Growth Rate Of Methane Hydrate Research Articles

Combined effect of NaCl and sodium dodecyl sulfate on the mechanism and kinetics of methane hydrate formation in an unstirred system

Interest in studying an effect of the mixed NaCl + SDS additive on gas hydrate formation is associated with the direct use of saline waters and seawater in hydrate-based technologies for the storage and transportation of natural gases. We performed studies of methane hydrate formation without stirring using pressures of 8, 12 and 16 MPa for water, aqueous solutions of NaCl and SDS, and the mixed additive of NaCl + SDS. A 3 wt% NaCl solution, as a model for seawater, and a 0.1 wt% SDS solution were used. The mixed additive was 3 wt% NaCl+0.1 wt% SDS. Data on the methane solubility, induction time of methane hydrate formation, water-to-hydrate conversion and methane hydrate growth rate, as well as data on morphology of methane hydrate formed with and without additives have been presented. It was found that the mechanism of methane hydrate growth in NaCl solution under static conditions was determined by the morphology of hydrate film at the gas-liquid interface and was pressure dependent. A liquid penetrable hydrate film at the gas-liquid interface formed in the presence of NaCl at moderate pressures (8 and 12 MPa) that allowed capillary-driven hydrate growth with a high rate and water-to-hydrate conversion. At high pressures (16 MPa), methane hydrate growth was limited by formation of impenetrable hydrate film at the gas-liquid interface, that restricted hydrate growth. In contrast to the existing concepts that the addition of NaCl to SDS solutions enhances surfactant micellization and accelerate hydrate formation, we found that SDS micelles did not form under the studied methane hydrate-forming conditions with NaCl. Evidence for SDS hydrate formation in the NaCl + SDS solution have been presented. Mechanisms of gas hydrate nucleation and growth in NaCl + SDS solution taking into account SDS hydrate formation and permeability of gas hydrate film at the gas-liquid interface are discussed.

Simultaneous measurement of water permeability and methane hydrate pore habit using a two-dimensional glass micromodel

In this study, we developed an in situ chamber to measure water permeability as a function of the methane hydrate (MH) habit in pore space using a two-dimensional glass micromodel by adding a methane-dissolved water source unit to prevent MH dissociation. This unit enabled us to adjust the amount of methane dissolved in the water by controlling the pressure and temperature. We simultaneously observed MH crystallization behavior and measured the water permeability of the porous media. The growth rate of MH and the pore habit formation changed with subcooling, ΔT. As ΔT increased, the shape of the pattern transformed from a hexagonal plate to a dendrite and hexagonal plate, and finally, to a dendrite. The glass pillar played a role in inhibiting the growth of dendritic patterns. The plugging process of the porous media following MH formation was also observed. We compared our results with various water permeability models of MH sediments and found that the nonempirical relative permeability (NRP) models showed relatively good agreement. This was likely because the NRP models enhanced the effect of the gas phase. However, a gap remains between the NRP model predictions and our experimental results. On the other hand, there was no possibility of agreement other than the NRP models because the gas phase was not included in the equation.

Inhibition Effect of Kinetic Hydrate Inhibitors on the Growth of Methane Hydrate in Gas–Liquid Phase Separation State

The effect of kinetic hydrate inhibitors (KHIs) on the growth of methane hydrate in the gas–liquid phase separation state is studied at the molecular level. The simulation results show that the kinetic inhibitors, named PVP and PVP-A, show good inhibitory effects on the growth of methane hydrate under the gas–liquid phase separation state, and the initial position of the kinetic hydrate inhibitors has a major effect on the growth of methane hydrates. In addition, inhibitors at different locations exhibit different inhibition performances. When the inhibitor molecules are located at the gas–liquid phase interface, increasing the contact area between the groups of the inhibitor molecules and methane is beneficial to enhance the inhibitory performance of the inhibitors. When inhibitor molecules are located at the solid–liquid phase interface, the inhibitor molecules adsorbed on the surface of the hydrate nucleus and decreased the direct contact of hydrate nucleus with the surrounding water and methane molecules, which would delay the growth of hydrate nucleus. Moreover, the increase of hydrate surface curvature and the Gibbs–Thomson effect caused by inhibitors can also reduce the growth rate of methane hydrate.

Growth Kinetics of Methane Hydrate in a Pilot-Scale Flow Loop

Methane hydrate growth kinetics and deposition behavior were investigated in a pilot-scale high-pressure flow loop under an isothermal and isobaric operating condition. The pressure range was from 3 to 7 MPa with temperature ranging from 273.15 to 281.15 K. The growth kinetics was characterized by the variation in the methane gas consumption with time. The effects of liquid loading (LL, the percentage of total volume of liquid water used in the experiments compared to the total volume of the flow loop), flow rate, pressure, and temperature on the growth rate were systematically studied. The formation of methane hydrate mainly took place at the interface of gas and water, and a layer of methane hydrate film was also found to form on the wetted inner wall of the flow loop. A threshold LL was found to exist below which the growth rate of methane hydrate was significantly higher, and here, all of the water could convert to methane hydrate in less than 2 h. The deposition behavior of the methane hydrate varied...

