考虑环空压力的生产套管CO2腐蚀速率预测

Prediction of CO2 Corrosion Rate of Production Casing Considering Annulus Pressure

目的预测考虑环空压力条件下不同产量、温度变化碳钢套管的腐蚀速率。方法利用优化的经典半经验模型对碳钢套管的腐蚀速率进行预测。明确海洋环境碳钢套管CO2腐蚀的机理,找出海水中生产套管发生腐蚀的主要影响因素及腐蚀机理,通过CO2溶解度模型优化腐蚀速率预测模型,考虑温度、环空压力、产量等变化对腐蚀的影响规律,预测生产套管的腐蚀速率。结果计算了产量变化后环空的压力分布,产量越大,环空压力相对越大,但产量增大到一定值后,环空压力的增加不再明显。产量会影响环空的温度分布,而温度的变化又关系着热膨胀压力,影响套管的腐蚀速率。通过高温高压室内腐蚀实验验证了腐蚀预测模型的可靠性,对比实验结果,模型的预测误差在10%以内,满足现场腐蚀预测需要。结论产量、温度、CO2溶解度、环空压力等因素均对腐蚀有较大影响,考虑环空压力变化条件下生产套管总体的腐蚀速率远超NACE标准中度腐蚀的0.125 mm/a,需要采取一定的缓蚀措施。

To predict the corrosion rate of carbon steel casing with different productions and temperature changes in consideration of annulus pressure.The optimized classical semi-empirical model is used to predict the corrosion rate of carbon steel casing.The CO2 corrosion mechanism of carbon steel casing in marine environment is clarified,and the main influencing factors and corrosion mechanism of production casing in seawater arefound out.The corrosion rate prediction model is optimized by the CO2 solubility model,and the corrosion rate of production casing is predicted by considering the influence of temperature,annulus pressure,and production.The annulus pressure distribution after the production change is calculated.The higher the production is,the greater the annular pressure is,but the increase of the annular pressure will be no longer obvious when the production increases to a certain value.As the production can affect the annulus temperature distribution,the temperature change is related to the thermal expansion pressure and can affect the corrosion rate of casing.The reliability of the corrosion prediction model is verified by high temperature and high pressure indoor corrosion experiment.The experimental results show that the prediction error of the model is less than 10%,which meets the needs of corrosion prediction.Production,temperature,CO2 solubility,annulus pressure,and other factors have a great impact on corrosion.Considering the change of annulus pressure,the overall corrosion rate of production casing is far higher than the industry standard of 0.076 mm/A,so some corrosion inhibition measures should be taken.