Portland cement solutions for ultra-high temperature wellbore applications

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• 作者：Roderick B. Pernites ; Ashok K. Santra ; ^{ashok.santra@lubrizol.com" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Portland cement ; Strength retrogression ; Permeability ; Crystalline silica ; Silica fume
• 刊名：Cement and Concrete Composites
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：72
• 期：Complete
• 页码：89-103
• 全文大小：2814 K

文摘

Designing highly stable and low permeability high-strength oil well cement above 500 °F (>260 °C) is extremely difficult because the Portland cement undergoes strength retrogression starting at 230 °F (110 °C). Thus, fine crystalline silica stabilizer is required in the cement slurry design when cured until 400 °F (204.4 °C) to prevent this problem. However, the optimum particle size and the right practical dosage of silica in the cement slurry have not been clearly determined and studied for cement that will be subjected at such extremely high temperature (>500 °F), condition applicable for many ultra-deep geothermal and steam injection wells. Due to extreme heating conditions and tedious experimentation, there are only few published studies to date toward understanding the behavior of Portland cement used at that exceedingly high temperature; and thus, making the initial cement design highly challenging. Based on thorough experimental study, this paper presents new understanding and provides proper guidance to designing highly stable non-retrogressing and low steady permeability oil well cement for ultra-high temperature use. Moreover, this research carefully investigates the effect of the particle size of crystalline silica to the compressive strength, porosity and permeability of the cured cement. Finally, the substitution of crystalline silica with amorphous silica material in the ultra-high temperature cement is also exploited. Supplementary powder X-ray diffraction measurement identifies high temperature stable crystal phase Xonotlite (Ca₆Si₆O₁₇(OH)₂) in the silica-stabilized Portland cement. However, based from these current experimental results, it is observed that formation of Xonotlite crystal phase does not completely guarantee the longer term mechanical integrity of the cement sheath at ultra-high temperature, especially when the mixture contains amorphous-type silica in the blend.