Hydrate Formation Rate Research Articles

Enhanced Study of CO2 Hydrate Formation in Marine Oil–Gas Based on Additive Effect

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.

Evaluation of the synergic effect of amino acids for CO2 hydrate formation and dissociation

Gas hydrate formation is a very challenging problem in the oil and gas industry. The chemical inhibition method is the best practicable hydrate mitigation method by injecting hydrate inhibitors such as Thermodynamic Hydrate Inhibitors (THIs) and Kinetic Hydrate Inhibitors (KHIs) into the pipeline. However, the hydrate inhibitors' biodegradability and limited data on dual functional inhibitor mixtures raise concerns in this study. This study aims to investigate and compare thermodynamic and kinetic inhibition on CO2 hydrate by using biodegradable amino acid inhibitor mixtures of Glycine and Alanine. In this study, the inhibitor mixtures were prepared by mixing Glycine and Alanine in 3 different mixture ratios, followed by the Thermodynamic and Kinetic inhibition tests. Thermodynamic Inhibition Test was conducted by using 10 wt% of inhibitor mixtures in a CO2-water system under pressure of 4.0, 3.5, 3.0 and 2.5 MPa, while Kinetic Inhibition Test was carried out by using 1 wt% of the sample in the CO2-water system at a constant pressure of 4.0 MPa and temperatures at 274.15K. The analysis methods for the Thermodynamic Inhibition Test were Hydrate Liquid-Vapor Equilibrium (HLVE) Curve, Average Depression Temperature and Molar Dissociation Enthalpy, while the Induction Time method, the number of CO2 moles consumed, the formation rate of CO2 gas hydrate and RIP were used in the Kinetic Inhibition Test. In this study, all inhibitor mixtures exhibit dual functional inhibition on the CO2 hydrate. For THI, 50% Gly: 50% Ala shows the best thermodynamic inhibition strength with an average depression temperature of 2.42 K. All the inhibitor mixtures for THI have the dissociation enthalpies within the CO2 hydrate enthalpy range, which show that the inhibition is due to the influence on the water molecules’ interaction only. For KHI, 75% Gly: 25% Ala shows the highest kinetic inhibition strength on CO2 formation with the longest induction time of 115.2 min and the highest RIP of 0.40. In the KHI experiment, there is a drop in the CO2 uptake capacity with the presence of inhibitors used, where the highest difference of CO2 moles consumed is 0.0057 mol. A synergistic effect of inhibitor mixtures was observed in this study on 50% Gly: 50% Ala for THI and 75% Gly: 25% Ala for KHI. However, the “degradation” effect was also exhibited on 75% Gly: 25% Ala and 25% Gly: 75% Ala for THI and 50% Gly: 50% Ala and 25% Gly: 75% Ala for KHI, where the performance of the inhibitor mixtures is poorer than the concentrated amino acids. The “degradation” effect of the inhibitor mixtures at certain ratios was not covered in this study and it requires a further understanding of the chemistry behind the inhibition mechanism.

Numerical Simulation of Secondary Hydrate Formation Characteristics and Effectiveness of Prevention Methods

The exploitation of natural gas hydrates by the pressure reduction method is affected by the decomposition heat absorption effect, and the range of the formation temperature reduction area is expanding. At the same time, the temperature reduction phenomenon is more significant around the production wells under the influence of gas throttling and expansion effects, and hydrate formation will occur under certain temperature and pressure conditions, leading to blockage of effective seepage channels in the reservoir in the region and elevation of seepage resistance, which may affect the output of hydrate decomposition gas. A numerical simulation model is constructed for the purpose of studying the secondary hydrate generation pattern around the well, analyzing the impact of secondary hydrates around wells on the production capacity, and assessing the effectiveness of prevention methods to inform the actual production of hydrates. The results demonstrate that secondary hydrate is typically formed in the near-well area of the upper part of the production well, and the secondary hydrate around the upper part of the production well is the first to be formed, exhibiting the highest saturation peak and the latest decomposition. The formation of the secondary hydrate can be predicted based on the observed change in temperature and pressure, and the rate of secondary hydrate formation is markedly rapid, whereas the decomposition rate, approximately 0.285 mole/d, is relatively slow. Additionally, the impact of secondary hydrates on cumulative gas production is insignificant, and the effect of secondary hydrates on capacity can be ignored. Hot water injection, wellbore heating, and reservoir reconstruction can effectively eliminate secondary hydrates around the well. Reservoir reconstruction represents a superior approach to the elimination of secondary hydrates, which can effectively enhance production capacity while preventing the generation of secondary hydrates.

