Shale Gas Supply Chain Design and Operations toward Better Economic and Life Cycle Environmental Performance: MINLP Model and Global Optimization

ACS Sustainable Chemistry & Engineering (May 31, 2015; DOI: 10.1021/acssuschemeng.5b00122) / by Jiyao Gao and Fengqi You
http://pubs.acs.org/doi/pdf/10.1021/acssuschemeng.5b00122

[Phys.org ] [Fengqi] You has designed computational models to analyze the “well-to-wire” life cycle of electricity generated from shale gas. His models account for a number of stages in the process, including freshwater acquisition, shale well drilling, fracking, and processing, wastewater management, and , as well as transportation and storage. By discovering optimal design and operations for the shale gas supply chain, You believes the United States will benefit both environmentally and economically…

“We talk about carbon dioxide, and we think it’s bad because it causes global warming,” You said. “But methane is even worse. One unit of methane is 86 times worse than one unit of carbon dioxide from a two-year horizon in terms of its ability to trap heat in the atmosphere.”

Through modeling, You found that these issues can be mitigated by restructuring the supply chain. First, You recommends using a network of pipelines to transport freshwater to drilling sites and transport shale gas to processing and power plants. By removing trucks from the equation, the industry would save on gas and cut exhaust emissions.

Next, You suggests developing a better drilling schedule. After drilling a vertical shale well, workers drill more wells horizontally to reach more targets. Horizontal drilling can result in 20 to 30 wells in one place. This requires more water, transportation, and storage then needed to meet demand, and it releases more methane. By evenly distributing drilling activities at each well site over the years instead of drilling all at once, the industry would avoid transporting the gas to long-term storage facilities. It would also reduce the amount of water needed at one time. As a result, facilities can be designed with a more suitable capacity, reducing the capital investment and negative ecological impacts.

Finally, You evaluated ways to handle the highly contaminated wastewater that is a fracking byproduct. Some companies have been disposing it in abandoned wells. But because these wells are few and far between, they have to drive farther and farther distances to find wells with room for disposal. The other option is to treat the water, which is difficult because of the high volume.

“Onsite water treatment requires a lot of energy,” You said. “Treatment technologies like reverse osmosis need electricity, which may come from a coal-fired plant. Disposing the water into a well is easier and cheaper but not for the long term. Through life-cycle analysis, we found that water treatment is actually a more sustainable solution.”

While the treated water may not be fit to drink, it could be recycled back into the process and used again for . This cuts the truck emissions and costs of transporting the water to far away facilities. And the more time a truck spends on the road, the greater the chances that the contaminated water will leak.

You said that because the industry is young, companies are still learning how to manage it. He believes that optimizing operations will help the industry have better control of the entire system. Not only will it benefit companies financially, it will do less damage to the environment…

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