Kinetic and rheological study of methane hydrate formation in water-in-oil emulsion: Effects of emulsion composition and silica sands

Gas hydrate blockage in the emulsifying crude oil poses security risks to the subsea multiphase flow transportation. The kinetic and rheological properties of methane gas hydrate in the water-in-oil emulsion were in situ characterized by experiments in a high-pressure rheometer with particular focus on the effects of emulsion composition and silica sands. Results demonstrated that the methane hydrate growth rate and yield stress increased with the surfactant concentration and water fraction, while the hydrate formation in the emulsion of pure light alkanes was faster than that in the mineral oil emulsion. Moreover, the presence of silica sands shortened the hydrate nucleation time, eliminated the stochasticity of nucleation, and induced the occurrence of hysteresis by affecting the transient and steady state viscosity of hydrate-in-oil slurry. Overall, this study was of added knowledge to the hydrate formation mechanisms in the water-in-oil emulsion, which highlighted the fact that the high emulsification degree, high water fraction, and the high concentration and large particle size of silica sands in the multiphase flow would increase the risks of hydrate blockage in the oil-gas transportation pipelines.

A new class of promising biodegradable kinetic/anti-agglomerant methane hydrate inhibitors based on castor oil

This study is devoted to the evaluation of vegetable oils (in this case castor oil) as an inexpensive, sustainable, environment-friendly, natural and promising resource to design/synthesis efficient kinetic/anti-agglomerant methane hydrate inhibitors. The castor-based waterborne polyurea/urethanes (CWPUUs) were synthesized on the basis of the waterborne technique. The high-pressure autoclave cell and high-pressure micro-differential scanning calorimeter (HP-μDSC) using methane gas were applied to evaluate the inhibition performance of CWPUUs as an inhibitor for methane gas hydrate formation. The results of gas uptake tests confirm that the CWPUUs show high efficiency as kinetic hydrate inhibitors (KHIs). The CWPUUs with ∼3.2 and 6.8 kD molecular weight delayed the onset time of methane hydrate formation by a factor of 26.8 and 13 times and reduced the methane hydrate growth rate by a factor of 3.8 and 2.5 times in comparison with pure water. The results were further confirmed through DSC measurements, in which the usage of CWPUUs with ∼3.2 and 6.8 kD molecular weight decreased the mean onset temperature of methane hydrate formation on 6.1 and 4.7 °C compared to pure water, respectively. Additives of CWPUUs (1 wt % solution) increased the mean onset time of methane hydrate formation from 2.3 h for pure water to 8.7 and 6.4 h. CWPUUs also demonstrated the thermodynamic inhibition by decreasing the melting temperature of methane hydrates comparing to the pure water system. On the other hand, the torque measurements were used to assess anti-agglomerant performance of CWPUUs. During the methane hydrate formation in the presence of CWPUUs, the torque changes remained constant that suggests the hydrate particles stayed separate without aggregation. Moreover, synthesized CWPUUs can be related to biodegradable substances because their BOD5/CODcr value measured in this work is equal to 0.389. Hence, the application of CWPPUs can be a prospective option for delaying the onset time/temperature of hydrate formation, reducing hydrate growth rate and preventing agglomeration of hydrate particles, and this strategy refers to the terms of green chemistry.

In situ chamber built for clarifying the relationship between methane hydrate crystal morphology and gas permeability in a thin glass micromodel cell.

We developed a novel in situ chamber to investigate the relationship between gas hydrate crystal morphology and gas permeability in a glass micromodel that mimics marine sediment. This high-pressure experimental chamber was able to use a thin glass cell without high pressure resistance. The formation of methane hydrate (MH) in the glass micromodel was observed in situ. We investigated the relationship between the MH growth rate and the degree of super cooling ΔT. In addition, we successfully performed the in situ observation of both hydrate morphology and gas permeability measurement simultaneously.

Promotion Effect of Carbon Nanotubes-Doped SDS on Methane Hydrate Formation

To achieve greater performance of a low concentration of sodium dodecyl sulfate (SDS) in methane hydrate formation, SDS solutions were doped with pristine carbon nanotubes (pCNTs) and the oxidized forms (OCNTs). With nanotubes as the predominant accelerant in the mixed promoters, the nucleation stage could be shorten efficiently due to the continuous Brownian motion of more nanoparticles. The mixed promoters exerted more pronounced influence on the methane hydrate growth rate compared to the pure SDS, with the OCNTs-SDS system performing slightly better owing to the high dispersion and stability of the OCNTs in the aqueous SDS solutions. Nevertheless, the promotion effects of highly concentrated pCNTs or OCNTs could be weakened possibly due to the aggregation of nanotubes.

