Category Methane Gas Hydrate

Economic and Political Issues

The economic production of natural gas from oceanic hydrate deposits will require new offshore drilling systems and methods. Also, the product of hydrate dissocia­tion may be relatively low pressure, wet gas, especially where the excess pressure produced by hydrate dissociation can be equilibrated rapidly through high-porosity sediments. Natural gas derived from hydrate may result in low local production rates. The low production rate requires low-cost drilling methods to ensure eco­nomic viability. Recovering methane and economically transporting it pose a chal­lenge to technologists and scientists. Ideas have been conceptualized and research has been initiated to address these challenges.

Methane hydrate will be commercially exploited only when the price of petro­leum oil and conventi...

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Possible Transportation Routes

If commercial production from oceanic natural gas hydrates is eventually estab­lished, there are at least three ways to transport the gas ashore: (1) by conventional pipeline; (2) by converting the gas hydrates to liquid middle distillates via the newly improved Fischer-Tropsch process and loading them onto a conventional tanker or barge; or (3) by reconverting the gas into solid hydrate and shipping it ashore in a close-to-conventional ship or barge.

Methane could be transported from the production site to the shore through submarine pipelines as is done for long-distance transportation of natural gas. However, submarine pipelines are expensive and the geological hazards of the continental slope make this option difficult...

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Seafloor Drilling of the Hydrate Zone for Exploration and Production of Methane

The main cost here is only that of the pipeline used to transport the gas to the pro­duction platform. For subsea systems that do not produce to a fixed platform, a drilling template must be used that connects to a group of wells.

Drilling capabilities developed for conventional deepwater hydrocarbon explo­ration and production are presently sufficient for drilling and completing produc­tion in hydrate and associated gas deposits. Hydrate system deposits are always to be found relatively close to the seafloor. Hydrated sediments are expected in water depths between 500 and 2,000 m. Semisubmersible drilling systems with this depth capacity are currently available; however, the costs are extremely high (Brandt et al. 1998)...

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Marine Hydrates

Subsurface occurrences of natural gas hydrate can be classified into six types: (1) pore-space hydrate, (2) platy hydrate, (3) layered/massive hydrate, (4) dissemi­nated hydrate, (5) nodule hydrate, and (6) vein/dyke hydrate. The anomalies of chloride contents in pore water, core temperature depression, core observation, as well as visible gas hydrates confirmed well-interconnected and highly saturated pore-space hydrates as an intergranular pore filling within sand layers within the methane hydrate stability zone. Hydrate saturations are higher than 60% through­out most hydrate-dominant sand layers and in some parts there is close to 100% pore saturation. Muddy sediments such as silts and clays are free of hydrate or contain low concentrations.

Figure 5...

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Arctic Hydrates

Gas hydrates are found within and beneath permafrost on the North Slope of Alaska, in the Canadian Arctic, and in northern Siberia. The Arctic hydrates have the potential to become economically viable sources of natural gas. The best do­cumented Alaskan accumulations are in the Prudhoe Bay-Kuparuk River area, which contains approximately 30 trillion standard cubic feet of natural gas, about twice the volume of conventional gas found in the Prudhoe Bay field (Collett 2002). The proximity to highly developed oilfield infrastructure makes the Prudhoe Bay-Kuparuk River accumulation particularly attractive. The main technology barrier is the lack of validated methods for economically viable production of natu­ral gas from hydrate...

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Gas Hydrate Reservoirs

There are two gas hydrate reservoirs. They are Arctic hydrates and marine hy­drates. Gas hydrates are found within and under permafrost in Arctic regions. They are also found within a few hundred meters of the seafloor on continental slopes and in deep seas and lakes. The reservoir architecture, technology needs, and eventual economic importance of hydrates in Arctic and marine environments may be very different. The commercial utilization of Arctic and marine gas hy­drate resources is different.

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Chemical Inhibitor Injection Process

The third method is chemical inhibition, a concept similar to the chemical means presently used to inhibit the formation of water ice. This method seeks to displace the natural gas hydrate equilibrium condition beyond the hydrate stability zone’s thermodynamic conditions through injection of a liquid inhibitor chemical adja­cent to the hydrate. The chemical inhibitor injection method is also expensive, although less so than the thermal stimulation method, owing to the cost of the chemicals and the fact that it also requires good porosity. Figure 5.3 shows gas production by the chemical inhibitor injection process.

In the inhibitor injection process, an inhibitor such as methanol is injected into the gas hydrate zone...

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Thermal Stimulation Process

The second method is thermal stimulation, in which a source of heat provided directly in the form of injected steam or hot water or another heated liquid, or indirectly via electric or sonic means, is applied to the hydrate stability zone to raise its temperature, causing the hydrate to decompose.

In the thermal stimulation process, heat energy can be released into the methane hydrate strata to dissociate the gas. This process has a favorable net energy balance, as the heat energy required for dissociation is about 6% of the energy contained in the liberated gas. In simple terms, steam or hot water can be pumped down a drill hole to dissociate the hydrate and release methane. The methane released can then be pumped to the surface of the seafloor through another drill hole (Desa 2001).

The ...

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