Ethane Hydrate Research Articles

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.

Apigenin Cocrystals: From Computational Prescreening to Physicochemical Property Characterization

Apigenin (4′,5,7-trihydroxyflavone, APG) has many potential therapeutic benefits; however, its poor aqueous solubility has limited its clinical applications. In this work, a large scale cocrystal screening has been conducted, aiming to discover potential APG cocrystals for enhancement of its solubility and dissolution rate. In order to reduce the number of the experimental screening tests, three computational prescreening tools, i.e., molecular complementarity (MC), hydrogen bond propensity (HBP), and hydrogen bond energy (HBE), were used to provide an initial selection of 47 coformer candidates, leading to the discovery of seven APG cocrystals. Among them, six APG cocrystal structures have been determined by successful growth of single crystals, i.e., apigenin–carbamazepine hydrate 1:1:1 cocrystal, apigenin–1,2-di(pyridin-4-yl)ethane hydrate 1:1:1 cocrystal, apigenin–valerolactam 1:2 cocrystal, apigenin-(dl) proline 1:2 cocrystal, apigenin-(d) proline/(l) proline 1:1 cocrystal. All of the APG cocrystals showed improved dissolution performances with the potential to be formulated into drug products.

Direct observation of pressure-induced amorphization of methane/ethane hydrates using Raman and infrared spectroscopy.

The pressure-induced amorphization (PIA) of ice and clathrate hydrates occurs at temperatures significantly below their melting and decomposition points. The PIA of type I clathrate hydrates containing methane and ethane as guest molecules was investigated using Raman and infrared (IR) spectroscopy. With isothermal compression at 100 K, methane hydrate (MH) underwent PIA at 2-3.5 GPa, whereas ethane hydrate (EH) underwent PIA at 4.0-5.5 GPa. The type I clathrate structure consists of small (512) and large (51262) cages. The Raman results revealed that the collapsed small and large cages in the amorphous forms of MH and EH were not distinguishable. The collapsed cages, including the methane and ethane molecules, were similar to the small and large cages, respectively. Their water networks were folded or expanded during the PIA process so that the cavity sizes of the collapsed cages were compatible with those of the guest molecules. Peaks in the IR spectra of crystalline MH assignable to the ro-vibrational transition of methane in large cages were observed in the C-H stretching wavenumber region below 40 K. The ro-vibrational IR band disappeared after amorphization, suggesting that the rotational motion of the methane molecule in the large cage was frozen by the collapse, as reported in previous dielectric spectroscopic and simulation studies. This study contributes to a better understanding of the changes in the local structure around guest molecules during PIA and the dynamics of the guest molecules.

Wetting Properties of Clathrate Hydrates in the Presence of Polycyclic Aromatic Compounds: Evidence of Ion-Specific Effects

Polycyclic aromatic hydrocarbons (PAHs) have attracted remarkable multidisciplinary attention due to their intriguing π–π stacking configurations, showing enormous opportunity for their use in a variety of advanced applications. To secure progress, detailed knowledge on PAHs’ interfacial properties is required. Employing molecular dynamics, we probe the wetting properties of brine droplets (KCl, NaCl, and CaCl2) on sII methane–ethane hydrate surfaces immersed in various oil solvents. Our simulations show synergistic effects due to the presence of PAHs compounded by ion-specific effects. Our analysis reveals phenomenological correlations between the wetting properties and a combination of the binding free-energy difference and entropy changes upon oil solvation for PAHs at oil/brine and oil/hydrate interfaces. The detailed thermodynamic analysis conducted upon the interactions between PAHs and various interfaces identifies molecular-level mechanisms responsible for wettability alterations, which could be applicable for advancing applications in optics, microfluidics, biotechnology, medicine, as well as hydrate management.

Recent advances in density functional theory and molecular dynamics simulation of mechanical, interfacial, and thermal properties of natural gas hydrates in Canada

AbstractGas hydrates are inclusion compounds of a water backbone that encloses gaseous molecules. Thanks to their applications in gas recovery, carbon capture and storage, gas storage, and flow assurance, generating high quality data and predictions of their properties is paramount. A review of novel techniques using first principles density functional theory and molecular dynamics simulations methods coupled to auxiliary simulations methods is presented herein. Structure I (sI), structure II (sII), and structure H (sH) hydrates have been studied extensively, with studies of their material strength showing that it is often misleading to use the properties of ice instead of the difficult‐to‐determine gas hydrate properties. Key differences between the three structures and their possible guests are presented. The interfacial properties of gas hydrates display key behaviours that control nucleation and growth, which are important phases in controlling and monitoring their formation. Gas hydrate thermal properties are also examined, with key differences existing between guests and some unusual alignment in the cages shown for carbon dioxide, ethane, and ethylene oxide sI hydrates. First principles infrared spectroscopy is also examined, with techniques showing that these signatures can be tied to and predict material properties to improve the speed of analysis. Therefore, by quantifying, modelling, predicting, and explaining their formation and dissociation, and linking these to their thermal, material, and interfacial properties, a database of reliable data for science and engineering methods and applications is formed to provide a basis for further work.

