Methods for predicting and adapting to high frequency torsional oscillation
An accurate and elegant model is provided to characterize HFTO. For Type 1 HFTO, the model can predict frequency of the HFTO based on the distance between a reference location on the bottomhole assembly (e g., the end of the drill bit) and a point 40% up the motor. In short BHA strings there is the fundamental frequency while in longer BHA the first harmonic is used. For Type 2 HFTO, the model can predict frequency of the HFTO based on distance between a reference location on the bottomhole assembly (e.g., the end of the drill bit) and the first slick contact point, which is optionally in the middle of a long flex joint.
1 . A method comprising:
measuring frequency of high frequency torsional oscillation (HFTO) in a bottomhole assembly (BHA);
using a model correlating frequency of the HFTO to distance relative to a reference location on the BHA to identify a position of a HFTO node in the BHA;
when the HFTO node is at a contact point in a curve of a drilled wellbore, reducing dogleg severity or sending a recommendation to reduce dogleg severity;
when the HFTO node is at a contact point in a lateral of the drilled wellbore, back reaming or sending a recommendation to back ream;
when the HFTO node is in a motor of the BHA, changing drilling parameters or sending a recommendation to change drilling parameters; and
after drilling, performing post event analysis and re-designing the BHA for a subsequent well, the redesigned BHA including at least one of different or additional wear band placement, replacement of heavy weight drill pipe with drill collars or vice versa, or changing a distance between components such that the HFTO node is located away from a sensitive component.
2 . The method of claim 1 , wherein:
the model includes a linear function that relates characteristic frequency for the HFTO to a length representing distance from the reference location on the BHA to a first significant node of the HFTO.
3 . The method of claim 1 , further comprising:
using the model to determine a type of the HFTO.
4 . The method of claim 3 ,
wherein the drilling parameters are dependent on determining a first type of HFTO that occurs above the motor.
5 . The method of claim 1 , wherein the model is correlated from experimental data representing different types of HFTO.
6 . The method of claim 1 , wherein the model is further based on an acoustic velocity.
7 . The method of claim 1 , wherein the model is further based on a constant.