Securing energy means grasping the key link in the national development and security strategy. Under the goals of carbon peak and carbon neutrality, the overall tendency of energy development is to increase the proportion of natural gas while stabilizing oil consumption, and the global primary energy is entering the era of natural gas. Gas hydrate in deep seabed shallow strata and extremely cold permafrost regions has piqued the interest of researchers due to its abundant resources, widespread distribution, and high energy density. Although the drilling of hydrate wells is still fraught with unknowns and challenges due to the technological barriers between countries, complex on-site working conditions, and unique physical chemical properties, accumulation forms, and occurrence characteristics of gas hydrate, more than ten successful trial productions around the world have opened the door of hope for the development of this potentially new energy. The gas hydrate reservoir drilling technique is the frontier and hotspot of scientific and technological innovation and competitiveness around the globe today, reflecting the level of oil and gas technical advancement. At the national level, it possesses strategic and revolutionary features. Innovative drilling techniques, scientific well location layout, appropriate wellbore structure and well trajectory design, efficient drilling fluid, qualified drilling and completion equipment, and successful pressure-temperature preserved coring may all provide a strong guarantee for the successful completion of gas hydrate wells. This review comprehensively reviews the drilling techniques and engineering measures that can be used to develop gas hydrate. It focuses on the research advancement of important hydrate drilling technologies and the enlightening significance of these developments in the application of hydrate drilling. This work will deliver valuable experience as well as comprehensive scientific information for gas hydrate exploration and drilling.

Natural gas hydrate is a potential energy source in the future, which widely occurs in nature and industrial activities, and its formation and decomposition are identified by phase equilibrium. The calculation of multicomponent gas phase equilibrium is more complex than that of single component gas, which depends on the accurate model characterized by enthalpy and free energy. Based on the Kvamme-Tanaka statistical thermodynamic model, theoretical and experimental methods were used to predict and verify the phase equilibrium of pure methane hydrate and carbon dioxide hydrate in the temperature range of 273.17–289.05 K. The phase equilibrium curves of methane-containing gases such as CH₄+CO₂,CH₄+C₂H₆,CH₄+H₂S and CH₄+CO₂+H₂S under different mole fractions were drawn and analyzed, and the decomposition or formation enthalpy and free energy of hydrate were calculated. The results show that, the phase equilibrium curves of the methane containing systems is mainly related to the guest molecule type and the composition of gas. The evolution law of phase equilibrium pressure of different gases varies with composition and temperature, and the phase splitting of CO₂at the quadruple point affects the phase equilibrium conditions. Due to the consideration of the interaction between the motion of guest molecules and the vibration of crystal lattice, the model exhibits a good performance, which is quantified in terms of mean square error (MSE) with respect to the experimental data. The magnitudes of MSE percent are respectively 1.2, 4.8, 15.12 and 9.20 MPa²for CH₄+CO₂, CH₄+C₂H₆, CH₄+H₂S and CH₄+CO₂+H₂S systems, and the values are as low as 3.57 and 1.32 MPa²for pure methane and carbon dioxide, respectively. This study provides engineers and researchers who want to consult the diagrams at any time with some new and accurate experimental data, calculated results and phase equilibrium curves. The research results are of great significance to the development and utilization of gas hydrate and the flow safety prediction of gas gathering and transportation.

The drilling fluid invasion into hydrate-bearing sediments will change the geomechanical properties of the reservoir and may lead to uncontrolled geological disasters in the worst case. Native sediments are replaced with artificial samples in this study to investigate the effect of drilling fluid invasion on the strength behaviors of hydrate-bearing sediments. The triaxial test is used primarily to assess the strength behaviors of hydrate-bearing sediments at varying temperatures, pressures, and hydrate saturation levels. The process of water-based drilling fluid penetrating into hydrate-bearing sediments is then experimentally imitated under various experimental conditions, with reservoir temperature of 4°C and pore pressure of 10 MPa. The possible repercussions of drilling fluid invasion and hydrate phase transition are identified by testing the mechanical properties of sediments under various invasion times and temperatures. The findings reveal that when hydrate saturation rises from 5% to 35%, the gas hydrate sediments shift from strain hardening to strain softening, with the critical hydrate saturation value of transition is between 15% and 25%. Peak strength increases with increasing hydrate saturation and pressure, and decreases with increasing temperature, whether drilling fluid invasion is present or not. The peak strength, Young’s modulus, shear modulus, and secant modulus of hydrate sediments all decreased significantly after drilling fluid invasion, although the Poisson’s ratio rose. These mechanical parameters are related to temperature and pressure under the action of drilling fluid. Finally, engineering and research recommendations for reducing the risk of drilling fluid invasion and hydrate dissociation are made based on experimental findings and theoretical analysis. This study innovatively examine the geomechanical mechanical properties of drilling fluid invading hydrate reservoir, which is critical for avoiding production concerns.