Accelerating the Pace of Hydrate Research

Methane hydrate—the “ice that burns”—has been the subject of increasingly intense scientific research worldwide over the past three decades. There are many excellent reasons to study this unusual substance: it may contain more energy than all other fossil fuels combined, it could pose a safety hazard to offshore oil and natural gas operations, and it could play a critical role in the environment, including long-term global climate change. Now a research program led by the U.S. Department of Energy’s National Energy Technology Laboratory (NETL) has made significant strides in understanding and potentially harnessing this resource.

Until recently, most methane hydrate research and development focused on gaining a basic understanding of its characteristics, origins, and occurrence and estimating its potential as an energy resource. Today we are on the path to producing natural gas from arctic hydrate reservoirs and understanding how to safely drill in the presence of methane hydrate.

From an academic curiosity . . .
In the early 1800s, Michael Faraday and his mentor, Sir Humphrey Davy, experimented with mixtures of chlorine and water that formed solid materials when they cooled. This was the first confirmation of the existence of clathrate hydrates—a class of crystalline solids that form when gas molecules are trapped inside lattice-like “cages” made up of hydrogen-bonded water molecules.

	In methane hydrate, a methane molecule (shown here in gray and green) is sur-rounded by a cage-like structure of water molecules (shown here in red and white).
	In 1997, vast colonies of strange, rosy-pink worms,1–2 inches in length, were found burrowing in mounds of methane-rich ice erupting from the seafloor in the Gulf of Mexico.

The Davy-Faraday discovery—and subsequent study—of clathrate hydrates was important in advancing the chemistry and physics of the time, but because these substances did not seem to occur in nature, they were treated as largely an academic curiosity for a century.

All that changed in the 1930s when an American chemist, E. G. Hammerschmidt, determined that hydrates of methane—the main component of the natural gas that heats your home—were forming within and plugging natural gas pipelines, especially those in cold environments. Subsequent research focused on how to predict their formation and then inhibit that process by injecting chemical additives in the pipelines.

Clathrate hydrate science was again turned on its head in the late 1960s when naturally occurring methane hydrate was found in subsurface sediments in a natural gas field in Western Siberia. A few years later, a limited test of a hydrate-bearing sandstone on Alaska’s frigid North Slope yielded a small, non-commercial volume of methane, proving that methane could be released from hydrate by decreasing pressure. The science began to further evolve as speculation grew that the combination of low temperatures and high pressures found in arctic permafrost and in deep-water, near-shore ocean environments meant that the occurrence of methane hydrate could be extensive worldwide.

Most curious of all may be the 1997 discovery of a previously unknown centipede-like life form— the “ice worm”—living on gas hydrate mounds in the deep water Gulf of Mexico. It was quickly becoming evident that methane hydrate had great implications for our understanding of the global carbon cycle, the development and stability of the continental shelves, and the nature of deep sea ecosystems.

. . . To an enormous potential resource
Recovering deep ocean samples of methane hydrate can prove tricky because of the nature of the substance. Although ice-like in appearance, methane hydrate does not melt. At atmospheric pressure and temperature, the solid ice cage will turn into water, releasing the methane gas molecules into the air—a process called dissociation. If you hold a lit match next to a chunk of methane hydrate, the methane molecules will burn as they are released—giving you “burning” ice. Today, methane hydrate samples are recovered as drilled-well cores with pressurized core samplers.

Estimates of the world’s methane hydrate resource range from merely jaw-dropping to the truly staggering. When dissociated at normal surface temperature and pressure, one cubic foot of solid methane hydrate will release about 164 cubic feet of gaseous methane—equal to the energy content of 1.5 gallons of gasoline. Given methane hydrate’s energy potential and the fact that its occurrence may be widespread, it’s easy to see why this resource is garnering so much interest in the energy community.

The U.S. Geological Survey (USGS) reported in 1988 that the organic carbon content of the world’s gas hydrate deposits roughly doubled that contained in all known oil, natural gas, and coal deposits combined. In 1995, USGS completed the first systematic effort to appraise America’s methane hydrate deposits, reporting a mean estimate of 320,000 trillion cubic feet of methane. With the collection of more concrete data, it has been suggested that a modest downward reduction in the assumed values for hydrate saturation is needed, resulting in a revised, as-yet unofficial estimate of 200,000 trillion cubic feet. If the technology could be developed to extract a tiny fraction of the methane from this resource, the U.S. could more than double its future natural gas resource base.

Finding the Answers
Just as Faraday collaborated across disciplines to understand hydrates—substances whose existence stems from a unique “marriage” of the right conditions of pressure and temperature—it takes a cross-cutting approach and extensive collaboration to tackle the challenges of methane hydrate today. Geology, geophysics, chemistry, hydrology, sedimentology, biology, climatology, and state-of-the-art drilling technology are just a few of the disciplines that come into play in understanding all the aspects of methane hydrate as a resource and as an element of the world’s environmental systems.

With this in mind, NETL leads an interagency effort to advance the science and technology of gas hydrate. Participating are the U.S. Department of Energy, USGS, U.S. Bureau of Land Management (BLM), Minerals Management Service, Naval Research Laboratory, National Oceanic and Atmospheric Administration, and the National Science Foundation.

Recent activities in the arctic, the deep oceans, the laboratory, and elsewhere have provided a series of landmark accomplishments and discoveries that are bringing the resource potential and environmental role of gas hydrate into focus.

	Drilling in Alaska’s Milne Point Field in 2007. Read more about the project and view a photo gallery.