Optimizing CO2 Hydrate Sequestration in Subsea Sediments through Cold Seawater Pre-Injection

Carbon sequestration technology offers a solution to mitigate excessive carbon dioxide emissions and sustainable development in the future. This study proposes a method for subsea carbon sequestration through the injection of cold seawater to promote CO2 hydrate formation. Using a self-developed simulator, we modeled and calculated the long-term sequestration process. The study focuses on analyzing the thermal regulation of the seabed following cold seawater injection, the multiphysical field evolution during CO2 injection and long-term sequestration, and the impact of seawater injection volumes on sequestration outcomes. The feasibility and leakage risks of this method were evaluated on a 100,000-year timescale. Results indicate that the injection of cold seawater significantly improves the pressure–temperature conditions of subsea sediments, facilitating early hydrate formation and markedly increasing the initial CO2 hydrate formation rate. Consequently, the distribution pattern of hydrate saturation changes, forming a double-layer hydrate shell. Over the long term, while cold seawater injection does not significantly reduce CO2 leakage, it does increase the safety margin between the hydrate layer and the seabed, enhancing the safety coefficient for long-term CO2 hydrate sequestration. Through detailed analysis of the behavior of CO2 components during sequestration, this study provides new theoretical insights into subsea CO2 hydrate storage.

Synergistic effect of alcohol polyoxyethylene ether sodium sulphate and copper foam on methane hydrate formation

AbstractNatural gas is the cleanest fossil energy source and its consumption is increasing rapidly, so an efficient natural gas way of storing and transporting is urgently needed. Solidified natural gas (SNG) technology is gaining traction because of its higher safety, lower cost, and flexible storage and transportation modes. To improve the methane uptake rate in SNG technology, this work investigated the growth of methane hydrate in fatty alcohol polyoxyethylene ether sodium sulphate (AES) solution with the addition of three different pores per inch (PPI) of copper foam (CF). The results showed that the addition of AES caused the hydrate to grow upwards along the wall, and the methane uptake in the 300 ppm AES solution was increased by 623% compared to pure water. CF not only provided more nucleation sites for hydrate but also transferred the heat generated during hydration. Moreover, there was a synergistic effect between AES and CF and the solution could continuously transport upward along the continuous metal skeleton to increase the gas–liquid contact area. Thus, the formation rate and induction time of methane hydrate improve. Hydrate had the highest methane uptake in the 20 PPI CF system and the lower the pressure, the greater the ability of CF to promote hydrate formation. The methane uptake improved by 27.6% and the induction time was reduced by 59.7% compared to the pure AES system at 6 MPa. This work is aimed at advancing SNG technology (especially at low pressure) and informs the theoretical foundation.

Spatial evolution of CO2 storage in depleted natural gas hydrate reservoirs and its synergistic efficiency analysis

Carbon neutrality is now a common strategic target worldwide, with geological storage seen as the mainstream scheme to address CO2 emissions and the greenhouse effect. Depleted natural gas hydrate reservoirs (DNHR), with their high-pressure, low-temperature environment, could capture CO2 in the form of hydrates, being an innovative way for carbon storage. A lab-scale reactor was used in this work to simulate CO2 injection into the reservoir after gas hydrate exploitation. As expected, it was found that the low-temperature environment of the depleted reservoir at the end of gas production provided a high driving force and accelerated the rate of CO2 hydrate formation. Consequently, the maximum gas storage capacity was increased by 66% by optimizing the injection timing and reducing the gas injection flow rate to enable enough hydrate formation. Besides, the formation of CO2 hydrate in the DNHR could also help stabilize the reservoir to achieve a more efficient CH4 production and CO2 storage. This study provides a novel strategy for gas hydrate exploitation as well as subsequent geological storage of CO2 in depleted natural gas hydrate reservoirs by making full use of their favorable conditions.

