Gas Hydrate Research Articles

Pore Characteristics of Hydrate-Bearing Sediments from Krishna-Godavari Basin, Offshore India

Pore-filling hydrates are the main occurrence forms of marine gas hydrates. Pore characteristics are a vital factor affecting the thermodynamic properties of hydrates and their distribution in sediments. Currently, the characterization of the pore system for hydrate-bearing reservoirs are little reported. Therefore, this paper focuses on the Krishna-Godavari Basin, via various methods to characterize the hydrate-bearing sediments in the region. The results showed that X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and cast thin section (CTS) can better characterize the mineral composition in the reservoir, high-pressure mercury injection (HPMI) focused on the contribution of pore size to permeability, constant-rate mercury injection (CRMI) had the advantage of distinguishing between the pore space and pore throat, and nuclear magnetic resonance cryoporometry (NMRC) technique can not only obtain the pore size distribution of nanopores with a characterization range greater than nitrogen gas adsorption (N2GA), but also quantitatively describe the trend of fluids in the pore system with temperature. In terms of the pore system, the KG Basin hydrate reservoir develops nanopores, with a relatively dispersed mineral distribution and high content of pyrite. Rich pyrite debris and foraminifera-rich paleontological shells are observed, which leads to the development of intergranular pores and provides more nanopores. The pore throat concentration and connectivity of the reservoir are high, and the permeability of sediments in the same layer varies greatly. The reason for this phenomenon is the significant difference in average pore radius and pore size contribution to pore permeability. This article provides a reference and guidance for exploring the thermodynamic stability of hydrates in sediments and the exploration and development of hydrates by characterizing the pores of hydrate reservoirs.

Gas hydrate inhibition by urea and its blends with vinyl lactam polymer: Paving the way to green hybrid inhibitors

Urea is an environmentally benign substance considered a promising gas hydrate inhibitor in flow assurance. Nevertheless, its effect on gas hydrate formation kinetics remains poorly understood. This study investigates the impact of urea and hybrid urea/polymer KHI samples on the nucleation and growth kinetics of sII natural gas hydrates. Hydrate formation was observed at a lower onset temperature with increasing urea and polymer concentration. The nucleation of sII hydrate in aqueous urea solutions occurred at a higher subcooling (7.50 ± 0.58 K at 30 mass%) than in pure water (5.17 ± 0.69 K). These findings indicate that urea acts as a nucleation inhibitor of sII hydrates, although its capacity is not as potent as that of polymer KHI.The analysis of the hydrate nucleation probability distributions revealed that the sII hydrate nucleation rate exhibited a significant decline, approximately one order of magnitude, at subcooling of 5.3–6 K for 20 mass% urea compared to water. A similar behavior was noticed in an aqueous solution of polymer KHI. Urea has succeeded in providing a total benefit of up to 10 K in hydrate onset temperature due to a shift in the hydrate stability zone and nucleation retardation.Consequently, urea is a green dual-acting anti-hydrate chemical that inhibits the formation of sII hydrates by thermodynamic and kinetic mechanisms. Besides, adding 10 mass% urea increases the cloud point temperature of vinyl lactam polymer Luvicap 55W by 14 K. Urea is an additive that considerably augments the stability of the polymer in aqueous solutions at elevated temperatures. These findings make urea an effective and environmentally friendly top-up inhibitor that significantly enhances the anti-hydrate properties of polymer KHI.

Kinetics of methane hydrate formation in a 1200 ml unstirred reactor for natural gas storage

Solidified natural gas (SNG) technology via clathrate hydrates, enhanced by promoters such as tetrahydrofuran (THF), promises large-scale natural gas storage due to its high volumetric capacity and mild storage conditions. Despite its potential for industrial scale-up, limited research exists on methane hydrate formation behaviors in large reactors (>1000 cm3), which is crucial for evaluating practical storage performance. In this study, methane hydrate formation kinetics were investigated in a scaled-up unstirred reactor (1200 cm3) at 288.15 K and 283.15 K, and 5.0 MPa. Methane uptake, system pressure, gas and liquid phase temperatures, and hydrate morphologies were analyzed to describe the dynamic hydrate formation process. Results reveal three effects of increased reactor size in contrast to smaller reactors: (i) heterogeneous distribution of THF-rich and methane-rich hydrates; (ii) hydrate bulk show a hollow inner structure with a cavity due to the wall-climbing behavior of hydrate growth; (iii) optimal THF concentration no longer always agrees with stoichiometric 5.56 mol%, which is case-dependent. These effects are attributed to higher diffusion resistances for methane molecules and more intensive heat accumulation. These findings provide some insight into the kinetics of methane hydrate formation in industrial reactors, which is critical for the commercialization of SNG technology.

