基于腐蚀时间效应的含H_2S/CO_2环境中的腐蚀速率预测模型

高含H_2S/CO_2高温高压气井中井筒油管、套管的腐蚀已成为制约井筒完整性的主要因素,一旦井筒完整性失效将会给油气田的开发造成重大影响,并可能导致严重的人员安全、环境及经济损失。由于高温高压H_2S/CO_2环境腐蚀机理较为复杂,国际上使用较为广泛和经典的DE Waard腐蚀速率计算模型已不能预测类似高温高压复杂环境下井筒的腐蚀速率。目前,实验室通常开展短期的腐蚀测试试验,并以此数据预测长期的腐蚀速率,但长期的腐蚀速率与短期腐蚀速率差异甚大。因此,为了准确地预测服役寿命周期内油套管的腐蚀状况,采用自主设计制造的高温高压材料损伤试验平台,模拟气井井筒的实际腐蚀环境,开展CO_2、H_2S腐蚀环境中的电化学腐蚀速率测试试验,研究了不同测试时间下的腐蚀速率,分析了腐蚀速率的时间效应。结果表明:在管柱服役早期,其腐蚀速率较大,随着服役时间的延长,由于形成了腐蚀产物膜以及腐蚀性气体浓度的降低,腐蚀速率逐渐降低直至稳定于某一较低值。最后,利用数理统计方法建立了考虑腐蚀时间效应的腐蚀速率预测模型,可为合理选择油套管材质和油气井的安全评价提供依据。

Prediction Model of Corrosion Rate Based on Corrosion Time Effect in the Environment Containing H2S and CO2

With the increasing demand for oil and gas resources,H2S/CO2 corrosion has become the dominant factor,which harms wellbore integrity in the process of gas field development.H2S/CO2 corrosion can lead to some major accidents and a huge economic cost.The corrosion mechanism is so complex in the high-temperature and high-pressure environment containing H2S/CO2 that DE-Warrd corrosion predict model can not predict corrosion rate in such environment.At present,the short-term corrosion test is always conducted in the laboratory and the researchers often use short-term experimental data to predict the long-term corrosion rate.However,there is a great difference between short-term data and long-term data.Thus,in order to predict the corrosion condition of casing and tubing service life accurately,the self-designed high-temperature and high-pressure reactor was applied to simulate the condition of the gas wellbore actual corrosion environment,and the electrochemical corrosion rate test in the CO2/H2S environment was carried out.Besides,the corrosion rates under different test time and the correlation between time and corrosion rate were also analyzed.Results indicated that in the early years of corrosion,the corrosion rate was high.As the service time went on,the corrosion rate had a gradual decrement trend and ended at a lower stable data due to the formation of corrosion product and the decrease of corrosive gas.At last,the model of corrosion rate and testing time was built by the mathematical statistic method,which would provide the basis for the material selection of casing and tubing and the safety evaluation of the oil and gas well.