During the past few decades, the technologies of the higher-shot densities, larger perforating guns and tubing-conveyed perforation (TCP) combined well testing have been used widely used for well completions. This results in a large increase of impact loads in the tubing during TCP. The safety of the tubing is directly related to the success of perforation combined well test,which is the key link in the oil and gas production. In this study, the influence factors of perforating impact load have firstly been analyzed. Also the dynamic response of tubing during TCP in three dimensions has been studied by numerical simulation. According to the computing results, the vulnerable parts of tubing during TCP have been found, where the axial impact load is the strongest and it is concluded that the axial shock absorber has the optimal installation position to achieve the best shock absorption effect, which is verified by the case. This study proposes a novel method for the safety analysis of the tubing, which has important significance to provide guidance for the design of field perforating operations and to improve security.

To address whirling- and vibration-induced failures in ultra-deep well drill strings caused by high slenderness ratios and complex loading conditions, this study establishes a nonlinear dynamic finite element model for a steel–titanium alloy composite drill string. The model is discretized with Euler–Bernoulli beam elements and solved using Newmark time integration combined with an iterative node-based spatial solution. Weight on bit, torque, wellbore–wall friction, impact/contact force, and equivalent drilling-fluid damping are considered. The model is used to evaluate how titanium alloy section size, length, wall thickness, and installation position affect whirling, lateral vibration, and torsional vibration. The results show that increasing drill-string diameter reduces the whirling range and lateral vibration intensity; when the diameter exceeds 149.23 mm, wall-impact frequency decreases markedly. Although the titanium alloy section exhibits approximately 60% higher local lateral vibration intensity than the steel section, the upper steel section experiences an approximately 18% reduction in lateral vibration. Installing the titanium alloy section in the middle of the string rather than near the bit reduces the overall lateral vibration intensity by approximately 30% and torsional vibration intensity by approximately 40%. Based on comparative sensitivity analysis, a titanium alloy section length of 1000–2000 m, diameter not less than 139.7 mm, and wall thickness not less than 12.7 mm are recommended for the simulated ultra-deep well conditions. These findings provide quantitative guidance for safer and more stable composite drill-string design.

This study investigates the influence of rotary speed on drill string whirl and vibration in 10,000 m ultra-deep wells through dynamic similarity experiments. A 1:4 geometrically scaled drill string–wellbore model was tested at 50–400 rpm under a weight on bit of 0.7 t and a torque of 100 N·m. Three laser rangefinders were used to reconstruct the drill string center trajectory and determine its translational and orbital responses. Forward whirl occurred at 50 and 100 rpm, a transition in whirl direction emerged at 350 rpm, and sustained backward whirl developed at 400 rpm, identifying 350–400 rpm as the critical transition interval. After zero-phase Butterworth filtering, the maximum center velocity increased from 0.241 to 0.579 m/s, while the maximum center acceleration rose from 3.014 to 15.813 m/s² and approached a plateau. The signed orbital angular velocity reversed from approximately +2975 rpm at low speeds to −2857 rpm at 400 rpm, whereas orbital angular acceleration exhibited a non-monotonic response. The measured vibration acceleration at 100 rpm was comparable in magnitude to field data from well SHY001-X3, supporting the physical plausibility of the observed trends. These results demonstrate that drill string vibration risk should be evaluated using multiple dynamic indicators. The experiments support qualitative identification of whirl transition and vibration risk intervals, although quantitative field prediction requires coupled models that account for fluid effects, structural dynamics, and contact interactions, together with calibration against full-scale measurements.

During the detachment of a polymer chain initially anchored at both ends to an impenetrable substrate, the loop structure degenerates into a tail structure as one end detaches, ultimately resulting in complete detachment from the substrate. Many previous studies on the dynamics of polymer detachment have focused on tail structures anchored to the substrate at one end, whereas the mechanisms and kinetics of loop detachment remain incompletely understood. To understand the dynamics by which the loop gradually detaches to form a tail, it is necessary to determine the detachment time of a single breakable link, which is modeled as a spring. Compared with the escape of a Brownian particle from the potential well of a spring, geometric constraints significantly reduce the conformational entropy of a loop structured polymer adsorbed on the hard-wall, thereby accelerating its detachment. In this work, we investigate the detachment rate of polymer loop structures anchored to an impenetrable hard-wall, derive an analytical expression for the mean detachment time of the breakable link, and examine how the detachment time depends on parameters such as chain length and anchor-point separation. We find that the detachment time is strongly sensitive to changes in chain length, whereas the anchor-point separation has little influence.