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

3.5 Solids Analysis

Basic solids analysis calculations

NOTE: Steps 1 — 4 are performed on high salt content muds. For low chloride muds begin with Step 5.

Step 1 Percent by volume saltwater (SW)

SW = (5.88 × 10^-8) × [(ppm Cl)^1.2 +1] × % by vol water

Step 2 Percent by volume suspended solids (SS)

SS = 100 − %by vol oil − % by vol SW

Step 3 Average specific gravity of saltwater (ASGsw)

ASGsw = (ppm Cl)^0.95 × (1.94 × 10-6) + 1

Step 4 Average specific gravity of solids (ASG)

$\text{ASG}=\frac{(12\times \mathrm{MW})-(\text{\% by vol SW}\times \text{ASGsw})-(0.84\times \text{\% by vol oil})}{\mathrm{SS}}$

Step 5 Average specific gravity of solids (ASG)

$\text{ASG}=\frac{(12\times \mathrm{MW})-\text{\% by vol water}-\text{\% by vol oil}}{\text{\% by vol solids}}$

Step 6 Percent by volume low gravity solids (LGS)

$\text{LGS}=\frac{\text{\% by vol solids}\times (4.2-\mathrm{ASG})}{1.6}$

Step 7 Percent by volume barite

Barite, % by vol = % by vol solids − % by vol LGS

Step 8 Pounds per barrel barite

Barite, lb/bbl = % by vol barite × 14.71

Step 9 Bentonite determination

If cation exchange capacity (CEC)/methytene blue test (MBT) of shale and mud are KNOWN:

a. Bentonite, lb/bbl:

Bentonite, lb/bbl = 1 ÷ (1 − (S ÷ 65)) × ((M − 9) × (S ÷ 65)) × % by vol LGS
OR
$\text{Bentonite, lb/bbl}=\frac{1}{1-\frac{S}{65}}\times \frac{(M-9)\times \frac{S}{65}}{}\times \text{\% by vol LGS}$

Where S = CEC of shale
M = CEC of mud

b. Bentonite, % by volume:

Bent, % by vol = bentonite, lb/bbl ÷ 9.1

If the cation exchange capacity (CEC)/methylene blue (MBT) of SHALE is UNKNOWN:

a. Bentonite, lb/bbl:

$\text{Bentonite, \% by volume}=\frac{M-\text{\% by volume LGS}}{8}$

where M = CEC of mud

b. Bentonite, lb/bbl:

Bentonite, lb/bbl = bentonite, % by vol × 9.1

Step 10 Drilled solids, % by volume

Drilled solids, % by vol = LGS, % by vol − bentonite, % by vol

Step 11 Drilled solids, lb/bbl

Drilled solids, lb/bbl = drilled solids, % by vol × 9.1

Example:
Mud weight = 16.0 ppg
Chlorides = 73,000 ppm
CEC of mud = 30 lb/bbl
CEC of shale = 7 lb/bbl
Retort Analysis:
water = 57.0% by volume
oil = 7.5% by volume
solids = 35.5% by volume

1. Percent by volume saltwater (SW)

SW = [(5.88 × 10^-8)(73,000)^1.2 + 1] × 57
SW = [(5.88 × 10^-8 × 685468.39) + 1] × 57
SW = (0.0403055 + 1) × 57
SW = 59.2974 percent by volume

2. Percent by volume suspended solids (SS)

SS = 100 − 7.5 − 59.2974
SS = 33.2026 percent by volume

3. Average specific gravity of saltwater (ASGsw)

ASGsw = [(73,000)^0.95 × (1.94 × 10^-6)] + 1
ASGsw = (41,701.984 × 1.94 × 10^-6) + 1
ASGsw = 0.0809018 + 1
ASGsw = 1.0809

4. Average specific gravity of solids (ASG)

$\text{ASG}=\frac{(12\times 16)-(59.2974\times 1.0809)-(0.84\times 7.5)}{33.2026}$
ASG = 3.6625

5. Average specific gravity of solids (ASG)

Because a high chloride example is being used, Step 5 is omitted.

6. Percent by volume low gravity solids (LGS)

$\text{LGS}=\frac{33.2026\times (4.2-3.6625)}{1.6}$
LGS = 11.154 percent by volume

7. Percent by volume barite

Barite, % by volume = 33.2026 − 11.154
Barite = 22.0486 % by volume

8. Barite, lb/bbl

Barite, lb/bbl = 22.0486 × 14.71
Barite = 324.3349 lb/bbl

9. Bentonite determination

a. Bentonite, lb/bbl

$\text{Bentonite, lb/bbl}=\frac{1}{1-\frac{7}{65}}\times \frac{(\mathrm{30}-9)\times \frac{7}{65}}{}\times \text{11.154}$
lb/bbl = 1.1206897 × 2.2615385 × 11.154
Bent = 28.26965 lb/bbl

b. Bentonite, % by volume

Bent, % by vol = 28.2696 ÷ 9.1
Bent = 3.10655% by vol

10. Drilled solids, percent by volume

Drilled solids, % by vol = 11.154 − 3.10655
Drilled solids = 8.047% by vol

11. Drilled solids, pounds per barrel

Drilled solids, lb/bbl = 8.047 × 9.1
Drilled solids = 73.2277 lb/bbl

⬆ Table of Content