A theoretical comparison of cement slurry mixing energy in field and laboratory conditions

Abstract

The cementing of gas wells, especially those used for underground storage, requires precise understanding of cement properties. CO2 sequestration projects require very-long-term cement integrity, which means that the only way to test the properties of cements used in such applications is in the laboratory. It is common knowledge in the oil and gas industry that the properties of cement slurry obtained from laboratory and field mixing do not correlate very well. This is due to differences in the mixing equipment and procedures followed (API laboratory Waring blender vs. field mixer). The dissimilarity has triggered several research studies that have resulted in the mixing energy concept. This study investigates whether the mixing energy concept can be relied on to reconcile laboratory and field results. Results to date suggest that adequate reconciliation cannot be achieved using calculated mixing energies only, and the authors propose the use of shear rate instead. Additionally, this work evaluates the change in shear rates while pumping slurries through coiled tubing and pipes of different diameters, and the associated possible alteration of cement slurry properties. Two different techniques were simulated in the study, namely the API laboratory method and accepted field mixing, which highlighted the need for a review of laboratory mixing practices towards better prediction of field cement slurry properties.