Natural Gas Hydrate Decomposition Research Articles

Preparation of hydrated calcium silicate phase change microcapsules and its application of temperature regulation in deep-water natural gas hydrate layer cementing process

The effective hydration of cement at low temperatures is a critical factor affecting the sealing stability of the cement sheath. Effective hydration of cement slurry is typically accompanied by significant exotherm, and can cause the decomposition of natural gas hydrates, ultimately leading to gas migration and affecting cementing quality. To ensure effective hydration with low exothermic cement slurry, hydrated calcium silicate (C-S-H) shell phase change microcapsules (TDCSH) were prepared by oil-in-water emulsification with chemical precipitation. Compared with traditional phase change microcapsule with polymer shell, the rough C-S-H shell with large surface area improves the thermal conductive area of the microcapsules and their compatibility with the cement composition. Results showed that the TDCSH has a high phase change enthalpy of 169.9 J/g and 65.25% encapsulate efficiency compared to other inorganic shell materials. Furthermore, the addition of 3% TDCSH can reduce the hydration temperature of cement by 3.9°C and increase the compressive strength by 19.0% under the curing condition of 20°C. The mechanism of action of microcapsules in cement was analyzed. The results showed that the incorporation of TDCSH reduced the heat of hydration of cement while promoting the generation of more hydration products and increased the compressive strength of cement.

Development and application of low-melting-point microencapsulated phase change materials for enhanced thermal stability in cementing natural gas hydrate layers

In the exploration of deep-water oil and gas resources, encountering natural gas hydrate (NGH) layers poses significant challenges, particularly during cementing operations critical for wellbore stabilization. This study proposes a strategy employing cement slurries integrated with micro-encapsulated phase change materials (MPCMs) to address the destabilization of NGH layers, a key obstacle in deep-water cementing. MPCMs containing BaCO3 shell and low-melting binary PCMs in the core were synthesized by the self-assembly method. The structure and thermal properties of MPCMs were thoroughly characterized. MPCMs exhibited a distinct core-shell structure with a hydrophilic and well-sealed shell. Their phase change temperatures were in closely matched the temperatures found in NGH formations, at 3.5 °C and 13.9 °C. A comprehensive evaluation of the fundamental properties of cement slurries containing MPCMs (CSM) was conducted, including thermal stability, setting time, pore structure, and mechanical strength. Additionally, a laboratory device was employed to simulate cementing operations, allowing for intuitive analysis of the impact of hydration heat evolution on NGH stability—a notably underexplored aspect in related literature. The results demonstrated that MPCMs effectively reduced the hydration heat generated by cement slurry within the initial 36 h. Specifically, at a 9% MPCMs dosage, the hydration heat of CSM decreased by 19.0%, resulting in the sustained stability of NGH. In contrast, the control group's cementing process directly led to the complete decomposition of NGH. Even at lower MPCMs concentrations, the decomposed NGH was more likely to recrystallize and return to a stable state due to the slower hydration heat release rate of CSM. This study not only provides evidence of the effectiveness of MPCMs as heat inhibitors in reducing the disruption of hydrate stability during well cementing but also provides theoretical guidance for the design and application of cement slurries for NGH reservoirs. By enhancing the stability of NGH layers, this work supports the safe and efficient exploitation of undersea hydrocarbon resources, contributing to shaping future global energy strategies.

Molecular dynamics simulations to evaluate the decomposition properties of methane hydrate under different thermodynamic conditions

Understanding the thermodynamic effect on methane hydrate decomposition is beneficial for designing controllable methane recovery processes under conditions of continental margins and oceanic sediments. In this work, we systematically examined the effects of varying temperatures and pressures on the natural gas hydrate decomposition in the presence of 20 mol% methanol through the molecular dynamics approach. Taking advantages of key parameters of angular order parameter (AOP), radial distribution function (RDF), mean square displacement (MSD), and potential energy, we mainly aimed to explore the impact of temperature and pressure on the decomposition of methane hydrate. It can be founded that high temperature is a positive factor for the methane hydrate decomposition, and as the temperature increases from 272.15 K to 277.15 K, the promotion effect becomes more obvious, resulting in a reduction of decomposition time by 3.93 ns. On the contrary, pressure has a negative effect on the methane hydrate decomposition, and as the pressure increases from 1 bar to 200 bar, the inhibitory effect becomes smaller. Additionally, the potential energy as a function of time can be used to evaluate the decomposition rates under different thermodynamic conditions. The obtained results underscore the significant dependence of methane hydrate decomposition rates on temperature and pressure, providing essential guidelines for optimizing gas hydrate decomposition processes.