Effect of complex ionic liquid additives on the formation kinetics and separation efficiency of binary gas mixture hydrates

Rising carbon emissions worldwide have necessitated the discovery of efficient CO2 separation and capture technologies. Owing to their good CO2 selectivity, imidazolium-based ionic liquids (ILs) have been used as additives in hydrate-based gas separation (HBGS) technologies. Sodium dodecyl sulfate (SDS) can notably improve the rate of hydrate formation when used as a surfactant. However, the synergistic effect of imidazolium-based ILs and SDS remains unknown. This study aimed at investigating the synergistic effect of imidazolium-based ILs and SDS on the hydrate formation kinetics of binary gas mixtures of CO2/N2 at different temperatures. The carbon capture and storage capacity was determined, and HBGS was evaluated using pure imidazolium-based IL 1-butyl-3-methylimidazolium octyl sulfate ([BMIM] [OS]) and composites of IL and SDS as additives. Compared with pure water, [BMIM] [OS] effectively promoted gas hydrate formation and increased CO2 consumption by 107.9 %. The maximum CO2 separation factor was obtained at 273.15 K, and the mixed additive significantly enhanced gas consumption by 11.1 %. X-ray diffraction and Raman spectroscopy analysis indicated that the hydrate samples were type I structural hydrates and that [BMIM] [OS] improved the mass transfer process. The results of this study provide a theoretical basis for CO2 gas separation and capture.

Mechanistic Study on the Influence of Wax on Hydrate Formation Process.

To manage the interactions between wax and hydrate formation, a comprehensive understanding of the system's thermodynamics and flow characteristics is essential. Wax and hydrates coexist under low-temperature and high-pressure conditions, mutually influencing each other both thermodynamically and kinetically. This study focused on two main aspects: how wax affects the rate of hydrate formation in the oil-water system and how hydrate formation influences the thermodynamics of wax crystal precipitation. The presence of wax decreased the rate of hydrate formation, especially at higher wax contents. In systems with high wax content, over 70% of wax precipitated before hydrate formation, leading to less precipitation within the hydrate formation temperature range. With low water content, there were more nucleation sites for wax crystals in the oil phase, resulting in a greater difference in precipitation rates among different wax contents. For water content greater than 10%, the differences in precipitation rates were less significant, indicating a diminished effect of water content on wax crystal precipitation rates. Hydrates' hydrophilic nature had a limited impact on wax crystal nucleation and growth. Generally, wax crystals precipitate before hydrate formation, necessitating control measures for wax deposition during production processes.

Large-Scale Experimental Investigation of Hydrate-Based Carbon Dioxide Sequestration

Hydrate-based CO2 sequestration is a novel approach that can not only realize permanent CO2 sequestration but can also form an artificial cap to prevent its upward migration. In this work, a self-developed large-scale 3D apparatus was employed to investigate hydrate formation characteristics in hydrate-based CO2 sequestration at a constant liquid CO2 injection rate through a vertical well for the first time. Temperature and pressure evolutions in the sediment were analyzed in detail. Key indicators, including cumulative sequestered CO2, CO2 in hydrate and liquid phases, the instantaneous hydrate conversion, and liquid CO2 retention rates, were calculated. The results show that hydrate continuously forms with increased CO2 injection and exhibits strong heterogeneity due to the variation in hydrate formation rate and quantity. Severe liquid CO2 heterogeneous figuring phenomena occur since hydrate deteriorates the effective pore structure and topology, resulting in relatively small cumulative sequestered CO2 when a large amount of CO2 is released from the outlet. Meanwhile, the instantaneous hydrate conversion and liquid CO2 retention rates have large fluctuations owing to water consumption and variation in the effective contact area between liquid CO2 and water. However, hydrate formation does not cause blockage of wellbore and formation nearby under given experimental conditions, which is beneficial for hydrate formation in deeper sediment. This study provides insights into hydrate formation and liquid CO2 immigration regularity during hydrate-based CO2 sequestration and demonstrates its feasibility at a field scale.

