碳化和氯离子侵蚀作用下井筒钢套管劣化研究

A study on the degradation of steel casing in wellbore under carbonation and chloride ion ingress

CO_(2)泄漏可能性和井筒耐久性评估是地质碳封存研究的关键问题,本文预测了碳化和氯离子侵蚀耦合作用下井筒钢套管的锈蚀劣化过程。建立了氯离子在碳化水泥中扩散数值模型,考虑碳化对结合氯离子的影响提出碳化井壁水泥中氯离子浓度的预测模型。通过模拟CO_(2)地质储存环境下的钢套管快速锈蚀试验确定了钢套管锈蚀临界氯离子浓度,考虑多参数建立了临界氯离子浓度计算模型,并进行了井筒结构可靠度分析。结果表明:环境温度和水泥浆的水灰比对钢套管锈蚀临界氯离子浓度影响显著。可靠度理论预测发现水泥浆的水灰比为0.6,环境温度为70℃时,井筒结构的最短使用寿命为36.8 a。

The possibility of CO_(2) leakage and wellbore durability assessment are critical issues in geological carbon sequestration research.This study predicts the corrosion deterioration process of steel casing in wellbores under the coupling action of carbonation and chloride ingress.A numerical model for the diffusion coefficient of chloride ions in carbonation cement was established.Furthermore,a prediction model for the concentration of free chloride ions in carbonized wellbore cement was proposed,accounting for the influence of carbonization on binding chloride ions.Rapid corrosion tests in a simulated CO_(2) geological storage environment were used to determine the critical chloride ion concentration.Based on these tests,a calculation model for critical chloride ion concentration was established,with solution temperature and the water-to-cement(w/c)ratio as parameters.The reliability of the wellbore structure was then analyzed.Results indicate that environmental temperature and the w/c ratio significantly affect the critical chloride ion concentration for steel casing corrosion.The reliability theory predicts that when the w/c ratio of cement is 0.6,and the temperature is 70℃,the shortest service life of the wellbore structure is 36.8 years.