TABLE OF CONTENTS Breakover point between stripping and snubbing
Example: Use the following data to determine the breakover point:
| DATA: | Mud weight | = 12.5 ppg |
| Drill collars (6-1/4 in. ? 2-13/16 in.) | = 83 lb/ft | |
| Length of drill collars | = 276 ft | |
| Drill pipe | = 5.0 in. | |
| Drill pipe weight | = 19.5 lb/ft | |
| Shut-in casing pressure | = 2400 psi | |
| Buoyancy factor | = 0.8092 |
Determine the force, lb, created by wellbore pressure on 6-1/4 in. drill collars:
Force, lb = 6.25 2 0.7854 2400 psi
Force = 73,631lb
Determine the weight, lb, of the drill collars:
Wt, lb = 83 lb/ft 276 ft 0.8092
Wt, lb = 18,537 lb
Additional weight required from drill pipe:
Drill pipe weight, lb = 73,631 lb ? 18,537 lb
Drill pipe weight, lb = 55,094 lb
Length of drill pipe required to reach breakover point:
Drill pipe length, ft = 55,094 lb (19.5 lb/ft 0.8092)
Drill pipe length, ft = 3492 ft
Length of drill string required to reach breakover point:
Drill string length, ft = 276 ft + 3492 ft
Drill string length = 3768 ft
Minimum surface pressure before stripping is possible
Example: Drill collars 8.0 in. OD 3.0 in. ID = 147 lb/ft
Length of one stand = 92 ft
Minimum surface pressure, psi = (147 lb/ft 92 ft) ...
