基于数值模拟的CO_(2)对油井水泥石腐蚀规律研究

Numerical Simulation of Carbon Dioxide Corrosion on Oil Well Cement

CO_(2)对水泥石的腐蚀是长期以及多因素影响的过程。为研究CO_(2)对水泥石的腐蚀规律,基于溶质运移理论、化学反应动力学定律和物料守恒原理,建立了CO_(2)腐蚀水泥石的溶质运移反应模型,以数值计算的手段再现了CO_(2)腐蚀水泥石的物理化学过程,并得出了适用于数值模拟的腐蚀深度测定方法及腐蚀区域的定量划分方式。研究结果表明:C-H在腐蚀过程中最先耗尽,当C-H大量消耗后C-S-H才开始参与反应。水泥石外侧溶蚀作用使水泥石性能劣化,而内部CaCO_(3)沉积使水泥石孔隙度降低。同时,温度升高加会加剧水泥石腐蚀,碳酸溶液中Ca^(2+)摩尔浓度和p H值提高会抑制腐蚀,但溶液pH值只有在较低范围内(<3)变化才会对腐蚀深度产生明显影响。

The corrosion of cement by CO_(2) is a long-term and multi factor process.In order to get the corrosion law,based on the theory of solute transport,the law of chemical reaction kinetics and the principle of conservation of mass,a reactive transport modeling of cement stone corroded by CO_(2) was established,the physicochemical process of CO_(2) corrosion on cement paste was reproduced by means of numerical calculation,and the corrosion depth measurement method and quantitative division method of corrosion area suitable for numerical simulation were obtained.According to the research results,C-H was first exhausted in the corrosion process,and C-S-H began to participate in the reaction when C-H was consumed largely;the dissolution on the outside of the cement paste deteriorated the performance of the cement stone,while the internal CaCO_(3) deposition reduced the porosity of the cement stone.The increase of temperature aggravated the corrosion of cement,and the increase of Ca^(2+)molar concentration and pH value in carbonic acid solution could inhibit the corrosion,but the corrosion depth could be significantly affected only when the pH value of the solution changed in a low range(<3).