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It is expected that the resultshave immediate relevance in transportation and energy storage, CO2 capture, environmentaland geological processes and flow assurance in pipelines of oil and gas. Start date Between and. Thermodynamic study on gas hydrate formation and dissociation Study on the formation and dissociation of gas hydrates at high pressure Kinetic study on gas hydrate formation and dissociation Determination of specific heat of methane and methane hydrates at high pressures Structural study of gas hydrates at high pressures Experimental simulation of the effects of energetic particles ions and electrons November 01, - February 28, Field of knowledge: Engineering - Chemical Engineering Principal Investigator: Maria Dolores Robustillo Fuentes Grantee: JP Abstract The study and understanding of the mechanisms of gas hydrates formation anddissociation have applications in various areas such as flow assurance of oil and gas, waterpurification, capture and sequestration of CO2 and also in the possible use as an alternativeenergy source to other fuels such as oil or coal.

Research Grants - Young Investigators Grants. November 01, - February 28, Engineering - Chemical Engineering.

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Gas hydrates and seafloor stability

The mechanics of plug formation are not yet well understood, although it is known that certain geometries, such as flow restrictions at chokes, are prone to hydrate plug formation. Control of hydrates relies on keeping the system conditions out of the region in which hydrates are stable. During oil production operations, temperatures are usually above the hydrate formation temperature, even with the high system pressures at thewellhead on the order of to 10, psi.

However, during a system shutdown, even well-insulated systems will fall to the ambient temperatures eventually, which in the deep GoM is approximately 38 to 40 F. Many methods are available for hydrate formation prediction.

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Most of them are based on light gas hydrocarbon systems and vary in the complexity of the factors utilized within the computational procedures. The Peng-Robinson method is one typical equation of state EOS method that is currently extensively utilized to predict hydrate boundaries. Knowledge about hydrates has significantly improved in the past 10 years. Hydrate disassociation can be predicted within 1 to 3 with the exception of brines that have a high salt concentration.

Formation and dissociation mechanisms of clathrate hydrates

The hydrate disassociation curves typically provide conservative limits for hydrate management design. The effects of thermodynamic hydrate inhibitors, methanol and ethylene glycols, can be predicted with acceptable accuracy. When the temperature and pressure are in the hydrate region, hydrates grow as long as water and light hydrocarbons are available and can eventually develop blockages.

Clearing hydrate blockages in subsea equipment or flowlines poses safety concerns and can be time consuming and costly. Hydrate formation is typically prevented by several methods including controlling temperature, controlling pressure, removing water, and by shifting thermodynamic equilibrium with chemical inhibitors such as methanol or monoethylene glycol, low-dosage hydrate inhibitors. The hydrate inhibition abilities are less for substances with a larger molecular weight of alcohol, for example, the ability of methanol is higher than that of ethanol and glycols.

With the same weight percent, methanol has a higher temperature shift than that of glycols, but MEG has a lower volatility than methanol and MEG may be recovered and recycled more easily than methanol on platforms. Salt, methanol, and glycols act as thermodynamic hydrate inhibitors that shift the hydrate stability curve to the left. Salt has the most dramatic impact on the hydrate stability temperature. On a weight basis, salt is the most effective hydrate inhibitor and so accounting correctly for the produced brine salinity is important in designing a hydrate treatment plan.

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The solubility of salt to water has a limit based on the temperature. More small molecular components results in a lower hydrate formation at the same pressure.

More weight percentage of methanol leads to a greater temperature shift of the hydrate formation curve. They inhibit hydrate formation by reducing the temperature at which hydrates form. This effect is the same as adding antifreeze to water to lower the freezing point.

Methanol and MEG are the most commonly used inhibitors. LDHIs include anti-agglomerates and kinetic inhibitors. LDHIs have found many applications in subsea systems in recent years. Unlike thermodynamic inhibitors, LDHIs do not change the hydrate formation temperature.


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They either interfere with formation of hydrate crystals or agglomeration of crystals into blockages. Anti-agglomerates can provide protection at higher subcooling temperatures than can kinetic hydrate inhibitors. However, low-dosage hydrate inhibitors are not recoverable and they are expensive.

Gas hydrate

LDHIs are preferred for regular operations because they reduce volumes and can work out to be cheaper. For transient events, the volumes required are not usually that large, so there is not much benefit in LDHIs, and methanol becomes the preferred inhibitor. THIs inhibits hydrate formation by reducing the temperature at which hydrates form by changing the chemical potential of water.

This includes methanol, glycols, and others. In general, methanol is vaporized into the gas phase of a pipeline, and then dissolves in any free water accumulation to prevent hydrate formation.


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They are dissolved in a carrier solvent and injected into the water phase in pipelines. These inhibitors work independently of water cuts, but are limited to relatively low subcooling temperatures less than 20 F , which may not be sufficient for deepwater applications. For greater subcooling, KIs must be blended with a thermodynamic inhibitor.

Additionally, the inhibition effect of KIs is time limited and, thus, their benefit for shut-down is limited. Long-term shutdowns will require depressurization, which complicates the restart process, and methanol without KIs will be required for restarts. KIs are generally environmentally friendly. Anti-agglomerates AAs are surfactants, which cause the water phase to be suspended as small droplets. When the suspended water droplets convert to hydrates, the flow characteristics are maintained without blockage.

They allow hydrate crystals to form but keep the particles small and well dispersed in the hydrocarbon liquid. They inhibit hydrate plugging rather than hydrate formation. AAs can provide relatively high subcooling up to 40 F, which is sufficient for deepwater applications and have completed successful field trials in deepwater GoM production systems.

AA effectiveness can be affected by type of oil or condensate, water salinity, and water cut.

Methanol may still be required for shutdown and restart. Facilities Engineering into the Next Millennium