What are the three types of drillstring vibration?
Drillstring vibrations can be divided into three types, or modes: axial, torsional, and lateral (Fig.
How do you stop a stick slip drilling?
The textbook response to mitigate stick slip is to first manually decrease the weight on the bit and then increase the rotary speed of the drill string. This process is repeated until stick slip is mitigated to a point where normal drilling operation can resume.
What is meant by torsional vibration?
Torsional vibration is angular vibration of an object—commonly a shaft along its axis of rotation. Also, the components transmitting the torque can generate non-smooth or alternating torques (e.g., elastic drive belts, worn gears, misaligned shafts).
What causes bit bounce?
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.
Under what conditions does stick slip occur?
Stick slip refers to the fast movement that occurs between two sides of a fault when the two sides of the fault become unstuck. The rock becomes distorted, or bent, but holds its position until the earthquake occurs.
What does slip stick mean?
1. slipstick – analog computer consisting of a handheld instrument used for rapid calculations; have been replaced by pocket calculators. slide rule. analog computer, analogue computer – a computer that represents information by variable quantities (e.g., positions or voltages)
What is lateral vibration?
A vibration in a helicopter in which the rotor moves back and forth in a lateral plane, or side-to-side direction. Lateral vibration is often caused by an unbalanced main rotor.
How is torsional vibration detected?
Torsional vibration can be measured using a torsiograph, encoder, or laser vibrometer. These devices will determine angular oscillation and/or angular velocity.
What is bit bounce?
Bit bounce is one of the forms of vibrations which can be faced during drilling operations. It happens when the bit loses contact with the formation. Bit bounce can cause severe damage to the drilling bit and the other BHA components like PDM motors and MWD tools.
What is sticking friction?
Sticking friction is when the work surface adheres to the surface of the tool rather than slides against it; it occurs when the friction stress is greater than the shear flow stress of the metal.
What is friction instability and how it is related to stick-slip process?
What is friction instability and how it is related to stick slip process? Ans: Friction instability generally occurs due to large difference in the value of static and kinetic coefficients of friction.
What is slip friction?
Definition of slip friction : a friction clutch permitting slip when excessive power is transmitted.
What causes the drillstring to vibrate?
The vibration of the drillstring occurs when the frequency of the applied force equals the natural vibration frequency of the drillstring. Rotation of the drillstring at its natural resonant frequency results in excessive and rapid wear of the drillstring and can result in fatigue failure.
How can I reduce the vibration of a drill string?
The main source of excitation of drillstring vibration is the rotation of the bit and the drillstring. It follows that downhole vibrations can be reduced by rotating the drillstring and bit at an RPM that is less tor more than the excitation RPM. Avoiding rotating the string at the natural resonant frequency of the drillstring
What are the different types of vibrations in drilling?
Three types of vibrations that occur during drilling are axial, torsional, and lateral. The destructive nature of each type is different. Tool joint failure, washouts, twist-offs, stabiliser and drill collar wear, BHA components, motor and MWD failure, damaged drill bit and Top-drive vibrations.
What is a drill string?
“A drillstring is an extremely slender structure with a ratio between length and diameter larger than in a human hair. Because the string has a smaller diameter than the borehole it is free to vibrate laterally. These lateral or bending vibrations are especially important in the lower part of the drillstring.