By George P. Mitchell and Mark D. Zoback
Natural gas is a wondrous fuel. It emits less carbon dioxide, less mercury, less nitrogen oxide, less sulfur oxide than any other hydrocarbon energy source. Natural gas is the perfect bridge fuel on the way to a less carbon-dependent economy. There is no question that accidents have occurred and mistakes have been made during the rush to develop this vast new resource, but this remarkable resource can be developed by industry following region-specific best practices and regulators carefully monitoring industry activities.
Far below the city of Fort Worth is a geological formation of sedimentary rocks that was shaped 354 to 323 million years ago – give or take an eon.
Take a much smaller jump back in time, to the 1970s, when an independent Texas company, Mitchell Energy & Development Corp., drilled into this ancient formation without much success. Company rigs had pulled up some curious rock samples of organic-rich shales (sedimentary rocks with large amounts of clay) indicating that natural gas in abundance, millions of years old, was trapped in these sediments. But because of the extremely low permeability of the shales, even the best engineers and geologists in the industry had no way to produce it in commercial quantities.
Innovation loves a challenge, however. After seven long years of effort, the Mitchell company devised a method that combined horizontal drilling and hydraulic fracturing of the shale formation, that released the gas in commercial quantities. It was a stunning victory not just for Mitchell, but for the nation’s small, independent energy companies, achieved with an approach mostly ignored or abandoned by the international oil and gas giants.
In the petroleum industry, hydraulic fracturing goes back at least to the 1940s, but the adaptation of fracturing in horizontal wells was critical to the success of Mitchell Energy & Development Corp.’s efforts. If you drill a vertical well through a relatively impermeable rock formation, even if you hydraulically fracture the rock to increase its permeability, the pay-zone is still limited to the formation thickness. If you drill horizontally through the gas-bearing formation, as the dogged Mitchell company engineers were finally able to do, and create multiple hydraulic fractures along its length, you dramatically increase the producing zone of the well.
Rather than keeping this breakthrough a secret, the company quickly allowed the broad publication of its methods, and one of the most profound revolutions in the international energy industry was unleashed. At this point, we are only beginning to realize and appreciate its profound implications.
We now believe that the Barnett Shale, which underlies not only Fort Worth but also 17 counties and 5,000 square miles of Texas, may have one of the largest producible reserves of any onshore natural gas field in the United States. The key word, of course, is producible, and it was the technology using hydraulic fracturing in horizontal wells that made the difference.
As a result of this phenomenal breakthrough, other organic-rich shales in the United States were suddenly productive. The methods first perfected near Fort Worth quickly succeeded in the Haynesville and Fayetteville shales that stretch underneath Louisiana, East Texas and Arkansas. Next came the Marcellus Shale, a vast rock formation extending beneath the southern tier and Finger Lakes region of New York, northern and western Pennsylvania, western Maryland, most of West Virginia and extreme western Virginia.
So why has it been so difficult to celebrate the recent discovery of unexpected and immense recoverable natural gas reservoirs in our country?
As the horizontal hunt for shale gas has spread, so has concern over its environmental impact. At the request of President Barack Obama, a high-level U.S. Department of Energy subcommittee was convened to explore those issues.
The group’s tough report left no doubt that shale gas resources were of enormous importance to the United States. This carefully composed panel of top academics, industry experts and investigators concluded that this resource could be developed in an environmentally responsible manner. That said, the subcommittee made 20 carefully considered recommendations toward improving industry practice and government regulations to accommodate this new technology.
Wells and waste water
The DOE subcommittee was candid about the need to immediately strengthen state regulatory practices governing well construction, waste control and disclosure of the chemicals used in hydraulic fracturing and the composition of the water that flows back from the well after hydraulic fracturing. The panel determined that there is no question that accidents have occurred and mistakes have been made during the rush to develop this vast new resource. However, they can be addressed by operators following industry best practices and with regulators carefully monitoring industry activities.
The committee pointed out that in nearly all of the areas where shale gas is being exploited in the United States, the actual shale formations are separated from aquifers by thousands of feet of nearly impermeable rock. In such cases it is virtually impossible for hydraulic fracturing to affect water supplies.
The problems associated with contamination of water supplies in areas where shale gas development is under way are mostly traceable to the improper casing or cementing of production wells. In some instances, these appear to be old and abandoned wells that contaminated subsurface aquifers before gas development activities. Similarly, poorly constructed or badly maintained wastewater containment areas can breach whether or not they are associated with hydraulic-fracturing processes.
