Help needed on drilling fluids

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mitko007
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Joined: Fri Apr 23, 2010 11:02 pm

Help needed on drilling fluids

Post by mitko007 »

Hi,
i have a question about drilling fluid rheology. Why do we use non-newtonian fluids instead of newtonian fluid?

If i got it correctly, the basic idea is that we aim at a lower viscosity at higher shear rates (in the drill pipe) and high viscosity in the annulus where the shear rate isn't that high (since the viscosity for the non newtonian fluids isn't shear rate dependent)


Is this correct and is there anything else that is important to know?

Thanks
arturo82
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Post by arturo82 »

First off we have to point the difference between newtonian and non newtonian fluids, which is the solids content

in a drilling mud, we need solids to increase density, like barite in example, instead of a newtonian fluid like water that has no yield point nor solids

we also need to have certain properties like a yield point and a plastic viscosity, these properties can be adjusted with solids added to the drill mud

remember the main functions of the drill mud
rcaenn
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Post by rcaenn »

You need a non-newtonian fluid (shear thinning, psuedoplastic) for hole cleaning and suspension. Those properties are best measured with the n &K paramters rather than plastic viscosity and yield point.

The viscosity for a Newtonian fluid is not shear rate dependent. A Newtonian fluid has constant viscosity no matter how fast it is moving, shear stress = (coefficient of viscosity)(shear rate). Real muds need two other terms added to Newton's formula, the shear rate is raised to a power (n) and a term is needed for the true yield stress of the mud.
arturo82
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Post by arturo82 »

the n parameter indicates the type of fluid, n=1 newtonian, n>0.5 plastic, n>0.5 pseudoplastic
k parameter indicates the solid content

a hole cleaning indicator is the Low Shear Rate Viscosity (LSRV), it should be something like this:

L6 or L3 > Hole diameter

a suspension indicator could be the drillcuts on surface, torque, drag and pump pressure
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