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STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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DRILLING MUD HYDRAULICS<br />

Drilling Mud Hydraulics 829<br />

Rheological Classification of Drilling Fluids<br />

Experiments performed on various drilling muds have shown that the shear<br />

stress-shear rate characteristic can be represented by one of the functions<br />

schematically depicted in Figure 4-185. If the shear stress-shear rate diagram is<br />

a straight line passing through the origin of the coordinates, the drilling fluid<br />

is classified as a Newtonian fluid, otherwise it is considered to be non-Newtonian.<br />

The following equations can be used to describe the shear stress-shear rate<br />

relationship:<br />

Newtonian fluid<br />

= P(-z) dv<br />

(4-85)<br />

Shear Rate<br />

Figure 4-185. Shear stress-shear rate diagram. (a) Newtonian fluid. (b) Bingham<br />

plastic fluid. (c) Power law fluid. (d) Herschel-Buckley fluid.

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