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Effect of MgO expanding agent on early performance of oil well cement under three dimensional constraint
ZHU Hua-jun1, HUA Su-dong2, WU Qi-sheng1, ZHANG Chang-sen1, YANG Tao2
(1.School of Materials Engineering, Yancheng Institute of Technology, Yancheng 224051, China;2.College of Materials Science and Engineering, Nanjing University of Technology, Nanjing 210009, China)
Abstract:
In order to explore the effect of MgO expanding agent on the early performance of oil well cement under three-dimensional constraint, the early performance of oil well cement with the addition of MgO expanding agent and expansion mechanism of MgO were studied through the analysis of expansion rate, compressive strength, pore structure of cement and different methods of micro-analysis, such as XRD, DSC and SEM/EDS. The results show that under three-dimensional constraint the expansive force from MgO hydration can improve the compressive strength of oil well cement and porosity. The bonding strength and property for channeling prevention of cement sheath can also be enhanced. When the dosage of MgO expanding agent is 12%, the free-expansion rate of oil well cement curing at 80℃ for 1days and 7days are 0.034% and 0.072% respectively. Under three-dimensional constraint, compressive strength of cement with MgO curing at 80℃ for 3days and 7days were 27.5MPa and 31.6MPa, which increase by 41.8% and 49.1% compared with that of cement paste, and 9.6% and 16.2% compared with that of free-expansion cement paste, respectively. The porosity of cement with MgO under three-dimensional constraint, which is 22.7%, decreases by 30.8% compared with that of cement paste and 16.8% compared with that of free-expansion oil well cement, and the pore size tendes to be smaller (harmless pores). A Mg(OH)2diffraction peak exists in the XRD spectrum of oil well cement curing at 80℃ for 7days. Endotherm peak of Mg(OH)2appears at 365℃ in DSC curves. The compactness of cement structure and existence of Mg(OH)2crystal proved the reaction behavior that MgO forms Mg(OH)2.
Key words:  oil well cement  three-dimensional constraint  expanding agent  compactness