Fines migration characteristics of illite in clayey silt sediments induced by pore water under the depressurization of natural gas hydrate

Marine gas hydrate is widely distributed in clayey silt sediments, which have high clay content and low permeability. The decomposition of natural gas hydrate will cause the mechanical failure of the reservoir and the decrease of pore water salinity, inducing the migration of clay minerals to clog the pore throat, which has a significant impact on the production efficiency of natural gas hydrate. In this work, the migration behaviour of illite in clayey silt sediments driven by pore water under the depressurization of hydrate was studied through pressure difference, pore throat and content changes. We studied the migration process of silt, excluding the interference of synergistic migration of silt and illite, and then studied the migration of illite under the change of flow rate and salinity. The results show that illite will migrate before silt and that critical flow rate and critical salinity exist. The flow rate mainly affects the torque generated by the forces detaching the illite particles. Illite particle detachment will occur if the flow rate exceeds the critical value and the torque balance is disrupted, and then the pore throat is clogged. There are two effects of salinity decrease on illite migration. Above the critical salinity, the expansion of the pore throat due to decomposition has a significant effect on illite migration. Below the critical salinity, the increase of the diffuse electric double layer thickness and the electrostatic repulsion will lead to an increase of the particle concentration in the pore water, making clogging more likely to occur even at low flow rates. This work suggests that clay migration has a complex impact on the development of clayey silt hydrate, and helps to consider the reasonable combination of saturation and production rate when designing a development plan to reduce the impact of permeability decline due to continuous pore throat clogging on development efficiency.

Investigation on hydrate exploitation in submarine slope: Insights from discontinuous pillar exploitation

The decomposition of natural gas hydrate (NGH) will cause a decrease in reservoir strength, which can easily induce submarine landslides when hydrate reservoirs are located on a submarine slope. Although there have been several studies on the stability of hydrate-bearing submarine slopes (HBSS), little attention has been paid to minimizing the risk of landslides due to NGH exploitation. The “multistage reduction method” based on strength reduction was described in this paper. Subsequently, “discontinuous pillar exploitation” was proposed to achieve safe extraction of NGH and avoid submarine landslides. Finally, the “discontinuous pillar exploitation” was analyzed using the “multistage reduction method”. The results show that NGH decomposition has a far-reaching impact on the HBSS; it reduces the stability of HBSS and can trigger submarine landslides. The “discontinuous pillar exploitation” can divide the continuous plastic failure zone into short discontinuous plastic zones through the setting up of pillars, which significantly improves the stability of HBSS. With the decrease in the exploitation ratio, the safety factor of the submarine slope increases continuously. When the “discontinuous pillar exploitation” is adopted for NGH production on a submarine slope, there are two positions that require special attention: the junctions between the pillars and the exploitation area (peak area of shear stress); the side of exploitation area near the top of the slope (peak area of tensile stress).

Numerical simulation on gas production from hydrate-bearing sediments by depressurization considering time-varying reservoir compressibility

Depressurization is a promising Natural Gas Hydrate (NGH) recovery method. However, the pressure drop can cause significant pore compression, particularly in clayey-silty reservoirs. Additionally, the decomposition of NGH will further weaken the reservoir strength, leading to the time-varying characteristics of reservoir compressibility. This study analyzed depressurization-based gas production under different NGH reservoir models and accounted for time-varying reservoir compressibility. The results showed that the increased reservoir compressibility caused by hydrate decomposition significantly affected the pressure propagation and permeability evolution, further diminishing gas production. The cumulative gas production from sandy reservoirs with lower reservoir compressibility could reach 60 times that from clayey-silty reservoirs with higher reservoir compressibility. The optimal bottom-hole pressure (BHP) gradually increased with the reservoir compressibility. For the reservoir with the higher compressibility, the cumulative gas production at a BHP of 3 MPa was 58% lower than at 9 MPa. Therefore, considering time-varying reservoir compressibility during hydrate decomposition is essential for accurately forecasting the gas production capacity of depressurization. Furthermore, BHP should be cautiously determined in reservoirs with higher reservoir compressibility.

