Cenosphere is a kind of sialic bead and tiny glass particle which is extracted from fly ash in thermal power plants, because it can float on the water, it is called cenosphere. Its chemical composition is SiO_{2 and Al2O3.}

Cenosphere is widely used as lightening admixture for oil-well cement, it can improve liquidity of cement slurry, delay weightlessness time of cement slurry, improve the anti-gas channeling ability of cement slurry, strengthen the stability of the cement slurry, and it can react with the cement hydration products and generated compounds have gelation property, and it can react with the cement hydration products and generated compounds have gelation property, conductivity coefficient and permeability of cement stone.