2.
n. [Drilling Fluids]
A parameter of the
Bingham plastic model. YP is the
yield stress extrapolated to a
shear rate of zero. (
Plastic viscosity, PV, is the other parameter of the Bingham-plastic model.) A Bingham
plastic fluid plots as a straight line on a shear rate (x-axis) versus
shear stress (y-axis) plot, in which YP is the zero-shear-rate intercept. (PV is the slope of the line.) YP is calculated from 300- and 600-rpm viscometer dial readings by subtracting PV from the 300-rpm dial reading. YP is used to evaluate the ability of a
mud to lift
cuttings out of the
annulus. A high YP implies a
non-Newtonian fluid, one that carries cuttings better than a fluid of similar density but lower YP. YP is lowered by adding
deflocculant to a
clay-based mud and increased by adding freshly
dispersed clay or a
flocculant, such as lime.