ABSTRACT
In this paper, the relationships between cement mixing and cement slurry quality are investigated. Laboratory mixing conditions, using a high shear mixer, are compared to field mixing conditions, including conventional jet mixer, recirculating type mixer and batch mixer.
All the mixing conditions can be reduced according to a single parameter, the specific mixing energy, that allows the comparison of laboratory and field mixing with confidence.
Typical cement slurry properties, like rheology, free water, fluid loss, thickening time and compressive strength, are measured as a function of the specific mixing energy. All these properties improve when the specific mixing energy increases. The efficiency of cement additives, like dispersants and fluid-loss agents, is also found to vary significantly with the energy. A tentative explanation is proposed through a mechanism of particle deflocculation and dissolution, leading to an increase in the available specific surface area.
Optimal slurry properties are obtained at specific energies close to that imparted by a laboratory mixing following the API Specification 10. The specific mixing energy parameter has been quantified for different pieces of typical field equipment and conditions, from mixers to centrifugal and high pressure positive displacement pumps, and pumping through orifices. Current standard field practices can represent as low as 10 %, of the specific energy imparted by the API procedure. Comparative measurements in the field have shown that the cement slurries mixed then in these conditions have considerably poorer properties than the same ones mixed in the laboratory.
As a consequence it is recommended to increase the field specific mixing energy to a value as close as possible to the API one. This provides optimum slurry quality and good similarity between laboratory and field conditions.
