Effect Of Hydrate Formation Research Articles

Evolution of effective thermal conductivity during hydrate formation and decomposition in natural sediments

Gas hydrates are regareded as a potential alternative energy sources for sustainable development. Thermal properties of gas hydrate-bearing sediments directly govern the heat transfer process during hydrate decomposition which couples with phase transitions and multiphase flows. Latest database on the thermal properties of natural sediments containing gas hydrates still remains limited. Here we report on point heat source measurements of the effective thermal conductivity of hydrate-bearing sediments through a thermistor-based method and evaluation of existing models. Effective thermal conductivity of water saturated natural sediments and partially saturated hydrate-sediment are obtained, showing a significant effect of compaction on the effective thermal conductivity of the sediments. The evolution of thermal conductivity during hydrate formation, decomposition and reformation indicates that the variation of the components in the pores could play a crucial role in the effective thermal conductivity. A higher saturation of hydrates in the pores and a smaller porosity could contribute to a better thermal conductivity. The evolution of the effective thermal conductivity with hydrate formation and decomposition also demonstrates a temperature dependence. Moreover, the reformation process after hydrates are fully decomposed significantly impacts the variation of the effective thermal conductivity, which could be attributed to the solution migration during decomposition and the local inhomogeneity of hydrate reformation. The slightly increase in the thermal conductivity below zero degree Celsius implies the small fraction of ice generation during the cooling process. The results could provide some insights into the effect of hydrate formation and decomposition on the effective thermal conductivity of natural sediments, which would be helpful in the heat transfer evaluation and gas production simulation in the field test.

Impact on water surface due to deepwater gas blowouts

This paper presents a study on the impact of underwater gas blowouts near the ocean surface, which has a greater relevance to assess Health, Safety, and Environmental risks. In this analysis the gas flux near the surface, reduction of bulk density, and gas surfacing area are studied for different scenarios. The simulations include a matrix of scenarios for different release depths, release rates, and initial bubble size distributions. The simulations are carried out using the MEGADEEP model, for a location in East China Sea. Significant changes in bulk density and gas surface flux near the surface are observed under different release conditions, which can pose a potential threat for cleanup and rescue operations. Furthermore, the effect of hydrate formation on gas surfacing is studied for much greater release depths. The type of outcomes of this study is important to conduct prior risk assessments and contingency planning for underwater gas blowouts.

Emulsion stability of surfactant and solid stabilized water-in-oil emulsions after hydrate formation and dissociation

Hydrates are ice-like crystalline compounds that can cause plugging of crude oil pipelines. Stable water-in-oil emulsions aid in preventing hydrate particle agglomeration and hydrate plug formation in crude oil pipelines. The type of stabilizers present in water-in-crude oil emulsions also influences hydrate formation. Therefore, the effect of hydrate formation and dissociation on the stability of water-in-oil emulsions stabilized using either surfactants or solid particles was investigated. In addition, the difference in the effect of hydrate formation and dissociation on water-in-oil emulsions stabilized using solid particles of varying hydrophobicity was investigated. Furthermore, the effect of hydrate formation and dissociation on droplet size of the water-in-oil emulsions was quantified. The results showed that, the water-in-oil emulsions stabilized using moderately hydrophobic solid particles resisted emulsion destabilization, after hydrate formation and dissociation, unlike water-in-oil emulsions that were stabilized using either surfactants or highly hydrophobic solid particles. Also, after hydrate dissociation, for surfactant stabilized emulsions, the droplet size of water in the residual emulsion increased by more than 85% as compared to the droplet size before hydrate formation. On the contrary, for solid stabilized emulsions, no significant change in the droplet size of the residual emulsion was observed after hydrate dissociation as compared to the water-in-oil emulsion before hydrate formation. A conceptual mechanism was proposed to explain the observed difference in the stability of solid stabilized water-in-oil emulsions when subjected to hydrate formation and dissociation. Additionally, dynamic interfacial tension measurements were carried out to explain the difference in the initial droplet size of solid stabilized and surfactant stabilized water-in-oil emulsions.

