Hydrated Portland cement undergoes a slow phase transition above 230°F in which the calcium silicate hydrate (CSH) gel phase reacts with calcium hydroxide and is transformed into crystalline dicalcium silicate hydrate (α-C2SH) which is much weaker. This process is known as strength retrogression. However, in the presence of excess silica it does not occur. Silica flour is therefore added to oilwell cement formulations for wells in which the bottomhole static temperature (BHST) is near or above 230°F to prevent it.
Our silica flours are ground to a particle size distribution similar to oilwell cement, which ensures optimum reactivity without generating excess viscosity.
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