Structural changes due to the ordered guest molecules in deuterated ethane hydrate

Ethane hydrate, a natural gas hydrate, has been considered to only have a cubic symmetry known as structure I. Neutron diffraction measurement of deuterated ethane hydrate was performed from 10 K to 150 K. The diffraction patterns of deuterated ethane hydrate drastically changed below 30 K. A new hexagonal crystal structure with ordered ethane molecules was found as a clathrate hydrate structure. This phase transition was concerned with the thermal motion of the ethane molecules.

First-Principle Molecular Dynamics Study of Methane Hydrate

Currently, much attention of the scientific community and the gas industry is focused on the structural, physical and thermodynamic properties of gas hydrates. This interest is explained by the fact that there is a prospect of using natural gas hydrates as a new fuel source. This article presents the results obtained during the first-principle molecular dynamic study of the thermal and electronic properties of hydrates. For hydrates of methane with cubic sI and hexagonal sH configurations, the average heat capacity Cv was computed. The densities of electronic states are studied for filled and unfilled configurations of sI and sH hydrates. The spectra of electron energy were calculated for sI hydrate, which has unfilled molecular cages. Also, for methane and ethane hydrates, the binding energies between the framework and the gas molecule are calculated.

Experimental determination of dissociation temperatures and enthalpies of methane, ethane and carbon dioxide hydrates up to 90 MPa by using a multicycle calorimetric procedure

This work presents the application of a multicycle procedure to determine the dissociation temperature and enthalpy of gas hydrates using high-pressure microcalorimetry (HP-µDSC). In the multicycle procedure, a sample of water in contact with the gas undergoes successive cooling and warming cycles below hydrate dissociation temperature, increasing the conversion of water into hydrate. This technique has been previously used in literature to increase water conversion during carbon dioxide hydrate formation up to 2.0 MPa, but its applicability has not been assessed for higher pressures and with different guest molecules. New experimental equilibrium data for methane, ethane, and carbon dioxide hydrates were obtained through HP-µDSC up to 90 MPa using the multicycle procedure. The advantages and limitations of the method are discussed. Dissociation temperatures are in good agreement with data previously obtained from a HP-µDSC standard method, which confirms the reliability to determine this property by both methods. Nevertheless, the enthalpy of hydrate dissociation obtained by the direct integration of thermograms provided by the HP-µDSC standard method is not accurate. Thus, it is usually calculated by using the Clapeyron equation from equilibrium temperature and pressure data obtained by the HP-µDSC standard method, as presented in previous work. The new dissociation enthalpies presented in this work were obtained experimentally by direct integration of thermograms using the multicycle procedure, which provides accurate data as the conversion is very high (above 97% of water converts into hydrate), the baselines are clearly established, and no exothermic peak related to metastable phases is observed.

Prediction of Gas Hydrate Formation at Blake Ridge Using Machine Learning and Probabilistic Reservoir Simulation

AbstractMethane hydrates are solid structures containing methane inside of a water lattice that form under low temperature and relatively high pressure. Appropriate hydrate‐forming conditions exist along continental shelves or are associated with permafrost. Hydrates have garnered scientific interest via their potential as a source of natural gas and their role in the global carbon cycle. While methane hydrates have been collected in multiple diverse geographic settings, their quantities and distribution in sediments remain poorly constrained due to sparse relevant data. Using statistical and machine learning approaches, we have developed a workflow to probabilistically predict methane hydrate occurrence from local microbial methane sourcing. This approach utilizes machine‐learned global maps produced by the Global Predictive Seabed Model (GPSM) as inputs for the statistical sampling software, Dakota, and multiphase reservoir simulation software, PFLOTRAN. Dakota performs Latin hypercube sampling of the GPSM‐predicted values and uncertainties to generate unique sets of input parameters for 1‐D PFLOTRAN simulations of gas hydrate and free gas formation resulting from methanogenesis to steady state. We ran 100 1‐D simulations spanning a kilometer in depth at 5,297 locations near Blake Ridge. Masses of hydrate and free gas formed at each location were determined by integrating the predicted saturation profiles. Elevated hydrate formation is predicted to occur at depths >500 meters below sea level at this location, and is strongly associated with high seafloor total organic carbon values. We produce representative maps of expected hydrate occurrence for the study area based on multiple realizations that can be validated against geophysical observations.

