Shears Plastic
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Shears Plastic
Plastic Viscosity (PV)
Plastic Viscosity (PV) is the resistance of fluid to flow. According to the Bingham plastic model, the PV is the slope of shear stress and shear rate. In the field, we can get the PV from a viscometer. Typically, the viscometer is utilized to measure shear rates at 600, 300, 200, 100, 6, and 3 revolutions per minute (rpm).
We can calculate the PV from the difference between the 600 and 300 rpm reading.
The formula looks like this: Plastic Viscosity (PV) = Reading at 600 rpm – Reading at 300 rpm
The unit of PV is Centi Poise (CP)
For example, you have these values from a viscometer.
Reading at 600 rpm = 56
Reading at 300 rpm = 35
Plastic Viscosity (PV) = 56 – 35 = 21 CP
Any increase in solid content in drilling mud as barite, drill solid, lost circulation material, etc will result in higher the plastic viscosity. In order to lower the PV, you must reduce the solid content that can be achieved by using solid control equipment and/or diluting drilling mud with base fluid. With increasing temperate while drilling deeper, the plastic viscosity of the drilling mud will decrease because the viscosity of the base fluid decreases.
Normally, the higher mud weight, the higher PV will be. However, if you have an increasing trend of PV with constant mud weight, it means that there is an increase in ultra-fine drill solid content in the mud system. Moreover, if you use oil base mud, please keep in mind that emulsified water in oil base drilling fluid will act like a solid, and it will increase the viscosity dramatically.
Several impacts of PV on drilling operation are as follows;
Equivalent Circulating Density (ECD) – The more PV you have, the higher ECD will be.
Surge and Swab Pressure – The PV has the same effect as ECD. If the PV increases, surge and swab pressure will increase.
Differential Sticking – A chance for differential sticking will increase, especially in water base mud, when the plastic viscosity increases because of increases in solid content.
Rate of Penetration (ROP) – The ROP will be directly affected by the plastic viscosity. If you drill a well with the high PV drilling mud, you will drill at slower ROP than low PV mud.
About the Author
If you are interested in drilling mud, please visit this blog, drilling mud. This is good resource to learn about basic knowledge of drilling mud.
Rachain J. is working in drilling operations and he would like to share basic knowledge about drilling formulas and drilling operations. For more information about drilling formulas, please read on his blog, drilling formulas. This is good resource to study about drilling formulas and calculations.
How do you pre-shear a plastic anchor?
I bought all-in-one anchor hanger with a cupped hook. I drilled a hole with a 5/16" drill bit but it said in soft walls (this is through panelling 1/8 inch thick) you might need to preshear the driving pin. How the heck do I do that?
This may be a situation where you have to ignore the directions - all too often they were originally prepared in another language and translated into English.
If you have a plastic anchor, drill a hole just slightly smaller than the anchor and tap into the hole. Screw the cup hook into the anchor and put some weight on it. If it holds you're done. If it fails to hold you'll need to address the situation differently - you just have to wade in and see what works. Consider it a learning experience; in many instances do-it-yourselfers consider instructions to be nothing more than suggestions.
Good luck with it!
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