With the continuous expansion of deepwater oil and gas development, annular pressure buildup in gas wells has become an increasingly critical safety concern. Rupture discs, as passive pressure relief devices, have attracted attention for potential application in annular pressure management in deepwater wells. However, their performance under complex downhole environments characterized by high temperature, dynamic loading, gas flow, and corrosion remains insufficiently understood. In this study, a laboratory-scale rupture disc burst-pressure experimental system with independently controllable temperature, pressure, and gas flow rate was developed. By simulating the coupled loading process caused by thermal expansion and controlled gas pressurization in a sealed annulus, a series of systematic experiments considering multiple operating factors were conducted to investigate rupture disc activation behaviour under representative deepwater well conditions. The experimental programme examined the effects of temperature, annular pressure ramp rate, gas flow rate, and acidic corrosion degradation. The results show that increasing temperature, higher annular pressure ramp rates, and elevated gas flow rates significantly reduce the rupture disc burst pressure and increase its statistical dispersion, indicating a transition of the loading state from quasi-static to dynamically coupled conditions. Under high flow rates and rapid pressurization, transient stress redistribution and amplification of local defects become dominant, shifting the failure mechanism from strength-controlled to defect-controlled behaviour. In contrast, corrosion degradation exhibits a stage-dependent influence: although burst pressure decreases with increasing corrosion time, the reduction rate gradually stabilizes, and the variability of burst pressure decreases as corrosion severity increases. These findings provide experimental insights into rupture disc behaviour under coupled environmental and operational factors and offer useful guidance for rupture disc selection and safety margin design in annular pressure control systems for deepwater gas wells.

To address the severe shielding of conventional electromagnetic signals by metallic pipelines and the inherent design trade-off under fixed-voltage excitation, whereby increasing coil size suppresses current and limits magnetic field intensity, this study proposes an independently parallel-fed multistage coil enhancement scheme for the transmitter of through-wall magnetic induction communication. Based on electromagnetic theory and COMSOL6.3 simulations, a coupled analysis framework for multistage coils was established to systematically evaluate the effects of axial partitioning, radial partitioning, nonuniform turn allocation, and magnetic-core loading on branch-current amplitude and phase consistency as well as spatial magnetic field intensity. The results show that, under in-phase, equal-frequency excitation, the resultant magnetic field intensity increases approximately linearly with the number of partitions. The partition scheme significantly alters the mutual inductance distribution among sub-coils, thereby affecting current synchronization and magnetic field synthesis efficiency. The introduction of a high-permeability magnetic core markedly improves the amplitude and phase consistency of the radially partitioned structure and enhances output stability. Considering magnetic field output, current synchronization, and engineering feasibility, the axial–radial hybrid four-partition structure with a magnetic core was identified as the preferred configuration. These findings provide a theoretical basis and structural guidance for transmitter design in low-frequency through-wall magnetic induction communication under metallic shielding conditions.

To improve the bending resistance and support the domestic development of deepwater subsea wellhead equipment, a three-dimensional finite element model (FEM) of the SXW-15 subsea wellhead system was established in ANSYS Workbench considering contact nonlinearity and rigid-locking mechanisms. Based on representative deepwater drilling and completion conditions, the effects of the friction coefficient, locking preload, blowout preventer (BOP)/lower marine riser package (LMRP) top load, casing hanger internal pressure, and tubing load on the ultimate bending capacity of the system were systematically investigated. The results show that the bending capacity increases with increasing friction coefficient and locking preload, whereas it decreases with increasing top load and tubing weight. The internal pressure of the casing hanger exhibits a pronounced nonlinear influence on the bending resistance, and the maximum bending capacity occurs at an internal pressure of approximately 4000 psi. Based on the mechanical analysis, several innovative designs were proposed, including a layered load-bearing structure, a gravity-set metal sealing assembly, a self-supporting rigid-locking mechanism, and an integrated multifunctional tool system, aiming to improve load-transfer efficiency, connection stiffness, and high-pressure sealing stability. Land-based testing and offshore field applications were subsequently conducted to verify the engineering applicability of the system. The subsea wellhead system with innovative designs maintained satisfactory structural integrity and sealing reliability under conditions of 15,000 psi internal pressure and 12.7 million lb axial load. Good agreement was obtained between finite element predictions and field test results. The present study provides theoretical support and guidance for the structural designs and engineering applications of deepwater subsea wellhead systems.