Rapid formation of carbon dioxide hydrate governed by the natural nano-clay for effective carbon dioxide capture

Gas hydrate can separate and capture enormous carbon dioxide (CO2) only using water cages. Capturing CO2 in hydrate form is viewed as a green and effective technology to reduce the global CO2 emission. However, the sluggish kinetics and high cost of kinetics promotors of CO2 hydrate formation limited the application of hydrate-based CO2 capture technology. Here, we used the nano-clay prepared by cheap natural clay to promote the formation kinetics of CO2 hydrate. At the low concentration range, the formation period of CO2 hydrate in the two-dimensional nano-clay dispersion was significantly shorter than that of the one-dimensional nano-clay dispersion. The induction time (5 min) obtained in vermiculite nanoflakes dispersion was shorter than most solid promotors of CO2 hydrate formation kinetics in reported works. Besides, we found that the water molecules near the negatively charged two-dimensional nano-clay surface were more likely to form the cage-like structure than those around the one-dimensional nano-clay surface. The similar hydrogen-bonded structure of the cage-like water with CO2 hydrate made them favorable for the CO2 hydrate formation. These results shed light on the design of the effective kinetics promotors of CO2 hydrate and contribute to develop the hydrate-based CO2 capture technologies.

Variations in deep-sea methane seepage linked to millennial-scale changes in bottom water temperatures ~ 50–6 ka, NW Svalbard margin

During the last glaciation, the northern hemisphere experienced profound millennial-scale changes (termed Dansgaard-Oeschger (DO) events) in atmospheric and oceanic temperatures. In the North Atlantic, the fluctuations resulted in extremely unstable bottom water conditions with bottom water temperatures (BWT) varying up to > 5 °C. We have studied these changes in a core from 1,300 m water depth at Vestnesa Ridge, northwestern Svalbard margin to investigate a possible connection between BWT and seepage of methane from the seafloor covering the period ~ 50–6 ka. Beneath Vestnesa Ridge, gas hydrates containing vast amounts of methane are kept stable due to the high pressure and low temperatures. Release of gas is shown by numerous pockmarks on the seafloor. The pockmarks at 1,300 m water depth are presently inactive, but they bear witness of earlier activity. Our study shows that from ~ 50–6 ka, the core site experienced repeated increases in BWT and in the emissions of gas, both following the pattern of the DO events. This correspondence in time scale indicates that BWT was the primary forcing factor for the variability in methane release. However, the releases were delayed by up to > 1,000 years compared to the initial increase in BWT.

Introduction of Cyclic Structures into Phosphonium Salts As Potential Guest Substances for Ionic Clathrate Hydrates

An ionic clathrate hydrate composed of tri-n-butylbenzyl-phosphonium chloride has been investigated from the viewpoint of phase equilibrium (temperature-composition) relations in comparison with an ionic clathrate hydrate with tri-n-butyl(cyclohexylmethyl)phosphonium bromide. The highest dissociation temperature of the ionic clathrate hydrates composed of tri-n-butylbenzylphosphonium chloride and tri-n-butyl(cyclohexyl-methyl)phosphonium bromide were 274.4 ± 0.1 K and 276.0 ± 0.1 K, respectively at the atmospheric pressure. The dissociation enthalpy of tri-n-butylbenzyl-phosphonium chloride ionic clathrate hydrate was 192 ± 3 kJ·kg−1. These results allow us to suggest that controlling steric structures in the guest compounds might be one of the options for tuning the equilibrium temperatures of ionic clathrate hydrates.

Development and Evaluation of Insulation Materials for Deepwater Cementing.

