Category Methane Gas Hydrate

Depressurization Process

There are at least three means by which commercial production of natural gas hydrates might eventually be achieved, all of which alter the thermodynamic con­ditions in the hydrate stability zone such that the gas hydrate decomposes.

The first method is depressurization. Production is based on the depressuriza­tion-induced dissociation of the hydrates. Depressurization takes place in the sec­tion by pumping, especially within the free gas below the BSR. The hydrate may then dissociate downward into the low-pressure gas layer. However, the latent heat of dissociation must still be provided...

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Processes for Methane Production from Gas Hydrates

5.1 Introduction

The gases in the natural gas hydrate sediment are primarily methane molecules (Kvenvolden 1995). Methane hydrates are considered a major potential source of hydrocarbon energy and could be important in meeting natural gas demand in the future (Chi et al. 2006). Natural gas hydrates are a vast potential, though not pres­ently commercial, source of additional natural gas. One of the most appealing aspects of this potential new gas source is that large deposits are located near the areas where demand for energy is expected to grow. Some countries, such as Ja­pan, do not have indigenous oil or gas resources but do have nearby oceanic natu­ral gas hydrate deposits. Means of economically and safely producing methane from gas hydrate deposits are not yet on the drawing board...

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Properties of Seawater

Seawater is a mixture of 96.5% pure water and 3.5% other material, such as salts, dissolved gases, organic substances, and undissolved particles. The physical char­acteristics of seawater are determined by the physical properties, which are tem­perature, salinity, density, transparency, and ability to transmit light and sound. The most important physical factors for marine organisms are light, temperature, salinity, hydrostatic pressure (the weight of the water acting on a unit area), and acid-base balance. Physical parameters such as pressure, temperature, conductiv­ity, and pH are measured through the water column. Salinity, density, and sound velocity are calculated from these measurements. Vertical profiles of temperature and salinity change locally...

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Gas Hydrate Research and Development

Researchers have identified a need to better understand how the geological fea­tures in the permafrost regions and on continental margins control the occurrence and formation of methane hydrates. They have underscored the need to understand fundamental aspects (porosity, permeability, reservoir temperatures) of the geo­logical framework that hosts the gas hydrate resource to improve assessment and exploration, to mitigate the hazard, and to enhance gas recovery.

Together with advances in research and development, economic viability will depend on the relative cost of conventional fuels, as well as other factors, such as pipelines and other infrastructure needed to deliver methane gas hydrate to market...

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Disposal of Impurities from Methane

In situations where natural gas and associated gas contain a lot of nitrogen, carbon dioxide, and hydrogen sulfide, hydrate technology can potentially be used to sepa­rate these gases from the source gas. This is because gas hydrates are thermody­namic equilibrium products. Mass transfer operations can be designed to carry out the separation and cleaning processes. In situations where saline water and brackish water need to be cleaned, gas hydrates can be produced and separated from the con­centrated solution. This is because gas hydrates consume just water and gas, not other constituents such as dissolved salts and biological materials.

In situations where volatile organic compounds need to be recovered, for ex­ample, on oil tankers and receiving terminals, the hydrate-forming gases ca...

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Facilities for Recovery of Methane from Methane Hydrate

Scientists are researching specific concerns about methane hydrate recovery and use which include drilling safety issues, potential influences on global climate change as methane is a potent greenhouse gas and the natural release of vast quan­tities from hydrate deposits would affect the global carbon cycle, cost-effective transportation of the gas to the surface, and the possible impact of hydrate removal on ocean floor stability.

There are four main possibilities for recovering of methane:

1. Add heat and raise the temperature to above that necessary for hydrate dissocia­tion.

2. Depressurize the section by pumping, especially within the free gas below the BSR. The hydrate may then dissociate downward into the low-pressure gas layer...

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Methane Hydrate Stability

Under suitable conditions of low temperature and high pressure, a gas molecule will react with water to form hydrates according to

G + AHH2O = GAH H2O,

where G is a gas molecule and AH is the hydration number. Of particular inter­est are hydrates formed by hydrocarbon gases when the gas molecule is an alkane, especially methane, in which case AH = 6, and 1 vol of hydrates contains about 164 vol (at standard temperature and pressure) of gas Natural hydrates in geologi­cal systems also include CO2, H2S, and N2 as guests. Natural hydrate deposits involve mainly methane, and occur in two distinctly different geological settings where the necessary low temperatures and high pressures exist for their formation and stability: in the permafrost and in deep ocean sediments.

Gas hydrates are stabl...

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Properties of Methane Hydrates

Methane hydrates are common in sediments deposited on high-latitude continental shelves and at the slope and rise of continental margins with high bioproductivity (Kvenvolden 1988b). High biological production provides the organic matter bur­ied in the sediment, which, during early diagenesis and after exhausting oxygen, sulfate, and other electron acceptors, eventually generates methane through fermen­tative decomposition and/or microbial carbonate reduction (Suess 2002). The prop­erties of sediment-hosted gas hydrates are strongly determined by the texture, struc­ture, and permeability of the sediment and the mode of supply of methane.

According to the well-known hydrate model, the water molecules from a well – defined crystal lattice (the host lattice) containing cavities into which...

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