3. Drilling Fluids

Table of Content

1. Increase Mud Weight
2. Dilution
3. Mixing Fluids of Different Densities
4. Oil Based Mud Calculations
5. Solids Analysis
6. Solids Fractions
7. Dilution of Mud System
8. Displacement - Barrels of Water/Slurry Required
9. Evaluation of Hydrocyclone
10. Evaluation of Centrifuge

3.10 Evaluation of Centrifuge

a. Underflow mud volume:

$\mathrm{QU}=\frac{[\mathrm{QM}\times (\mathrm{MW}-\mathrm{PO}\left)\right]-[\mathrm{QW}\times (\mathrm{PO}-\mathrm{PW}\left)\right]}{\mathrm{PU}-\mathrm{PO}}$

b. Fraction of old mud in Underflow:

$\mathrm{FU}=\frac{35-\mathrm{PU}}{35-\mathrm{MW}+\frac{\mathrm{QW}}{\mathrm{QM}}\times (35-\mathrm{PW})}$

c. Mass rate of clay:

$\mathrm{QC}=\frac{\mathrm{CC}\times [\mathrm{QM}-(\mathrm{QU}\times \mathrm{FU}\left)\right]}{42}$

d. Mass rate of additives:

$\mathrm{QD}=\frac{\mathrm{CD}\times [\mathrm{QM}-(\mathrm{QU}\times \mathrm{FU}\left)\right]}{42}$

e. Water flow rate into mixing pit:

$\mathrm{QP}=\frac{[\mathrm{QM}\times (35-\mathrm{MW}\left)\right]-[\mathrm{QU}\times (35-\mathrm{PU}\left)\right]-(0.6129\times \mathrm{QC})-(0.6129\times \mathrm{QD})}{35-\mathrm{PW}}$

f. Mass rate for API barite:

$\mathrm{QB}=(\mathrm{QM}-\mathrm{QU}-\mathrm{QP}-\frac{\mathrm{QC}}{21.7}-\frac{\mathrm{QD}}{21.7})\times 35$

where :
MW = mud density into centrifuge, ppg
PU = Underflow mud density, ppg
QM = mud volume into centrifuge, gal/m
PW = dilution water density, ppg
QW = dilution water volume, gal/mm
PO = overflow mud density, ppg
CD = additive content in mud, lb/bbl
CC = clay content in mud, lb/bbl
QU = Underflow mud volume, gal/mm
QC = mass rate of clay, lb/mm
FU = fraction of old mud in Underflow
QD = mass rate of additives, lb/mm
QB = mass rate of API barite, lb/mm
QP = water flow rate into mixing pit, gal/mm

Example:
Mud density into centrifuge (MW) = 16.2 ppg
Mud volume into centrifuge (QM) = 16.5 gal/mm
Dilution water density (PW) = 8.34 ppg
Dilution water volume (QW) = 10.5 gal/mm
Underfiow mud density (PU) = 23.4 ppg
Overflow mud density (P0) = 9.3 ppg
Clay content of mud (CC) = 22.5 lb/bbl
Additive content of mud (CD) = 6 lb/bbl

Determine:
Flow rate of Underflow
Volume fraction of old mud in the Underflow
Mass rate of clay into mixing pit
Mass rate of additives into mixing pit
Water flow rate into mixing pit
Mass rate of API barite into mixing pit

a. Underflow mud volume, gal/mm:

$\mathrm{QU}=\frac{[16.5\times (16.2-9.3\left)\right]-[10.5\times (9.3-8.34\left)\right]}{23.4-9.3}$
QU = 7.4 gal/mm

b. Volume fraction of old mud in the Underflow:

$\mathrm{FU}=\frac{35-23.4}{35-16.2+\frac{10.5}{16.5}\times (35-8.34)}$
$\mathrm{FU}=\frac{11.6}{18.8+(0.63636\times 26.66)}$
FU = 0.324%

c. Mass rate of clay into mixing pit, lb/mm:

$\mathrm{QC}=\frac{22.5\times [16.5-(7.4\times 0.324\left)\right]}{42}$
QC = 7.55 lb/min

d. Mass rate of additives:

$\mathrm{QD}=\frac{6\times [16.5-(7.4\times 0.324\left)\right]}{42}$
QD = 2.01 lb/mm

e. Water flow into mixing pit, gal/mm:

$\mathrm{QP}=\frac{[16.5\times (35-16.2\left)\right]-[7.4\times (35-23.4\left)\right]-(0.6129\times 7.55)-(0.6129\times 2)}{35-8.34}$
$\mathrm{QP}=\frac{310.2-85.84-4.627-1.226}{26.66}$
QP = 8.20 gal/mm

f. Mass rate for API barite:

$\mathrm{QB}=(\mathrm{16.5}-\mathrm{7.4}-\mathrm{8.20}-\frac{\mathrm{7.55}}{21.7}-\frac{\mathrm{2.01}}{21.7})\times 35$
QB = (16.5 − 7.4 − 8.20 − 0.348 − 0.0926) × 35
QB = 0.4594 × 35
QB = 16.079 lb/mm

⬆ Table of Content