The effect of PVP and PVA on hydrate formation kinetics of ethane and propane mixture in the presence of kaolin nanoparticles

AbstractThe blockage of gas transmission pipelines due to gas hydrates poses a significant challenge for the gas industry. Low‐dosage hydrate inhibitors (LDHI) are utilized to influence the kinetics of hydrate formation, including nucleation, growth, and/or agglomeration. In the current study, a series of batch, isochoric, and isothermal tests were carried out to investigate the impacts of two LDHIs, poly N‐vinylpyrrolidone (PVP) and polyvinyl alcohols (PVA). This study examined the influence of these inhibitors on nucleation and growth of ethane+propane mixture in the presence of kaolin nanoparticles. In laboratory studies and using pure constituents, the rate of hydrate formation is low to investigate the inhibitors effect. To enhance the rate of hydrate formation, kaolin nanoparticles were utilized as they serve as a suitable representative for solid minerals commonly found in pipelines. The gas phase's compositional change were measured using a gas chromatograph. The results revealed that the growth stage of mixed‐gas exhibited two distinct steps, attributed to the formation of two different structures known as structure II and structure I. During the first step, structure II was formed, and the cavities were occupied by both gas components. In the second stage, structure I was formed by ethane. The effect of temperature on the induction time (nucleation rate) and the growth rate during the second stage was lower than that at the first stage. The increase in PVA concentration resulted in an increase in the induction time and a decrease in the rate of growth during the first stage. The performance of PVA was found to be affected by temperature. Lower temperatures resulted in the formation of less foam, providing improved performance for PVA at −0.5°C. PVP had a stronger impact on induction time and both growth steps compared to PVA, indicating stronger inhibitory impact of PVP on nucleation of hydrates initiated by propane and the growth of both propane and ethane hydrates.

Experimental study on gas separation from the oil–water-emulsion mixture via hydrate method

The gas separation technology based on hydrate method offers several advantages, including a short process flow, simple equipment, no pollution, less corrosion, and lower energy consumption. It has a broad application prospect in the acid gas purification, biogas purification and CO2 sequestration., etc. However, demanding hydrate formation conditions and lower gas separation effects constrain its application. Oil-water emulsion shows promise in improving mass and heat transfer efficiency, enhancing hydrate slurry fluidity, and reducing hydrate aggregates. Thus, this study investigates the effects of different oil–water ratios, promoter concentrations, and surfactants on hydrate formation and separation efficiency in an oil–water emulsion system. At an oil–water ratio of 1:1, the purification rate increased to 6.06, five times higher than in a pure water system. The addition of 1,3-Dioxolane (DIOX) facilitated bidirectional growth properties of hydrate formation on droplet surfaces, enhancing hydrate nucleation and formation, leading to a CO2 recovery increase to 87% with 1.5 wt% DIOX. Furthermore, lipophilic surfactants were more likely to promote hydrate slurry fluidization. The addition of Span80 reduced hydrate agglomeration and increased the rate of hydrate formation as concentration rose. The results suggest that adding DIOX and increasing the concentration of Span80 could improve the hydrate method’s separation efficiency at an oil–water ratio of 1:1.

