|Awash in Natural Gas
"America is the Saudi Arabia of natural gas," is how one prominent Texas oilman put it. He was summing up the contents of the Potential Gas Committeeís 2009 assessment on technically recoverable natural gas. Released on June 18 by the Mines-affiliated committee, the biennial assessment was the highest in the committee's 45-year history. In plain terms, the report suggests we have almost enough recoverable natural gas to see us to the end of the century.
The 40 percent jump from 1,320.9 trillion cubic feet (TCF) in2007 to 1,836.4 in 2009 does not, for the most part, signify newly discovered resources; rather it represents improvements in recovery methods. The assessment only tallies gas that can be tapped using proven technologies. Over the last two years, operators have demonstrated they can access gas in what was previously considered a source rock, not a reservoir, which added a huge amount of gas to the assessment's bottom line. "New and advanced exploration, well drilling, and completion technologies are allowing us increasingly better access to domestic gas resources - especially unconventional gas," said Curtis.
Unconventional natural gas is a broad term covering coal bed methane, tight gas sands, shale gas and gas hydrates, all of which share a common characteristic: "They need some kind of of stimulation or enhanced recovery to make them economical," said Jennifer Miskimins, associate professor of petroleum engineering at Mines. "These are not reservoirs where you just drill and turn on the tap." Unconventional gas accounts for more than half of the 20.5 TCF of domestically recovered natural gas produced in 2008. And of the additional 515.5 TCF seen in this year's report, 85 percent is unconventional.
The Boon in Shale Gas
While unconventional gas in general accounts for 85 percent of the jump in technically recoverable natural gas this year, shale gas is the real newsmaker; it went from 200 TCF in 2007, to 616 TCF in 2009, and therefore accounts for almost all of the increase.
One person who can speak firsthand about successfully extracting shale gas is Harvey Klingensmith '75, who double-majored in geophysical engineering, and geology and geological engineering, and recently founded Stone Mountain Resources. Operating in northwest British Columbia, his company is producing 27 million cubic feet of gas per day from the area's thick shale-gas formations. "It's a brute force approach," said Klingensmith. "We go down about 10,000 feet and then drill horizontally for about 5,000 feet. We hit the shale with a hydraulic hammer of water and sand. We're pumping it in at almost 10,000 pounds of pressure per square inch."
Miskimins, who is director of the Fracturing, Acidizing, Stimulation Technology (FAST) Consortium, explains: "During the creations of these fractures, a high-grade sand or artificial proppant is placed in the fractures to keep them 'propped' open, thus creating a highly permeable channel for the natural gas to flow from the reservoir to the well." Some of Miskimins' research examines the transport of these proppants out into the fracture and the monitoring of fracture growth by micro-seismic tools that listen for miniature earthquakes that the fractures create.
Environmental and Politico-Economic Benefits
The Potential Gas Committee's assessment was widely quoted in national and international media, including The New York Times, The Financial Times, the BBC, and a detailed two-part report on National Public Radio. The reason it attracted so much attention is because the economic, political and environmental implications are profound.
The U.S. spent $390 billion importing foreign oil in 2008. Since most imported oil is used for transportation, and the technology to run cars on natural gas has been around for decades, it is conceivable that natural gas could significantly decrease U.S. spending on foreign oil. Furthermore, a greater degree of energy-independence makes the U.S. less vulnerable to interruptions in supply and it stems the flow of U.S. dollars to potentially unfriendly nations.
Natural gas also offers a way to quickly and significantly lower the country's carbon footprint and buy time to accomplish a long-term transition to carbon-neutral energy technologies. On a per-BTU basis, natural gas emits about half as much carbon dioxide as coal, and a quarter less than gasoline. Presently, coal is used to generate the largest share of the nation's electricity, 45 percent, with natural gas a distant second, at 25 percent. (The remainder comes from nuclear, hydro and renewable sources.) Shifting this balance in favor of natural gas is widely seen as a realistic pathway to lower carbon emission. Similarly, vehicles running on natural gas could make a substantial impact.
Production of natural gas has been climbing steadily for years, with an increasing proportion coming from unconventional resources. If a swing in national energy policy were to accelerate demand, the energy industry would be working harder than ever to develop the countryís plentiful endowment of these resources.
Miskimins illustrates the issue by describing the country's gas supplies as a pyramid, with the lower parts representing unconventional gas resources, and the top representing conventional reservoirs. "These are small in quantity," she said. "But it's easy to get the gas out. As you move down the pyramid, the amount of gas increases, but so does the expense and the technology required to get at them."
Thanks to improvements in fracturing, the U.S. is clearly reaching farther down the pyramid. In 2000, domestic U.S. natural gas production totaled 19.2 TCF, with less than a quarter coming from unconventional resources. In 2008, production rose to over 20 TCF, with 10.4 TCF sourced from unconventional resources.
The Mother Lode of Unconventional Gas
Another way technology can reach deeper into unconventional natural gas resources is to develop a means of tapping the largest category of them all: clathrate hydrates. "There's a tremendous resource in hydrates," said Miskimins. "We just don't know how to economically produce it right now."
Tremendous indeed. A conservative study by the U.S. Department of Energy estimates U.S. deposits at about 200,000 TCF. Another study by the U.S. Geological Survey suggests that global deposits of gas hydrates may contain more organic carbon than the world's stock of coal, oil and non-hydrate gases combined.
Clathrate hydrate deposits look rather like ice and are found below the Arctic permafrost and in sediments along coastal regions around the world. On a molecular level, the hydrocarbon gas is actually trapped inside crystalline cages that remain stable so long as they are kept under high pressure and low temperature. "If you raise temperature or reduce the pressure, the gas can escape," said Carolyn A. Koh, associate professor of chemical engineering and codirector of the Mines Center for Hydrate Research.
However plentiful, gas hydrates are the most difficult unconventional gas to recover; nevertheless, with such a potential bonanza at stake, some of the world's biggest energy companies are looking for ways to tap into the resources. ConocoPhillips is working on a method involving pumping carbon dioxide into gas hydrate fields, which liberates the gas and simultaneously sequesters the carbon dioxide. Field testing begins in the next few months.
While extracting gas hydrates from Arctic permafrost may be simpler, the bulk of this resource is found in ocean sediments below 1,300 feet, where recovery is a much greater challenge. Even so, Japan is determined to try. "The Japanese expect to recover ocean hydrates by 2016," said Koh. "They have huge deposits off their coastline and they are investing heavily because they have limited domestic fossil fuel resources."
While much of the enthusiasm for natural gas stems from its environmental benefits, Koh is quick to point out that they are approaching recovery with a great deal of care; natural gas, also known as methane, is a greenhouse gas 20 times more potent than carbon dioxide.
It is ironic that such a potent greenhouse gas might end up helping to slow the mounting concentrations of carbon dioxide in the atmosphere, but it could. And when the economic benefits are also considered, the mounting interest is hardly surprising.
Many at Mines welcome the renewed enthusiasm for natural gas sparked by the Potential Gas Committee's report. "For a long time, people have said we are running out of oil and gas," said Miskimins, "but that's not entirely accurate. It's the easily accessible part that we're running low on. There is a huge amount of unconventional gas, and Mines is going to play an important role in developing the technology to unlock it."