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

2.12 Differential Hydrostatic Pressure Between Cement in the Annulus and Mud Inside the Casing

1. Determine the hydrostatic pressure exerted by the cement and any mud remaining in the annulus.
2. Determine the hydrostatic pressure exerted by the mud and cement remaining in the casing.
3. Determine the differential pressure.

Example:
9-5/8 in. casing — 43.5 lb/ft in 12-1/4 in.
hole: Well depth = 8000 ft
Cementing program:
LEAD slurry 2000 ft = 13.8 lb/gal
TAIL slurry 1000 ft = 15.8 lb/gal
Mud weight = 10.0 lb/gal
Float collar (No. of feet above shoe) = 44 ft

Determine the total hydrostatic pressure of cement and mud in the annulus

a. Hydrostatic pressure of mud in annulus:

HP, psi = 10.0 lb/gal × 0.052 × 5000 ft
HP = 2600 psi

b. Hydrostatic pressure of LEAD cement:

HP, psi = 13.8 lb/gal × 0.052 × 2000 ft
HP = 1435 psi

c. Hydrostatic pressure of TAIL cement:

HP, psi = 15.8 lb/gal × 0.052 × 1000 ft
HP = 822 psi

d. Total hydrostatic pressure in annulus:

psi = 2600 psi + 1435 psi + 822 psi
psi = 4857

Determine the total pressure inside the casing

a. Pressure exerted by the mud:

HP, psi = 10.0 lb/gal × 0.052 × (8000 ft − 44 ft)
HP = 4137 psi

b. Pressure exerted by the cement:

HP, psi = 15.8 lb/gal × 0.052 × 44 ft
HP = 36 psi

c. Total pressure inside the casing:

psi = 4137 psi + 36 psi
psi = 4173

Differential pressure

PD = 4857 psi — 4173 psi
PD = 684 psi

⬆ Table of Content