Transient Dynamics of Rubber Plug/Casing Nipple Interaction and Pressure Fluctuation Control

Summary In this study, to address the challenge of insufficient accuracy in the position monitoring of rubber plugs under complex well conditions due to spurious signal interference, we systematically investigate the generation mechanism and regulation law of pressure signals by establishing a transient dynamics model of the rubber plug/casing nipple system, combined with multiparameter coupling analysis and full-scale experimental verification. The results show that the interference magnitude plays a dominant role in signal amplitude, while the axis length ratio and displacing speed synergistically regulate the signal frequency. Within the speed range of 250–1,500 mm/s, the signal frequency exhibits a linear relationship with the displacing speed (error < 5%). High interference magnitude (>26 mm) causes abrupt changes in mechanical behavior, leading to the migration of strain and peak contact stress from the fifth cup to the first cup. Through normalized sensitivity analysis, the influence weight of each parameter is quantified. Moreover, a combined filtering/matching verification method is adopted, confirming that the errors of amplitude and frequency between simulation and experimental signals are approximately 9% and 5%, respectively, indicating high model reliability. Finally, parameter design criteria integrating safety, sealing performance, and signal distinguishability are established, with the recommendation that the interference magnitude does not exceed 26 mm and the axis length ratio is greater than 0.25. Additionally, an engineering implementation scheme for drillable/dissolvable casing nipples is proposed, providing a complete solution from theoretical design to engineering guidance for the real-time tracking of cementing rubber plugs.