Marine oil and gas resources are abundant in deepwater regions, where the shallow seabed harbors natural gas hydrate layers due to the cold temperature and high-pressure environment. Hydrates are prone to thermal decomposition, which can compromise the integrity of cement sealing and even lead to accidents like blowouts. While current low-hydrated heat cement systems mitigate hydrate decomposition from cement hydration heat during the waiting period for cementing, they do not address heat transfer from deep strata to shallow hydrate layers through fluid circulation in the tubing during deep oil and gas development. Rather than utilizing costly pipe insulation technology, adjusting the thermal conductivity of well cement emerges as a cost-effective approach to prevent heat loss in the wellbore to the hydrate layer and thus inhibit hydrate decomposition. The critical aspect lies in utilizing insulation functional materials. This study delves into the functional and structural design of insulation materials suitable for cement slurry systems in well cementing, outlining the preparation methods and processes for two insulation materials (SDBW and SDBW-II) tailored for deepwater well cementing. SDBW and SDBW-II are both nuclear shell structural materials. The core is made of high-strength hollow microspheres, produced by using a reverse suspension polymerization method to form spheres followed by high-temperature sintering. The shell consists of a wear-resistant BPA epoxy resin layer, with the surface of SDBW-II also containing highly reflective glass microspheres. Incorporating 20% of material SDBW into the cement reduces the thermal conductivity of the cement stone from 0.8 to 0.31 W·(m·K)-1 while achieving a compressive strength of 6 MPa after 24 h at 20 °C. Material SDBW-II offers both thermal resistance and reflection functions, increasing reflectivity (R) from 0.3 to 0.5. By adding 20% of this material to the cement, under the same conditions, although the compressive strength decreases to 4.2 MPa, the thermal conductivity can be reduced to 0.27 W·(m·K)-1. Furthermore, there is no significant change within 180 days, demonstrating long-term thermal insulation stability. These developed insulation materials can effectively improve the thermal insulation performance of the cement sheath, thereby maintaining the stability of the upper natural gas hydrate layer in the oil and gas production process of deepwater wells, providing an innovative solution for the long-term operation of deepwater oil and gas wells.

Parameters Variation of Natural Gas Hydrate with Thermal Fluid Dissociation Based on Multi-Field Coupling under Pore-Scale Modeling

Parameters Variation of Natural Gas Hydrate with Thermal Fluid Dissociation Based on Multi-Field Coupling under Pore-Scale Modeling

Insight into the micro-mechanism of hydrate-based methane storage from active ice

Gas hydrate formation in active ice holds significant potential for solidified natural gas storage, while the deep understanding of its micro-mechanism is required for the futural application of such a technology. In this study, the kinetics and micro-properties of methane hydrate formation enhanced by active ice (porous ice containing an unfrozen solution layer of sodium dodecyl sulfate) were investigated via experiments and molecular dynamics (MD) simulations. Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray diffraction (XRD) differential scanning calorimetry (DSC) characterization, and in-situ visual observation confirmed the formation of sI methane hydrate in the active ice system and the occurrence of single-crystal hydrate, and also indicated the occurrence of active water near the surface of porous active ice during the active ice formation. A sensitivity analysis of the hydrate kinetics experiments suggested that temperature is the primary driver of rapid methane hydrate formation in the active ice system. The shortest induction time and t90 for hydrate formation were recorded at 5 s and 5.5 min, respectively. Furthermore, MD simulations indicated that the direct hydrate nucleation and growth in the active water, heat transfer from gas hydrate to ice, and the diffusion of active water (1.24 × 10-9 m2/s) and methane (7.10 × 10-8 m2/s) into the porous ice structure are the primary mechanism that enhances hydrate formation kinetics and methane storage capacity. This work provides an essential microscopic mechanism of the “active ice → active water → gas hydrate” circulation that contributes to the deep understanding and futural application of the efficient hydrate-based solidified methane storage in active ice system.

Experimental Study on the Transport Behavior of Micron-Sized Sand Particles in a Wellbore

In the process of natural gas hydrate extraction, especially in offshore hydrate extraction, the multiphase flow inside the wellbore is complex and prone to flow difficulties caused by reservoir sand production, leading to pipeline blockage accidents, posing a threat to the safety of hydrate extraction. This paper presents experimental research on the migration characteristics of micrometer-sized sand particles entering the wellbore, detailing the influence of key parameters such as sand particle size, sand ratio, wellbore deviation angle, fluid velocity, and fluid viscosity on the sand bed height. It establishes a predictive model for the deposition height of micrometer-sized sand particles. The model’s predicted results align well with experimental findings, and under the experimental conditions of this study, the model’s average prediction error for the sand bed height is 12.47%, indicating that the proposed model demonstrates a high level of accuracy in predicting the bed height. The research results can serve as a practical basis and engineering guidance for reducing the risk of natural gas hydrate and sand blockages, determining reasonable extraction procedures, and ensuring the safety of wellbore flow.

