How Long Can a Fracker Frack?

A new study from the University of Texas at Austin has found that fracking may not be as viable as previously thought. The study’s results, published this week in the PNAS,  indicate that the Barnett Shale gas wells (the US’s oldest shale being fracked) will begin to show exponential decline in their output within ten years and their total output will end up being between 10 and 20 trillion standard cubic feet of natural gas for the next 50 years, contrary to another recent estimate that put the total pull from the Barnett at 40 trillion standard cubic feet by 2050.

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A map of the US natural gas shale reserves. The Barnett is located in North Texas (Source: http://www.dailykos.com

Fracking has, more or less, revolutionized the American energy market. As this paper points out, only a decade ago American natural gas cost 50% more than Russian gas, whereas it currently costs three times less. The cause of this impressive price drop was the advent of shale extraction, which allowed American corporations to quickly and cheaply tap huge stores of natural gas throughout the country. There has been immense public outcry about fracking, what with all the health and environmental concerns detailed in documentaries and the news (or this news or this news, seriously it’s everywhere). Beyond the heated debate around fracking’s effects though, there is also the question of how long the process will stay viable and whether it will end up being profitable in the long run.

Up until this point, estimating how quickly we are depleting shale gas wells has been difficult because, quite frankly, it’s such a young process. We just hadn’t been doing it long enough to establish a consistent model for how quickly a well empties out and how its output will decline as it empties. Now though, with fracking moving into its second decade, these estimates are starting to crop up. This study out of Texas is unique among other studies trying to determine how wells behave over time in that it considers the physical dynamics of a horizontal well. Older studies have been applying the models from petroleum and gas drilling, which were all vertical drilling operations. Fracking is a horizontal process though, with the mining extending out across underground shale plates and fracturing them to release natural gas deposits inside the rock, which provides a very different environment for gases to move around in compared to your standard vertical pockets from the past.

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A simple diagram of how fracking works. A high pressure mixture of water and cement is pumped down into the shale to fracture it, then the gas is released. Notice how the well is horizontal though? That’s what sets fracking apart from traditional gas and petroleum drilling, which are vertical operations (Source: http://www.sciencefocus.com)

The group designed a new model for how gas will behave in a fracking well, and then compared their model to over 2,000 Barnett horizontal mines that have been functioning long enough to begin aligning with the model. Their model fit well performance for those 2,000 wells, showing the beginnings of exponential decline in well output with interference beginning to arise after around 5 years of drilling. They estimated a lower limit of 10 trillion standard cubic feet and an upper limit of 20 trillion standard cubic feet of natural gas to be extracted over the next fifty years, about half of previous estimates for the same time period.

Should these wells end up being more short lived than originally expected, the overall benefits of fracking may not outweigh the financial costs of mining, not to mention the serious environmental problems the process seems to be creating. Understanding how these wells perform as time passes is incredibly important in deciding the future of fracking, which is quickly becoming the same thing as deciding the future of the American domestic energy market.

Original article:

http://www.pnas.org/content/110/49/19731.full

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