Study on Improving the Performance of Cement Slurry with Spherical Ultra-fine Mineral and the Application Thereof

Conventional ultra-fine minerals are used to improve the degree of density of cement powders. The use of these ultra-fine minerals, however, leads to increase in the amount of water required, and the results in enhancing the degree of density and compressive strength of the set cement are not as good as expected. To resolve these problems, a new spherical ultra-fine mineral was prepared using special ball milling technique. Improvement made to the packing of cement powders, rheology of cement slurry and compressive strength of set cement with the use of the spherical ultra-fine mineral was studied. It was found that use this new spherical ultra-fine mineral, close packing of cement powders can be realized, and the amount of water used to mix cement slurry remained almost unchanged. The mobility of the cement slurry reached 21 cm. The compressive strength of the set cement was increased by at least 15%. The percentage of poor volume in the set cement was less than 4%. These data show that the spherical ultra-fine mineral filled the pores in the set cement very well, and improved the pore structure of the set cement, remarkably enhancing the degree of density of the set cement. The cement slurry has density that is adjustable between 1.89 g/cm³ and 2.35 g/cm³, and has anti-channeling ability, low filtration rate and stable rheology. Good and obvious effects have been gained in using the spherical ultra-fine mineral on ultra-deep wells drilled in Chuanyu area.