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| Effect of nano-SiO2 sol on strength of cement with addition of silica sands under high temperature |
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WANG Chengwen1,2, ZHOU Wei2, CHEN Xin3, CHEN Zehua2, LI Yong4
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(1. Key Laboratory of Unconventional Oil & Gas Development (China University of Petroleum (East China)), Qingdao 266580, China;2.School of Petroleum Engineering in China University of Petroleum (East China), Qingdao 266580, China;3.Department of Civil and Environmental Engineering, University of Alberta, Edmonton T6G1H9, Canada;4.OMAX Oilfield Technology Company Limited, Chengdu 610041, China)
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| Abstract: |
| The effects of nano-SiO2 sols on the compressive strength of cement stone containing silica sands were investigated at 150 ℃ and 20.7 MPa, and the influencing mechanisms were analyzed, including the effects of the types of the hydration products formed by the nano-SiO2 sols, their morphology and microstructure on the strength of the cement. The results show that the effect of nano-SiO2 sol on the properties of cement stone is controlled by its dosage at high temperature. At a low dosage of 1%-2%, the nano-SiO2 particles are mainly absorbed onto the surface of cement particles, which can affect the cement hydration process and slightly reduce the strength of the cement stone. At a moderate dosage of 3%-8%, the number of growth sites of hydration products can be increased through the nucleation effect of the nano-SiO2 sol, thus, the microstructure of the hydration products are improved. Meanwhile, the nanoparticles can fill in the pores of the hydration products(with different size) in the forms of aggregates. Consequently, the density (due to pore filling) and strength of the cement stones are enhanced and maintained at high temperature. However, at a high dosage of the nano-SiO2 sol (>10%), large amount of the nano-SiO2 particles are absorbed onto the surface of cement particles, and a dense coating layer made of CSH gel can be formed due to the reaction of nano-SiO2 and Ca(OH)2. Meanwhile, larger aggregates are formed, which is unfavorable for their filling in the pores of cement slurry. Therefore, the microstructure and strength of the cement stones are undermined significantly. For field application, the dosage of the nano-SiO2 sol should be controlled strictly to maximize the nucleation and filling-in effects of the nano-SiO2 sols in order to improve the microstructure of the cement stone and increase its compressive strength. |
| Key words: high temperature cement nano-SiO2 sol oil-well cement silica particles compressive strength |
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