Thermodynamic phase equilibria of binary SF6–N2O hydrates and their structural analysis for the hydrate-based greenhouse gas capture

The increasing greenhouse gas (GHG) emissions from industrial activities have driven the development of efficient and environmentally safe GHG capture technologies. Clathrate hydrates, primarily composed of water, have attracted significant attention for their potential in GHG capture due to their ability to manage large emissions and their environmental advantages over materials like amine-based sorbents and metal-organic frameworks. This study investigates the hydrate-based capture of SF6 and N2O, two potent GHGs, to develop an effective GHG capture process. Phase equilibrium measurements demonstrate that binary SF6-N2O hydrates can form under moderate thermodynamic conditions, even with a small proportion of SF6, highlighting the feasibility of using hydrate-based methods to capture GHG mixtures. Furthermore, the formation of binary SF6-N2O hydrates enhances GHG volumetric storage capacity compared to pure SF6 hydrates. The guest compositions calculated for each binary SF6-N2O hydrate phase, along with spectroscopic analyses (Powder X-Ray Diffraction and Raman spectroscopy), confirm that the high GHG uptake in binary hydrates results from N2O molecules occupying the small cages of structure II hydrates, which are inaccessible to the larger SF6 molecules. These findings suggest that both the small and large cages of sII hydrates can be practically utilized for efficient capture of GHG mixture (SF6 and N2O) under mild conditions, thereby increasing the storage density of GHGs within the hydrate structure.

Intriguing phenomenon of hydrogen molecules occupancy in clathrate hydrate cages: Implications for hydrogen storage

The occupancy of hydrogen in hydrate cages plays a significant role in the hydrogen storage capacity of hydrate-based. Here, we have found two intriguing phenomena of multiple hydrogen molecules occupancy in hydrate cages under relatively mild conditions. We observed the double hydrogen molecule occupancies in the small cages with large-molecule guest substance (1,2-Epoxycyclopentan (ECP)) as the thermodynamic promoter. The discovery illustrates that the stereotypical idea that light guest molecules are always necessary for double hydrogen occupancy in the 512 cages needs to be reconsidered. And we also observed the coexistence of double hydrogen molecules occupancy in the 51264 cages, which is the prerequisite of high hydrogen storage capacity in clathrate hydrates. The discovery obtained in this study can also provide further insight into the mechanism of hydrate formation and significant advances in hydrate-based hydrogen storage technology.

Prediction of hydrate formation boundaries in pure water and salt/alcohol containing systems based on prior knowledge and artificial intelligence

As an efficient and clean energy source, natural gas plays a crucial role in optimizing the global energy consumption structure. However, the formation and accumulation of hydrates in pipelines during the exploitation and transportation of natural gas greatly jeopardize the production safety. Accurately predicting hydrate formation boundaries remains challenging due to the complex interation among various influencing factors. Although mechanistic models provide insights, they often fall short in accuracy. Conversely, machine learning models, while promising, may face limitations related to small sample sizes and a lack of physical interpretability. To overcome these limitations, this study proposed a physically guided neural network (PGNN) based on the Chen-Guo model, which integrated thermodynamic mechanisms with a neural network framework. This proposed model utilized pressure calculated from the Chen-Guo model as an input variable and incorporates physical inconsistencies into its loss function. A comparative analysis using literature data that PGNN achieved superior prediction accuracy, with an R2 value of 0.9768 for gas hydrate formation pressure prediction. The integration of thermodynamic mechanisms enhanced the prediction accuracy, as evidenced by an increase in the R2 value by 0.036, and a reduction in the MSE value by 5.56. Furthermore, the PGNN maintained a high level of prediction accuracy, ranging from 0.96 to 0.98, even with limited sample sizes, thus confirming its applicability and stability. This study validated the feasibility of PGNN for predicting gas hydrate formation conditions and offered insights into hydrate-based applications and hydrate management strategies.

Simulation of CO2 hydrate formation in porous medium and comparison with laboratory trial data

