Shale oil production generates greenhouse gas emissions at levels similar to conventional crude oil production, according to a pair of new studies released by the US Department of Energy’s Argonne National Laboratory.
The research, conducted by Argonne researchers in collaboration with Stanford University and the University of California, Davis, analyzed the Eagle Ford shale formation in Texas and the Bakken play mainly in North Dakota. Eagle Ford and Bakken are the second and third largest oil-producing shale formation regions in the United States, during the last three years. In 2014, Bakken and Eagle Ford together accounted for 54% of oil production and 19% of gas production among the top seven production regions. These are shale formations with low permeability and must be hydraulically fractured to produce oil and gas.
Light crude oil trapped in rock, such as shale, is called tight oil. Its production is accompanied by a significant amount of energy product, including natural gas, some of which gets flared or vented off at the well site. Until now, little information has existed about how production methods impact greenhouse gas emissions at these sites.
Both Argonne studies showed that, after taking into consideration flaring and venting of natural gas, the greenhouse gas emissions associated with shale/tight oil production are similar to those generated at conventional crude oil reserves. This emission intensity stays consistent during the lifespan of extraction at the oil play. This contradicts an earlier estimate that the Bakken play might produce greenhouse gas emissions 20% higher more than for crude oil production.
For the Bakken, GREET-derived WTR (well-to-refinery gate) GHG intensities range from 4.3 g CO2eq/MJ for gasoline blendstock, 5.0 for diesel, and 5.1 for jet fuel. Total well-to-wheels (WTW) GHG intensities are 94.6, 93.2 and 86.6 g CO2eq/MJ, respectively.
For Eagle Ford, GREET-derived WTR (well-to-refinery gate) GHG intensities range from 8.8 g CO2eq/MJ for gasoline blendstock, 10.2 for diesel, and 10.3 for jet fuel. Total well-to-wheels (WTW) GHG intensities are 89.2, 87.8 and 82.5 g CO2eq/MJ, respectively.
As reported in a 2015 paper by Rahman et al., recovery emissions (from the drilling of the oil well and associated land-use change, crude extraction, processing of crude oil, associated gas and water, and flaring) for conventional oils range from as low as 3.04 CO2e/MJ for Mars oil from the Gulf of Mexico, to 6.06 to Alaska North Slope crude, to 30.98 for California Kern County heavy oil. The total WTW life cycle GHG emissions range from 97.55g-CO2eq/MJ-gasoline derived from Mars crude to 127.74 g-CO2eq/MJ-gasoline derived from California’s Kern County heavy oil.
Drilling and fracturing wells for shale oil is more energy intensive than conventional drilling, but these wells have higher productivity and require less energy to produce and process the crude. Flaring of gas is a key issue in the Bakken, and if flaring were controlled, the Bakken crude would have lower emissions than conventional crude.—Adam Brandt, lead author of the Bakken study and a professor at Stanford University
The Eagle Ford study looked at crude oil produced from different production zones for 2009–2013. Some zones produced more oil while others produced more gas. The study showed that wells in the gas-rich zone used roughly twice as much energy as wells in the oil-rich zone, which used an average of 1.2% of energy produced for production, extraction, and processing. Additionally, the water usage rate was generally higher at the gas-rich wells.
It was challenging to calculate the net energy use and net greenhouse gas emissions for Eagle Ford because of the wide range of products produced at these places, and there were no publicly available tools for horizontal drilling and hydraulic fracturing. The collaboration provided greater transparency and understanding of energy and climate impacts of oil production in these regions.—said Sonia Yeh, lead author on the Eagle Ford study and a researcher with the Institute of Transportation Studies at UC-Davis
These studies calculate energy consumption and greenhouse gas emissions associated with the crude oil and natural gas extraction using the Oil Production Greenhouse Gas Emissions Estimator (OPGEE) model with production data collected for shale oil well operations in both plays. This model estimates energy for the lifecycle from the initial exploration to the refinery entrance gate and includes production, processing, and transport.
The research team put the OPGEE-produced results into the GREET model developed at Argonne National Laboratory for modeling lifecycle greenhouse gas emissions.
The research was funded by the Vehicle Technology Office and the Bioenergy Technology Office of the Energy Efficiency and Renewable Energy Office of the US Department of Energy to improve the petroleum baseline estimate that serves as the comparison point for alternative vehicle-fuel pathways.
Md. Mustafizur Rahman, Christina Canter, Amit Kumar (2015) “Well-to-wheel life cycle assessment of transportation fuels derived from different North American conventional crudes” Applied Energy 156 (2015) 159–173 doi: 10.1016/j.apenergy.2015.07.004