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 |