The first prerequisite for the efficient and safe exploitation of gas hydrate resources is to accurately analyze the primary mechanical performance of hydrate-bearing sediments (HBSs). The mechanical performance of HBSs is complex and affected by many factors, including the reservoir environment in situ (temperature, pore pressure, salinity). Several published studies have demonstrated a correlation of the mechanical behavior of hydrates with temperature and pressure (T-P_P). However, the research on the effect of salinity on the mechanical properties of hydrates or HBSs is still a relatively blank field. This study found that the strength of HBSs decreased with increasing salinity. This phenomenon can be attributed to the influence of salinity on the phase equilibrium state of hydrates. NaCl changed the relationship between the phase equilibrium curve of the hydrate and the T-P_P conditions. The distance between the T-P_P conditions and equilibrium curve was reduced with increasing salinity, which in turn led to a decline in sample strength. Moreover, the effect of the phase equilibrium of hydrates on the mechanical performance of HBSs was further explored. NaCl was added to HBSs to regulate the phase equilibrium state of the hydrate. When the T-P_P conditions were on the phase equilibrium curve, the strength behaviors of HBSs showed a high degree of consistency.

Using acrylic acid advanced ester and styrene as raw materials, the long-chain polyester polymer, polyacrylic acid advanced ester-styrene pour point depressant (P-PPD), was synthesized by molecular design, and its structure was characterized by infrared spectroscopy and nuclear magnetic resonance. In addition, this study experimentally investigated the effect of P-PPD on the phase equilibrium and induction time of natural gas hydrate inhibitors in deionized water (DW) and crude oil/water (O/W) systems, respectively. Polyvinylpyrrolidone (PVP) and mono ethylene glycol (EG) were selected as representatives of kinetic hydrate inhibitor (KHIs) and thermodynamic hydrate inhibitor (THIs), respectively. The results exhibit that P-PPD played a sight role in the phase equilibrium of hydrate, while the addition of P-PPD significantly prolonged the induction time of methane hydrate both in O/W + PVP, OW + EG and O/W + PVP + EG system, indicating that the addition of as-synthesized PPD has a synergistic inhibition effect on the nucleation ability of methane hydrate and can prevent hydrate from formatting during oil and gas transport process, and thus guarantee the flow assurance. The findings of this work will provide a data reference for the hybrid use of hydrate inhibitors and pour point depressants in oil and gas transport.

During marine oil–gas extraction, significant amounts of carbon dioxide (CO₂) gas are often produced. Effectively separating these associated CO₂ gases during extraction has become a critical technical challenge. Therefore, this paper aims to enhance the efficiency of CO₂ hydrate-based capture technology and conduct relevant research. The goal is to increase the driving force for hydrate formation by combining the traditional thermodynamic additive TBAB with pressure modulation and to improve the hydrate formation rate through the use of multiple kinetic promoters. This paper presents the initial investigation into the effect of the thermodynamic accelerator tetrabutylammonium bromide (TBAB) on the characteristics of CO₂ hydrate formation. The promotion effects of TBAB solutions with varying mass concentrations (3%, 5%, 7.5%, 10%) and reaction pressures (3 MPa, 4 MPa) were subjected to a systematic analysis, and the optimal conditions were identified as 4 MPa and a 5 wt% TBAB concentration. Subsequently, the impact of combining TBAB with kinetic promoters (SDS, nano Al₂O₃, L-methionine, L-leucine) on CO₂ hydrate generation characteristics was further investigated. In this paper, the effect of a single promoter on the generation characteristics of CO₂ hydrate was investigated, and the efficient carbon trapping ability of the complex promoter was verified, which provides theoretical support for the application of CO₂ trapping technology using the hydrate method.

The development of marine resources and deep-sea engineering construction is a crucial strategy for national security and sustainable development. However, the potential engineering geological hazards such as reservoir subsidence, wellbore instability, and submarine landslides during the extraction process necessitate precise pre-extraction analysis of reservoir characteristics. Cone Penetration Testing (CPT), an effective in-situ exploration technique, enables accurate analysis of soil types, soil layer boundaries, and physical-mechanical properties of deep-sea sediments and hydrate reservoirs by measuring penetration resistance, pore pressure changes, and other data. This study optimized the laboratory CPT testing method based on in-situ CPT tests conducted in deep-sea environments and validated it through experiments. It was found that for a 600mm-high specimen, the experimental data were most accurate when the penetration depth was between 300-400mm. An increase in the penetration rate led to an increase in both the cone tip resistance and the sidewall friction resistance. Furthermore, experiments conducted on South China Sea sediments under varying effective confining pressures demonstrated that an increase in effective confining pressure also augmented these resistance values. Based on these experimental results, this study preliminarily established empirical formulas for laboratory CPT experiments on deep-sea sediments, providing a scientific basis for reservoir safety assessments in deep-sea geotechnical engineering.

Huge gas hydrate reserves exist worldwide, and over 90% of them occur in fine-grained reservoirs with poor permeability, such as the hydrate reservoir in the South China Sea (SCS). This type of hydrate reservoir is characterized by non-diagenesis and weak cementation, and hydrate exploitation is prone to trigger reservoir settlement and deformation. Therefore, the key to achieving the safe exploitation of hydrate resources is to conduct in-depth research into the geophysical and geomechanical features of hydrate-bearing sediments (HBSs) in the SCS. Based on this, the geophysical and geomechanical characteristics of the hydrate reservoirs in the Shenhu area of the SCS were thoroughly researched in this work. For the geophysical properties of HBSs, the host sediments of SCS belong to well-graded clayey silts, with particles arranged in a layered configuration face-to-face. Its principal mineral components include quartz, plagioclase, calcite and some clay minerals. For the geomechanical properties of HBSs, the strength, stiffness and volumetric strain of HBSs of SCS increase with effective confining pressure (ECP) under drained conditions. When the pore water is not emptied, the extra pressure is positive, demonstrating substantial shear contraction, and the fitting failure line is unaffected by the ECP. The aforementioned research contents can serve as a guide for future constitutive model and numerical simulation development on hydrate reservoir stability of SCS.

A comprehensive study of the mechanical behaviors of hydrate-bearing sediments (HBSs) is the key to safely exploiting hydrate resources. The mechanical behaviors of HBSs are related to many variables, among which hydrate saturation (S h) and pore pressure (PP) are vital factors. In addition, S h and PP are related to the location of hydrates in the subsea layer, so it is of positive significance to investigate their comprehensive influence on the mechanical behavior of HBSs. In this work, a series of triaxial tests were conducted on the HBSs synthesized in the laboratory to explore the influence of S h and PP on the mechanical properties of the HBSs. The results show that the strength of HBSs increases with increasing PP and S h. With increased PP and S h, the stress-strain behaviors will shift from strain-hardening to strain-softening. Moreover, under different S h conditions, a critical PP point of strain-hardening and softening transition exists in numerical perspective. The critical PP point will develop towards low pressure with increased S h.