As an important drilling tool, the landing string will be directly exposed to seawater during surface riserless drilling operations, and it will undergo complex deformation under the action of environmental loads such as ocean currents and waves and the displacement, heave and vibration of the drilling platform. At the same time, with the increase in water depth, the floating weight of drill pipe and casing also increases significantly, and the landing string will bear great tensile loads, which can easily cause accidents. Therefore, in this paper, based on ANSYS software, the finite element analysis models of three stages of the landing string lowering operation were established, and finite element simulations under different combinations of working conditions were carried out. Through theoretical analysis and numerical simulation, the ultimate load and stress distribution of the string under different operating sea conditions were obtained, and the external force requirements for restraining the lateral displacement of the string were proposed according to the existing standards of the industry. Thereby, the recommended safe operating time, safe operating conditions window and the required restraint reaction force of the support mechanism are given for landing string lowering operation throughout the year.

Shallow gas drilling in polar seas poses severe geological hazards, particularly unexpected eruptions that threaten platform safety and the marine environment. Accurate prediction of shallow gas occurrence and eruption risk is therefore essential for safe deep-water operations. However, previous studies seldom considered the coupled effects of gas pressure and pore-structure evolution on acoustic wave velocity, leading to deviations in hazard assessment. In this study, laboratory experiments and numerical simulations were conducted to clarify these mechanisms. Results revealed a non-monotonic relationship between porosity and P-wave velocity in shallow gas-bearing sediments: P-wave velocity decreases with increasing porosity at low porosity levels but increases beyond a critical threshold. This is attributed to changes in particle interactions and cementation that enhance the shear modulus. The inflection porosity for shallow gas (78%) highlights the diagnostic role of pore-structure evolution in predicting shallow gas distribution. A mathematical correlation between P-wave velocity and formation pressure was further established, and MP-PIC simulations showed that higher pressure coefficients significantly accelerate eruption rates, with a 0.1 increase in the pressure coefficient raising the instantaneous eruption velocity by 5.27 m³/min. Based on these findings, a quantitative evaluation method was developed to assess shallow gas hazard risk, providing engineering guidance for site selection and real-time risk prediction, and contributing to safer offshore drilling and ecological protection in polar environments.

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.