Transportation fuels: LCA of Well-to-Tank and Tank-to-Wheels GHG emissions


Well-To-Tank (WTT) Life Cycle Analysis of a petroleum based fuel pathway includes all steps from crude oil recovery to final finished fuel. Tank-To-Wheel (TTW) analysis includes actual combustion of fuel in a motor vehicle for motive power. WTT and TTW analysis are combined to provide a total Well-To-Wheel (WTW) analysis.

Following up on my previous post Comparison of Lifecycle Greenhouse Gas Emissions of Various Electricity Generation Sources, I have looked into the GHG contributions of the various parts of the hydrocarbon-fuel part of the transportation cycle. Crude Refining contributes on the order of 13% of the total WTW life cycle of hydrocarbon fuel based transport. Roughly 80% of the emissions are consumption, burning the damn stuff, downstream of the supply chain which puts the fuel into the vehicle tank. Refining is a bit over half of the fuel supply chain. Of course, “your mileage may vary” as there are many variables depending on location, fuel choice, how that fuel is supplied, and how it is consumed.

First, regarding questions about the oil sands GHG footprint, the US Congressional Research Service has recently surveyed just this: Canadian Oil Sands: Life-Cycle Assessments of Greenhouse Gas Emissions. The CRS report begins with this summary:

CRS surveyed the published literature, including the U.S. Department of State-commissioned studies for the Keystone XL pipeline project in both the August 2011 Final Environmental Impact Statement (EIS) and the March 2013 Draft Supplementary EIS. The primary literature reveals the following:

  • Canadian oil sands crudes are on average somewhat more GHG emission- intensive than the crudes they may displace in U.S. refineries, as Well-to-Wheel GHG emissions are, on average, 14%-20% higher for Canadian oil sands crudes than for the weighted average of transportation fuels sold or distributed in the United States;
  • discounting the final consumption phase of the life-cycle assessment (which can contribute up to 70%-80% of Well-to-Wheel emissions), Well-to-Tank (i.e., “production”) GHG emissions are, on average, 70%-110% higher for Canadian oil sands crudes than for the weighted average of transportation fuels sold or distributed in the United States;
  • compared to selected imports, Canadian oil sands crudes range from 9% to 19% more emission-intensive than Middle Eastern Sour, 5% to 13% more emission- intensive than Mexican Maya, and 2% to 18% more emission-intensive than various Venezuelan crudes, on a Well-to-Wheel basis;
  • compared to selected energy- and resource-intensive crudes, Well-to-Wheel GHG emissions for Canadian oil sands crudes are within range of heavier crudes such as Venezuelan Bachaquero and Californian Kern River, as well as lighter crudes that are produced from operations that flare associated gas (e.g., Nigerian Bonny Light);

The above graphic on GHG for transportation fuels focuses on LCA of the Well-to-Wheels. This is from the Jacobs Consultancy slide deck: Life Cycle Well to Wheels Assessment of GHG Emissions from North American and Imported Crude Oils [PDF slide deck 34pp]. The data source for that particular slide is the Detailed California-Modified GREET Pathway for Ultra Low Sulfur Diesel (ULSD) from Average Crude Refined in California [PDF 47 pp]. GREET is the Argonne National Laboratory LCA Model. That report is focused on ULSD, but it confirms the general magnitude of the refining GHG footprint, with the entire supply chain contributing about 21%:


For estimates of how large is the supply chain GHG contribution associated with process heat or electricity I am reviewing the in-depth 2012 study by Jacobs titled: EU Pathway Study: Life Cycle Assessment of Crude Oils in a European Context [PDF 364pp]. This is an industry-funded study, for the Alberta Petroleum Marketing Commission. The study was prepared for the EU context – EU refineries, EU crude oil sources, etc.  I am curious how big a GHG reduction would be obtained by replacing these heat and electricity inputs with nuclear plants. For oil sands the nuclear substitution would improve both recovery (esp. steam generation) and refining.

Comparison of Lifecycle Greenhouse Gas Emissions of Various Electricity Generation Sources


The following is excerpted from an email conversation on the Baucus proposal. My engineer friend emailed:

This one caught my eye: “…the bill would take the entire life-cycle into account when judging the fuel.” Ha, does anyone really know how much energy is required to produce that gallon of gasoline, 

Good question, how do we know the life-cycle GHG emissions? Fortunately there are a lot of Life Cycle Analysis studies (LCA) published – it is the bread and butter of the energy business. I am aware of a number of those relevant to electricity generation (not so much those in the transport sector). E.g., this is a good resource because it is a meta-study of a range of LCA by universities, government agencies and industry-associations: Comparison of Lifecycle Greenhouse Gas Emissions of Various Electricity Generation Sources. The chart above summarizes the results of that WNA meta-study.

especially if the base material comes from tar sands?

I’ve not read any of the LCA studies on tar sands. But Mr. Google finds this meta-study of thirteen studies that looks credible: Understanding the Canadian oil sands industry’s greenhouse gas emissions

Off the cuff I wouldn’t expect a lot of precision to be so critical for tar sands because they are so off scale no sane formula would incentivize their production. The LCA for tarsands oil & gas varies due to energy sources, local infrastructure and energy supplies. E.g., if instead of natural gas as the heat source, you installed SMRs (small modular reactors) at the site to generate process heat, then the carbon emissions from the natural gas feedstock would go away. Even using nuclear process heat tar sands would not be competitive carbon-wise with conventional oil.

As far as I know, no oil company has published the calculation mapping the full energy content of just the refining process, never mind all the ancillary energy costs such as transportation/distribution… ignoring the energy content of the capital investment in the first place…

Refining is a well-understood and researched technology. The purpose of LCA is to capture everything from mining/extraction to construction to operating to decommissioning of plant. It is a lot of work, and not trivial to understand the results. And not trivial to assess the validity of a specific methodology. For me that means I need to assess whether the people are trustworthy. I have read through all the detail of one of the Sydney University studies – they could hide dozens of errors that I will not find because I’m not motivated to audit their work. Instead I focus on auditing the source of the product – the people or the institution. The LCA work from IEA, US EIA, OECD, IAEA is excellent.

Still there are scope differences – e.g., coal is never charged with waste management cost (waste is just piled into mountains next to plant, and of course dumped into the atmosphere). Similarly wind and solar are never properly charged for the cost of intermittency. In contrast the LCA for nuclear is charged for every gram of “waste”, even though roughly 98% of the “waste” is actually high value fuel for fast reactors.

Sadly, publishing and interpreting life cycle analysis is not good for TV ratings. Not good for media ratings in general.