Method and apparatus for determining drill string movement mode

An apparatus for determining destructive torque on a bottom hole assembly, comprising:

• a sensor measuring angular acceleration at at least one location along the drill string;
• means for comparing angular acceleration to a selected threshold operatively coupled to the sensor, the selected threshold related to a moment of inertia of selected components of the bottom hole assembly and a maximum torque applicable to threaded connections between the selected components;
• and
• means for generating a warning indication when the angular acceleration exceeds the selected threshold.

A method for determining an excessive torque condition in a wellbore, comprising:

• measuring a parameter related to torque on components of a drill string in the wellbore;
• determining a torque exerted by a drill bit coupled to a lower end of the bottom hole assembly;
• determining a torque needed to rotate a drill string coupled above the bottom hole assembly;
• determining a difference between a sum of the drill bit torque and the required drill string torque, and a torque determined from the measured parameter required to rotate the drill string from the earth's surface;
• and
• indicating the excessive torque condition when the difference exceeds a selected threshold.