VOLUME 12, NUMBER 2
MARCH/APRIL 1998
© Copyright 1998 American Chemical Society
Special Section on Gas Hydrates Gas Clathrate Hydrates1 Robert P. Warzinski* and Gerald D. Holder† Federal Energy Technology Center, U.S. Department of Energy, P.O. Box 10940, Pittsburgh, Pennsylvania 15236-0940 Received January 16, 1998 Prior to the relatively recent discovery of their natural occurrence in suboceanic and permafrost environments, gas clathrate hydrates, commonly referred to as gas hydrates, were originally considered a laboratory curiosity that later became prominent as a nemesis for the natural gas transportation and production industry. Because of their abundant natural occurrence and potential role in global warming, international interest in gas hydrates has intensified over the past several years. Current gas hydrate resource estimates indicate that there is more carbon in this form, primarily as methane, than in all other forms of fossil fuels combined. This methane resource could conceivably be used as a low-carbon-content supplement or replacement for much of the world’s existing carbon-rich energy resources. In addition, the dissociation and formation of gas hydrates themselves may play a significant role in global climate change for a number of other generally unrelated reasons. Methane yields just over half as much carbon dioxide as coal per unit of energy produced. The technology for fuel switching is available; however, conventional sources of methane, while sufficient for current use, are not sufficient to replace other fossil fuels on a large scale. Production of methane from gas hydrates could, the primary limitation being the lack of proven large-scale recovery technologies. † School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (1) A paper in this section, Gas Hydrate Formation in the Deep Sea: In Situ Experiments with Controlled Release of Methane, Natural Gas, and Carbon Dioxide, by Peter G. Brewer, Franklin M. Orr, Jr., Gernot Friederich, Keith A. Kvenvolden, and Daniel L. Orange, was published in the January/February issue: Energy Fuels 1998, 12, 183188.
To facilitate utilization of gas hydrates, potential recovery technologies must be more fully understood and developed. One concept involves depressurization, caused by the extraction of any free methane in contact with gas hydrate formations, as a means to destabilize the gas hydrate and release additional methane for subsequent recovery. Another means of recovery is slurry mining where hot water or brine is injected into the gas hydrate-bearing strata causing the gas hydrates to melt, decompose, and produce gas. In this case, technologies have to be developed for injecting warm water or brine, contacting the fluid and gas hydrate, trapping and producing the released gas, and transporting the potentially hydrate-forming slurries. Gas hydrate formation can also be a problem as natural gas and oil are produced in colder and deeper marine environments because all of the water usually cannot be removed from the gas or oil before reaching processing facilities. In these more hostile environments, gas hydrate formation is possible in the transportation systems. Currently, methanol is injected into the pipeline to act as an antifreeze and prevent gas hydrate formation. The quantities and associated costs associated with this gas hydrate prevention strategy are significant. Recently developed polymeric kinetic inhibitors have the ability to delay the onset of gas hydrate formation at low concentrations without affecting thermodynamic stability. This new approach may be more cost-effective, especially in production situations where large volumes of additives are problematic. Another recent area of interest involving gas hydrates is the use of carbon dioxide hydrate as a means of sequestering anthropogenic carbon dioxide emissions. Carbon dioxide hydrates can form in seawater and if
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190 Energy & Fuels, Vol. 12, No. 2, 1998
properly formed are more dense than the seawater phase and would therefore sink in the ocean, thus facilitating sequestration. Also, carbon dioxide could possibly be used to displace methane from gas hydrate formations and subsequently form the carbon dioxide hydrate in its place. Such a strategy would limit disruption of the undersea strata and prevent suboceanic landslides. While much of the current research is focused on recovery, transportation, and climate change issues associated with gas hydrates, other research on gas hydrates is of great scientific interest. For example, scientists have been interested in the extraterrestrial occurrence of gas hydrates. NASA has sponsored research to understand the physical and chemical properties of various gas hydrates that may occur on bodies in our solar system. Proper identification and understanding of the behavior of these species is vital in interpreting the data collected by our probes. The work reported in the Glenn Award paper in this issue by Stern et al. was directed at these objectives. Clearly, many critical issues are related to the various roles gas hydrates may play in meeting world energy requirements and climate change mandates. This issue is thus timely and significant and should be of broad interest. A complete exploration and understanding of
Warzinski and Holder
the potential roles of gas hydrates in energy supply and climate change issues will require a collaboration between individuals from a wide variety of technical fields, including petroleum, mining, geology, oceanography, environmental science, and chemical engineering. The papers presented in this issue represent a sampling of some of the most important research problems associated with understanding and utilizing gas hydrates that scientists and engineers face. These papers were originally part of a Division of Fuel Chemistry Symposium on Gas Hydrates held during the American Chemical Society National Meeting in 1997 in San Francisco, California. Preprints of the 24 papers presented are contained in the Division of Fuel Chemistry Preprints, Volume 42, Number 2. This was the first time this subject has been a symposium topic for the Division of Fuel Chemistry. In closing, we would like to thank all of the authors for making this Symposium a success, especially those who chose to expand the description of their work for this issue. A special thanks goes to Dr. E. Dendy Sloan, Jr. of the Center for Hydrate Research at the Colorado School of Mines in Golden, Colorado, who provided an excellent overview of gas hydrates and related current research activities. EF980007Q