Pore-scale investigation on the morphology evolution and micro-mechanism of methane hydrate formed from free gas and dissolved gas

The distribution characteristics of gas hydrates in the pores of sediments are critical to predict the macroscopic properties of hydrate reservoirs and the efficient production of gas hydrates. In this study, the experiments of methane hydrate formation were conducted in a glass micromodel, and the morphology evolution of hydrate formed from the free gas and dissolved gas in the pores were observed through a video microscope. Observation results showed that the hydrate formed from free gas grew preferentially along the gas–water interface and subsequently toward the center of the gas phase. For the hydrate formed from dissolved gas, it was preferentially occurred on the surface of the hydrate crust formed from free gas and gradually grew toward the water phase. The hydrate formation rate was determined by the concentration of methane molecules in surroundings water. The hydrate formed from free gas was porous structure and composed of many tiny hydrate crystals, and the hydrate formed from dissolved gas was smooth and transparent polyhedral hydrate crystal. For the hydrate formed by free gas, the occurrence pattern of hydrate in the pores might change from the grain-cementing to the contact-cementing or the patchy. The occurrence pattern of the hydrate formed from dissolved gas could be the pore-filling or the load-bearing. This study could be helpful for explaining the phenomenon of macro-experiments, the model construction for the macro-properties of hydrate-bearing sediments, and the exploring of gas hydrates reservoirs.

CO2 capture through gas hydrate formation in the presence of polyethyleneimine-surface-grafted clay

CO2 capture through gas hydrate formation was performed using a stirring-type vessel in the presence of nanoclay and polyethyleneimine-grafted nanoclay. First, the grafting process was implemented via the wet impregnation method. The nanoparticles were characterized using FT-IR, FESEM, EDS, BET, XRD, TGA, Zeta potential, and DLS analyses. The characterization analyses confirmed surface-grafting of the nanoclay. Then, the hydrate formation experiments were implemented at three various nanoparticle loadings (200, 400, and 500 ppm). Water-to-hydrate conversion, CO2 gas consumption, apparent rate constant, and hydrate storage capacity were obtained and compared. Prior to conducting the CO2 hydrate formation experiments in the presence of nanoparticles, the rocking-type and stirring-type vessels were compared to evaluate the hydrate formation rate (using pure water). Stirring-type vessel exhibited higher hydrate formation rates than rocking-type vessel along with improved gas storage performance which resulted in a 22.4% increase in CO2 consumption. Thus, the effect of additives was examined using the stirring-type vessel. Surface-grafted nanoclay led to higher CO2 consumption compared to nanoclay at all concentrations. Using 500 ppm of modified nanoclay, grafted by 50 mass% polyethyleneimine (PEI) solution as additive, the maximum enhancement of CO2 consumption in the hydrate phase in comparison with pure water was obtained, along with the greatest water to hydrate conversion value (39.67). This study introduces a new technique by modifying nanoclay with PEI to improve CO2 storage in gas hydrate phase, presenting potential advancements in gas storage technology.

Effects of multi-walled carbon nanotubes on microstructure transformation of water before carbon dioxide hydrate formation

There is no consensus on the micro mechanism of gas hydrate formation. The essence of water conversion into hydrates is the transformation of disorderly arranged water into the water with specific structure under a certain condition. This study used different multi-walled carbon nanotubes (MWCNTs) as solid promoters for gas hydrate formation. By comparing the effects of nanotubes modified with hydroxyl, carboxyl and amidogen on the microstructure transformation of water before CO2 hydrate formation, the micro mechanism and influence rules of gas hydrate formation were systematically study. The results indicated that the conversion of water to hydrates mainly manifested as the mutual conversion of strong/weak hydrogen bonding water. Due to the Brownian motion and dispersion of MWCNTs, the hydrogen bonds of the weak hydrogen-bonded water weakened (the corresponding peak blue shifts), and the distance between water molecules (dO−O) expanded, forming relatively loose hydrate, which was conducive to gas diffusion in the solid hydrate phase and increased the final gas consumption. Meanwhile, the strengthening of strong hydrogen bonded water increased the rate of hydrate formation.

