Effect Of Hydration Products On CO₂ Corrosion Resistance Of Oil Well Cement

Carbon dioxide capture and storage technology(CCS)is one of the important measures to scientifically reduce greenhouse gases during the period of extreme growth of energy demand.Under long-term storage conditions,CO₂ injected into the formation will react with cement paste,corrode the cement sheath and reduce its sealing performance,thereby increasing the risk of CO₂ escaping along the wellbore.In order to explore the corrosion law of cement paste under the condition of CO₂ storage,this paper uses the method of combining theoretical analysis,indoor experiment and mathematical simulation to clarify the change law of mineral content and porosity and permeability in cement paste in time and space,and to explore the influence of hydration products on the corrosion law.Firstly,starting with the material characteristics of oil well cement,the internal causes of carbon dioxide corrosion of cementing cement paste are clarified.The reaction equation and reaction products between CO₂ and cement paste are described,and the reaction law between CO₂ and cement paste is revealed.High temperature and high-pressure static corrosion experiments were carried out to verify the mechanism analysis and provide reference for numerical simulation.By means of scanning electron microscope and X-ray diffraction analysis,the phase composition and microstructure of cement paste at different corrosion depths and the corrosion depth at different corrosion times were obtained.According to the kinetic reaction mechanism of CO₂ and cement paste,based on the solute mass conservation,mass action law and kinetic rate equation,a solute transport reaction model is established to accurately describe the corrosion process of cement paste.Through numerical simulation,the evolution laws of corrosion depth,mineral composition and porosity and permeability parameters are analyzed.The simulation is in good agreement with the experimental results.Based on the simulation analysis results,the quantitative division method of corrosion zoning and the evaluation standard of corrosion degree are put forward.The effect of hydration product s of cement on CO₂ corrosion of oil well cement was studied,and the effects of calcium hydroxide content and hydrated calcium silicate calcium silicon ratio on the corrosion damage of cement paste were explored.The simulation results show that reducing the calcium silicon ratio of hydrated calcium silicate in cement paste can improve the corrosion resistance of cement paste.At the same time,the volume fraction of calcium hydroxide in cement paste should be maintained at 5%?10%.Too much and too little calcium hydroxide in cement paste will reduce the corrosion resistance of cement paste.The research results are helpful to improve the understanding of the corrosion law and corrosion mechanism of cementing cement sheath under the condition of carbon dioxide storage,and provide theoretical and technical support for the study of wellbore integrity under the condition of carbon dioxide storage.