Researchers assess Marcellus Shale greenhouse gas emissions

Credit: Adelaide Cole/Art Editor Credit: Adelaide Cole/Art Editor

Natural gas extraction from the Marcellus Shale, a giant rock formation that runs through much of the northeastern United States, has been a polarized and highly debated subject during the past few years.

Advocates for extraction argue that it will help create jobs and lessen the country’s dependence on foreign oil, while opponents of extraction articulate their concern over the detrimental effects the extraction processes may have on the environment. Specifically, residents of western Pennsylvania are concerned with the way gas extraction from the Marcellus Shale may affect the quality of drinking water, as well as local air quality. Recently, a team of Carnegie Mellon researchers looked at one aspect of these possible environmental impacts: greenhouse gas emissions.

“The essential tool of this study is the life cycle assessment methodology,” said Mohan Jiang, a Ph.D. student in the department of civil and environmental engineering. The life cycle assessment methodology is a way of quantifying all of the impacts of an entity; in this case, natural gas extracted from the Marcellus Shale, over the course of its entire lifetime.

Greenhouse gases are emitted during almost every step of the process of turning natural gas into energy, from extraction all the way to the burning of the gas to convert it into electricity for consumers. These greenhouse gases, which act as heat absorbers and aid in and warming the Earth, are of major concern for climate.

Jiang explained that in order to look at these greenhouse gas emissions, the life cycle of this natural gas was grouped into two main parts: the extraction of the shale gas from the Marcellus Shale, and the process of converting the gas into electricity. The emissions that were considered for first part of the life cycle, the extraction procedures, were from processes such as trucking water to and from the well site and operation of the drilling and fracturing equipment. The emissions involved in the second part of the life cycle, the conversion of the gas into electricity, were solely from combustion: natural gas is burned to create energy, and this final step is where the bulk of the greenhouse gas emissions were found.

The results of this study, which were recently published in Environmental Research Letters, show that energy derived from Marcellus Shale gas results in 20 to 50 percent less greenhouse gas emissions than energy produced from coal.

“I state clearly that we are only considering the greenhouse gas emissions,” Jiang noted. “There is a lot of water involved in the development of the Marcellus Shale gas, and this may have very bad impacts on the aquatic ecosystem, but just in the sense of greenhouse gas emissions, it is obviously better than coal.”

The study also mentions that extraction of natural gas from the Marcellus Shale is slightly different from extracting natural gas from conventional sources. “We estimate that shale natural gas has slightly higher emissions than conventional gas for production, but the production emissions are typically small compared to combustion emissions,” explained Chris Hendrickson, a professor and co-author of this study in the department of civil and environmental engineering, in a press release. The reason for this difference is the fact that the Marcellus Shale is much further underground than conventional natural gas sources, and requires more energy and resources to recover.

As Jiang mentioned, there are many more aspects to the environmental impacts of shale gas extraction to be studied, and she plans to integrate more of these issues into her future research.

“I’m going to look at the life cycle assessment tool application in the water-use impacts assessment,” Jiang said. “I will try to implement the tool in the Marcellus Shale water-use, and then to make our study more comprehensive to take into consideration the water as well.”