Heterogeneous nucleation of CO2 hydrate: A thermodynamics analysis considering effects of wall characteristics and solution activity

The massive emission of greenhouse gas CO2 has significant effects on global climate and environment, causing worldwide concern. It has been proposed to store CO2 in clathrate hydrates as a possible strategy for reducing atmospheric CO2 emission. Nevertheless, the CO2 hydrate formation rate is slow and its associated heterogeneous nucleation mechanisms are not well understood, which limit commercial applications of this technology. This study developed a thermodynamic model based on the change in availability function approach, considering effects of surface characteristics (including surface topography, roughness, curvature radius, and wettability), and CO2 dissolution on the solution's activity. The critical nucleation radius and energy barrier of CO2 hydrate nucleation are determined. Effects of pressure, temperature, wall characteristics and solution activity on the nucleation radius of CO2 hydrate are discussed. The results of this paper contribute to advancing carbon capture and storage technology based on hydrate methods.

Enhanced CO2 hydrate formation using hydrogen-rich stones, L-Methionine and SDS: Insights from kinetic and morphological studies

One promising proposal for CO2 capture and storage is based on hydrate technology, which grapples with challenges related to stringent formation conditions and slow formation rates. In this study, the induction time, gas uptake and the rate of CO2 hydrate formation were measured with varying concentrations (ranging from 0.05 wt% to 0.2 wt%) of L-Methionine (L-Met) and sodium dodecyl sulfate (SDS). Remarkably, the novel additive hydrogen-rich stone significantly reduced the induction time by 89.74 % and 85.16 %, even under static conditions. The morphology analysis reveals that L-Met foster the creeping growth of hydrates, resulting in an approximate 41.89 % increase in the initial 1 h gas uptake. The efficient heat diffusion further enables the rapid formation of hydrates, resulting in a high gas uptake in a short period. L-Met outperforms SDS in terms of induction time and gas uptake, with the optimal choice for CO2 hydrate formation being 0.1 wt% L-Met. This study briefly describes the mechanisms of three different kinetic promoters for hydrate formation, which provides new ideas for subsequent studies on CO2 capture and storage via hydrate technology.

Study on formation of methane hydrate in rotating packed bed

Offshore oilfield development process often carries a large amount of associated gas, most of it needs to be emptied or burned, resulting in a large amount of waste and environmental pollution. Hydrate storage and transportation technology has the advantages of simple process treatment, good offshore adaptability, good safety and relatively low investment. It is one of the important recovery technologies for associated gas in offshore oil fields. However, the long induction period of hydrate formation, the difficulty of gas dissolution, and the difficulty of continuous formation hinder the improvement of hydrate formation rate and gas storage density, and hinder the development of hydrate storage and transportation technology. High-gravity technology may be one of the development directions of new hydrate rapid formation reactors due to its small size and high mass transfer capacity. In this paper, a small-scale RPB was designed independently, and the effects of high-gravity factor, initial pressure, and packing type on hydrate formation were assessed by calculating the gas consumption, gas consumption rate, gas storage density, and gas conversion rate of hydrate formation under each experimental condition. The results show that in the range of high-gravity factor and pressure tested in the experiment, the increase of high-gravity factor and pressure can significantly accelerate the hydrate formation rate, which can be increased by up to 177 %, and the maximum gas storage density can reach 148.88 V/V. The type of packing has a strong influence on the rate of hydrate formation, and the principle of packing selection changes when dealing with solid-containing systems, and the rate of hydrate formation can be increased by 20 % with the proper selection of packing type. This study can provide a basis for subsequent high-gravity hydrate experiments and industrial applications.

Methane hydrate efficient formation in a 3D-rGO/SDBS composite.

The optimization of storage space and material composition can significantly improve the generation rate and storage capacity of methane hydrate, which is important for the industrial application of solidified natural gas (SNG) technology. In our report, the effects of the presence of SDBS (sodium dodecylbenzene sulfonate), GO (graphene oxide), 3D-rGO (3D-reduced graphene oxide) and 3D-rGO/SDBS (3D-reduced graphene oxide/sodium dodecylbenzene sulfonate) on the methane hydrate generation process are investigated. The results show that the heterogeneous effect on the solid-phase surface of 3D-rGO/SDBS and its interconnected three-dimensional (3D) structure can achieve rapid nucleation. In addition, the presence of 3D-rGO/SDBS can increase the dissolution and dispersion of gas in solution and further enhance the gas-liquid mass transfer, thus realizing efficient methane storage. The maximum methane storage capacity of 188 v/vw is obtained with 600 ppm of 3D-rGO/SDBS in water, reaching 87% of the theoretical maximum storage capacity. The addition of 3D-rGO/SDBS also significantly reduces the induction time and accelerates the formation rate of methane hydrate. This study reveals that 3D graphene materials have excellent kinetic promotion effects on methane hydrate formation, explores and enriches the hydrate-promoting mechanism, and provides essential data and theoretical basis for the research of new promoters in the field of SNG technology.

