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Aparameter of the Bingham plastic model. PV is the slope of the shear stress/shear rate lineabove the yield point. PV represents the viscosity of a mud when extrapolated to infinite shearate on the basis of the mathematics of the Bingham model. (Yield point, YP, is the other

parameter of that model.) A low PV indicates that the mud is capable of drilling rapidly becausthe low viscosity of mud exiting at the bit. High PV is caused by a viscous base fluid and byexcess colloidal solids. To lower PV, a reduction in solids content can be achieved by dilution othe mud.

Khi PV th p th kh n ng khoan s t ng ln do nh t th p u m i khoan, PV cao gy nn nh t c a dung d ch v do cc h t r n t p trung. lm gi m PV, c n thi t gi m hm l ng ch t r n b ng cch pha long dung d ch. Gi tr ny ty thu c vo t tr ng v lo i dung d ch.

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YP c s d ng nh gi kh n ng a mn khoan ln theo kho ng khng vnh xuy n. A parameter of the Bingham plastic model. YP is the yield stress extrapolated to a shear rate of zero. (Plasticviscosity, PV, is the other parameter of the Bingham-plastic model.) A Binghamplastic fluid plots as a straig

line on a shear rate (x-axis) versus shear stress (y-axis) plot, in which YP is the zero-shear-rate intercept. (PV

the slope of the line.) YP is calculated from 300- and 600-rpm viscometer dial readings by subtracting PV fr

the 300-rpm dial reading. YP is used to evaluate the ability of a mud to liftcuttings out of the annulus. A higYP implies anon-Newtonian fluid, one that carries cuttings better than a fluid of similar density but lower Y

YP is lowered by adding deflocculantto aclay-based mud and increased by adding freshly dispersed clay orflocculant, such as lime.

Yield Point (YP) is resistance of initial flow of fluid or the stress required in order to move the fluid. You ca

simply say that the Yield Point (YP) is the attractive force among colloidal particles in drilling mud.

Practically, you can calculate the YP by this following formula.

Yield Point (YP) = Reading from a viscometer at 300 rpm Plastic Viscosity (PV)

A unit of YP is lb/100 ft2.

You can determine the Plastic Viscosity (PV) by this formula.

Plastic Viscosity (PV) = Reading at 600 rpm Reading at 300 rpm

For example, you have these values from the viscometer.

Reading at 600 rpm = 56

Reading at 300 rpm = 35

Plastic Viscosity (PV) = 56 35 = 21 CPYield Point (YP) = 35 21 = 14 lb/100 ft2.

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The YP indicates the ability of the drilling mud to carry cuttings to surface. Moreover, frictional pressure los

directly related to the YP. If you have higher YP, you will have high pressure loss while the drilling mud is

being circulated.

In water-based mud, the YP will be increased with following items;

High temperature the high temperature environment tends to increase the YP in the water base mud.

Contaminants such as carbon dioxide, salt, and anhydrite in the drilling fluids

Over treatment the drilling mud with lime or caustic soda

In oil-based mud, the causes of increasing in YP are listed below;

Drill solid the more drill solid you have, the more YP will be.

Treatment CO2 in the mud with lime (CaO) The lime (CaO) will chemically react with CO2 to form

Calcium Carbonate (CaCO3) which will increase the YP.

Low temperature in the oil base system, the low temperate will increase the viscosity and the YP. Pleas

keep in mind that this is opposite to the water base system.

Operational impacts of the YP are as follows;

Equivalent Circulating Density (ECD) The ECD typically increases when the YP increases.

Hole Cleaning - When you drill a large diameter hole, the YP in the drilling mud must be high in order to he

hole cleaning efficiency.

In order to get the most optimized valve of PV for each a particular drilling campaign. It is very difficult to show high of PV should be because it depends on several factors. Especially, if you are drilling in the new fie

you may need to start with general YP values, and then you will learn once you have experience in a particul

field.