Hydrate Formation In Pipelines Research Articles

CFD Analysis of Hydrate Formation in Pipelines

Offshore oil and gas exploration and production is increasingly moving further into the deep sea where temperature and pressure conditions favor hydrate. Hydrate formation in gas pipeline is one of the major flow assurance problems, which is enhanced as lower temperature and higher pressure condition. This study explores the CFD analysis of hydrate formation behavior in subsea pipeline by performing sensitivity studies exploring the effects that flow (velocity, diameter) and fluid (viscosity and water fraction) parameters on hydrate formation. The results generated showed that changes in flow conditions or fluid properties have significant effects on the hydrate formation in the pipeline.

Influences of large molecular alcohols on gas hydrates and their potential role in gas storage and CO2 sequestration

In this study, the influences of large molecular alcohols (LMAs) including pinacolyl alcohol (PCA) and tert-amyl alcohol (tAA) on thermodynamic phase behaviors and structural characteristics of CH4 and CO2 hydrates were investigated for their potential use in gas storage and CO2 sequestration. The experimentally measured hydrate phase equilibria demonstrated that CH4 hydrates were stabilized in the presence of PCA and tAA. 13C NMR and Raman spectroscopy confirmed sH hydrate formation from both CH4+PCA+water and CH4+tAA+water systems, resulting from the enclathration of LMAs in the large 51268 cages. The sH hydrate formation of the CH4+PCA+water system was also confirmed by an endothermic dissociation thermogram from a differential scanning calorimeter (DSC). In contrast with CH4 hydrates, the addition of both PCA and tAA to CO2 hydrates resulted in thermodynamic inhibition. Through Raman and powder X-ray diffraction (PXRD) analyses, both CO2+PCA and CO2+tAA hydrates were characterized as sI hydrates, indicating that LMAs simply inhibit the formation of CO2 hydrates without being captured in the hydrate lattices. Therefore, PCA and tAA are expected to function as thermodynamic promoters which reduce the hydrate forming pressure in natural gas storage applications, while they can serve as thermodynamic inhibitors which prevent CO2 hydrate formation in pipelines for CO2 transportation to sequestration sites.

DEVELOPMENT OF THE METHOD FOR PREDICTING FIELD DOSAGE OF KINETIC HYDRATE INHIBITOR

The increased application of low dosage hydrate inhibitors in oil and gas production has made it necessary to develop a method for determining the consumption rates of kinetic hydrate inhibitors, as no techniques are currently available for that purpose. The method was developed in the experiments with the kinetic hydrate inhibitor SONHYD-1801A, representing a stereoregular copolymer of N-vinylpyrrolidone and caprolactam. The currently used technology for application of kinetic hydrate inhibitor SONHYD-1801A has been improved, allowing effective prevention of hydrate formation in pipelines. It is stated that the chemical can be used for continuous injection in the oil, oil-gas and oil/gas-condensate fields to prevent hydrate formation during the production and transportation of associated gas within the limited temperature and pressure range. For the experiment, a model gas hydrate-forming mixture was prepared, consisting of methane and propane in the ratio of 60/40 respectively, and with a 99.98% purity of the components. This gas mixture simulates the composition of both associated gas and gas produced from oil-gas-condensate fields. Based on the investigations performed, it is established that the kinetic hydrate inhibitor SONHYD-1801A is able to reduce the hydrate equilibrium temperature within the range of 14˚C against the equilibrium temperature. The operating pressure range is up to 15 MPa, and the inhibiting capacity is not reduced considerably as in the case with low temperatures. An empirical equation has been obtained that shows kinetic hydrate inhibitor consumption vs. pressure, temperature and water content of the gas mixture. Based on the equation, a method has been developed for optimal consumption of kinetic hydrate inhibitor under various gas flow regimes.

Efficient Hydrate Plug Prevention

A primary focus of flow assurance engineers during project development is the prevention and management of gas hydrate formation in pipelines. Historically, engineers have focused on hydrate formation prevention by injecting sufficient quantities of thermodynamic inhibitors to “shift” the hydrate stability region outside of the range of pressure and temperature operating conditions. However, as developments of hydrocarbon production occur in ever more extreme environments, the practice of complete prevention of hydrate formation may become prohibitively expensive because of the large amounts of inhibitor required. The example of high methanol dosage in equal volumes of inhibitor for water implies a cost of $84 per barrel of water produced at a methanol cost of $2/gallon. As the produced water volume increases during field life, the operators may not be able to pay for hydrate inhibition even with $100 per barrel of oil. The past decade has seen intensive research to discover strategies for transitioning f...

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.

Hydrate formation process with consideration of heat and mass exchange

Results are offered from numerical experiments involving hydrate formation in pipelines during quasisteady state flow of a moist gas.