The use of water in shale exploration has long been a major source of environmental concerns. To start with, hydraulic fracturing – or fracking – requires very large amounts of water. According to Chesapeake Energy, an initial drilling operation may consume from 6,000 to 600,000 US gallons of water-based fracking fluids, rising to an additional 5 million gallons of water for full operation and possible restimulation frac jobs.
And even though a study carried out in New Mexico found that oil and gas exploration used only about 0.06 percent of water in the state – with the majority of water used for agriculture and public water use – water-free fracking has been a dream pursued by many scientists studying hydrocarbon exploration.
One of the more promising ideas is replacing water with cold liquid nitrogen or liquid carbon dioxide to fracture the shale rock.
Scientists at the Colorado School of Mines in Golden hope that the ultra-cold thermal shocks that occur when liquid nitrogen meets shale rock will have a similar effect as water, creating enough stress to crack open the subterranean stores of oil and gas.
And because the liquid nitrogen would evaporate underground, cryogenic fracturing could form bigger canals for oil and gas to flow through than water-based fracturing, boosting oil and gas production. It would also solve the problem of extracting shale gas from clay-rich shales.
This is the problem currently facing many shale extraction companies in China – the shale basins are in particularly arid areas and the high clay content in the shale makes water-based fracking ineffective.
“Essentially, some shale absorbs water very quickly, and the entire formation swells in size and closes up any pathways,” explained Kent Perry, vice president of onshore programs at the Research Partnership to Secure Energy for America, which administered a $2.6 million Department of Energy research contract for the project.
“When you’re using water in shale formations, even where you’re successful with the development, recovery is still low, and part of that is water trapping.”
Fracking with liquid nitrogen is already used by some companies both in the U.S. and abroad. Susan Alvillar, a spokesperson for the exploration company WPX Energy, attributed the company’s low usage of water to improvements which include the use of nitrogen.
About 1,200 barrels of water are used to drill and frack a well that penetrates between 4,000 and 5,000 feet vertically and about 4,000 feet horizontally. When the rig begins to drill, Alvillar said, the water is used to form mud. The mud is composed of dirt and other materials to keep the bit lubricated. When fracking begins, she said, they use mostly nitrogen foam to frack the rock formation. The fracking mixture is about 70 percent nitrogen and 30 percent water.
South African Department of Mineral Resources has also been looking at instances of nitrogen usage in fracking, in order to find the best extraction strategy for the Karoo desert shale deposits.
Deputy Director General Mosa Mabuza has remarked that “Qatar which is a complete desert even drier than the Karoo uses […] nitrogen and the point that is to be made is that to fracture you don’t only use the natural resources as is the case with fresh water, there are other fluids that will be considered.”
However, the use of liquid nitrogen is not totally problem-free. It’s been pointed out, that liquid nitrogen, like many of the alternatives to water that the oil industry has tried, lacks the energy capacity – called viscosity – to carry sand and proppants.
“You can’t energize the fluid efficiently because the viscosity of the fluid is significantly lower than water, which you can put a lot of energy behind,” Ramanan Krishnamoorti, a professor of petroleum engineering at the University of Houston said. “People have been thinking about this for a while. It’s still a long way before it can truly be applied.”
Krishnamoorti said oil field service companies have reported some success with waterless fracturing technologies, “but never where they’re comparable to hydraulic fracturing.”
Not everybody agrees, though. Yu-Shu Wu, a professor at the Colorado School of Mines, wrote in a paper for the Research Partnership that while cryogenic nitrogen and carbon dioxide lack significant viscosity, it’s possible to create stronger forces in a fluid’s flow “by increasing the velocity of the fluid allowing for adequate transportation of the proppant.”
There are also other concerns. Liquid nitrogen is expensive. It is also much more difficult to handle, given that it needs to be kept chilled to more than minus -321 degrees Fahrenheit (minus -160.5 degrees Celsius).
Still, with the challenges it brings considerable benefits. The reduction in the use of water is one. The ability to successfully frack shale formations that resist water-based frac fluids is another. But the most important benefit would be the solution to the problem of the disposal of produced water.
The management of produced water – the water that flows back from the well after fracking – is the biggest environmental concern associated with shale exploration.
“Almost everyone who has studied the risks of fracking, either narrowly or broadly defined, is more concerned about the risks of managing flow-back fluid than they are about the potential environmental effects of fracturing itself,” said Scott Anderson, a senior policy director in the climate and energy program at the advocacy group Environmental Defence Fund.
“To the extent it reduced the need to dispose of water, [using liquid nitrogen] would reduce the likelihood of disposal-induced earthquakes, which are a bigger risk than fracturing-induced earthquakes,” Anderson said.
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