From Formulas and Calculations for Drilling, Production and Workover: All the Formulas You Need to Solve Drilling and Production Problems, Second Edition

Stripping/Snubbing Calculations

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) ...

Copyright Elsevier Science (USA) 2002 under license agreement with Books24x7

Products & Services
Snubbing Units
Snubbing units are used to perform well intervention on live or dead oil and gas wells. They are used to drive pipe into a well bore and overcome well pressure that is preventing conventional drill rig operations.
Drill Collars
Drill collars are a component of the drill string that makes up part of the bottom hole assembly (BHA). They are thicker-walled, heavier, and more rigid than drill pipes and are primarily used to weigh down the drill bit while dampening vibration and impact forces.
Drilling Rigs
Drilling rigs are machines that creates holes (boreholes) and/or shafts in the ground. They are equipped with deck engines or truck engines, hoists or lifts, compressors, pumps, and pipe-handling equipment.
Rotary Subs
Rotary subs are short sections of API certified threaded pipe used for crossover connections, tool handling, lifting, or other specialty application related to the making and breaking of the drill string.
Measurement While Drilling (MWD) Systems
Measurement while drilling (MWD) systems perform in-situ monitoring of the drill string and surrounding earth. MWD systems are used to perform directional drilling, horizontal drilling, and guide the drill bit through the path of least resistance.

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OVERVIEW This appendix presents the detailed MathCad solutions for the illustrative examples in Chapter 11. Illustrative Example No. 11.1: DTH MathCad Solution (USCS) F-2 Illustrative Example No.