The Analysis Of The Drill Collar Thread Failure And Research Of Improving Method

The quality of the thread connections below the drill string has straight relation with the span of the usage of the GroupWare of the lower drill string, because the effect of the centralized stress of connecting threads and the effect of the alternating bending stress the accident of the lower drill string failure happened frequently, it cause huge economical loss. The people pay attention on raising the span of the usage of the thread of drill collars and preventing the accident of drill string thread failure. We started with the diagnosis of what cause drill collar thread failure and the studying the mechanism of the drill collar thread failure by using line elasticity finite element method, we have created the analysis model about the connecting thread of the drill string and estimated two types of threads of drilling strings NC46, developed STT button which are often used at present, we put forward four designing projects to develop the NC46 button and STT button differently using cutting main aspects of the pin button, cutting main aspects of the box button, changing the taper and superficial dig main aspects of the box thread. After calculating and analyzing, we found: Cutting main aspects of the pin button can reduce the weight born up by main aspects reduced to 85% without effect on the weight born by forepart. By changing the taper the level of the stress on the joggling main aspects can be reduced largely. The weight born by main aspects can be reduced to 98%. By cutting the root of main aspects of the box button in reason. The level of the stress centralized on the thread at the root can be reduced largely; section chopping is smoothed, and slack line come into being.To NC46 and STT, cutting the root of main aspects of the box button and changing the taper can avoid the thread failure effectively. As a result these tow improving method have value in practice. Except changing the structure of the thread, we bring forward other technical measure, which prevent the thread from being invalidated and provide gist in theory for the application in scene.