Study On Corrosion Law And Anticorrosion Countermeasures Of Cementing Cement Stone In Acidic Environment

Lingshui deepwater gas field contains CO₂ and H₂S corrosive gas.Under the condition of high temperature and high pressure,the cementation performance of cementing cement stone is reduced and the compressive strength is lost under the erosion of acid medium,resulting in interlayer channeling,well wall collapse and other problems.The performance decline of cement stone provides a channel for the flow of acid medium,which further erodes the casing,seriously affects the production of oil and gas wells,and even leads to the scrapping of oil and gas wells,resulting in serious economic losses.Therefore,this paper tests the corrosion of cement stone used in Lingshui deepwater gas field,predicts the surface corrosion depth of cement stone,and puts forward anti-corrosion countermeasures.（1）Using the high temperature and high pressure reactor experimental system,the effects of CO₂and H₂S on the permeability,corrosion depth,micro morphology and compressive strength of cementing cement stone under the condition of high temperature and high pressure water humidity are tested and analyzed.The results show that after 30 days of corrosion,the maximum corrosion depth of section is 7.60mm and the minimum is 5.70mm;After 90 days,the maximum core permeability is 1.24md and the minimum is 0.28md.In addition,some cement stones are completely corroded;（2）The microscopic appearance analysis of cement stone after corrosion shows that the cement stone is relatively dense without obvious loose structure,and there are some particles with different particle sizes in all samples.EDS energy spectrum analysis is carried out for the particles in the corroded area and the non corroded area,and the main elements of the particles are Si or C;The components of corrosion products are calcium carbonate（containing different crystal forms）and silicon dioxide（containing different crystal forms）,or calcium silicate,and the content of calcium carbonate in some corrosion areas increases significantly;（3）The variation law of cement paste surface corrosion depth is simulated by using multi physical field coupling software COMSOL.The results show that the concentration of CO₂and H₂S,temperature,pressure and corrosion depth show linear changes;The grey correlation method is used to calculate the correlation degree between the factors affecting the corrosion depth of cement paste.The results show that the factor with the largest correlation degree is CO₂ concentration,followed by H₂S concentration,pressure and ambient temperature;（4）By optimizing the existing corrosion prediction models,a corrosion depth prediction model based on grey correlation method GM（1,1）is established according to the experimental results,and the corrosion depth of 1#,2#,3#,4#is predicted.Due to the great difference between cement stone components,the results show that the fitting degree of 4#core is high,and the relative residual error is 10.3%.The section corrosion prediction depths of 4#core after 120 days,150 days and 180 days are 8.72mm,11.33mm and 13.96mm。...