Alpha-alumina(α-Al_2O_3) platelets were prepared via solid-state reaction using pseudo-boehmite as the starting material, while NH_4F and nano-SiO_2 were used as additives, and nitric acid was used as the binder. The...Alpha-alumina(α-Al_2O_3) platelets were prepared via solid-state reaction using pseudo-boehmite as the starting material, while NH_4F and nano-SiO_2 were used as additives, and nitric acid was used as the binder. The effect of these additives on properties of the alumina platelets was determined via scanning electron microscopy, X-ray diffraction, and measurements of the surface area and silicon content. A mechanism governing their role in the synthesis process was proposed. The results indicated that NH_4F could promote the formation of highly crystalline platelets. Addition of nano-SiO_2 could lead to increase in the diameter and reduction in the thickness of the platelets, and could also prevent their transformation to α-Al_2O_3. This addition weakened the effect of NH_4F because of the reaction of nano-SiO_2 with F-species and the formation of volatile SiF_4.展开更多
Strength retrogression of cement stone is one of the major challenges in oil well cementing under high temperatures.Nano-SiO_(2) exhibits the potential to mitigate this problem,but there is lack of reports about the r...Strength retrogression of cement stone is one of the major challenges in oil well cementing under high temperatures.Nano-SiO_(2) exhibits the potential to mitigate this problem,but there is lack of reports about the role of nano-SiO_(2) playing within cement stone under high temperatures.Therefore,in this study,we experimentally determined the effect of nano-SiO_(2) sol on the compressive strength of Class-G oil well cement stone cured under high temperature(150℃/35 MPa).Then we provided the explanations for the cement strength variation by analyzing the mineral compositions and microstructures of cement.The experimental results are summarized as follows:(1)The cement stone with 2%nano-SiO_(2) sol does not perform a strength reduction after cured for 5 days,and its XRD patterns indicate that low-dose nano-SiO_(2) sol will yield little effect on the cement hydration products;(2)While with a high dose,nano-SiO_(2) can react with calcium hydroxide,resulting in microstructure change of cement and the generation of a novel honeycomb calcium silicate hydrate gel(Ca/Si ratio is about 1.5);(3)Nano-SiO_(2) particles make the microstructure of cement stone more compact through impaction and filling into the pore among cement hydration products,which helps to prevent cement stone from strength retrogression under high temperatures.Generally,this study lays a theoretical foundation for the nano-SiO_(2) used as cement additive and sheds light on the design of high-temperature cement slurry system.展开更多
基金supported by the Technology Development(Commission) Project of SINOPEC Catalyst Co.Ltd(Grant No.14-05-01)
文摘Alpha-alumina(α-Al_2O_3) platelets were prepared via solid-state reaction using pseudo-boehmite as the starting material, while NH_4F and nano-SiO_2 were used as additives, and nitric acid was used as the binder. The effect of these additives on properties of the alumina platelets was determined via scanning electron microscopy, X-ray diffraction, and measurements of the surface area and silicon content. A mechanism governing their role in the synthesis process was proposed. The results indicated that NH_4F could promote the formation of highly crystalline platelets. Addition of nano-SiO_2 could lead to increase in the diameter and reduction in the thickness of the platelets, and could also prevent their transformation to α-Al_2O_3. This addition weakened the effect of NH_4F because of the reaction of nano-SiO_2 with F-species and the formation of volatile SiF_4.
基金Project supported by Joint Funds of the National Natural Science Foundation of China"Basic study on construction and control methods of safe and efficient wellbore working fluid in ultra-deep wells"(No.:U1762212)National Natural Science Foundation of China"Corrosion mechanism of oil well set cement under the cooperative action of carbon dioxide,sulfate and magnesium salt in storage of salt water layer of CCS"(No.:51704325)+1 种基金Natural Science Foundation of Shandong Province"Study on the regulation method and mechanism of high temperature and high density cement paste stabilization"(No.:ZR2017MEE056)Program for Changjiang Scholars and Innovative Research Team(IRT_14R58).
文摘Strength retrogression of cement stone is one of the major challenges in oil well cementing under high temperatures.Nano-SiO_(2) exhibits the potential to mitigate this problem,but there is lack of reports about the role of nano-SiO_(2) playing within cement stone under high temperatures.Therefore,in this study,we experimentally determined the effect of nano-SiO_(2) sol on the compressive strength of Class-G oil well cement stone cured under high temperature(150℃/35 MPa).Then we provided the explanations for the cement strength variation by analyzing the mineral compositions and microstructures of cement.The experimental results are summarized as follows:(1)The cement stone with 2%nano-SiO_(2) sol does not perform a strength reduction after cured for 5 days,and its XRD patterns indicate that low-dose nano-SiO_(2) sol will yield little effect on the cement hydration products;(2)While with a high dose,nano-SiO_(2) can react with calcium hydroxide,resulting in microstructure change of cement and the generation of a novel honeycomb calcium silicate hydrate gel(Ca/Si ratio is about 1.5);(3)Nano-SiO_(2) particles make the microstructure of cement stone more compact through impaction and filling into the pore among cement hydration products,which helps to prevent cement stone from strength retrogression under high temperatures.Generally,this study lays a theoretical foundation for the nano-SiO_(2) used as cement additive and sheds light on the design of high-temperature cement slurry system.
