Sukumar Laik

Methane hydrate formation and dissociation in synthetic seawater

Abstract The formation and dissociation of methane gas hydrate at an interface between synthetic seawater (SSW) and methane gas have been experimentally investigated in the present work. The amount of gas consumed during hydrate formation has been calculated using the real gas equation. Induction time for the formation of hydrate is found to depend on the degree of subcooling. All the experiments were conducted in quiescent system with initial cell pressure of 11.14 MPa. Salinity effects on the onset pressure and temperature of hydrate formation are also observed. The dissociation enthalpies of methane hydrate in synthetic seawater were determined by Clausius-Clapeyron equation based on the measured phase equilibrium data. The dissociation data have been analyzed by existing models and compared with the reported data.

Biosurfactant as a Promoter of Methane Hydrate Formation: Thermodynamic and Kinetic Studies.

Natural gas hydrates (NGHs) are solid non-stoichiometric compounds often regarded as a next generation energy source. Successful commercialization of NGH is curtailed by lack of efficient and safe technology for generation, dissociation, storage and transportation. The present work studied the influence of environment compatible biosurfactant on gas hydrate formation. Biosurfactant was produced by Pseudomonas aeruginosa strain A11 and was characterized as rhamnolipids. Purified rhamnolipids reduced the surface tension of water from 72 mN/m to 36 mN/m with Critical Micelle Concentration (CMC) of 70 mg/l. Use of 1000 ppm rhamnolipids solution in C type silica gel bed system increased methane hydrate formation rate by 42.97% and reduced the induction time of hydrate formation by 22.63% as compared to water saturated C type silica gel. Presence of rhamnolipids also shifted methane hydrate formation temperature to higher values relative to the system without biosurfactant. Results from thermodynamic and kinetic studies suggest that rhamnolipids can be applied as environment friendly methane hydrate promoter.

Influence of Electrolytes on Methane Hydrate Formation and Dissociation

Natural gas hydrate creates a lot of problems during its transportation and production by plugging gas pipelines and process equipment. This work envisages the effect of electrolytes (NaCl and CaCl2) at different concentrations on methane hydrate formation and dissociation. Extensive observations on equilibrium pressure and temperature during hydrate formation and dissociation have been made. The experiments were conducted in the temperature range of 261 to 270 K and pressure range of 2.6 to 3.0 MPa. Both sodium chloride and calcium chloride salts were found to have significant inhibiting effects on hydrate formation and dissociation with the latter having stronger effects. Gas consumption was found to vary with the progress of the hydrate formation as well as the concentration of salts in the hydrate cell. The dissociation enthalpies of methane hydrates in the presence of the above salts were also determined using the Clausius-Clapeyron equation based on the phase equilibrium data.

Experimental and modeling study of kinetics for methane hydrate formation in a crude oil-in-water emulsion

A low-viscosity emulsion of crude oil in water can be believed to be the bulk of a flow regime in a pipeline. To differentiate which crude oil would and which would not counter the blockage of flow due to gas hydrate formation in flow channels, varying amount of crude oil in water emulsion without any other extraneous additives has undergone methane gas hydrate formation in an autoclave cell. Crude oil was able to thermodynamically inhibit the gas hydrate formation as observed from its hydrate stability zone. The normalized rate of hydrate formation in the emulsion has been calculated from an illustrative chemical affinity model, which showed a decrease in the methane consumption (decreased normalized rate constant) with an increase in the oil content in the emulsion. Fourier transform infrared spectroscopy (FTIR) of the emulsion and characteristic properties of the crude oil have been used to find the chemical component that could be pivotal in self-inhibitory characteristic of the crude oil collected from Ankleshwar, India, against a situation of clogged flow due to formation of gas hydrate and establish flow assurance.

Role of Rhamnolipid: A Biosurfactant in Methane Gas Hydrate Formation Kinetics

Naturally occurring methane gas hydrate is a vast source of methane gas which is trapped in crystalline ice-like structure present in permafrost regions and under the sea in outer continental margins. It is purposed that total amount of carbon in the form of methane hydrates is almost twice the carbon content in all the fossil fuel reserves put together, and hence these are supposed to be the future potential energy resource. This paper investigates the laboratory investigations on effect of a biosurfactant rhamnolipid on methane hydrate formation kinetics. Rhamnolipid was produced by Pseudomonas aeruginosa strain A11. The presence of P. aeruginosa has been reported in Gulf of Mexico gas hydrate samples. Biosurfactant reduced the surface tension of water from 72 to 36 mN/m with CMC of 70 mg/L. The biosurfactant dose is studied at two different concentrations in the solution at 100 and 1000 ppm. Kinetic of hydrate formation and growth is compared at 0, 100, and 1000 ppm of rhamnolipid showing that rhamnolipid acts as a hydrate promoter at these concentrations. Thus, small dosages of rhamnolipids produced by P. aeruginosa strain A11 must clearly affect the gas hydrate formation kinetics in natural sites (as in Gulf of Mexico).

Modeling of Gas Hydrate Formation in a High Pressure Reactor

Gas hydrates are now gaining importance in oil and gas industries because they are considered a future source of energy and a means for the transport of natural gas. On the other hand gas hydrates create problems by plugging the pipelines during transportation. Obviously, predicting the conditions in which hydrates are formed would be valuable. In the present study, experiments were performed to observe the conditions, which favor the formation of an ethane gas hydrate. The results of the hydrate formation are elucidated with the help of a conceptual kinetic model. An empirical correlation is developed to predict the rate of formation of the hydrate in terms of the operating and geometric variables of the system. A simple kinetic model based on the dissolved ethane gas is also developed which shows that the hydrate formation follows the first order rate equation.