Viscosity and friction pressure measurements of fiber suspensions

Fiber additions can improve the performance of well construction fluids, such as drilling fluids and completion fluids, by reducing fluid loss to permeable formations and improving hole cleaning. Fibers can also impart ductility to hardened cements, and improve its resistance to tensile crack propagation. Polyvinyl alcohol (PVA) fibers have been identified as an interesting addition for well cement slurries, but its impact on the rheological properties of the suspension has not been studied before. To this end, we study the viscosity and friction pressure of Newtonian and non-Newtonian fiber suspensions with increasing concentration of PVA fibers. We report viscosity measurements of the suspensions using an eight-speed viscometer equipped with a narrow gap and a wide gap Couette geometry, and fit measurements to constitutive viscosity models. Subsequently, friction pressure measurements for the fiber suspensions are acquired from a pipe flow loop and compared to predictions based on the viscosity characterization. We find a small viscosifying effect of increasing fiber concentrations. Friction pressure measurements for the non-Newtonian fiber suspension are in excellent agreement with theoretical predictions for generalized Reynolds numbers over three orders of magnitude.