Some gas-bearing formations, such as those common with coal-bed methane development, are found closer to the surface. In such a case, aquifers can be easily endangered and extra care must be taken to avoid problems.
A newer and more sensational controversy has risen over the past couple of years regarding the role of hydraulic fracturing in triggering local earthquakes, such as those experienced in Texas in 2009, Arkansas in 2011 and Ohio in the past month. Similar investigations of quakes in Oklahoma are underway. At issue, however, isn’t the removal of shale gas, but the improper disposal of wastewater produced by the deep-shale drilling. Disposal wells should be sited so as to avoid injection into active faults, injection rates should be limited so as to avoid causing substantial increases in pore pressure at depth, and seismic monitoring networks should be installed so that if small earthquakes begin to occur, injection rates can be decreased or stopped altogether to prevent larger earthquakes from occurring.
The chemicals used in hydraulic fracturing represent less than 1 percent of what is mostly water and sand. While virtually none of the chemicals added, familiar to most homeowners, are considered particularly toxic, all responsible producers should be willing to fully disclose to regulators and to the public the exact chemical composition of hydraulic fracturing fluids being pushed down any well, the precise composition of what comes back up, and the nature of its disposal. To aid in this process, the DOE subcommittee recommended the creation of public databases on water quality in and around shale gas drilling sites, as well as data on water quality before the drilling commences.
Best practices and regulations are already in place for drilling, whether wells or oil or natural gas recovery, and for the safe disposal of wastes. It is critically important for these best practices and regulations to reflect local geologic and hydrologic conditions. It is also important to recognize that establishing best practices in any industry is never a static process. As time moves on, responsible energy companies learn more, continuously improve procedures, and incorporate feedback from the communities and environments most affected by each company’s progress. The DOE committee recommended that it is equally important that there be a continuous improvement of best practices for minimizing impacts on the environment, communities and ecosystems. As our nation develops this great and unexpected resource, all stakeholders – gas producing companies, service companies and suppliers, affected communities, public interest advocates, and regulators – must be sought out and integrated for our country to fully realize this promise, a process the DOE committee referred to as organizing for best practice. The new abundance of natural gas will strengthen our nation’s energy independence only if its production is sustainable, completely transparent, and fiercely sensitive to nearby publics, ecosystems, habitats and protected resources.
Only now have we become totally aware of what the liberation of gas from shale rock portends for our own country. This technology will be equally transformative far beyond our borders.
Last month, China Petrochemical Corp., that nation’s second largest crude oil producer, and Total SA, Europe’s third-largest oil company, invested $7 billion in U.S. and Canadian shale rock formations. Why would China, with 50 percent more technically recoverable shale gas than the United States, invest in North America? They have come here to learn the craft, and that is a good thing.
Countries like Poland and Ukraine in Europe and China and India in Asia are too dangerously dependent on foreign sources of energy to sustain their growth. Bluntly put, proof that they may now have abundant supplies of clean energy below their own homelands and within their own borders lowers the tripwires of future conflicts and war. We all gain from that.
But as these resources are developed worldwide, America assumes an additional burden. Practices in so many industries that have become global are often first tested and perfected here in North America. Let’s make sure the United States develops this resource in a responsible manner. Our citizens deserve it and it is an opportunity for world leadership that can bring prosperity and stability to billions abroad for decades to come.
Mitchell, a petroleum engineer and geologist, is the founder of Mitchell Energy & Development Corp., which pioneered the use of hydraulic fracturing of rock for the horizontal drilling of natural gas. He is also the developer of The Woodlands, one of the first master-planned new towns in the United States, and sponsor of the International George and Cynthia Mitchell Prize, dedicated to sustainable development. Zoback, a geophysicist, is the Benjamin M. Page Professor of Earth Sciences at Stanford University. He is the author/co-author of more than 300 technical research papers and a textbook titled “Reservoir Geomechanics.” He served on both the Department of Energy committee investigating shale gas development and environmental protection and the National Academy of Engineering committee investigating the Deepwater Horizon accident. The Academy of Medicine, Engineering & Science of Texas presented The Shale Gas Miracle: A Tribute to George P. Mitchell, during the opening session of its annual conference in Houston. Zoback was among the featured speakers in the tribute to Mitchell.