Study on acoustic properties of hydrate-bearing sediments with reconstructed CO2 hydrate in different layers during CH4 hydrate mining

Natural gas hydrate (NGH), a clean energy source with huge reserves in nature, and its safe and efficient exploitation fits perfectly with the UN Sustainable Development Goals (SDG-7). However, large-scale NGH decomposition frequently results in subsea landslides, reservoir subsidence, and collapse. In this work, in order to achieve safe and efficient exploitation of NGHs, the stability variation of different reservoir layers by depressurization/intermittent CO2/N2 injection (80:20 mol%, 50:50 mol%) was investigated using acoustic properties (P-wave velocity, elastic modulus), as well as reservoir subsidence under an overburden stress of 10 MPa. The P-wave velocity increased from 1282 m/s to 2778 m/s in the above-reservoir and from 1266 m/s to 2564 m/s in the below-reservoir, significantly increasing reservoir strength after CO2 hydrate formation. The P-wave velocity and elastic modulus in the top reconstructed reservoir were continually decreased by the shear damage of the overlying stress, while they remained stable in the bottom reconstructed reservoir during hydrate mining. However, due to superior pressure-bearing ability of the top CO2 hydrate reservoir, which was lacking in the bottom CO2 hydrate reservoir, the reservoir subsidence was relieved greatly. Despite the stiffness strength of reconstructed reservoir was ensured with CO2/N2 sweeping, the skeletal structure of CH4 hydrate reservoir was destroyed, and only the formation of CO2 hydrate could guarantee the stability of P-wave velocity and elastic modulus which was most beneficial to relieve reservoir subsidence. A large amount of CO2 was used in reservoir reconstruction and CH4 hydrate mining, which achieved the geological storage of CO2 (SDG-13). This work provided a new idea for safe and efficient NGHs mining in the future, and the application of acoustic properties served as a guide for the efficient construction of reconstructed reservoirs and offers credible technical assistance for safe exploitation of NGHs.

Numerical Simulating the Influences of Hydrate Decomposition on Wellhead Stability

Natural gas hydrate reservoir has been identified as a new alternative energy resource which has characteristics of weak cementation, low reservoir strength and shallow overburden depth. Thus, the stability of subsea equipment and formation can be affected during the drilling process. To quantitatively assess the vertical displacement of the formation induced by hydrate decomposition and clearly identify the influence laws of various factors on wellhead stability, this study established a fully coupled thermo-hydro-mechanical-chemical (THMC) model by using ABAQUS software. The important factor that affects the wellhead stability is the decomposition range of hydrates. Based on this, the orthogonal experimental design method was utilized to analyze the influence laws of some factors on wellhead stability, including the thickness of hydrate formation, initial hydrate saturation, overburden depth of hydrate sediment, and mudline temperature. The results revealed that the decomposition of hydrate weakens the mechanical properties of the hydrate formation, thus leading to the compression of the hydrate formation, further causing the wellhead subsidence. When the duration of drilling operations was 24 h and no decomposition of natural gas hydrate occurs, the wellhead subsidence is recorded at 0.053 m, this value increases with an increase in drilling fluid temperature. The factors were listed in descending order as following, according to their significance of influences on wellhead stability: the thickness of hydrate formation, initial hydrate saturation, overburden depth of hydrate sediment, and mudline temperature. Among the above factors, statistical significance of the mudline temperature was less than 15% confidence level, suggesting that the effect of mudline temperature on wellhead stability is negligible. These findings not only confirm the influence of hydrate decomposition on wellhead stability, but also suggest important implications for the drilling of hydrate-bearing formation.

Моделирование процесса распада гидрата метана путем закачки горячей воды

To extract natural gas from hydrates by injection of hot water, the decomposition of natural gas hydrates in a porous medium under the influence of a heat flow was experimentally and numerically simulated. It is assumed that the radial diffusion model describes the decomposition of natural gas hydrates in a porous medium due to the injection of hot water, and the decomposition of hydrates is a first-order reaction. By combining the decomposition reaction rate equation with the heat transfer rate equation and the heat balance equation, the relationship between the accumulatedamount of methane (n -n ) and the decomposition time t was obtained. By comparing the results of the experiment0 Hand numerical simulation, it was found that under the experimental conditions, the hydrate decomposition ratecoefficient is consistent with the results of the obtained analytical dependences.

