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) ...


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.
Measurement While Drilling (MWD) Systems
Measurement while drilling (MWD) systems report wellbore position, drill bit performance, and drill string orientation to an operator to maximize drilling productivity. It is related to logging while drilling (LWD).
Drill Pipe
Drill pipe is hollow, thick-walled piping used on drilling rigs to transmit drilling fluid and torque through the wellbore to the drill bit.
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.
Horizontal Directional Drilling Machines (HDD)
Horizontal directional drilling (HDD) machines are steerable, trenchless drilling rigs for the installation of pipes, conduits, and cables underground.

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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.

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