Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China? † ‡ § † ‡ Yue Qin, Ryan Edwards, Fan Tong, and Denise L
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Policy Analysis pubs.acs.org/est Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China? † ‡ § † ‡ Yue Qin, Ryan Edwards, Fan Tong, and Denise L. Mauzerall*, , † Woodrow Wilson School of Public and International Affairs, Robertson Hall, Princeton University, Princeton, New Jersey 08544, United States ‡ Department of Civil and Environmental Engineering, E-Quad, Princeton University, Princeton, New Jersey 08544, United States § Department of Engineering and Public Policy (EPP), Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States *S Supporting Information ABSTRACT: To increase energy security and reduce emissions of air pollutants and CO2 from coal use, China is attempting to duplicate the rapid development of shale gas that has taken place in the United States. This work builds a framework to estimate the lifecycle greenhouse gas (GHG) emissions from China’s shale gas system and compares them with GHG emissions from coal used in the power, residential, and industrial sectors. We find the mean lifecycle carbon footprint of shale gas is about 30−50% lower than that of coal in all sectors under both 20 year and 100 year global warming potentials (GWP20 and GWP100). However, primarily due to large uncertainties in methane leakage, the upper bound estimate of the lifecycle carbon footprint of shale gas in China could be approximately 15−60% higher than that of coal across sectors under GWP20. To ensure net GHG emission reductions when switching from coal to shale gas, we estimate the breakeven methane leakage rates to be approximately 6.0%, 7.7%, and 4.2% in the power, residential, and industrial sectors, respectively, fi fi under GWP20.We nd shale gas in China has a good chance of delivering air quality and climate cobene ts, particularly when used in the residential sector, with proper methane leakage control. 1. INTRODUCTION production may result in a worse lifecycle climate performance 14,16 Facing serious domestic air pollution and growing international for shale gas than coal. Thus, it is critical to determine pressure to address climate change, the Chinese government whether shale gas in China can bring net greenhouse gas has been vigorously promoting the substitution of natural gas (GHG) emission reductions. Constrained by its production size ’ and data availability, there have been very few studies that for coal to address both issues. Inspired by the U.S. s shale gas fi ’ boom, China has been encouraging domestic shale gas quanti ed the environmental impacts of China s shale develop- development. According to the U.S. Energy Information ment. Chang et al. (2014, 2015) estimated the shale-to-well Administration (EIA), China has the world’s largest technically energy consumption and air pollutant emissions, as well as lifecycle GHG emissions of shale gas-fired power generation recoverable shale gas resources at around 31.6 trillion cubic ’ fi meters (tcm).1 However, due to challenges including greater based on data from China s rst shale well in Sichuan basin, formation depth, inadequate water resources, limited experi- using an input-output (IO) lifecycle inventory (LCI) modeling approach.17,18 However, as less than 20% of China’s natural gas ence with horizontal drilling and hydraulic fracturing, under- 19 developed pipeline infrastructure, and government-controlled is used in the power sector, a detailed comparison of the − gas prices, China’s current shale gas development is sluggish.2 4 lifecycle GHG emissions between coal and shale gas across China’s major natural gas end-uses is needed. Overall, the Until recently, commercial shale gas production only existed in ’ Sichuan and Chongqing regions, with a total output of 1.3 climate impacts of China s shale gas development have received ’ less attention than they deserve. billion cubic meters (bcm) in 2014, meeting just 1% of China s fi total domestic natural gas production that year.5 However, This work serves as one of the rst attempts to build a ’ framework to estimate the lifecycle GHG emissions for China’s China s shale gas has large future potential, driven by factors ff such as large shale resources, favorable policies, improving shale gas, based on the major di erences between conventional infrastructure, natural gas market reform, and advancing − technologies.6 9 Received: August 12, 2016 In the U.S., substantial efforts have been made to compare Revised: February 2, 2017 the lifecycle carbon footprint of conventional gas, shale gas, and Accepted: February 8, 2017 − coal.10 15 Concerns exist that methane leakage from shale gas Published: February 8, 2017 © 2017 American Chemical Society 2554 DOI: 10.1021/acs.est.6b04072 Environ. Sci. Technol. 