Application of a biomimetic wellbore stabilizer with strong adhesion performance for hydrate reservoir exploitation

Natural gas hydrate (NGH) in marine is usually reserved in the pores or cracks of weakly cemented argillaceous siltstones. Moreover, the hydrates are susceptible to variations in temperature and pressure conditions when water-based drilling fluids (WBDFs) are drilled into hydrate reservoirs, leading to the hydrate in-situ decomposition and severe sand production. In this work, an inexpensive and facilely prepared biomimetic wellbore stabilizer with strong adsorption of multiple hydrogen bonds was prepared by fusing catechol-rich tannic acid (TA) and polyvinyl alcohol (PVA) with polyol hydroxyl adsorption function, referred to as TA-PVA complex (TA-PVA). TA-PVA was added to WBDFs to strengthen the NGH reservoir wellbore for ensuring the safety of drilling process in a wide temperature range (2-60℃). The microscopic characterization of TA-PVA and its cohesion mechanism with argillaceous siltstone was investigated by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties of skeleton of the artificial hydrate cores were evaluated by compressive strength test, with maximum compressive strength reaching 0.45 MPa. And the adhesion force of TA-PVA to the probe modified by silica microsphere (PSM) was further studied by AFM. Meanwhile, the adhesion forces between TA-PVA and cyclopentane hydrate particles were measured at 1.5℃. Adhesion test results demonstrate that TA-PVA can bond clay particles, quartz sand and hydrate particles together. In detail, the adhesion force between TA-PVA and PSM reaches more than 164.46 mN/m, the adhesion force between TA-PVA droplet and cyclopentane hydrate particle reaches 43.19 mN/m. The differential scanning calorimetry (DSC)curves demonstrate that TA-PVA releases no heat between 0 and 60 °C, indicating that TA-PVA has no impact on the decomposition of NGH, showing the potential to maintain the integrity of NGH reservoir.

Numerical Modeling on Dissociation and Transportation of Natural Gas Hydrate Considering the Effects of the Geo-Stress

A deep understanding of the dissociation and transportation mechanism of natural gas hydrate (NGH), taking into account the effects of geo-stress, contributes to optimizing the development strategy and increases the exploitation efficiency of NGH. In this paper, the mathematical model, coupled with fluid heat and mass transfer, multiphase flow mechanics, and reaction kinetics with phase change in the process of hydrate decomposition was established. An axisymmetric two-dimensional model was developed to simulate the depressurization decomposition process of natural gas hydrate in the Berea sandstones. FLUENT software was used to solve the fundamental governing equations of the multi-phase flow, and UDF programming was employed to program the hydrate decomposition model and the modified permeability model in the dissociation and transportation of NGH. The simulation results were then validated by Masuda’s experimental data. The effects of gas saturation, outlet pressure, temperature, absolute permeability and geo-stress on the decomposition of natural gas hydrate were studied. The results indicated that a higher absolute permeability, higher initial gas saturation, lower outlet pressure, and higher initial temperature advance the decomposition rate of hydrate. Thus, an optimized production plan is essential to promote the extraction efficiency of the NGH. The geo-stress causes a decrease in the porosity and permeability of the porous rock, which restricts the efficiency of the heat and mass transfer by the fluid flow, leading to a slower dissociation and transportation rate of the NGH. Thus, it is important to take geo-stress into consideration and balance the extracting efficiency and the well pressure, especially when the NGH is developed by depressurization.

The effect of decomposition of natural gas hydrate on deep-water drilling

One of the significant challenges in deep-water drilling is calculating BHP during kickoff caused by natural gas hydrate decomposition. In this paper, the heat transport theory, seepage mechanics, and hydrate decomposition kinetics serve as the foundation for the hydrate decomposition and bottom hole pressure model. Research shows 42.8 m3 of gas have entered Well X cumulatively, resulting in a 1.66 MPa pressure decrease and a 6.9-hour-recovery period. The monitoring of high saturation and porosity formations needs to be strengthened, and drilling parameters need to be modified to protect the stability of the wellbore, according to the analysis of formation parameters and drilling parameters.

