2. Basic Calculations

Table of Content

1. Volumes and Strokes
2. Slug Calculations
3. Accumulator Capacity — Usable Volume Per Bottle
4. Bulk Density of Cuttings (Using Mud Balance)
5. Drill String Design (Limitations)
6. Ton-Mile (TM) Calculations
7. Cementing Calculations
8. Weighted Cement Calculations
9. Calculations for the Number of Sacks of Cement Required
10. Calculations for the Number of Feet to Be Cemented
11. Setting a Balanced Cement Plug
12. Differential Hydrostatic Pressure Between Cement in the Annulus and Mud Inside the Casing
13. Hydraulicing Casing
14. Depth of a Washout
15. Lost Returns — Loss of Overbalance
16. Stuck Pipe Calculations
17. Calculations Required for Spotting Pills
18. Pressure Required to Break Circulation

2.9 Calculations for the Number of Sacks of Cement Required

If the number of feet to be cemented is known, use the following:

Step 1 : Determine the following capacities:

a. Annular capacity, ft³/ft:

${\mathrm{Annular\; capacity,\; ft}}^3\text{/ft}=\frac{{\mathrm{Dh,\; in.}}^2-{\mathrm{Dp,\; in.}}^2}{183.35}$

b. Casing capacity, ft³/ft:

${\mathrm{Casing\; capacity,\; ft}}^3\text{/ft}=\frac{{\mathrm{ID,\; in.}}^2}{183.35}$

c. Casing capacity, bbl/ft:

$\mathrm{Casing\; capacity,\; bbl/ft}=\frac{{\mathrm{ID,\; in.}}^2}{1029.4}$

Step 2 : Determine the number of sacks of LEAD or FILLER cement required:

Sacks required = feet to be cemented × Annular capacity, ft³/ft × excess ÷ yield, ft³/sk LEAD cement

Step 3 : Determine the number of sacks of TAIL or NEAT cement required:

Sacks required annulus = feet to be cemented × annular capacity, ft³/ft × excess ÷ yield, ft³/sk TAIL cement

Sacks required casing = no. of feet between float collar & shoe × annular capacity, ft³/ft × excess ÷ yield, ft³/sk TAIL cement

Total Sacks of TAIL cement required:
Sacks = sacks required in annulus + sacks required in casing

Step 4 Determine the casing capacity down to the float collar:

Casing capacity, bbl = casing capacity, bbl/ft × feet of casing to the float collar

Step 5 Determine the number of strokes required to bump the plug:

Strokes = casing capacity, bbl ÷ pump output, bbl/stk

Example: Example: From the data listed below determine the following:
1. How many sacks of LEAD cement will be required?
2. How many sacks of TAIL cement will be required?
3. How many barrels of mud will be required to bump the plug?
4. How many strokes will be required to bump the top plug?
Data: Casing setting depth = 3000 ft
Hole size = 17-1/2 in.
Casing 54.5 lb/ft = 13-3/8 in.
Casing ID = 12.615 in.
Float collar (feet above shoe) = 44 ft
Pump (5-1/2 in. by 14 in. duplex @ 90% eff) 0.112 bbl/stk
Cement program:
LEAD cement (13.8 lb/gal) = 2000 ft slurry — yield = 1.59 ft3/sk
TAIL cement (15.8 lb/gal) = 1000 ft slurry — yield = 1.15 ft3/sk
Excess volume = 50%

Step 1 Determine the following capacities:

${\mathrm{Annular\; capacity,\; ft}}^3\text{/ft}=\frac{{17.5}^2-{13.375}^2}{183.35}$
Annular capacity = 0.6946 ft³/ft
${\mathrm{Casing\; capacity,\; ft}}^3\text{/ft}=\frac{{12.615}^2}{183.35}$
Casing capacity = 0.8679 ft³/ft
$\mathrm{Casing\; capacity,\; bbl/ft}=\frac{{12.615}^2}{1029.4}$
Casing capacity = 0.1545 bbl/ft

Step 2 Determine the number of sacks of LEAD or FILLER cement required:

Sacks required = 2000 ft × 0.6946 ft³/ft × 1.50 ÷ 1.59 ft³/sk
Sacks required = 1311

Step 3 Determine the number of sacks of TAIL or NEAT cement required:

Sacks required annulus = 1000 ft × 0.6946 ft³/ft × 1.50 ÷ 1.15 ft³/sk
Sacks required annulus = 906
Sacks required casing = 44 ft × 0.8679 ft³/ft ÷ 1.15 ft³/sk
Sacks required casing = 33
Total sacks of TAIL cement required:
Sacks = 906 + 33
Sacks = 939

Step 4 Determine the barrels of mud required to bump the top plug:

Casing capacity, bbl = (3000 ft − 44 ft) × 0.1545 bbl/ft
Casing capacity = 456.7 bbl

Step 5 Determine the number of strokes required to bump the top plug:

Strokes = 456.7 bbl ÷ 0.112 bbl/stk
Strokes = 4078

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