
Yield Point
 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 Binghamplastic model.) A Bingham plastic fluid plots as a straight line on a shear rate (xaxis) versus shear stress (yaxis) plot, in which YP is the zeroshearrate intercept. (PV is the slope of the line.) YP is calculated from 300 and 600rpm viscometer dial readings by subtracting PV from the 300rpm dial reading. YP is used to evaluate the ability of a mud to lift cuttings out of the annulus. A high YP implies a nonNewtonian fluid, one that carries cuttings better than a fluid of similar density but lower YP. YP is lowered by adding deflocculant to a claybased mud and increased by adding freshly dispersed clay or a flocculant, such as lime.
 apparent viscosity
 deflocculant
 deflocculated mud
 directindicating viscometer
 drill solids
 gelledup mud
 shear rate
 shear stress
 yield stress
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