Analytical–Empirical Approach for Estimating Kinematic-Response Relationships between Hydrate-Bearing Soils and Standard Soils

AbstractMethane hydrate within a soil pore space may significantly modify the mechanical behavior of the sediment. Previous studies have shown that the influence of hydrate on methane-hydrate-beari...

Cage occupancy and dissociation enthalpy of hydrocarbon hydrates

AbstractAn elaborated statistical mechanical theory on clathrate hydrates is applied to exploration of their phase equilibria and dissociation enthalpies. The experimental dissociation pressures of methane, ethane, acetylene, and propane hydrates are well recovered by the method we have proposed. We estimate water/hydrate and hydrate/guest two‐phase coexisting conditions in the temperature, pressure, and composition space in addition to three‐phase equilibrium conditions. It is shown that the occupancy of guest molecules and the two‐phase boundaries in the phase diagram vary depending sensitively on its size. Enthalpy components arising from the host and guest interactions are separately calculated from the temperature dependence of the corresponding free energy values. This enables to evaluate the dissociation enthalpy at any stable and metastable thermodynamic state taking account of the phase transition in the coexisting phase such as melting of ice, notably that along the three‐phase equilibrium line.

Laboratory Electrical Conductivity of Marine Gas Hydrate

AbstractMethane hydrate was synthesized from pure water ice and flash frozen seawater, with varying amounts of sand or silt added. Electrical conductivity was determined by impedance spectroscopy, using equivalent circuit modeling to separate the effects of electrodes and to gain insight into conduction mechanisms. Silt and sand increase the conductivity of pure hydrate; we infer by contaminant NaCl contributing to conduction in hydrate, to values in agreement with resistivities observed in well logs through hydrate‐saturated sediment. The addition of silt and sand lowers the conductivity of hydrate synthesized from seawater by an amount consistent with Archie's law. All samples were characterized using cryogenic scanning electron microscopy and energy dispersive spectroscopy, which show good connectivity of salt and brine phases. Electrical conductivity measurements of pure hydrate and hydrate mixed with silt during pressure‐induced dissociation support previous conclusions that sediment increases dissociation rate.

Evaluating Pressure in Deepwater Gas Pipeline for the Prediction of Natural Gas Hydrate Formation

This paper proposes the prediction of hydrate formation pressure in deepwater pipeline with an approach of intelligent optimization. The proposed novel correlation of hydrate formation is using the function of ordinary differential equation. The developed optimization prediction model was founded on the constant coefficients which were examined by a multiple set of experimental data of methane (CH4), ethane (C2H6), propane (C3H8), iso-butane (iC4), nitrogen (N), Carbon Dioxide (CO2) and hydrogen sulfide (H2S) hydrates. The consequences of this research are highly optimistic for the natural gas production industry.

Methane Hydrate Film Thickening in Porous Media

AbstractMethane hydrate formation accompanied by upward migration of methane in sediments was studied. Methane hydrate film forms initially along the interface between the gas and surrounding pore fluid when methane reaches the hydrate stability zone. Subsequent film thickening and related mass transfer are critical but have not been studied previously. Experimental and theoretical studies were performed to investigate the film thickening and rate‐limiting mechanisms. Initial gas density affects the stability of the growing hydrate film, and mass transfer through hydrate film is proposed as a rate‐limiting step for hydrate growth.

Study on ethane hydrate formation/dissociation in a sub-millimeter sized capillary

Study on the gas hydrates in porous medium has great significance to the formation, accumulation and exploitation of natural gas hydrate (NGH). Consequently, we investigated the formation/dissociation of ethane hydrate in a sub-millimeter sized capillary in this work, and observed the appearance and kinetic rate during the hydrate formation/dissociation process. The dissociation equilibria of ethane hydrate in capillary was measured first, then the influences of hydrate memory effect (dissociation temperature and time) and degree of subcooling on ethane hydrate formation were obtained, respectively. The results demonstrate that hydrate forms more difficultly in capillary than in conventional macro-reactor because of the fluid resistance effect and poor mass transfer of gas-liquid. The appearance and formation kinetics of ethane hydrate are greatly influenced by the memory effect and subcooling degree. The morphology of ethane hydrate formation on the bubble surface in water bulk phase shows that “bridge effect” occurs during the hydrate formation and growth in capillary.