The synergism of the binary and ternary solutions of polyethylene glycol, polyacrylamide and Hydroxyethyl cellulose to methane hydrate kinetic inhibitor

This study investigates the hydrate inhibition performance of three polymers, polyethylene glycol (PEG), polyacrylamide (PAM) and hydroxyethyl cellulose (HEC), with a well-known kinetic inhibitor, polyvinylpyrrolidone (PVP), to retard the hydrate onset as well as decelerating the crystal growth rate of methane hydrate. A high-pressure reactor with experimental operation conditions of temperature of 275.15 K, initial pressure of 6 MPa and stirring speed of 900 rpm has been utilized. It is observed that the addition of PEG, PAM or HEC to the PVP solution enhances inhibition efficiency, so that it causes a more increase (about 2–8 times) in the induction time and hydrate growth rate become slower than that of the inhibitor alone. The same concentrations of three additives (PEG, PAM and HEC) have represented different effects on the PVP solution. HEC and PAM solutions have respectively showed the highest induction time and the lowest crystal growth rate compared to other solutions. Also, it has been found that ternary solution of inhibitors can be better selection than binary solution of them to increase the hydrate inhibition performance, so that these solutions can prolong the hydrate nucleation up to 20 times and slow significantly down the crystal growth rate by 70% compared to the inhibitor alone.

Application of artificial intelligence (AI) in kinetic modeling of methane gas hydrate formation

This paper aims to present a kinetic study of formation of methane gas hydrate (GH) using artificial intelligence (AI) tools. Generally, study of the kinetics of GH formation will help to better understand this process in order to control it favorably. However, due to its complexity, this process is not fully understood yet. More studies in the literature are considering the thermodynamics of gas hydrate formation both experimentally and mathematically. However, there is no sufficient studies regarding the kinetics of gas hydrates and most of the experimental data and specifically the kinetic models in the literature are incomplete. That may be due to inherent stochastic behavior of GHs which makes it difficult to develop a deterministic model for it. Nowadays, Artificial Intelligence (AI) methods including Artificial Neural Network (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) have been proved as a novel and potential tools with acceptable accuracy for modeling of engineering systems. Therefore, this paper aims to investigate the kinetics of gas hydrate formation using ANN and ANFIS when the relation between growth rate of methane hydrate, temperature and pressure has been modeled. Moreover, this can also be achieved using complicated governing equations but AI provides a less complex and easier way to accomplish this goal. Experimental data considering the methane hydrate growth rate as a function of pressure and temperature were used and ANFIS as well as ANN were employed to duplicate them. In this study, the results reveal that ANIFS could better predict the methane hydrate growth rate in the prevailing pressure and temperature conditions compared to ANN. Generally this study shows the effectiveness of AI based techniques for kinetics modeling of gas hydrates formation.

Application of Artificial Intelligence (AI) Modeling in Kinetics of Methane Hydrate Growth

Determining thermodynamic and kinetic conditions for natural gas hydrate formation is an interesting subject for many researches. At the present, suitable information including experimental data and the thermodynamic models of hydrate formation are available which predict the thermodynamic conditions of hydrate formation. Conversely, there is no sufficient study about the kinetics of natural gas hydrate and most of experimental data and kinetic models in the literature are incomplete. Artificial Intelligence (AI) having sub-branches such as artificial neural network (ANN), and adaptive neuro-fuzzy inference system (ANFIS) has been proved as a novel tool with acceptable accuracy for modeling of engineering systems. Therefore, this paper aims to investigate the kinetics of hydrate formation by predicting the relationship of growth rate of methane hydrate with temperature and pressure using ANN and ANFIS. This goal can also be achieved by solving complicated governing equations while artificial intelligence provides an easier way to accomplish this goal. The result has shown that ANIFS is a more potential tool in predication relationship of kinetics of hydrate formation with temperature and pressure in comparison of ANN in present work.

Experimental investigation of methane hydrate formation on suspended water droplets

The formation of methane hydrate films at the surface of suspended water droplets has been experimentally investigated using a novel experimental apparatus. Experiments were performed at a temperature between 273.35 and 275.15 K and a pressure between 4.01 and 6.65 MPa. The observed morphology of hydrate films showed that the growth rate of methane hydrate formed at the droplet surface is significantly increased as the supersaturation (Δ μ/ kT) is increased and the droplet size is reduced. The induction time of hydrate nucleation is influenced by the degree of supersaturation. A longer induction time was obtained at a lower supersaturation. The measured induction times were correlated to an induction time model developed based on the nucleation theory. A high value of kinetic constant and a low value of effective surface energy were obtained. The results indicated that heterogeneous nucleation of methane hydrate was occurring at the suspended water droplets. The diffusion resistance in the hydrate film was increased as the temperature was decreased and the hydrate film thickened.

