Dynamic analysis of top-excited vibration assisted stuck release in vertical borehole with fatigue-like model

Stuck release operation is one of the largest contributions for the increase of non-productive time and consequently the increase of the well cost. Traditional stuck release operations including the jarring operations, changing flow rate, varying mud density are expensive and time-consuming. Recently, a surface vibration apparatus is introduced to the drilling industry and the stuck release time is highly reduced with this new apparatus. In this paper, a fatigue-like stuck release model is introduced to analyze the release mechanism of the stuck pipe excited by the vibration agitator. First, the drill string vibration behavior subjected to surface vibration agitator is analyzed. The natural frequencies and mode shapes are calculated analytically. The damping effect of drill mud is intensively investigated by assuming the laminar flow and Newtonian fluid. Second, the shear stress distribution on the stuck section is proposed analytically and verified with numerical examples. The influence of the shear parameter on the shear stress distribution is discussed and calibrated for certain configuration. Third, the stuck release behavior subjected to cyclic load is modeled with fatigue-like model, which is characterized by the formation release strength and stress factor. The stuck release process is progressive and three stuck release stages are identified. Finally, the top-excited drill string vibration is coupled with the release process on the stuck section. The top-excited vibration assisted stuck release system is modeled numerically. The stuck release processes operated at different resonant excitations are discussed. This paper casts light on the theoretical explanation of the vibration assisted stuck release mechanism and is important in optimizing the stuck release operations.