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| Fig. 1: Global Hydrate Resources. [1] (Courtesy of the U.S. Geological Survey.) |
Natural gas hydrates are attracting increasing interest in the energy industry due their abundance and their advantages to address future energy related challenges. Despite their abundance, there are problems observed during the production and exploration phases of these resources. Historical attempts to produce natural gas from these structures such as the one at the Messoyakha Field showed that natural gas hydrate reservoirs pose different problems than any other conventional or unconventional gas reservoirs and should be handled differently. [1,2] Conventional gas reservoirs consist primarily of gas that can flow in the pores of the reservoir rock. Unconventional gas reservoirs, on the other hand, consist of rocks that have gas in their pores, but this gas is "trapped" inside the pores of the rock. [3] That is why in the past decades technologies such as fracturing have been developed in U.S. to unlock this resource. With the natural gas hydrates however, the problem is harder to tackle. The main reason for the challenge is the fact that the reservoir "rock" is actually is an ice structure that starts melting as the gas inside it is produced.
Fig. 1 shows the proven reserves of natural gas hydrates around the world. [4] The yellow dots stand for areas at which a hydrate reserve is found by an indirect measurement method called Bottom Stimulating Reflector. The red dots are direct observations of hydrates made on samples collected at the reservoir depth. [4] The red squares indicate fields at which the production from hydrates has actually been undertaken. The number of such fields is small because of operational difficulties experienced during production. The first natural gas production from these formations was done in 1960s in Yakutia. Production was shut down due to stability issues.
Since then, hydrates have been investigated by many countries. One of the more important reasons is their distribution in the world. Countries that do not have access to conventional hydrocarbons could become energy independent through this resource. A good example is Japan, where there are vast resources of natural gas hydrates.
It is reported that there are 20,000 trillion m3 (at STP) in marine and coast accumulations of natural gas hydrates. This amount of gas would provide energy for 200 years at the current level of energy consumption. These reservoirs are relatively shallow ranging from 100 to 1100 m. below the sea floor.
Another concern of the energy industry is the increasing CO2 emissions and specifically CCS (Carbon Capture and Sequestration). [5] Reducing global warming requires that the amount of CO2 residing in the atmosphere should be decreased. Geologic storage of CO2 is one of the possibilities to achieve that goal.
A developing technique called swapping is catching the energy industry's attention, is the double-gain nature of the process. [5] As CO2 is injected into the hydrate structure, CH4 production is enhanced. This method provides a means of CO2 storage and enhanced CH4 production at the same time.
Natural gas hydrates are still at an experimental phase both for discovery and production. One of the toughest challenges is that they are hard to detect my using seismic methods, the main tool used by the oil industry. Moreover, producing the gas in hydrate structures causes the solid structure that is drilled to disintegrate causing problems for drilling in these formations.
Moreover, existing hydrocarbon resources still make this resource unfeasible for production. Also the resources near the ocean bottom may be affected by seasonal temperature changes of water temperature releasing natural gas thus decreasing resources.
Natural gas hydrates provide a viable source for the far future of energy. It has been recognized that there are challenges for producing these resources. However, as conventional resources are depleted and population continues to increase, there will be need for these energy resources as well. Production of these resources is sure to change the energy policies and energy politics, perhaps even turning countries that are importers of gas into exporters.
© Orhun Aydin. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] T. S. Collett, "Natural Gas Hydrates - Vast Resource, Uncertain Future," U.S.Geological Survey, Fact Sheet FS-021-01, March 2001.
[2] J. P. Kennett et al., Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis (Am. Geophys. Union, 2009).
[3] M. D. Max et al., "New Method for Extraction of Water From Natural Gas," One Petro 17771-MS, 1 May 06.
[4] T. Uchida et al., "Two-Step Formation of Methane-Propane Mixed Gas Hydrates in a Batch-Type Reactor," AIChE J. 50, 518 (2004).
[5] A. V. Milkov and R. Sassen, "Economic Geology of Offshore Gas Hydrate Accumulations and Provinces," Marine Pet. Geol. 19, 1 (2002).