The Kinetics on Hydrate Formation in Pipelines

This study presents the experimental apparatus of flow loop type to investigate the hydrate plugging phenomena. The experiments for formation and dissociation of methane hydrate were conducted using the experimental apparatus setup in this study. Through the experiments, (gas + water + hydrate) three-phase equilibrium conditions were measured and enthalpy change in the dissociation process was analyzed based on the equilibrium results. The equilibrium conditions and the enthalpy of dissociation have been found to be consistent with previously published reference data. To examine the effect of hydrate formation under the flowing condition, experiments were carried out at varying flow velocities under a constant pressure. As a result, hydrate forming temperature tends to increase linearly with increasing flow velocity. Therefore, it was verified experimentally that flow velocity can be considered as one of the significant factors triggering the increase in the formation temperature.

Comparison of torque measurements and near-infrared spectroscopy in characterization of a wet granulation process

The purpose of this study was to compare impeller torque measurements and near‐infrared (NIR) spectroscopy in the characterization of the water addition phase of a wet granulation process. Additionally, the effect of hydrate formation during granulation on the impeller torque was investigated. Anhydrous theophylline, α‐lactose monohydrate, and microcrystalline cellulose (MCC) were used as materials for the study. The materials and mixtures of them were granulated using purified water in a small‐scale high‐shear mixer. The impeller torque was registered and NIR spectra of wet samples were recorded at‐line. The torque and the NIR baseline‐corrected water absorbances increased with increasing water content. A plateau in the NIR baseline‐corrected water absorbances was observed for wet masses containing MCC. This was at the region of optimal water amount for granulation according to the torque results. In the case of anhydrous theophylline, the slope of baseline‐corrected water absorbance values increased at the same water amount as the impeller torque started to increase. The hydrate formation of theophylline during granulation was observed as a slight decrease in the impeller torque. In addition, the hydrate formation during granulation affected the granulation liquid requirement. The liquid requirement was different for monohydrate formed during granulation compared to one formed in high relative humidity before the granulation. The results suggest that NIR spectroscopy may be applicable to process monitoring of wet granulation, also in cases where monitoring of impeller torque is difficult to apply. © 2004 Wiley‐Liss Inc. and the American Pharmacists Association J Pharm Sci 93:2232−2243, 2004

The Effect of Hydrate Formation on the Pressure Release of Wet Carbon Dioxide

Experimental investigations on top vented vessel blowdown of pressurized carbon dioxide with dissolved water show that in spite of its low solubility, dissolved water significantly inhibits the outflow caused by the formation of hydrate in the venting line. The influences of initial conditions, release velocity and heating the venting line are studied. An existing simulation model is modified to take into account the inhibition by hydrate formation.

The effect of hydrate formation on the solubility of theophylline in binary aqueous cosolvent systems

The solubility at 30° C of theophylline in mixtures of water and the cosolvents ethanol, propylene glycol, dimethylformamide and PEG 400 has been measured. In all these systems the solid phase in equilibrium with the solution depended on the solvent composition; theophylline monohydrate was present for water-rich solutions and anhydrous theophylline for cosolvent-rich solutions. The volume fractions of water at which the transition between the solid phases occurred was f′ = 0.18, 0.35, 0.35 and 0.25 for ethanol, propylene glycol, dimethylformamide and PEG 400, respectively. Maxima in the solubility vs composition profiles occurred for ethanol and propylene glycol, but not for dimethylformamide. The effects of hydrate formation on the solubility are analysed quantitatively in the case of ethanol/water mixtures. Hydrate formation depresses the solubility in water-rich solutions and distorts the shape of the solubility profile. In comparing experimental solubilities with the predictions of regular solution theory in the extended Hildebrand approach it is necessary to take account of the effect of hydrate formation.

Effect of hydrate formation on informativity of indicators of petroleum potential

We note the reduced informativity of data on gas-oil ratio and gas aureoles as indicators of petroleum potential in low-temperature zones. We conclude that there is a loss of reliability of the indicators ..sigma..HHC (heavy hydrocarbons)/CH/sub 4/ and i -C/sub 4/H/sub 10//n-C/sub 4/H/sub 10/ based on computations of variation of gas composition as a result of hydrate formation. The effect of hydrate-forming processes should be taken into account while using any data on gases (both dissolved and free) as prospecting criteria of petroleum potential in the northern and eastern regions of the USSR.