In the arctic . . . NETL is collaborating with BP Exploration (Alaska), USGS, and BLM to investigate the gas hydrate accumulations that exist on Alaska’s North Slope. The goal of this effort is to characterize and quantify the hydrate in this area and to determine if it could be commercially produced. Researchers have identified more than a dozen hydrate prospects within the Milne Point area and have drilled a stratigraphic well—one designed to gather information about subsurface strata—on the Mount Ebert prospect in the Milne Point field.

Drilled in February 2007, the Mt. Elbert test well demonstrated the ability to safely and effectively operate in the sediments just below permafrost on the North Slope, and it yielded one of the most comprehensive datasets yet compiled from a naturally occurring methane hydrate deposit. The well achieved many technological firsts, including—

• The first sampling of gas and water collected through depressurization of gas hydrate reservoirs on the North Slope.
• The first open-hole tests of the pressure response of a gas hydrate reservoir.
• The first use of wireline-retrievable continuous coring on the North Slope (with 85 percent core recovery).

The successful discovery of two 50-foot thick, highly saturated reservoirs clearly demonstrated the viability of the prospecting methodology that has been used to assess and characterize gas hydrate resources across the North Slope. Researchers will use the information they have gathered to establish the first of a series of long-term hydrate production tests that will determine the potential productivity of hydrate-bearing sandstones.

	The Uncle John, a semisubmersible research vessel, used for gas hydrate research in the Gulf of Mexico in 2005. Read more about the cruise of the Uncle John, and view photos from the voyage.

In the deep oceans . . . NETL continues to conduct and support multi-well drilling and coring expeditions across the globe. These cruises are designed to assess both the scale and nature of the gas hydrate resource and to test the effectiveness of technologies for pre-drill prospect identification and characterization. NETL has provided critical support to the development and testing of advanced sampling and analysis technologies that are now standard features of all marine gas hydrate programs. These include—

• Tools for the accurate measurement of subsurface temperatures.
• Tools that use infrared and x-ray computed tomography to detect gas hydrate in sediment cores brought onboard the ship.
• Advanced coring and core analysis technologies that collect deep sea samples under pressure and gather critical data from them before the cores are compromised by dissociation.

Working in with the Chevron-managed Joint Industry Project, NETL drilled and cored two locations in the deepwater Gulf of Mexico in 2005 to assess drilling safety in areas of gas hydrate occurrences. The expedition resulted in an understanding that conventional oil and gas drilling in areas of disseminated hydrate occurrence could be carried out with minimal risk. In addition, methane hydrate was encountered in close agreement with pre-drill geological and geophysical predictions, providing proof that hydrate occurrence in the marine environment could be adequately detected and characterized using remote methods.

Internationally . . . NETL supported and provided scientific expertise to a series of international expeditions from 2005 to 2007: in the South China Sea and Korea’s East Sea, and offshore British Columbia (Canada), Chile, India, and New Zealand. Together, these international efforts are greatly advancing our understanding of the occurrence and behavior of gas hydrate in nature.

In the Bay of Bengal, a research group led by USGS and the government of India—and including U.S. Department of Energy scientists from NETL, Idaho National Laboratory, and Pacific Northwest National Laboratory—carried out the most complex and comprehensive gas hydrate field ventures to date. The 2006 expedition included discovery of one of the thickest and deepest gas hydrate occurrences known in the world, and provided a wealth of data over a range of geologic environments that will inform hydrate science for years to come.

In the laboratory . . . scientists can observe and measure natural phenomena under carefully controlled conditions. For methane hydrate, this means working with highly specialized devices that mimic deep sea pressures and temperatures. Recent laboratory advances include efforts to create hydrate samples in natural sediments through a variety of processes that closely mimic those active in nature. In addition, laboratory devices continue to increase in complexity and diagnostic capability as experimentalists continue to incorporate more and more of the variability found in nature into the lab.

Through computer simulation . . . scientists can explore the potential response of hydrate systems to an almost infinite variety of conditions. The ability to reliably model such a complex system, in which all phases of matter coexist and dynamically evolve, is a great challenge; however, it is absolutely essential to the proper planning and preparation of field events, as well as to the proper interpretation of field findings.

	Read more about the Methane Hydrate Reservoir Simulator Code Comparison Study.

To further advance this capacity, and to provide additional insight into the critical data needs to improve model validity, the users and developers of most of the world’s leading hydrate models are collaborating with NETL on a code-comparison effort—the Methane Hydrate Reservoir Code Comparison Study—in which all hydrate models will be run through a common set of basic problems of increasing complexity.

Hydrate modelers use many different conceptual models and mathematical algorithms; each approach has certain advantages and disadvantages, and none is either completely accurate or proven reliable from first principles. The study allows assessment of the models’ applicability under different scenarios and provides valuable opportunities for modelers to interact and strengthen each model’s capabilities.

Looking Ahead
In the spring of 2008, NETL plans to launch a major multi-site marine expedition, in collaboration with the Joint Industry Project, to explore and characterize the occurrence of gas hydrate in reservoir-quality sandstones in the Gulf of Mexico. The expedition will test newly emerging exploration models for hydrate occurrence, assess marine hydrate geological and geophysical prospecting methods, provide valuable information on the resource potential of hydrate in the Gulf, and aid in selecting locations for future hydrate investigations that will use a new generation of pressure coring and pressure core analysis equipment which are now in development.

Like conjuring fire from ice, that kind of progress—born of cross-disciplinary research and extensive collaboration among agencies, industry, and research organizations—is no mere magician’s trick.