水化过程中油井水泥/套管界面的性能与结构演变

Performance and Structure Evolutions of Interface between Oilwell Cement and Casing Steel during Hydration

油井水泥/套管界面对油气井的完整性起到关键作用。采用交流阻抗、界面剪切、显微硬度、微观形貌和物相分析技术研究了该界面在水化1天至7天的性能与结构演化规律。结果发现,电化学阻抗谱揭示水泥本体结构和界面结构逐渐达到稳定;界面结合强度和过渡区显微硬度显著增加;界面过渡区的水化程度远落后于水泥本体;该阶段界面过渡区的水化以C_2S水化、残余C_3S水化和C_3A水化产物之间的反应为主;界面结构演化表明水化使界面和结晶颗粒之间胶结更加紧密。升高养护压力提高了水化程度,改善了过渡区和界面的微观结构,从而提高界面性能。

The interface between oilwell cement and casing steel plays key role on the integrity of well. The methods of alternating current impedance, interracial shearing, micro hardness, microstructure and phase analysis were adapted to investigate on the performance and structure evolutions of the interface during hydration of oilwell cement from 1 day to 7 days. The electrochemical impedance spectrum discovers the ce- ment and the interface gradually become stability. The bonding strength of interface and micro hardness of transition region increase marked- ly. The hydration degree of transition region is much slower than the cement. The process includes hydration reactions of C2S, residual C3 S and products of C3 A in the transition region. The microstrncture indicates the cementation of crystalline particles as well as interface becomes stronger. Higher pressure enhances the hydration degree of cement, which improves the microstructures of interface and its transition zone. As a result,the interfacial performance is increased.