The storage of CO2 in gas hydrate form in the pore space in depleted natural gas reservoirs has been considered a method for greenhouse gas control. The formation of CO2 hydrate in porous medium is a strongly coupled Thermal-Hydraulic-Chemical (THC) problem under certain thermodynamic conditions. In this study, laboratory data on CO2 hydrate formation in silica sand, including the profiles of pressure, temperature, the amount of CO2, H2O, and CO2 hydrate, etc., were compared with results from numerical simulations. The minimized deviations between the simulation and experimental results, including the pressure drop, the significant temperature increase caused by hydrate formation, and the amount of CO2, water, and hydrate, were all less than 10 % in the numerical simulations. The sensitivities of the deviations between numerical simulations and experimental data to the domain discretization, thermal conductivity of the silica sand, absolute permeability, and kinetics of CO2 hydrate formation were analyzed. One of the major findings is that CO2 hydrate formation in the porous medium in this study is dominated by the kinetics of chemical reaction, rather than the heat or mass transfer. Another key finding of this study is the acquisition of the modeling parameters of the CO2 storage process in the laboratory-scale sand reservoir, including the thermal conductivity of the silica sand λs = 2.2 W/m/K, the absolute permeability k0 = 3.0 × 10−11 m2, and the kinetic constant Kf0 = 8.4 × 1011 kg/m2/Pa/s and the reduction exponent β = 5.3 in the kinetic model of CO2 hydrate formation. It is noteworthy that the mathematical models and the parameters faithfully fit three independent experiments of Run 1–3. The results of the experiments and corresponding numerical simulations provide a reliable method to evaluate the capacity, technical and commercial feasibility of CO2 storage in marine and permafrost reservoirs.

Effect of particle size, water saturation, inorganic salt and methane on the phase equilibrium of CO2 hydrates in sediments

Understanding the thermal stability of gas hydrate in complex marine geological environment is of importance to hydrate-based carbon sequestration. In this work, the factors affecting the equilibrium of CO2 hydrate in ocean sediments, including quartz sands, inorganic salts and gas impurities were quantitatively measured in a temperature range from 273 to 283 K and a phase equilibrium model of hydrate was established. To reveal the distribution in pore structure, the micro-morphologies of hydrate-bearing sediments were measured by cryo-SEM. Results showed that reduction of initial water saturation, addition of NaCl and CH4 were found to have inhibitory effect on CO2 hydrate equilibrium. Initial water saturation reduced the equilibrium temperature by the capillary pressure, but only 0.3–0.7 K temperature depression was observed as the water saturation reduced to 5 %. About 5.7 K in the average temperature depression was found by the addition of 10 wt% NaCl and 24 mol% CH4. NaCl and CH4 influenced the hydrate equilibrium by changing the water activity and chemical potential of hydrate water lattice. SEM images showed that the hydrate formed in pores of quartz sand had porous surface and coated the sand particles like a layer of cells which are 5–20 μm in diameter, suggesting the hydrate layer exists between the liquid and gas phase. Based on the van der Waals-Platteeuw model, a hydrate equilibrium model was developed. The model provided a good prediction of the hydrate equilibrium in the presence of quartz sand, NaCl and CH4 with an averaged deviation of ±4.2 %, which had the potential to be applicated in more complexed ocean sedimentary environment.

Gas hydrate stability for CO2-methane gas mixes in the Pegasus Basin, New Zealand: A geological control for potential gas production using methane-CO2 exchange in hydrates

Gas hydrate is an ice-like form of water containing gas, in nature mostly methane (CH4), which requires moderate pressures and low temperatures. The replacement of CH4 by CO2, which also forms a hydrate, could allow CH4 production from hydrate while sequestering CO2. A number of recent studies have focused on theoretical background, experimental simulations, and engineering approaches related to CH4-CO2 exchange in hydrates. We here investigate a key geologic constraint for possible CH4-CO2 exchange in sub-seafloor reservoirs, hydrate stability. We analyze seismic data and gas hydrate system models from the Pegasus Basin east of New Zealand, a region with evidence for abundant gas hydrates. Pressure-temperature conditions beneath the seafloor need to be within the stability fields for both CH4 hydrate and hydrate from the resulting gas mix after CO2 injection. Based on experimental and theoretical studies, we consider 64% a benchmark for maximum achievable CH4 replacement by CO2, resulting in a mix of 64% CO2 – 36% CH4, in hydrate. Down to a water depth of 1087 m, hydrate from this gas mix is stable within the entire CH4 hydrate stability field. A gap develops in deeper water with the base of gas hydrate stability (BGHS) for CH4 being deeper than for the 64% CO2 – 36% CH4 mix. In nature, most mechanisms for CH4 hydrate formation favor high saturation near the BGHS. For an evaluation of possible CH4-CO2 exchange, it is therefore important to investigate mixed-gas hydrate stability near the CH4-BGHS and to identify CH4 hydrates closer to the seafloor.

