Discovering the Secrets of Natural Gas Hydrates

Natural gas hydrate researchers in NETL’s Office of Research and Development (ORD) conduct field studies on research ships and at Arctic drilling rigs, and also work at NETL, using specialized laboratory equipment and computational models. Taken together, these integrated studies may hold the secret to greatly increasing our Nation’s natural gas supply, and understanding a possible factor in global climate change.

Hydrate is an informal term commonly used to describe a unique category of chemical substances in which molecules of water form an open solid lattice (like a cage) that encloses, without chemically bonding with, appropriately-sized molecules of another material (in this case, methane). Methane hydrate looks like ordinary ice, which is understandable because the methane contained within the ice is invisible. It is found at depth, offshore, in marine sediments where the pressure and depth-related pressures are appropriate, and in the Arctic. These photos show what the methane hydrate looks like in natural sediment, although most of the time, the hydrate fills the spaces between the grains of sediment and is not so visible. These specimens were collected in 2007 on an expedition sponsored by India’s Natural Gas Hydrate Program (NGHP).

Gas hydrate filled fractures in fine-grained sediment from National Gas Hydrate Program Expedition in 2007

The U.S. Geological Survey estimates that methane hydrate deposits likely contain more organic carbon than all the world's coal, oil, and non-hydrate natural gas combined. If we can figure out how to safely and economically extract the gas from these hydrates, we would have a resource that would far exceed the quantity of natural gas that we will use for heating, cooking, and power generation in this country for hundreds of years.  For more information on this topic, click here.

Since methane is a greenhouse gas, anything that leads to its release from the hydrate structure into the atmosphere, including warming of the Arctic regions or ocean bottom waters, could further accelerate global warming. NETL researchers are using computer simulations, field characterization, and laboratory studies to improve our understanding of where and why gas hydrates exist in the natural environment, how they may affect the global climate, and how to safely extract the methane locked within these deposits.

Since 2006, scientists from NETL have participated in methane hydrate research studies and field expeditions in India’s Bay of Bengal, South Korea’s East Sea, the South China Sea, the U.S. Gulf of Mexico, the North Slope of Alaska, Canada’s Cascadia Margin, and most recently, on an international expedition in the U.S. Beaufort Sea.

Kelly Rose (NETL) aboard the RV Joides Resolution examining sediment cores from the Indian NGHP 2006 expedition in the Bay of Bengal. These cores contained a type of clam shell commonly associated with methane seeps and methane hydrates.		Dr. Marta Torres (NETL-OSU) preparing sediment from the 2007 Mount Elbert-01 well, on Alaska’s North Slope, for inorganic geochemical analyses.

These studies are significantly advancing our understanding of where to find resource quality gas hydrates and have contributed to the growing number of studies that seek to understand what role gas hydrates might play in the global carbon cycle.

Click here to learn more about recent methane hydrate research.

To remain informed, simply sign up for NETL’s free electronic newsletter, Fire in the Ice, by sending an e-mail to: jennifer.presley@tm.netl.doe.gov.

Safely Extracting Natural Gas Hydrates

Natural gas hydrate deposits can be detected using specialized geophysical techniques, but safely and economically extracting them is a major challenge. Recently, NETL geoscientists and reservoir modelers helped develop a geologic-based model to assess the best location for upcoming gas hydrates production tests on the Alaska North Slope.

Two test wells are planned to evaluate the production potential of using different techniques: 1) depressurization, and 2) exchanging carbon dioxide (CO₂) for methane (CH₄) in the hydrate structure. The CO₂ exchange test will be the first of its kind world-wide and has significant implications both for producing methane gas and for potentially sequestering CO₂—a significant greenhouse gas.

Researchers at NETL are using numerical models to predict how the hydrate reservoirs targeted by the two wells will respond to each type of production testing. Brian Anderson (NETL-West Virginia University) and Eugene Myshakin (NETL-URS) have run a series of simulations that evaluate how changes in different key parameters will affect the rate of production from these types of wells. Brian has incorporated geologic heterogeneity into his production simulations, and has demonstrated that it could positively influence the rate of gas that is produced from these types of wells. A drilling rig like this, pictured below in the dusky glow of the Arctic in February, will be used to perform these first dedicated production tests from gas hydrates in Alaska.

