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

2.18 Pressure Required to Break Circulation

Pressure required to overcome the mud’s gel strength inside the drill string

Pgs = (y ÷ 300 ÷ d) × L

where Pgs = pressure required to break gel strength, psi
y = 10 mm gel strength of drilling fluid, lb/100 sq ft
d = inside diameter of drill pipe, in.
L = length of drill string, ft

Example: y = 10 lb/100 sq ft
d = 4.276 in. L= 12,000 ft

Pgs = (10 ÷ 300 ÷ 4.276) × 12,000 ft
Pgs = 0.007795 × 12,000 ft
Pgs = 93.5 psi

Therefore, approximately 94 psi would be required to break circulation.

Pressure required to overcome the mud’s gel strength in the annulus

Pgs = y ÷ [300 (Dh, in. − Dp, in.)] × L

where Pgs = pressure required to break gel strength, psi
L = length of drill string, ft
y = 10 mm. gel strength of drilling fluid, lb/100 sq ft
Dh = hole diameter, in.
Dp = pipe diameter, in.

Example: L = 12,000 ft
y = 10 lb/100 sq ft
Dh = 12-1/4 in.
Dp = 5.0 in.

Pgs = 10 ÷ [300 × (12.25 − 5.0)] × 12,000 ft
Pgs = 10 ÷ 2175 × 12,000 ft
Pgs = 55.2 psi

Therefore, approximately 55 psi would be required to break circulation.

⬆ Table of Content