Horizontal Drilling And Water Fracturing: The Keys To Shale Gas Production
Gas embedded in shale rock formations deep below the Earth's surface has long been considered inaccessible, due to high drilling costs. New horizontal drilling methods, combined with techniques to fracture the rock, have for the first time made shale gas production practical.
Roll over the red dots below for more information about the drilling methods.
This graphic requires version 8 or higher of the Adobe Flash Player.Get the latest Flash Player.
This interactive content is not supported by this device.
This diagram shows the particulars of horizontal and vertical drilling for natural gas.
Advances in technology have helped boost the growth of shale drilling in the United States over the past few years. But as the practice of harvesting natural gas embedded in shale rock deep below the Earth's surface has expanded, it has raised concerns about the impact this type of drilling has on the environment — especially on groundwater.
At issue is the practice of "hydraulic fracturing," which in combination with horizontal drilling is an essential part of the shale gas production process. The shale rock in which the gas is trapped is so tight that it has to be broken in order for the gas to escape. A combination of sand and water laced with chemicals — including benzene — is pumped into the well bore at high pressure, shattering the rock and opening millions of tiny fissures, enabling the shale gas to seep into the pipeline.
This fracturing technique has been in use since 1948, and industry sources say the procedure has been used in a million gas wells in the years since. But the practice has expanded in the past few years as energy companies began exploring shale formations.
The results have been so successful that energy analysts now see the development of shale gas reservoirs as a key step toward U.S. energy independence and a cleaner environment. When burned, natural gas produces about 25 percent less carbon dioxide than coal.
Benzene Contamination And Other Environmental Risks
Some landowners in shale gas areas, however, say the energy and environmental benefits of this new production are outweighed by the environmental risks it raises. NPR's Jeff Brady documented these issues in a report earlier this year.
Steve Harris, who resides near Dallas, told Brady that he noticed a foul odor coming from his tap water shortly after a gas company used hydraulic fracturing in a natural gas well near his house. Harris said he complained to the drilling company and to state authorities but without result.
"Basically, you get to the point where you think maybe everybody's working with the gas people and against the little guy," Harris said.
In 2008, a hydrologist found evidence of benzene contamination in a water well in Wyoming, in the vicinity of a large gas field. Residents near Dimock, Pa., have also complained of contamination of their water supply as a result of gas well drilling in their area. Dimock is in an area of Pennsylvania that sits atop the Marcellus shale formation, one of the largest in the country, and natural gas companies have been active there.
Critics of hydraulic fracturing suspect that the chemicals used in the process have somehow leaked into the groundwater supply. It has been difficult, however, to demonstrate a direct connection between these apparent instances of water pollution and the hydraulic fracturing procedures that have taken place nearby. Industry sources point out that the shale rock subjected to the fracturing is thousands of feet below the surface of the Earth, far below the aquifers that supply drinking water. Many layers of rock are in between. The well bores themselves are shielded from the surrounding earth by steel and cement casing.
Checking For Groundwater Contamination
Gas producers cite investigations by the Ground Water Protection Council, a national association of state agencies responsible for maintaining safe water supplies. To date, the GWPC has uncovered no documented instance of groundwater contamination clearly due to hydraulic fracturing.
"We have gone to the state regulators on this, but we don't have any good evidence right now," says Mike Paque, the GWPC's executive director. "A lot of it is anecdotal."
It is also true, however, that state regulators have not been able to disprove a connection between hydraulic fracturing and water contamination. Some problems loosely associated with gas wells seem to have been a result of preventable accidents. Gas well pipes have broken, resulting in leakage of contaminants into the surrounding ground.
There have also been cases of improper disposal of potentially toxic wastewater from a fracturing operation. In addition, the process of drilling a well has on at least one occasion disrupted a layer of limestone containing methane, which subsequently escaped.
Such instances argue for closer monitoring of shale gas drilling operations.
The GWPC has recently contracted with the U.S. Department of Energy to develop an environmental risk assessment for hydraulic fracturing. The assessment would create a database of fracturing operations so that it would be easier to identify any possible connection to subsequent contamination problems.
Just last week, the GWPC board approved a resolution encouraging Congress, federal agencies and state regulators to work with the GWPC "to evaluate the risks posed by [hydraulic fracturing]."
Still Identifying Potential Risks
The rapidly expanding development of shale gas reservoirs has left regulatory agencies and legislatures scrambling to keep up with the new environmental issues raised by the operations. In June, several members of Congress introduced the "Fracturing Responsibility and Awareness of Chemicals Act." The "FRAC Act" would amend the federal Safe Water Drinking Act to bring hydraulic fracturing under federal rather than state regulation.
In the resolution approved last week, however, the GWPC expressed concern that additional federal regulation of hydraulic fracturing "will divert compliance and enforcement resources from higher priority issues that pose significant threats of endangerment to underground sources of drinking water." GWPC's Paque says his organization, at this point, is more concerned about water contamination from agricultural practices and groundwater runoff than from hydraulic fracturing.
The "FRAC Act" would also require natural gas producers to disclose the chemicals they are using during hydraulic fracturing operations. The producers have been reluctant to reveal the chemical formulas used in their fracturing operations, for fear of disclosing proprietary information to their competitors.
In a statement accompanying the introduction of the bill, the sponsors said they do not oppose hydraulic fracturing but want "to ensure that the practices are done safely and do not threaten the health of the public."