Tradeoffs in water and carbon footprints of shale gas, natural gas, and coal in China

Abstract

China has set ambitious goals for developing its vast shale gas reserves. The rapid growth in shale gas needs to better understand its environmental implications. This study performs a comprehensive evaluation framework for identifying the tradeoffs in water and carbon footprints of China's shale gas, and compares the lifecycle greenhouse gas (GHG) emissions and water consumption of shale gas with that of conventional natural gas and coal. Scenario analysis and white noise are used for addressing system’s uncertainties. A deterministic mathematic method is then developed for identifying the optimal breakeven methane leakage and wastewater recycling rates. Results reveal that the carbon footprint of shale gas (39.71 g CO2/MJ) is slightly higher than that of conventional natural gas (35.51 g CO2/MJ), but their carbon footprints are lower than that of coal. When the downstream supply chain is considered, coal-fired technologies have a larger amount water consumption than gas-fired technologies. Theoretically, the water consumption can increase by approximately 2% when switching from conventional natural gas to shale gas. Shale gas development in China cannot lead to a significant increase in its total GHG emissions, whereas a coal-to-shale gas switch can offset some GHG emissions. The optimization solutions indicate that the methane leakage rate in shale gas technology decreases from 7.89% to 5.75% when the methane recovery rate in coal technology increases from 0 to 100%. This relationship implies that increasingly strict methane leakage regulations are necessary in the shale gas industry to achieve climate benefits of shale gas subsidization for coal.