Weighted muds are the ones that contain weighting materials. These mud systems are usually used for drilling at deeper depths because of increasing formation pressures. The typical composition of weighted clay/water mud is active clay, and inert solids like barite are used for enhancing the mud weight. As mentioned earlier, the mud arriving at the surface from the bottom while drilling is in progress contains active and inactive drilled solids. Hence, the low gravity solids must be removed first, using a screen, because their disintegration reduces the particle size to less than that of barite or in the similar range. This may cause a loss of costly barite if the mud is subjected to solids control. Once the larger particles are removed the mud must be passed through mud cleaner, where the hydrocyclones are used in series with screens. This system works best for muds with density less than 15.0 lbm/gal.

Since the mud is weighted, barite is assumed to be present in the system.

  1. Based on returns mud weight 16ppg, solids volume fraction 0.35 and CEC values:
  2. Low gravity solids fraction is 0.1245;
  3. Clay fraction is 0.20261;
  4. Drilled solids fraction is 0.0983;
  5. Barite fraction is 0.2255
  6. Amount of bentonite content in the system is 23.79 lbm/bbl
  • Present viscosity is 26 cp. The ret recommended range is from 11.15 cp to 26.31 cp. Your present viscosity is OK. Do not change by at least 0 cp.
  1. Present Yield Point is 9 lb/l00 ft2. The recommended range is 4.20 to 18.25 lb/100 ft2. Decide freely on this one.
  2. Contaminant hydrogen-sulfids and contaminating ion SULFIDE is present in 98.65 mg/L amount. To remove use:
  3. ZINC BASIC CARBONATB in 0.1213 lbm/bbl concentration.
  4. None in none lbm/bbl concentration.

Since the mud is weighted, the best treatment recommended is screening, forced settling, using Mud cleaners, and using Decanting centrifuge. Also for fine sand the particles size range between 20 and 190 microns. Hence it is advisable to primarily use Mud Cleaner. Equipment-wise recommendation:

Shale Shaker

For fine sand you may use Shale Shakers. Use B80 or S50 mesh, B100 or S60 mesh or B120 mesh with Shale shakers. Usually the maximum recommended flow rates for these mesh sizes for mud weight of 16 ppg are 711.82 GPM. 521.72 GPM and 255 GPM respectively.(Dual deck shale shaker are recommended)

Sand Trap

For fine sand Traps are important. For fine sand the settling rate of particles is roughly 0.066 to 5 feet per minute in 68 deg F water. Check the sand-trap for dumping accordingly. Do not dump completely however.


There is gas in the system, so line up Degasser. The Yield Point of the mud is less than 10 lb/100 sq. ft., hence the role of Degasser is less significant as the Shale-shaker will be able to handle the gas alone. Degassification is essential before fluid enters hydrocyclones.


The system is weighted, so using Desander is risky. Since cuttings type is fine sand you should never use it. If using Desander then use -none inch minimum -none nos. or -none inch minimum -none number of Hydrocyclones for 850 GPM of the feeder pump. (Round-off number of cyclones to next higher whole number).


The system is weighted, so avoid. using Desilters.

Mud Cleaner

Return fluid contains FINE SAND, SO Use Mud cleaner. Use Bl20 mesh or B200 mesh. For FINE SAND use 4 inch or 6 inch HydrocyClones and use minimum 17 nos. or 10 nos. respectively for 850 GPM of the feeder pump flow. (Round&off nos. to next whole number). Maintain the dilution water flow rate around 19.50 gallons Per hour.

Decanting Centrifuge

Mud type is weighted, and cutting type is FINE SAND, hence use of Decanting Centrifuge is very significant. Reclaim barite from underflow.


  1. Advisable to agitate the mud in suction tanks of Mud cleaner. No agitation in Sand trap.
  2. If you wish you to carry out calculations regarding Centrifuge Analysis please choose Calculations from main option.
  3. If any answer is prefixed by ‘-none’ then that part is not applicable for this case.


  1. Type of the mud is weighted;
  2. Type of cuttings in returns FINE SAND;
  3. Total solids fraction in the mud 0.35;
  4. Original Density of the mud 13 PW;
  5. Density of the Return mud 16 ppg;
  6. Density of water 8.33 ppg;
  7. Viscosity of Return mud 26 cp;
  8. Yield point of Return mud 9 lb/lab sq. ‘ft;
  9. The return flow rate is 900 gal/min;
  10. Feeder pump flow rate 850 gallon;
  11. Hydrocyclone slurry ejection rate 1 qts./30 sets;
  12. Drilled solids type BYDRCYZN SULFIDE;
  13. Cation Exchange Capacity of mud 9 meq/loO mu;
  14. Cation Exchange Capacity of bentonite 91 meq/100 mL;
  15. Cation Exchange Capacity of drilled solids 11 meq/100;
  16. Drilled solids major content FINE SAND;
  17. Major contaminant in mud HYDROGHN SULFIDE;
  18. Contaminating ion SULFIDE;
  19. Contaminating ion concentration 98.65 mg/mL.


Comments are closed.