Leon Robinson

Exxon, retired

Low-gravity solids in a drilling fluid may be calculated from the equation below:


  • pf = density of filtrate, g/cm3
  • pB = density of barite, g/cm3
  • pLG = density of low-gravity solids, g/cm3
  • p0 = density of oil, g/cm3
  • Vs = volume percentage of suspended solids
  • V0 = volume percentage of oil
  • MW = mud weight, ppg

The density of the filtrate may be calculated from the equation:

pf = 1.0 + 6.45 x 10-7[NaCl] + 1.67 x 10-3[KCl] + 7.6 x 10-7[CaCl2] + 7.5 x 10-7[MgCl2]


  • NaCl] = concentration of NaCl in filtrate, mg/L
  • KCl] = concentration of KCl in filtrate, ppb
  • CaCl2] = concentration of CaCl2 in filtrate, mg/L
  • MgCl2] = concentration of MgCl2 in filtrate, mg/L.

The total suspended solids, Vs, may be calculated:

Vs = 100 - Vo _ ^f _ 10-6{[NaCl] + [CaCl] + [MgCl]} - 0.00286[KCl]

where Vw is the volume percentage of water.

Low-gravity solids calculated by the equation include bentonite. The quantity of drilled solids in the drilling fluid would be the difference between the volume percentage of (%vol) low-gravity solids and the %vol bentonite.

For freshwater drilling fluids, assuming that the density of low-gravity solids is 2.6 and the density of barite is 4.2, the equation becomes

A 12.0-ppg drilling fluid with 20% volume of solids would contain 12.5% volume of low-gravity solids:

The retort is normally used to determine the volume percent solids in a drilling fluid.

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