Downhole Vibration

Causes of Downhole Vibrations

Types of Vibration	Causes
Bit Bounce	Bit/Formation Interaction Multilobe Pattern of roller cone bits WOB Variation Mud Pressure Fluctuation Coupling
Slip Stick	Bit/Formation Interaction High WOB/Low RPM Friction between the Drillstring/BHA and Hole Wall High Wellbore Tortuosity Coupling
Bit/BHA Whirl and Bending	Mass Imbalance Lack of Axial Symmetry Component Misalignment Lateral Deflection Steerable Motor BHA/Drillstring-Wellbore Interaction Bit/Formation Interaction Uneven Vertical Loading on Bit Face Imbalanced Cutter Forces High RPM/Low WOB Rotation Off Bottom Reaming Formation Hardness/Formation Change Oversize Hole Coupling

Eliminating Vibration

Types of Elimination	Causes
Bit Whirl	Increase WOB Decrease RPM
Slip-Stick	Decrease WOB Increase RPM Increase mud lubricity

Bit Whirl – the motion a bit makes when it does not rotate around its center, but in a spiral motion. This phenomenon usually occurs in softer formations and results in an oversize hole and excessive bit wear.

Slip Stick – A destructive vibration or oscillation caused by one of two things: bit or BHA. Slip Stick occurs when the bit bites into formation and, momentarily, sufficient torque is lacking to shear the formation. Thus, the bit “stops” while the torsional energy in the drill string builds up. Once enough energy is built up, the bit breaks free at rotational speeds much higher than normal resulting in bit failure/damage, BHA failure and lost time.

Coupling – Bending of the drill string coupled with WOB. Linear coupling is easy to visualize by taking a piece of paper, giving it a slight curve, and then pressing axially on the ends. The paper responds by additional bending in the plane of the initial curvature.

Bit Bounce – a downhole vibration caused mostly by bit/formation interaction. Bit bounce can occur when a bit cannot get a sufficient “bite” into formation to produce a smooth drilling action but actually bounces off the bottom of the hole.

	Identifying Vibration	Slip Stick	BHA Whirl	Bit Whirl	Bounce
	Real Tme
	Torque Fluctuation
	Torque Cyclicity
	MWD Shocks
	Torque
	High Frequency Downhole
	Lateral Torsional Vibration
	ROP
	WOB Fluctuation
	Surface Vibration
	Post Run
	Connection Over-Torque or Back-Off
	Twist-Off/Washout
	Cutter Impact Damage
	Over-Gauge Hole
	Tool Joint Wear
	Stabilizer Damage

Eliminating Vibration
Increase Weight on bit	to	Decrease Bit-Whirl
Decrease Weight on Bit	to	Decrease Slip-Stick
Increase Rotary Speed	to	Decrease Slip-Stick
Decrease Rotary Speed	to	Decrease Bit Whirl
Increase Mud Lubricity	to	Decrease Slip-Stick