Friction Loss of Fracturing Fluids

Abstract

Introduction For many years thickened fluids have been used in fracturing work. These fluids have included heavy oils, gels, and emulsions. It has long been recognized that it would be desirable to know the pressure losses due to friction while pumping, in order that the formation injection pressure could be known. Heretofore, all attempts to calculate pressure drop of emulsions and gels by standard engineering formulas have resulted in failure. The reason for this is that the apparent viscosity of gels and emulsions falls off sharply with an increase in shear rate [pumping rate], so that calculations based on laboratory viscosities usually give unrealistically high friction losses. The relationship between shear rate and viscosity has been thoroughly investigated in this paper. The gels and emulsions used in oil well fracturing were found to fall into a general class of fluids known as pseudoplastics. The name is derived from the property of these fluids to exhibit plastic flow at low rates of shear, yet behave as low-viscosity liquids at high rates of flow. These gels and emulsions will be referred to as pseudoplastics in this paper. General Correlation The pseudoplastic properties of these gels and emulsions can be characterized in the laboratory by a log-log plot of measured viscosity vs. shear rate. In this case, measured viscosity is that obtained on the Brookfield viscometer, and shear rate is represented by spindle rpm. This data is shown plotted in Graph 1 and in Table 1.