Drillstring vibrations create crooked holes
Boreholes in hard formations sometimes deviate when the drillstring runs rough or the kelly bounces severely. This article explains how drillstring vibrations produce crooked holes in hard formations. It shows how to reduce dog-leg severity through vibration control. Dog-legs are known to produce cyclic bending-type fatigue loads in drill pipe and collars. Longitudinal and torsional vibrational stresses are additive to rotational bending and further reduce the life of drillstring tubulars. Vibration-induced dog-legs are therefore more damaging to drillstrings than other dog-leg producing mechanisms because total cyclic fatigue loading is the combined effect of bending stress reversal due to rotation plus vibrational stress variations. The vibration-induced dog-leg concept is based on overall vibration response of drillstrings, resultant dynamic displacements of roller cone drill bits, and corresponding dynamic forces between bit and formation. The concept explains how dynamic forces generated by roller cone rock bits might produce helical bore holes in hard homogeneous formations. Dog-legs in hard formations may be due in part to drillstring vibrations. The wellbore deviation concept relates only to roller cone rock bits and is based on dynamically reorienting three-lobed formation pattern hammered out by bottomhole assembly resonance. Analytical studies are needed to determine the effect of bit force impact point location on chip formation and rock removal. Field studies of various bottom hole assemblies operating at critical rotary speeds coupled with directional surveys are needed to test the validity of this theory.
- Research Organization:
- Norton Drilling Systems, Houston
- OSTI ID:
- 6886490
- Journal Information:
- Oil Gas J.; (United States), Journal Name: Oil Gas J.; (United States) Vol. 82:2; ISSN OIGJA
- Country of Publication:
- United States
- Language:
- English
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Production
& Processing
BENDING
BOREHOLES
CAVITIES
CONES
DIMENSIONS
DIRECTIONAL DRILLING
DRILL BITS
DRILL PIPES
DRILLING
DRILLING EQUIPMENT
DYNAMICS
EQUIPMENT
FATIGUE
FORMATION DAMAGE
MECHANICAL PROPERTIES
MECHANICAL VIBRATIONS
MECHANICS
MOTION
ORIENTATION
PIPES
ROCK DRILLING
ROTATION
STRESSES
TORSION
VELOCITY
WELL DRILLING