Enhanced strategies for depressurization in offshore natural gas hydrate exploitation: An in-depth investigation into pathway optimization and production stability mechanisms

Natural gas hydrates have garnered widespread attention as a high-quality energy resource. Recent offshore extraction experiences suggest that depressurization is a technically mature and economically viable option. However, challenges such as reservoir temperature reduction, reservoir subsidence, secondary hydrate formation, and insufficient dynamics in later-stage hydrate decomposition still require improvements to the depressurization method. This study, based on field data from Japan's first offshore natural gas hydrate extraction, utilizes a self-developed numerical simulator to model and validate reservoirs at the field scale. Long-term production rate stability, total production, secondary hydrate formation, reservoir subsidence, evolution of permeability, and temperature-pressure paths were analyzed and optimized for the three mainstream depressurization modes: steady depressurization, stepwise depressurization, and cyclic depressurization. The results indicate that, under the condition of equal total work done throughout the entire depressurization process, steady depressurization with an effectively lower depressurization rate is the optimal choice. Cyclic depressurization, due to the formation of secondary hydrates reducing the permeability of certain reservoir zones, adversely affects gas production efficiency during the long-term stable production phase. This study enhances insights into the coupled evolution of multiple physical fields during the depressurization of offshore natural gas hydrates, providing valuable guidance for future on-site extraction plan designs.

FMAW-YOLOv5s: A deep learning method for detection of methane plumes using optical images

Natural gas hydrates stored in the subsurface seabed of continental margins are one of the most important carbon reservoirs on Earth. Research on natural gas hydrates is of great significance to global warming and ecological protection. Methane plumes caused by crustal dynamics are usually considered as a sign of existence of natural gas hydrates. Detection of methane plumes thus becomes the first step of cold seep research. This paper conducts comprehensive research on detection of methane plumes based on deep learning methods and optical images. First, we proposed a method of creating high quality and balanced datasets for methane plumes detection tasks using open-source videos. We then proposed a FMAW-YOLOv5s method for methane plumes detection. The FMAW-YOLOv5s method improves the traditional YOLOv5s in design of backbone network, neck network and loss function. The FMAW-YOLOv5s method can realize accurate and fast detection of methane plumes with a precision of 96.9% and FPS of 141.7. The lightweight feature of FMAW-YOLOv5s also enables the deployment in edge computing devices such as AUVs and ROVs. This research can not only promote the study of cold seep activities, but also provide meaningful insights for detection of other underwater events such as gas pipelines leakage.

Mechanical and acoustic characterization of carbon dioxide gas replacement of methane gas hydrate

CO2 replacement presents a promising approach for the extraction of natural gas hydrate, offering advantages in cleanliness and safety. In this study, CO2 replacement CH4 hydrate experiments were carried out by using the triaxial, hydrate specimens with varying replacement ratios were prepared through different methods, and triaxial tests were performed to evaluate the mechanical properties of sediments after replacement. The key findings are as follows: the shear damage behaviors of CH4, CO2, and their mixed hydrate specimens are similar. Acoustic data indicates that initial CO2 injection during replacement causes dissociation of CH4 hydrate, potentially reducing the failure strength of the reservoir. However, post-replacement hydrate specimens exhibited higher failure strength than their original counterparts. This study provides valuable insights into the mechanical stability of CH4 hydrate reservoirs during CO2 replacement process.

Undrained triaxial tests of underconsolidated overlying sediments of hydrate deposits in the South China Sea

The South China Sea (SCS) is an important repository for natural gas hydrates (NGHs), where some NGH deposits and their overlying sediments (OSs) are in an underconsolidated state. During the exploitation of NGHs, the stability of the OSs of the NGH deposits is one of the key factors in ensuring mining safety. Especially under different consolidation degrees, the mechanical response and stability of the OSs will vary, which directly affects the safety and efficiency of the NGH mining. This research explores the influence of different consolidation degrees on the mechanical properties of the OSs of NGH deposits in the SCS. The strength and pore pressure characteristics were analyzed through undrained triaxial shear tests. The findings indicate that an increase in consolidation degree enhances the strain softening behavior, and an increase in initial effective stress enhance the strain hardening and shear contraction behaviors of the samples. The failure strength, modulus, and maximum excess pore pressure increase with the consolidation degree and initial effective stress, and there is an approximately linear correlation between failure strength and consolidation degree. Therefore, the exploitation of NGHs in the SCS must comprehensively consider the burial depth and consolidation degree of the OSs. The findings of this study will assist in optimizing mining plans and enhancing safety during the exploitation process.