A rig similar to this one, used for the Mount Elbert test in 2007, will be used next year to perform the first dedicated production tests from gas hydrates in Alaska.

Brian also leads the International Gas Hydrates Code Comparison effort. The code comparison study was initiated in 2005 before any production information from subsurface natural gas hydrate reservoirs was available. The members of the code comparison study are currently working on running simulations based on the Alaska North Slope 2011 test sites. Once the short-term production tests are completed, each modeler can compare their results with the actual field data to assess the performance of their simulator.

Meanwhile, laboratory characterization of natural gas hydrate samples from key field sites has provided critical insights into the pore to core-scale distribution and occurrence of gas hydrates in porous media. NETL uses computed tomography (CT) to visualize what is going on inside core samples just like doctors use CAT (or CT) scanners to take non-destructive images inside the human body. In fact, one of the CT scanners used at NETL is a reconfigured medical CT scanner that scans fast enough to capture hydrate forming and dissociating inside cores. NETL also has a micro-CT and an industrial CT scanner for higher resolution imaging of gas hydrates contained within porous media. The real-time images have been used to improve numerical simulations and confirm phenomenon first observed in a numerical simulation. Numerical models have also been derived using CT images.

	Composite image of fine-grained sediment core after formation of fractures by in situ hydrate formation and dissociation.

Samples from actual field study sites are very rare and hard to preserve or obtain in the first place. At NETL, ORD researchers Yongkoo Seol and Jeong Choi have successfully formed natural gas hydrate in fractures in fine-grained sediments and are using the CT scanners to monitor experiments related to hydrate formation, dissociation, and production modeling to learn what processes are controlling the occurrence and release of gas hydrate. The figure below shows a composite micro-CT image of fine-grained sediment cores experimentally fractured (dark areas) with high pressure gas, shown after hydrate formed and dissociated; each section is about 4 mm (0.16 inches) in diameter.

NETL Reports Breakthrough in Rapid Gas Hydrate Formation

Large quantities of natural gas are routinely transported around the world after they are reduced in volume with elevated pressures and/or cooled to very low temperatures (−162°C, which is equal to −260°F).  However, compressing the natural gas in this manner requires a lot of energy, and the liquefied natural gas (LNG) must remain refrigerated at these low temperatures until it reaches its destination. A more economical and energy-efficient form of storage and transportation is required. 

	CLICK ON GRAPHIC TO ENLARGE
	a. Verification of methane hydrate formation by Raman Spectroscopy; b. methane hydrate snow being formed in the laboratory; c. a photograph of the NETL designed nozzle.
	A cross-section of the NETL nozzle designed to make gas hydrates.

Natural gas commonly occurs offshore in marine sediments and in permafrost as methane hydrate.  However, this is about a parallel development. Researchers at DOE’s NETL have developed a way to rapidly form methane hydrates. These synthetic hydrates can store 164 times their volume in natural gas at atmospheric pressure, with only moderate refrigeration (between -10 to -20°C, or 4-14°F). Thus, they potentially represent an economical and energy-efficient alternative to LNG.

Researchers at NETL are investigating the formation of synthetic gas hydrates, with an emphasis on rapid and continuous hydrate formation techniques. Typically, methane hydrates are formed in a batch process, requiring several hours (or days) of mixing to initiate hydrate formation. The process developed at NETL, illustrated below, eliminates the batch process and the long mixing time, forming hydrates within a few seconds.

In a paper recently published in Energies, NETL’s results are presented from numerous experiments conducted with high-pressure cells equipped with instrumentation to study rapid and continuous hydrate formation. This was accomplished using a nozzle designed at NETL to provide increased atomization, and thus provide the necessary intimate mixing of water and methane at the proper pressure and temperature favorable for hydrate formation.  A U.S. Patent application titled, "Rapid Gas Hydrate Formation Process" was filed this month.