Analysis of sensitivity to hydrate blockage risk in natural gas gathering pipeline

During the operational process of natural gas gathering and transmission pipelines, the formation of hydrates is highly probable, leading to uncontrolled movement and aggregation of hydrates. The continuous migration and accumulation of hydrates further contribute to the obstruction of natural gas pipelines, resulting in production reduction, shutdowns, and pressure build-ups. Consequently, a cascade of risks is prone to occur. To address this issue, this study focuses on the operational process of natural gas gathering and transmission pipelines, where a comprehensive framework is established. This framework includes theoretical models for pipeline temperature distribution, pipeline pressure distribution, multiphase flow within the pipeline, hydrate blockage, and numerical solution methods. By analyzing the influence of inlet temperature, inlet pressure, and terminal pressure on hydrate formation within the pipeline, the sensitivity patterns of hydrate blockage risks are derived. The research indicates that reducing inlet pressure and terminal pressure could lead to a decreased maximum hydrate formation rate, potentially mitigating pipeline blockage during natural gas transportation. Furthermore, an increase in inlet temperature and terminal pressure, and a decrease in inlet pressure, results in a displacement of the most probable location for hydrate blockage towards the terminal station. However, it is crucial to note that operating under low-pressure conditions significantly elevates energy consumption within the gathering system, contradicting the operational goal of energy efficiency and reduction of energy consumption. Consequently, for high-pressure gathering pipelines, measures such as raising the inlet temperature or employing inhibitors, electrical heat tracing, and thermal insulation should be adopted to prevent hydrate formation during natural gas transportation. Moreover, considering abnormal conditions such as gas well production and pipeline network shutdowns, which could potentially trigger hydrate formation, the installation of methanol injection connectors remains necessary to ensure production safety.

Enhanced formation of methane hydrates via graphene oxide: Machine learning insights from molecular dynamics simulations

Gas hydrates, with their significant applications in energy and environment sectors, have emerged as promising technologies for gas separation, natural gas and energy storage. The formation of methane hydrates occurs in substrate-contact conditions, where the properties of the substrate surfaces play a crucial role in determining hydrate formation pathways. Herein, the influence of the hydroxyl group (-OH) content on the graphene surface on methane hydrate formation in confined systems using molecular dynamics (MD) simulations with machine learning (ML) technique. The MD results show that increasing the oxidation degree effectively enhances the formation of methane hydrate within the oxidation degree of 10 %–40 %. This enhancement is attributed to the hydrophilicity of the (GO) surfaces. When the oxidation degree reaches 50 %, however, the formation rate of methane hydrates slows down compared to the GO-40 system. This deceleration can be attributed to the formation of dense water layers that adhere to the GO surfaces, resulting in impeding the hydrate formation process. Markov State Model (MSM) is employed to analyze the induction time of GO on methane hydrate formation, highlighting the important role of GO in the formation of methane hydrates. Additionally, an eXtreme Gradient Boosting (XGboost) ML model is developed to predict the formation behaviors of methane hydrates. Ternary water-ring aggregations (TWRAs) are adopted as indicators to understand to the formation behaviors, and the XGboost ML model facilitate the identification of key TWRAs associated with the formation process. This work provides molecular-level insights into the influence of –OH group on formation of methane hydrates, and offers a predictive framework for understanding and characterizing the formation clathrate hydrates in confined systems.