What Does
Yield Point Mean?
Yield point is generally defined as the elastic limit at which a material will lose its elasticity and deform permanently. For drilling fluids, yield point refers to the resistance of initial flow of the fluid or in other words, the stress required to start the movement of the fluid. It is a parameter of the Bingham plastic model.
The forces of attraction between the colloidal particles in the drilling fluid will prevent the fluid from flowing until the required stress is applied.
Trenchlesspedia Explains Yield Point
In the Bingham plastic model yield point is the shear stress extrapolated to a shear rate of zero. It is calculated from the 300-600 rounds per minute (rpm) viscometer dial readings by negating the plastic viscosity from the 300 rpm dial reading. Yield point gives an indication of the ability of the drilling mud to lift or remove the cuttings out of the annulus.
A drilling fluid with higher yield point will carry cuttings better than that with lower yield point.