Patent ID: 8002889

Claim:
A method of controlling the set of a well cementing slurry, comprising the addition of one or more silicates or silica comprising an alkali metal silicate of the general formula (SiO 2 )x(M 2 O) having a molar ratio falling in the range 1.68-3.37, wherein M is an alkali metal, and a set retarder to the well cementing slurry, characterised in that the amount of silicate or silica added to the slurry is sufficient to enhance the retarding effect of the set retarder under downhole conditions when compared to the retarding effect of the retarder alone, and is also sufficient to accelerate the set of the cement at temperatures below 80° C. when compared to the set of the cement containing the retarder wherein the addition of the silica or silicates allows the use of a lesser quantity of retarder than would be used alone for a given retarding effect at the bottom hole temperature above 90° C.