New lifecycle analysis of WTW GHG emissions of diesel and gasoline refined in US from Canadian oil sands crude
In a new, comprehensive study, a team from Argonne National Laboratory, Stanford University and UC Davis ITS has estimated the well-to-wheels (WTW) GHG emissions of US production of gasoline and diesel sourced from Canadian oil sands. The analysis uses an expanded system boundary including land disturbance-induced GHG emissions and also incorporates operating data that represent the average practices and technological advances of the oil sands industry since 2008. The study is published in the ACS journal Environmental Science & Technology.
The researchers examined 27 oil sands projects, representing four major oil sands production pathways, including bitumen and synthetic crude oil (SCO) from both surface mining and in situ projects. Overall, they found that pathway-average GHG emissions from oil sands extraction, separation, and upgrading ranged from ∼6.1 to ∼27.3 g CO2 equivalents per megajoule (in lower heating value, CO2e/MJ). This range can be compared to ∼4.4 g CO2e/MJ for US conventional crude oil recovery.
Depending on the extraction technology and product type output of oil sands projects, the WTW GHG emissions for gasoline and diesel produced from bitumen and SCO in US refineries were in the range of 100−115 and 99−117 g CO2e/MJ, respectively—on average, about 18% and 21% higher emissions than those derived from US conventional crudes.
Using diluents reduces WTW emissions by 3−5% and 4−6%, respectively, for gasoline and diesel produced from dilbit compared to those derived from bitumen, primarily because of the ∼36% lower amount of the bitumen component delivered to US refineries per MJ of dilbit compared to that per MJ of bitumen delivered.
WTW GHG emissions of gasoline and diesel derived from diluted bitumen ranged from 97 to 103 and 96 to 104 g CO2e/MJ, respectively, showing the effect of diluent use on fuel emissions.
Accounting for 9.4% of the total crudes processed in US refineries in 2013 and forecast to reach 13.6% in 2020, Canadian oil sands are an increasingly important factor affecting the carbon intensities of US petroleum fuels.
… Previous studies reported generally higher GHG emissions from production of oil sands-derived fuels than conventional crude-oil-derived fuels.The range of the reported higher emissions, however, varies among studies, mainly owing to the use of different data and analysis boundaries; different assumptions about the source, type, share, and fate of diluents; different electricity sources displaced by the surplus electricity from cogeneration facilities; and different refining efficiencies and emissions for fuel products.
… Canadian oil sands producers have recently improved the energy efficiency of their processes and deployed GHG mitigation technologies. The impacts of these efforts on the carbon intensities of Canadian oil sands products require evaluation. … Compared to previous work, this study improves the representativeness, transparency, and completeness of the carbon footprint estimates for the Canadian oil sands industry.—Cai et al.
Each oil sands project is distinct, the researchers noted, because of the differing characteristics of oil sands reservoirs, recovery technologies, and operational choices. The researchers focused on the multiyear production-weighted average energy efficiency and process fuel consumption for each pathway, primarily based on monthly records of energy consumption by fuel type and oil sands production from 2008 to 2012.
Characterizing the month-to-month variability in the operational energy requirements of oil sands extraction and upgrading among projects allowed them to analyze the impacts of variability on the performance of each oil sands pathway on GHG emissions.
To calculate land disturbance GHG emissions, they identified pre- and post oil sands land disturbances from 1985 to 2009 using satellite remote sensing observations and the associated soil carbon dynamics.
Despite such methodological and parametric differences, our finding that gasoline derived from oil sands products had WTW GHG emissions of 100−115 g CO2e/MJ was within the range of 100−120 g CO2e/MJ from earlier studies. The much greater energy intensity of extraction, separation, and upgrading of oil sands relative to conventional-crude recovery remained the major reason for the higher WTW GHG emissions of oil sands pathways than conventional-crude pathways in this and previous studies. Moreover, we found that gasoline and diesel derived from surface-mined bitumen had the lowest WTW GHG emissions, while those sourced from SCO produced from in situ projects exhibited the highest emissions, despite a significant degree of variability due to operating conditions. This finding agrees with previous work.
We estimated that WTW emissions of gasoline derived wholly from oil sands products ranged from 9% to 24%, on average, higher than those of gasoline produced from U.S. conventional crudes, compared to an increase of 14% according to a meta- analysis of 12 studies. Inclusion of land disturbance-induced emissions in our analysis explained about 2% of the difference.—Cai et al.
Hao Cai, Adam R. Brandt, Sonia Yeh, Jacob G. Englander, Jeongwoo Han, Amgad Elgowainy, and Michael Q. Wang (2015) “Well-to-Wheels Greenhouse Gas Emissions of Canadian Oil Sands Products: Implications for U.S. Petroleum Fuels” Environmental Science & Technology doi: 10.1021/acs.est.5b01255