Drilling Ahead

World Oilfield Forum

Plastic Viscosity (PV) is the resistance of fluid to flow. 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 plastic viscosity 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 Bartie, 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 without mud weight change, 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 plastic 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.

Reference: The Plastic Viscosity topic at drilling mud blog.

Views: 9486

Tags: Plastic, Viscosity, drilling, mud

Comment by Drilling Ahead on December 10, 2010 at 5:08am

Thank you Rachain-this is a very good blog and much of what you have shared concerning drilling fluids should be read and studied by derrickhands responsible for maintaining the drilling fluid.

As a derrickman myself reading a daily mud report I have always simplified things in my mind as Plastic Viscosity(PV)  is viscosity caused by solids in the mud -Yeild Point(YP) as viscosity produced by chemicals in the mud.

  I would also like to see more written on Water Loss , Dispersants and Gel Strengths also more on dispersing and "flipping" or when the YP and PV "flip"

 

Derrickmen with a good basic understanding of reading a mud report are a very valuable asset to any operation. Mud on most rigs is checked only once in each 24 hour peroid  by a mud man-and during that 24 hr peroid many things can change quickly and a good derrickman with a good understanding can remedy many problems as they occur...some tricks I have learned include when dispersing mud-after checking mud wt I can leave mud in the scales for 30 minutes or so...then come back and empty it-if it does not pour freely from the scales then it is need of more dispersant...also you can watch mud in your pits as it stirs and if the mud "rides over the top, like waves in the ocean" it is well dispersed...other tricks I have developed include looking at the size of "Dispersant rings" in the drilling mud...larger rings indicate a higher funnel viscosity...smaller tight circles of dispersants in the mud indicate a lower viscosity....there are many "Tricks" a derrickman can learn just by watching his mud...

 

Also looking forward to more information of the effects of PH- how most dispersants require a PH of around 11+ (Caustic Soda) to actually work and how dispersants lower the PV because they break up the solids in the mud...then it could be explained that when mud comes back thick because of gas(Flocking)-Lime is added and why. But when adding the lime-dispersants also have to be added to keep the mud thin while while the lime precipitates the gas as a solid...Also...if thick mud with a low ph needs to be quickly thinned because of anyhydrite or gypsum there  is a certain powerful dispersant(still trying to recall the name of this dispersant-I have been away to long) that can be added and works without high PH....

 

Also polymers when drilling shales and Aluminum Sterate as a defoamer...so much could be written


 An entire blog on drilling fluid basics in terms that derrickhands could understand has always been a blog that I have wanted to write, but I do not have the complete knowledge to do so.

Great job my friend- you are a credit to Drilling Ahead and I appreciate all the information that you share so freely here!

Comment by Rachain Jetjongjit on December 10, 2010 at 10:20pm

I will keep update my blog.

Thanks for reading my blog: )

Comment by Red Zone Co-Man on January 29, 2011 at 9:36am
...i too...would like like to see this topic "talked" more...very good points of interest curtis...

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