Abstract
An evaluation is presented of the practical usage of the Herschel-Bulkley viscosity model for drilling fluids. If data from automatic viscosity measurements exist, the parameters should be selected from relevant shear rate ranges to be applicable. To be able to be used properly, viscosity measurements must be measured with a sufficient accuracy. It is shown that a manual reading of standard viscometers may yield insufficient accuracy. It is also shown that the use of yield point/plastic viscosity (YP/PV) as measured using API or ISO standards normally provide inaccurate viscosity parameters. The use of the Herschel-Bulkley model using dimensionless shear rates is more suitable than the traditional way of writing this model when the scope is to compare different drilling fluids. This approach makes it also easier to make correlations with thermodynamic quantities like pressure and temperature or chemical or mineralogical compositions of the drilling fluid.
Highlights
The viscous properties of drilling fluids are measured for several purposes
When the measurements are conducted with automatic high accuracy instruments, as in the data used in Table 1, it is shown the importance of using data from the correct shear rate range in developing the viscosity model for the drilling fluid
The following conclusions can be drawn on the practical selection of Herschel-Bulkley parameters for describing drilling fluid viscosity
Summary
The viscous properties of drilling fluids are measured for several purposes. Viscous data valid at some shear rates are needed to forecast annular frictional pressure losses during drilling. These measurements values drilling industry equipment that are simple to use as no special trained operators may be available will be used to evaluate the applicability of using the Herschel-Bulkley parameters in hydraulic on site is needed. When the measurements are conducted with automatic high accuracy instruments, as in the data used, it is shown the importance of using data from the correct shear rate range in developing the viscosity model for the drilling fluid. When inaccuracies appear at the relevant shear rate data as being the case for the fluids shown, the average error for all the fluids seems to be relatively equal if the Herschel-Bulkley parameters are based on all the measurements or the measurements at the relevant shear rates. The viscosity is modelled with large errors in the relevant shear rate ranges for the annulus flow of drilling fluid.
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