Microcosmic Characteristics of Hydrate Formation and Decomposition in the Different Particle Size Sediments Captured by Cryo-SEM

Sand production and sand control studies in non-diagenetic reservoirs are the weak point in the conventional petroleum industry. However, natural gas hydrate (NGH) mainly exists in non-diagenetic strata, and sand production occurs during exploitation, which restricts the safe and sustainable production of NGH. To study the microcosmic characteristics of sand production, the hydrate decomposition behaviours in the sediments were captured by the Cryo-SEM method. The micromorphology of different particle sizes of sand samples containing NGH (the sand median diameter d50 is 150, 87, 55, 38, 24, and 13 µm) and the microcosmic processes of NGH decomposition were observed. Then, the microcosmic characteristics of sand production, during the decomposition process, were analysed. (1) The gas hydrate decomposition increases pore space and reduces reservoir strength; the expansion action of the decomposition of water and gas, the softening action of the decomposition of water, and the compression action by overlying stress (crustal stress) promoted sand production, deformation, and subsidence of the NGH reservoirs in the mining process. (2) The decomposition of NGH has a more significant impact on sediments with smaller particle sizes. (3) The particle size of NGH may be larger than the particle size of the mud in the reservoirs, and acting as “gravel” plays a particular role in sand control. Therefore, the particle size of NGH cannot be ignored in the design of sand control. (4) It has been revealed, and verified, that sputtering (splashing) is a unique process of sand production caused by NGH decomposition. In other words, the rapid expansion of the volume of the decomposed gas and water from NGH leads to the eruption and sputtering of hydrate particles, providing the driving force for sand migration, which is a different process of sand production than in conventional oil and gas.

Comparative study of the electrical characteristics of hydrate reservoirs before and after gas hydrate trial production in the Muli permafrost area of the Qilian Mountains, NW China

Natural gas hydrate (NGH) is considered one of the most promising alternative energy sources in the 21st century. The exploitation and decomposition of NGHs could cause geological disasters and eco-environmental problems related to climate warming, seawater blue tides, submarine landslides, drilling platform collapses, slope instability, etc. Thus, an investigation of the eco-environmental effects of NGH exploitation and decomposition has scientific and practical significance. In this paper, the electrical characteristics of NGH reservoirs before and after NGH trial production in the Muli permafrost area of the Qilian Mountains are comparatively examined for the first time. The electrical structure models before and after NGH trial production are obtained through two-dimensional and three-dimensional inversion of the NE audio-magnetotelluric (AMT) sounding profile around production test well SK2. Notably, the electrical structure of the NGH reservoir changes greatly. The research indicates that (1) after NGH trial production, the formation resistivity increases remarkably within 200 m and burial depths in the range of 120– 340 m around the production test well; (2) the main reason for the increasing resistivity after trial production is the Joule-Thomson effect caused by depressurization production and the endothermic effect of NGH decomposition, which lead to the formation of ice-bearing strata; afterwards, we explain the formation process of ice-bearing strata after NGH trial production; and (3) we speculate that the formation stability is not adversely affected after NGH trial production. These findings and research results can provide guidance for subsequent geoenvironmental safety risk assessments of NGH development in permafrost areas.

Influence of hydrate exploitation on stability of submarine slopes

The decomposition of natural gas hydrate will reduce the cementation effect of hydrate and produce ultra-static pore pressure, which will change the mechanical characteristics of the reservoir. Eventually, a series of geological disasters could be triggered, of which the submarine landslide is a typical example. In order to analyze the stability of hydrate-bearing submarine slopes and to explore the internal relationship between hydrate decomposition and submarine landslides, a “two-step reduction method” was described in this paper. This method was based on a strength reduction approach, which can be used to assess the effects of the initial geostress balance and hydrate decomposition on substrate strength reduction. This method was used to reveal the essence of hydrate decomposition, and then, a joint operation mode of multi-well was proposed. The internal relationship between hydrate decomposition and submarine landslides was analyzed in detail. And the development process and mechanism of submarine landslide were deeply discussed. The results showed that hydrate decomposition is a dynamic process of stress release and displacement, where the “stress inhomogeneity” distributed along the slope is transformed into “displacement inhomogeneity.” We concluded that hydrate decomposition could trigger a submarine landslide, especially along a sliding surface. The formation of submarine landslide is a gradual development process and presents the dual characteristics of time and space.

