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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