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.
Hollow-glass microspheres (beads) are widely used during oilwell cementing operations to produce lightweight cement slurries; this paper discusses a new method of blending hollow-glass beads into cement slurries by creating a storable liquid suspension of hollow-glass microspheres (liquid beads). This new method enables efficient delivery of lightweight cement slurries in offshore and remote locations by eliminating bulk-blending logistics. The concept of liquid beads is not new; however, earlier attempts to develop liquid beads or similar products generally failed to address the storability problem. The buoyancy force tends to lift the beads to the surface of the suspension, forming a gel or crust and causing the mixture to lose flowability within a relatively short period of time. A special chemical-additive package developed in this study significantly extends the storability of liquid beads. This paper compares the gelation time of different liquid-bead formulas and evaluates the performance of cement slurries prepared with liquid beads. Laboratory test data show that the chemical-additive package developed in this study can extend the storage time (shelf life) of liquid beads from a few hours to at least one month without reagitation at room temperature; the shelf life can be further extended to at least one year with regular reagitation of the mixture. Cement slurries prepared with dry-blended beads and those prepared with liquid beads exhibit similar performance in terms of laboratory test results, such as free fluid, fluid loss, thickening time, and hydration kinetics. The liquid-bead system developed can be produced with cement batch mixers for field use and remain stable in tote tanks for at least several months with regular recirculation. Liquid beads can be added to cement slurries through liquid-additive pumps during a cementing operation. A novel liquid-bead product that can be stored for extended periods of time without separation is presented here along with necessary laboratory testing, actual field applications, and field-application case histories using liquid beads to produce low-density cement slurries.
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. 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 often results in 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% v/v) of hollow glass spheres suspended in a dilute aqueous solution of bentonite and soda-ash. In addition, a patented attachment to the viscometer (called 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 being 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. 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 product with minimal experimentation, thus significantly shortening the development timeline.
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