Testing String Dynamics When Jarring Stuck Packer

Abstract

The jar, as a standard down-hole tool in oil well testing string, is widely used in order to free the packer when stuck. But its efficiency is not satisfied. Based on stress wave propagation theory, testing string dynamic behavior is studied during jarring process. Model analysis is performed with practical string parameters to investigate impact force and impulse. It is found that the triggering force, which is usually called overpull, is the most important parameter. Both impact force and impulse would increase in response to overpull. Both collar string length and jar stroke length have little influence on the maximum dynamic force transmitted to packer, but they have large influence on impulse delivered to the packer: longer collar or stroke will produce higher impulse value. While the ratio of impact force to overpull is not a sound factor to evaluate jarring effect.