The goal of this study is to identify the critical parameters for control of slurry quality during cementing operations.

It appears that the cement mixing process can be split into two different processes:

  • a mechanical one that includes the wetting of the powder, the deflocculation and the homogenisation of the resulting suspension, and

  • a physico-chemical one that includes during the first seconds the dissolution of some cement phases, the formation of supersaturated solutions and the precipitation of cement hydrates.

The validity of the mechanical process has been checked with inert suspensions of silica and barite as well as cement slurries of various reactivities and physical characteristics (particle size distribution). The physico-chemical process was investigated systematically first by looking at the precipitation kinetics, then inert suspensions and finally cement slurries.

The relevant mixing parameters were found to be the residence time of the slurry in the mixer and the rotational speed. Physical properties such as plastic viscosity and fluid loss are related to these two parameters via a single relation which is the mixing energy. Properties related to cement reactivities such as the yield value are affected very little by the rotational speed, but are highly dependent on the residence time in the mixer.

The influence of these two parameters on the response to different additives (dispersants, retarders, fluid-loss agents) is also presented. Finally, a comprehensive physico-chemical model of cement mixing is proposed.

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