Yifei Yan

The downhole engineering parameters measurement sub is a key component of the rotary steerable drilling system. To enable a measurement sub to serve reliably under downhole complex conditions, the structural parameters optimization of its key but weak elastic cell is systematically studied. First, the multiple relations among measurement sensitivities, structural stiffnesses, and strength during structural parameters design are summarized. Second, the selection of the structural parameters of the elastic cell is characterized as a multi-objective optimization model, which is solved using the non-dominated sorting genetic algorithm II (NSGA-II). Furthermore, the finite element method (FEM) is used to verify the measurement performance and static strength of the proposed structure. Finally, transient dynamics analysis is applied to investigate the dynamic strength of the designed structure. The results show that the proposed parameters optimization strategy can quickly obtain the database for the structural parameters design of an elastic cell. The static analysis results based on the FEM further verify the effectiveness of the proposed method. Transient dynamic analysis also reveals the relative rigor of the proposed methodology framework to some extent. This work has practical significance for improving the drilling efficiency and reducing drilling risks. In addition, this proposed methodology has good extensibility.

The tubing string exposed to transient flow may undergo nonlinear vibration due to sudden change in pressure in conveying gas. But, the drag on such structures often leads to fatigue failure of the strings that may significantly affect the vibrations through the combined effects of the first sections of gas injection, annulus pressure, the inclined structures, and the large transient flow component. In this paper, the nonlinear vibration analysis of tubing strings in underground gas storage using the multiscale wavelet transform has been studied. The vibration characteristics of strings in the steady gas injection process have been analyzed by numerical simulation. Results of the calculation model are compared to numerical ones reported previously, and the excellent agreement is obtained. The nonlinear vibration experiment of strings in the gas injection process has been studied for discussing the change rules of the string pressure, the wall velocity, and the amplitude in the gas injection process. The results show that the near‐injection port section and the inclined section of strings are the high‐incidence areas of nonlinear vibration of strings in underground gas storage. We also find that significant alteration of the dynamics is due to low‐frequency pressure fluctuation forces on the tubing strings.