2017, 51, 2554−2562 Environmental Science & Technology Policy Analysis and shale gas systems. We compare the lifecycle GHG 1 shows the fugitive EFs used in this study for China’s emissions of shale gas with that of coal in China’s major conventional natural gas system. Details are shown in the SI natural gas end-uses, using China’s domestic data whenever available, and supplementing with U.S. data otherwise. In Table 1. Methane Leakage Rates for Conventional Natural addition, we conduct a sensitivity analysis to identify key factors Gas System affecting our estimates of lifecycle carbon emissions of China’s a − shale gas system. We also estimate the breakeven methane processes mean (%) [low high] (%) leakage rates to ensure net carbon benefits from a coal-to-shale gas production and gathering 0.8627,28 [0.05−2.17]14,26 gas switch in China’s major end-uses to inform industrial gas processing 0.1128 [0.02−0.19]14,26 practices and aid policy design. gas transmission and storage 0.3230 [0.03−2.2]14,26 gas distribution 0.0929 [0.01−1.4]14,29 2. MATERIALS AND METHODS natural gas system total 1.37 0.11−5.96 a This section describes the method we use to estimate China’s Methane leakage rates are calculated as the ratio of total methane lifecycle GHG emissions from conventional natural gas, shale emissions within that stage to the national total gross natural gas production reported in that year. Refer to SI Table S2 for details. gas, and coal. Both upstream (energy extraction, processing, transport, and distribution) and end-use (power generation, residential cooking, and industrial boilers) processes are included within the lifecycle system boundary (Supporting Table S4 shows the energy efficiency and energy mix Information (SI) Table S1). Embodied emissions from information on upstream processes for China’s conventional − infrastructure construction are not included in this study. natural gas industry.33 35 Recent EFs estimates for fossil fuel GHG emissions included in our assessment are (1) Fugitive combustion are used to estimate CO2 emissions from upstream 36 CH4 emissions from both unintentional gas leakage and energy combustion. intentional vents due to safety concerns or engineering 2.1.2. Shale Gas in China. Shale gas and conventional 20 37 design; (2) CO2 emissions from both energy used to run natural gas typically have similar chemical composition, and the entire system and from end-use combustion. Global their primary difference is that the permeability of shale gas warming potential (GWP) values from the most recent IPCC geological formations is approximately 6 orders of magnitude 21 38,39 report are used to convert CH4 to CO2 equivalent (CO2eq). less than that of conventional gas. Therefore, shale gas IPCC estimates that over a 100 year time horizon, the same extraction is more technically demanding, energy intensive, and mass of CH4 traps 28 times more heat than CO2 (84 times for costly. As shown in SI Table S1, the upstream natural gas 20 years).21 As time scale choices have significant implications system has four stages including (1) preproduction and when evaluating the climate impacts of various fossil fuels, we production (referred hereafter as “(pre-) production”) and present the results based on both time horizons. gathering, (2) processing, (3) transmission and storage, and (4) As data scarcity prevents us to effectively characterize the distribution. In the (pre-) production stage, shale gas undergoes underlying distributions of emission sources,12,22 we estimate additional processes compared to conventional natural gas the lower bound, mean, and upper bound lifecycle GHG including horizontal drilling and hydraulic fracturing to enhance emissions of natural gas (both conventional and shale) and coal the flow of gas into the well. After production, shale gas goes under a corresponding low, most likely, and high estimate of through the same processes as conventional natural gas to reach upstream fugitive emissions and energy combustion emissions end users.14,40,41 Thus, the main differences in processes (SI Table S13). involving shale gas and conventional natural gas are in the (pre- 2.1. Upstream GHG Emissions for Natural Gas and ) production stage. Coal in China. 2.1.1. Conventional Natural Gas in China. As Unlike conventional natural gas production, which is China’s domestic natural gas production is small and is under relatively mature in both countries, shale gas production in the control of three national oil companies (NOCs), there is China is still at a nascent stage. Hence, different policy limited publicly available measurement data regarding fugitive regulations and industrial practices between China and the U.S. emission factors (EFs). Zhang et al. (2010, 2014)23,24 estimated may result in substantial differences in GHG emissions from ’ 25 ’ China sCH4 emissions based on Liu et al. (2008), which China and the U.S. shale gas production. Nevertheless, the provided CH4 EFs from various components of the oil and gas primary emission sources for shale gas production are likely to system on the basis of local conditions but primarily rely on the be the same since both countries use the same drilling 2006 IPCC Guidelines for Greenhouse Gas Inventories.26 technologies.