Xenon Hydrate as an Analog of Methane Hydrate in Geologic Systems Out of Thermodynamic Equilibrium

AbstractMethane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H2O and CH4·H2O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H2O is a good experimental analog to CH4·H2O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant.

Structural Transitions Range of Methane + Ethane Gas Hydrates during the Decomposition Process below the Ice Point

The structural transitions in the forming process of methane and ethane gas hydrate were reported previously, this phenomenon has also been observed during the dissociation process of methane and ethane gas hydrate. In our earlier work, the self-preservation and structural transition of 68 mol.% CH4+32 mol.% C2H6 hydrates during dissociation below the ice point have been studied. In this work, the dissociation process of a series of methane + ethane hydrate samples at atmospheric pressure and temperatures below the ice point (272.15 K-269.15 K) was analyzed using in suit Raman spectroscopic, suggesting the hydrate structures transfer from structure I to structure II over a methane vapor composition (yCH4) range of 50 mol.%-68 mol.%. Further investigation shows that the time of structure transition is reduced with the increasing yCH4 at the same decomposition temperature. Meanwhile, hydrate dissociation is retarded with decreasing temperature in this temperature region (272.15 K-269.15 K). The result of this work can be applied to hydrate exploitation in permafrost zone and seabed.

Coupled Numerical Modeling of Gas Hydrate‐Bearing Sediments: From Laboratory to Field‐Scale Analyses

AbstractMethane hydrates are ice‐like compounds made of gas methane and water. Hydrates are stable under low‐temperature and high‐pressure conditions constraining their occurrence in sediments to marine and permafrost settings. A shift from the stability condition triggers an endothermic hydrate dissociation with the associated release of gas and water, impacting (among others) on sediment pore pressure, temperature, and deformations. Therefore, the behavior of hydrate‐bearing sediments (HBS) is controlled by strongly coupled thermo‐hydro‐chemo‐mechanical actions. The analysis of available data from past field and laboratory experiments and the optimization of future field production studies require a formal and robust numerical framework able to capture the complex behavior of this type of soil. In this paper we used a fully coupled thermo‐hydro‐mechanical framework to study different problems involving HBS, from laboratory experiments involving natural hydrate samples to gas production tests. We also develop an analytical solution for the case of gas production via radial depressurization from a confined HBS reservoir. The analyses show the complexity of the thermo‐hydro‐mechanical phenomena associated with this type of system and contribute to better understand the behavior of HBS.

A Generalized Correlation for Predicting Ethane, Propane, and Isobutane Hydrates Equilibrium Data in Pure Water and Aqueous Salt Solutions.

Hydrate formation can cause serious problems in hydrocarbon exploration, production, and transportation, especially in deepwater environments. Hydrate‐related problems affects the integrity of the deepwater platforms, leads to equipment blockages, and also increases operational costs. In order to solve these problems, salts are used as thermodynamic inhibitors and also mixed with the drilling fluids in most drilling processes. A comprehensive understanding of hydrate formation in aqueous salt solutions is vital to overcome these problems. Statistical thermodynamic models are commonly used to predict hydrate formation conditions in different aqueous solutions. However, these models involve rigorous computations and are restricted to certain conditions. They give inaccurate predictions of hydrate equilibrium conditions for high‐temperature, high‐pressure, and high‐salinity systems. Therefore, it is paramount to develop a simple‐to‐use and reliable prediction tool. In this work, an empirical correlation is developed and successfully used to predict the equilibrium conditions of ethane, propane, and isobutane hydrates in pure water and aqueous solutions of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride. Experimental data on hydrate formation conditions for these components are regressed and a generalized correlation is obtained. The predictions in this work show excellent agreement with all the experimental data in the literature.

Application of Population Balance Theory for Dynamic Modeling of Methane and Ethane Hydrate Formation Processes

Natural gas hydrates are considered as a promising fuel source in the relatively near future. Kinetic modeling of various steps of the natural gas hydrate formation process, such as dissolution, nucleation, and growth processes, has received numerous attentions. A novel mechanism is introduced for the entire nucleation and growth steps, and a proper mathematical model is presented to estimate the gas consumption rate in a constant temperature and pressure process. The proposed model covers the entire dissolution, nucleation, and growth stages. The combined Lax–Wendroff/Crank–Nicolson method is employed to solve the population balance equation for estimation of total surface area of evolved hydrate particles and corresponding particle size distributions. A special class of artificial neural network (known as the Regularization Network) is used to predict the solid–liquid equilibria. The proposed model is successfully validated using experimental data borrowed from the literature for both methane and ethane...