[目的]研究镁橄榄石掺加对减轻超临界CO2环境下油井水泥石的腐蚀渗透性能.[方法]以镁橄榄石粉为外掺料配制不同的油井水泥,分析温度为150℃,CO2总压为50 MPa条件下镁橄榄石水泥石的抗压强度,优选出镁橄榄石粉的最佳掺量;利用渗透率、热重分析(thermo gravimetric analysis,TGA)、X射线衍射(X-Ray diffraction,XRD)和扫描电子显微镜(scanning electron microscope,SEM)进行测试,评价镁橄榄石对油井水泥石抗CO2腐蚀性能的影响,分析镁橄榄石对油井水泥石抗CO2腐蚀的作用机制.[结果]镁橄榄石粉的掺入不会影响油井水泥的流动度,当镁橄榄石粉的质量分数为2％时,对比腐蚀前油井水泥石的,抗压强度提高35.47％,渗透率降低0.0104 mD;腐蚀28 d后,镁橄榄石水泥石的抗压强度为空白水泥石的193.71％,且仍高于腐蚀前.[结论]镁橄榄石是一种抗CO2腐蚀外加剂,能提升油井水泥的抗CO2腐蚀性能.
Effect of magnesium olivine on CO2 corrosion resistance of oil well cement
Objective Using CO2 injection to enhance oil and gas recovery is crucial in the carbon neutralization process.However,the pres-ence of supercritical CO2 in CCUS wells poses higher demands on the corrosion resistance of wellbore cement.Magnesium olivine,characterized by abundant sources and low cost,has been extensively studied in the field of construction cement.Yet,research on enhancing the resistance of wellbore cement to CO2 corrosion using magnesium olivine is relatively limited.In this study,conducted in the unique environment of CCUS wells,corrosion experiments will be carried out using supercritical CO2-saturated solutions.Various testing methods,including compressive strength,permeability,X-ray diffraction(XRD),thermo-gravimetric analysis(TGA),and scanning electron microscopy(SEM),will be employed to investigate the optimal dosage of magnesium olivine and its role in the micro-mechanism of corrosion resistance.This research aims to provide new theoretical and practical support for enhancing the resistance of wellbore cement to CO2 corrosion,contributing technological solutions towards achieving the"carbon neutrality and peak carbon"goals.Methods Utilizing layered olivine magnesium with an average particle size of 23 μm as an additive and cement slurry with a den-sity of 1.92 g/cm3,oil well cements with varying additive concentrations(0,0.5％,1％,1.5％,2％,2.5％and 3％)were formulated and cured following GB/T 19139-2012.Under conditions of 150 ℃ and 50 MPa CO2 pressure,compressive strength and permeability were tested for both blank samples and samples with magnesium olivine,aiming to identify the optimal dosage of magnesium olivine.Thermal gravimetric analysis(TGA),X-ray diffraction(XRD),and scanning electron microscopy(SEM)were employed to analyze the impact and mechanisms of magnesium olivine on the CO2 corrosion resistance performance of the cement slurry.Results and Discussion Formulated cement slurries with different concentrations(0,0.5％,1％,1.5％,2％,2.5％and 3％)of magnesium olivine.No significant impact on the density of oil well cement slurries was observed with the addition of magne-sium olivine.Maintained good fluidity of the slurry,indicating favorable rheological properties.Conducted testing under condi-tions of 150 ℃ and 50 MPa CO2 pressure.Magnesium olivine addition enhanced the compressive strength of cement both before and after corrosion,showing a 35.47％increase at 2％olivine concentration.The compressive strength initially increased and then decreased with higher olivine concentrations.Improved compressive strength attributed to the filling of micro-pores by mag-nesium olivine,enhancing cement density.Super-critical CO2 corrosion resulted in the formation of calcium carbonate(CaCO3)on the cement surface.The presence of magnesium olivine contributed to the reduction of Ca(OH)2 and the formation of dense CaCO3,enhancing the cement's resistance to CO2 corrosion.The addition of 2％magnesium olivine demonstrated the highest compressive strength before and after corrosion.Extended corrosion testing up to 28 days revealed a gradual decrease in com-pressive strength for both control and magnesium olivine-added cement.Magnesium olivine-added cement showed better long-term performance,with slower deterioration in compressive strength compared to the blank cement stone,which improved by 193.71％.The permeability of the cement was effectively reduced by magnesium olivine,indicating improved resistance to CO2 corrosion.XRD and TGA analysis confirmed the presence of magnesium olivine and the formation of carbonates(CaCO3)in the corroded cement.The addition of magnesium olivine reduced Ca(OH)2 content and influenced the types of carbonate phases formed during corrosion.SEM images illustrated the microstructural changes in cement,showing the impact of magnesium oliv-ine on the formation of corrosion products.Magnesium olivine addition resulted in a denser microstructure,reduced pore forma-tion,and better overall cement integrity.The observed improvements in cement performance were attributed to the role of magne-sium olivine in hindering the penetration of CO2,optimizing microstructure,and promoting the formation of stable carbonate phases.The optimal addition of 2％magnesium olivine was identified as providing the best balance between enhancing compres-sive strength and resisting CO2 corrosion in oil well cement.The study demonstrates the potential of magnesium olivine as an effective additive for improving the durability and performance of oil well cement in the context of supercritical CO2 corrosion.Conclusion The optimal addition of 2％magnesium olivine was identified as providing the best balance between enhancing com-pressive strength and resisting CO2corrosion in oil well cement.The study demonstrates the potential of magnesium olivine as an effective additive for improving the durability and performance of oil well cement in the context of supercritical CO2 corrosion.
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