The Growth of Structure I Methane Hydrate from Molecular Dynamics Simulations

The key factors that affect the growth of methane hydrates are identified using molecular dynamics simulations. The three-phase molecular models consisting of methane gas, liquid water, and solid hydrate phase are used in this study. The melting temperatures of such a model at different pressures are found to be in good agreement with experiment. The growth rate of methane hydrate is found to be dominated by (1) the solubility of methane in the liquid phase, (2) the diffusivity of methane in water, and (3) the adsorption of methane by methane-filled incomplete water cages at the solid-liquid interface. The solubility, and hence the growth rate, increases with the partial pressure of methane in the vapor phase. The mass transport resistance from adsorption and the diffusion of methane are two competing factors, with the adsorption of methane at the interface found to be the rate-limiting step. The presence of a high concentration of incomplete clathrate hydrate cages presents strong affinity to dissolved methane at temperatures below the melting point. In addition to methane adsorption, water molecules must be expelled to form the complete clathrate cages. Both processes lead to a methane concentration minimum at 5-9 A in front of the growing interface. The methane concentration minimum provides the driving force for methane transport from the bulk to the interface. There are two types of solid layers of methane hydrate in the (1,0,0) direction. The growths of these layers are different, highly correlated, and affected by the methane concentration. A detailed mechanism of the layer growth is deduced from our simulations.

Inhibition of Methane Hydrate Formation by Ice-Structuring Proteins

In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitors of gas hydrates as many of those used today suffer from poor biodegradability. In this work, we have investigated experimentally whether ice-structuring proteins (ISPs) found in fish and insect, assumed biodegradable, are capable of inhibiting the growth of methane hydrate (a structure I hydrate). The ISPs investigated were type III HPLC12 (originally identified in ocean pout) and ISP type III found in meal worm (Tenebrio molitor). These were compared to polyvinylpyrrolidone (PVP) a well-known kinetic hydrate inhibitor. The results revealed that adding ISP in sufficient amounts caused the appearance of an initial nonlinear growth period. At a certain point during the growth process the growth pattern changed to linear which is identical to the growth observed for methane hydrate in the absence of inhibitors. The profile of the nonlinear growth was concentration-dependent but also dependent on the stirring rate. ISP type III HPLC12 decreased the growth rate of methane hydrate during the linear growth period by 17−75% at concentrations of 0.01−0.1 wt % (0.014−0.14 mM) while ISP from Tenebrio molitor and PVP decreased the growth rate by 30% and 39% at concentrations of 0.004 wt % (0.005 mM) and 0.1 wt % (0.1 mM), respectively. Considering the low concentration of Tenebrio molitor ISP used, these results indicate that ISP from Tenebrio molitor is the most effective hydrate inhibitor among those investigated. Thermal hysteresis ice formation experiments revealed that ISP from Tenebrio molitor causes higher thermal hysteresis for ice formation compared to type III ISP identified in ocean pout while PVP did not cause thermal hysteresis. This indicates that there might be a direct relationship between ISP performance for ice and hydrate inhibition, and that thermal hysteresis experiments can be used to screen ISPs as kinetic inhibitors.

Investigation of Methane Hydrate Formation in a Recirculating Flow Loop: Modeling of the Kinetics and Tests of Efficiency of Chemical Additives on Hydrate Inhibition

Gas hydrates can be formed when light gases, such as the components of natural gas, come into contact with water under particular conditions of temperature and pressure. These solid compounds give rise to problems in natural gas and oil industry because they can plug pipelines and process equipment. To prevent hydrate formation methanol and glycols are commonly and extensively used as inhibitors. Today, the thermodynamic equilibria of hydrate formation are well known, but the kinetics of gas hydrate formation and growth has to be studied in order to find means of controlling these processes and to explore the mechanisms for hydrate formation that follows non equilibrium laws. The present work deals with the kinetics of methane hydrate formation studied in a laboratory loop where the liquid blend saturated with methane is circulated up to a pressure of 75 bar. Pressure is maintained at a constant value during experimental runs by means of methane gas make-up. First the effects of pressure (35-75 bar), liquid velocity (0. 5-3 m/s), liquid cooling temperature ramp (2-15°C/h), and liquid hydrocarbon amount (0-96%), on hydrate formation kinetics are investigated. Then a new method is proposed to predict firstly the thermodynamic conditions (pressure and temperature) at the maximum values of the growth rate of methane hydrate and secondly the methane hydrate growth rate. A good agreement is found between calculated and experimental data. Finally the evaluation of the efficiency of some kinetic additives and some surfactants developed to avoid either nucleation or crystal growth and agglomeration of methane hydrates is tested based on the proposed experimental procedure.