In high production gas wells, premium connections are subject to alternating loads and vibration excitation due to the change of fluid pressure exerted on the tubing string. The energy dissipation on the sealing surface of premium connections affects the sealing performance of premium connections. The present study proposes a new energy dissipation analysis method for the sealing performance of premium connections using a microslip shear layer mode, a novel technique to overcome and improve the limitations of existing analysis method of premium connections. In this paper, based on a microslip shear layer model, a vibration equilibrium equation of premium connection was established with the constraints of the taper of the sealing surface, the thread, and the torque shoulder. Then, the control equilibrium equations of the stick and microslip were derived, and the critical microslip tangential force and force–displacement hysteresis curves under different interface parameters were obtained by solving the equilibrium equations. The influence of different interface parameters on the energy dissipation of premium connection was discussed by using a standardized regression coefficient method. It was found that the friction coefficient influenced both the minimum and maximum microslip tangential forces, while the shear layer stiffness influenced only the minimum microslip tangential force. The greater the stiffness of the shear layer, the smaller the minimum microslip tangential force and the relative displacement of the contact surface, which made it easier to generate energy dissipation. The influence of the friction coefficient on energy dissipation was much greater than the stiffness of the shear layer. There was positive correlation between the friction coefficient and energy dissipation. While, there was a negative correlation between the stiffness of shear layer and energy dissipation. The results can provide a theoretical guide for micro sealing failure mechanism of premium connections under dynamic loads and expand the analysis method of metal seals.

In the process of high flow rate fracture and high gas production, the sealing performance of the premium connection decreases due to the dynamic load and vibration of downhole tubing strings, which may cause accidents. Existing static analysis methods cannot effectively explain this phenomenon. The main objective of this paper is to propose a novel analytical method for evaluating the sealing performance of a premium connection. In this paper, a dynamic model of sealing surfaces of the premium connection is established based on the vibration equation of elastic rod, and the hysteresis characteristics and energy dissipation mechanism of sealing surfaces are analyzed. Considering the influence of spherical radius, internal pressure, axial cyclic load amplitude, and modal vibration, a spherical-conical premium connection finite element model is established to analyze the influence laws of the connection’s energy dissipation and sealing performance. The results show that the sealing performance of the premium connection under dynamic load can be effectively analyzed by using energy dissipation theory compared with traditional static contact analysis. Compared with the vibration of the tubing string, the dynamic loads caused by the change of fluid pressure and flow rate in the tubing string have a significant influence on the connection’s sealing performance. When the internal pressure and axial cyclic loads are 80 MPa, 400 kN, or 60 MPa and 500 kN respectively, serious plastic deformation occurs in the thread and sealing surfaces, and the energy dissipation of the sealing surfaces increases significantly, which could lead to sealing failure.

Tubular string temperature and pressure are important parameters in string mechanics analysis. Thus, accurately calculating temperature and pressure in the injection process is fundamental for analyzing the tubular string mechanics of CO₂ injection wells. Based on the S-W equation of state and Vesovic models, we modeled the physical properties of CO₂. Then, based on the physical properties of CO₂, combined with the theory of heat transfer and three conservation laws, a temperature–pressure coupling model of a tubular string was established. Lastly, the temperature and pressure field distributions of the G66X1 well were determined using the alternating iteration method. According to a comparison of the established model and the actual data, the maximum error in predicting temperature was 4.1% and the maximum error in predicting pressure was 2.3%; thus, the model exhibits a high level of accuracy. In the final section, the model was used to study the influence of injection temperature on the tubular string temperature and pressure field distribution. Next, we studied the influence of the injection time, displacement, and pressure on the bottom hole temperature. This study provides a reference for predicting the wellbore temperature and pressure in CO₂ injection wells.

Dual-phase high-strength titanium alloy has the properties of high specific strength and good toughness, which have resulted in its gradual use in the fields of oil and gas well engineering. The elevated-temperature service environment of deep strata is its key research direction. In this paper, the strength and fracture mechanism of a new type of α + β-phase titanium alloy tubing material in its service-temperature range are studied. Its fracture mechanism changed at 130 °C to 150 °C, from normal-stress ductile fracture to quasi-cleavage fracture formed by β-phase voids, which induced microshear, which significantly reduced the elongation of the material and accelerated the rate of yield strength decline with temperature. This mechanism provides a new guiding idea for the design of the microstructure and element content of dual-phase high-strength titanium alloy. For titanium alloy materials in service within the temperature range of the fracture mechanism transition, which is between 130 °C and 150 °C, reducing the void-inducing factors in the β-phase or reducing the content of the β-phase to avoid microshear failure should be considered.