Rheological Characterization of Suspension of Hollow Glass Beads

Summary Hollow glass spheres (beads) are widely used as density and rheological modifiers for various oil and gas process fluids, particularly cement. One of the primary uses is to achieve lightweight slurries with good mechanical properties of the set cement. This paper discusses a concentrated, yet pumpable, suspension of these spheres for offshore cementing applications. Providing the lightweight spheres in a liquid suspension eliminates the risks associated with dry blending these materials. The development of the liquid suspension of hollow beads enables on-the-fly mixing of cement slurries with desired density profiles. Currently, the beads are premixed in the cement powder before they are shipped to offshore locations, which could result in the segregation of the beads during delivery and storage, and limits operations to the predetermined density (concentration of beads) of the slurry. This paper presents the rheological behavior of the concentrated suspension (up to 60% vol/vol) of hollow glass spheres suspended in a dilute aqueous solution of bentonite and soda ash. In addition, an attachment to the viscometer (called Fann Yield Stress Adaptor or FYSA) was used to characterize the flow behavior. A rheological model was developed to highlight the bead/bead surface interactions as a major component controlling flow behavior. Four different variants of beads were studied. These were selected to represent a range in surface area per unit volume of beads. Increasing the concentration of beads or the bentonite in solution correlated to increased yield stress and fluid viscosity at operational shear rates. In addition, a Krieger-Dougherty-type relation captured well the effect of the bead concentration, with the maximum packing fraction of beads as a function of surface area per unit volume of the beads. Overall, the Herschel-Bulkley (HB) model best described the suspension rheology with the shear-thinning exponent in the range of ≈0.8 to 1.0. Surface area of the beads linearly correlated to the yield stress of the corresponding concentrated bead solution. Results of this study and the model developed can be used to develop variants of the system with minimal experimentation, thus significantly shortening the design time.