Effects of creep characteristics of natural gas hydrate-bearing sediments on wellbore stability

Natural gas hydrate (NGH) reservoirs consist of the types of sediments with weak cementation, low strength, high plasticity, and high creep. Based on the kinetics and thermodynamic characteristics of NGH decomposition, herein a heat-fluid-solid coupling model was established for studying the wellbore stability in an NGH-bearing formation to analyze the effects of the creep characteristics of NGH-bearing sediments during long-term drilling. The results demonstrated that the creep characteristics of sediments resulted in larger plastic yield range, thus aggravating the plastic strain accumulation around the wellbore. Furthermore, the creep characteristics of NGH-bearing sediments could enhance the effects induced by the difference in horizontal in situ stress, as a result, the plastic strain in the formation around the wellbore increased nonlinearly with increasing difference in in situ stress. The lower the pore pressure, the greater the stress concentration effects and the higher the plastic strain at the wellbore. Moreover, the lower the initial NGH saturation, the greater the initial plastic strain and yield range and the higher the equivalent creep stress. The plastic strain at the wellbore increased nonlinearly with decreasing initial saturation.

Research progress on the effects of nanoparticles on gas hydrate formation.

Gas hydrate has great application potential in gas separation, energy storage, seawater desalination, etc. However, the intensity of mass and heat transfer is not enough to meet the needs of efficient hydrate synthesis. Nanoparticles, different from other liquid chemical additives, are considered as effective additives to promote hydrate formation due to their rich specific surface area and excellent thermal conductivity. This work summarizes the effect of the nanoparticles on the thermodynamics and kinetics of hydrate formation. And also, this work probes into the mechanism of the effect of the nanoparticles on the formation of hydrate as well as provides some suggestions for future research. It is found that it's difficult for nanoparticles to effectively promote the formation of the gas hydrate without the use of surfactants, because the adhesion characteristics of the nanoparticles make them easily agglomerate or even agglomerate in solution. In addition, at present, the research on the influence of nanoparticles on the formation and decomposition of natural gas hydrate is still very fragmented, and the micro mechanism of the influence is not clear, which requires more systematic and specific research in the future. At the same time, the development of nanoparticles that can promote the formation of natural gas hydrate should also become the focus of future research.

Can low hydration heat cement prevent the decomposition of natural gas hydrate under high pressure and low temperature?

In this article, an in-house device is used to study the prevention of natural gas hydrate (NGH) decomposition performance and the mechanism of the low-heat cement for cementing. The results show that the natural gas hydrate can decompose to different degrees due to the hydration heat of the G-class oil well cement at the experimental conditions of 281.15 K & 8 MPa and 277.15 K & 6.5 MPa. Decomposition occurs within the period of hydration heat peak. The visualization window allows observing the decomposition and reduction of natural gas hydrate. The low-heat cement can effectively prevent the decomposition of natural gas hydrate at the experimental conditions of 281.15 K & 8 MPa, 277.15 K & 6.5 MPa, and 273.15 K & 4.5 MPa. The hydration heat experiment found that with the decrease in the hydration environment temperature, the hydration temperature rise appeared significantly later, the induction period was delayed into the acceleration period, the maximum of hydration temperature rise exhibited a decreasing phenomenon, and the hydration temperature rise of low hydration heat cement was far lower than that of the G-class oil well cement.

Design of a drilling unit for deep-sea stratum drilling robot

Marine natural gas hydrate has attracted much attention due to its broad energy prospects. With the deepening of research on natural gas hydrate, researchers have found that the decomposition of natural gas hydrate is an important inducer for many natural disasters. This paper proposes a design idea of a deep-sea stratum drilling robot used in gas hydrate test mining area. It can carry out long-term and effective real-time monitoring of the surrounding terrain and environmental changes. The specific structure and function of each component of the robot are introduced, and the locomotion principle of the drilling robot is elaborated. This paper focuses on a drilling unit as one of the key technologies for developing the robot, and the design of drilling unit of robot will be presented in detail. Then, the feasibility of the robot movement and the effect of the drill bit rotation on the soil are obtained through mechanical analysis and simulation. The work of this paper provides guidelines for the development of deep-sea stratum drilling robot in the future.

Molecular and Carbon Isotopic Characteristics during Natural Gas Hydrate Decomposition: Insights from a Stepwise Depressurization Experiment on a Pressure Core

Molecular and Carbon Isotopic Characteristics during Natural Gas Hydrate Decomposition: Insights from a Stepwise Depressurization Experiment on a Pressure Core