures. Therefore, based on the thermodynamic and kinetic principles of electrochemical corrosion and relevant theories of column mechanics, and considering the influences of temperature, pressure, water cut, CO₂ partial pressure, flow rate, deflection angle, and pH based on actual operating conditions at the site, a corrosion prediction model was used to calculate the corrosion rates of a CO₂ huff-and-puff well at different stages of the huff-and-puff process. Methods for calculation of the post-corrosion residual strength and the maximum number of huffand-puff cycles were established. A large number of simulation calculations were performed to predict the casing corrosion patterns and residual wall thickness of the huff-and-puff well under gas injection, soaking, pressure release, and production conditions, as well as the maximum number of huff-and-puff cycles for the well.