Deciphering the true life cycle environmental impacts and costs of the mega-scale shale gas-to-olefins projects in the United States

This paper addresses the techno-economic-environmental analysis of large-scale olefin production from shale gas in the major shale regions of the U.S. (including Appalachian, Gulf Coast, Mid-Continent, and Rocky Mountain regions) and investigates its environmental footprints. To decipher the true production costs and environmental impacts, we first develop shale gas supply and olefin production network models to estimate pipeline distances, numbers of wells, well-sites, and gathering systems needed in the near- and mid-term. Next, detailed process design, modeling, and integration methods for alternative technologies are developed. We conduct life cycle analysis (LCA) to systematically evaluate the energy-water-carbon nexus. Based on the economic and LCA results, we compare the influences of gas composition, project operating time, well lifetime, and the allocation method. The results indicate that the four shale regions considered would in total supply feedstocks for U.S. ethylene production for at least 130 years. However, only olefins produced from Gulf Coast and Mid-Continent regions demonstrate economic advantage ($668 per t and $255 per t) over ethylene in the current market. Based on the mass-based allocation approach, for the four shale regions evaluated, the energy consumption is 13.8-17.2, 14.3-16.7, 13.3-16.7, and 12.2-14.5 GJ per t olefins, and the freshwater footprint is 3.31-4.28, 5.34-5.65, 3.05-3.56, and 4.68-5.03 kg kg^-1 olefins, respectively. In addition, normalized GHG emissions indicate that shale gas can be categorized as a low-carbon feedstock (0.75-1.05 kg CO₂-eq per kg) based on a mass-based allocation approach, or a high-carbon feedstock (1.24-2.13 kg CO₂-eq per kg) based on an economic value-based allocation approach.