MUD RHEOLOGY

Rheology is the study of

how matter deforms and flows 

VISCOSITY

Resistance to flow of a fluid

FUNNEL VISCOSITY

• 100 centipoise (cp)  =  1 poise
• Centipoise is the dimension used to express:
• Plastic viscosity
• Apparent viscosity
• Effective viscosity

• The dimensions of lb/100 sq ft are used for expressing:

1. -Yield point
2. - Initial gel
3. - 10-minute gel

 SHEAR  STRESS

• Internal force that resists flow
• System pressure loss (circulating pressure on the rig)
• Simulated by the dial reading on a V G meter

SHEAR RATE

The velocity at which one layer of fluid moves past another

• The bulk (average) velocity at which a fluid is moving
• Annular velocity in the circulating system is an example of bulk velocity
• Velocity is the RPM on a V G meter

Viscosity

Factors Influenced by Mud Rheology

• Hole cleaning
• Suspension of solids
• Hole stability
• Solids control
• Equivalent circulating densities
• Surge / swab pressures 

Measurement - Rotational Viscometer

Effect of Temperature & Pressure

• Temperature reduces viscosity
• Pressure increases viscosity
• High temperature

1. Breakdown of polymers
2. Gelation of solids
   
   Plastic Viscosity
   
   

   • Resistance to flow due to mechanical frictio
   • Affected by:

   1. Solids concentration
   2. Size and shape of the solids
   3. Viscosity of the fluid phase

    Plastic Viscosity Increased by:
   
   

   Hydratable Drill Solids

   
   

   Clays, shales

   
   

   Inert Drill Solids

   
   

   Sand, limestone, etc.

   
   

   Colloidal Matter

   
   

   Starch, CMC

    

   Particles breaking, thus increasing surface area and more friction

   Weight material to increase density

    Area Increase by Breaking of Solids
   

   

    Effect of Particle Size on Viscosity
   
   

   

   
   

   

    Plastic Viscosity Decreased by

   Removal of Solids
   Shale shaker
   Desanders, desilters, and centrifuges
   Lowering of gel strength allows larger particles to settle out
   Dilution of solids with water

   How Solids Affect Mud Viscosity

   

   
   

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