Uncovering the dynamic evolution mechanism of natural gas hydrate reservoir properties is crucial for realizing efficient resource exploration and safe trial mining. Obtaining high-quality hydrate reservoir cores and conducting comprehensive testing and analysis are important prerequisites for obtaining real information about hydrate reservoir. Pressure-holding transfer and testing of natural gas hydrate reservoir cores is a powerful means of accumulating in situ physical analysis data. This report summarizes the current state of development of pressure-holding transfer and testing techniques for natural gas hydrate reservoir cores from both research and application aspects. The advantages and disadvantages of existing gas hydrate reservoir core pressure-holding transfer and testing systems are comprehensively reviewed. The basic methods of pressure core processing, including buckling decomposition, permeability measurement, triaxial testing and integrated measurement, are analyzed, as well as the advantages and disadvantages of these methods. These reviews not only help researchers to better understand the current status of pressure-holding transfer and testing techniques for natural gas hydrate reservoir cores, but also have important reference significance for the in-depth development of future hydrate reservoir core testing technology.

In recent years, a new type of natural gas hydrate reservoir (designated as Class 1S reservoir) has been discovered in the Qiongdongnan Basin. Within this hydrate reservoir, free gas and hydrate coexist within the same stratum. The Class 1S reservoir is comprised of three distinct zones: the gas accumulation zone, the three-phase zone, and the hydrate-bearing zone. It exhibits significant commercial development potential. This paper analyzes the formation mechanism and geological context of Class 1S hydrates. A geological model was established and numerical simulation methods were employed to evaluate its production capacity, elucidating the evolutionary patterns of hydrate saturation distribution at different well locations. The simulation results indicate that production wells should be prioritised in gas accumulation zones in order to achieve the highest cumulative gas production. Additional production wells may be considered in later stages to enhance recovery rates. Secondary hydrate formation significantly impacts production in Hydrate-bearing zone and three-phase zone. Measures such as wellbore heating can be employed to minimize secondary hydrate formation around the wellbore.

Accurate and robust positioning of drilling robots within subsea strata is a critical prerequisite for deep-sea resource exploration and geological monitoring. However, conventional underwater and underground positioning methods are often ineffective due to severe signal attenuation in sediment. This paper proposes a novel fused positioning method specifically for subsea stratum drilling robots, which integrates a magnetic beacon system with a MEMS-IMUs array cable. A Piecewise Constant Curvature (PCC) kinematic model is established to reconstruct the spatial morphology of the array cable, providing a continuous position estimate free from temporal integration drift. This estimate is then fused with absolute position and orientation data derived from a magnetic dipole model of the beacon. To handle the high nonlinearity of the magnetic measurements and the complementary error characteristics of the two subsystems, we develop a tightly-coupled sensor fusion framework based on an Iterated Extended Kalman Filter with Leven-berg-Marquardt optimization (IEKF-LM). Simulation and experimental results demonstrate that the proposed system effectively overcomes the limitations of individual sensors. The array cable excels in near-field accuracy, while the magnetic beacon provides superior far-field performance. The IEKF-LM fusion algorithm successfully combines their strengths, achieving high-precision and robust localization in both static and dynamic scenarios simulating in-stratum conditions. The results indicate that the proposed fusion method effectively mitigates the limitations of individual sensor modalities, offering a viable positioning solution for subsea exploration robots.

Natural gas hydrates are regarded as a vital strategic energy resource for the future owing to their high energy density and clean combustion characteristics. To facilitate research into the physical and mechanical properties of pressure-maintained hydrate samples, this paper presents an integrated multi-parameter online analysis system capable of rapidly measuring the P-wave velocity, electrical resistivity, thermal conductivity, and shear strength of core samples under pressure-maintaining conditions. The system comprises hardware acquisition boards based on ZYNQ and ARM platforms, specialized measurement probes, and comprehensive data acquisition and analysis software. To mitigate the susceptibility of P-wave signals to noise interference, an improved denoising algorithm combining Empirical Mode Decomposition (EMD) and wavelet thresholding is proposed. By employing autocorrelation function analysis, the algorithm identifies the transition boundary between noise-dominated and signal-dominated Intrinsic Mode Functions (IMFs), subsequently applying wavelet soft-thresholding to the noise-dominant components. Experimental results demonstrate that the proposed algorithm achieves a superior signal-to-noise ratio (SNR) compared to traditional EMD methods, particularly under low SNR conditions. System validation indicates measurement accuracies of 3.2% for P-wave velocity at 20 °C, 1.76% for electrical resistivity at 25 °C, and within 7% for both thermal conductivity and shear strength. Furthermore, sea trials conducted aboard the “HAIYANG SHIYOU 708” drilling vessel confirm that the system operates stably and effectively fulfills the requirements for deep-sea core parameter characterization.

The bionic pectoral fin serves as the primary propulsion component of ray-inspired robots. In our previous research, a motion equation was proposed for the real pectoral fin, which can be modeled as a series of NACA airfoil-shaped cross-sections distributed along the spanwise direction. Each cross-section undergoes two coupled rotational motions about its chord line and spanwise rotational axis. To achieve this type of motion, this article introduces a novel bionic pectoral fin mechanism driven by a series of differential gear units. The differential unit generates two coupled rotational motions corresponding to the cross-section of the pectoral fin in motion. A series of interconnected differential units provides a unique topology for the bionic mechanism and can generate a diverse range of motions. Through kinematic analysis, the motion equation was mapped onto the rotational angles of motors in the differential units. The proposed bionic mechanism was then fabricated and subjected to experimental test, demonstrating its effectiveness with a maximum thrust of 0.71 N. The distinctive structure of this bionic mechanism differentiates it from conventional designs and is expected to provide some inspiration for bionic pectoral fins and ray-inspired robots.

Processing and analyzing hydrate pressure cores in an in situ environment is of great significance for accurately assessing reservoir properties, safeguarding mining safety, and improving the efficiency of resource development. Aiming at the problem of decomposition due to temperature and pressure changes during the processing of hydrate cores, in this paper, a set of pressure maintenance and temperature control systems with active pressure and temperature regulation is designed to maintain the in situ environment of the cores. Through the establishment of a mathematical model of the system and the analysis of time‐domain dynamic characteristics, it is found that the pressure maintenance system has good stability and no steady‐state error, but there are problems of slow response speed and large overshooting; the temperature control system has fast response and small overshooting, but the steady‐state error is large. On the basis of the comparative analysis of proportional–integral–derivative (PID) control strategies, the optimization scheme of using proportional–derivative control for the pressure system and PID control for the temperature system is proposed. The experimental results show that the system can stably control the temperature in the device within the range of 3.0°C–4.5°C and the pressure fluctuation ≤ 3.8% during the core processing, which verifies the feasibility and validity of the designed system, and provides a reliable technical support for the hydrate pressure preservation core processing.