Abstract: The present invention relates to a slurry containing water, amorphous silica panicles having a particle size less than 1 micron and silica flour with a particle size between 2-200 microns. In order to stablize the slurry, the slurry contains a polysaccharide. The invention further relates to a method for the production of a slurry containing water, amorphous silica having a particle size below 1 micron, and silica flour with a particle size between 2-200 microns, where a polysaccharide is added to a slurry of water and amorphous silica, whereafter the silica flour is mixed into the slurry of amorphous silica.

Abstract: The cement slurry of the present invention is gas tight, very low strength retrogression at high temperature, and substantially no tendency to settle or segregate. The cement slurry is made with a hydraulic cement, 5-85% microsilica based on the weight of the cement, 5-250% of a high density filler material based on the weight of the cement, 0-5% of a retarder (dry weight) based on the weight of the cement, 0-12% of a thinner (dry weight) based on the weight of the cement, 0-8% of a fluid loss additive (dry weight) based on the weight of the cement, 0-30% silica flour and/or silica sand based on the weight of the cement and water in such an amount that the cement slurry has a density between 1.95 and 2.40 g/cm.sup.3.

Abstract: Hydraulic cement slurry for use in cementation of oil wells containing hydraulic cement, 5-100% microsilica based on the weight of cement, 2-200% light weight aggregate with a real particle density between 0.1 and 1.5 g/cm.sup.3 based on the weight of the cement, 0-5% thinner (dry weight) based on the weight of the cement, 0-10% fluid loss additive (dry weight) based on the weight of the cement, and water in such an amount that the cement slurry has a density between 0.8 and 2.0 g/cm.sup.3.The cement slurry according to the present invention is gas tight and can thereby be used for cementation of oil well in fields having gas containing formations.