Energy Returned on Energy Invested: Part 2 – Oil
01.11.2023
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Welcome back to our series on EROEI, or Energy Returned on Energy Invested. Our last post discussed the primary EROEI for various energy sources.
Setting the stage:
Oil and gas reservoirs, coal mines and wind and solar farms are often far from energy demand centres.
In Oil’s specific case, it’s also not in a form we can readily use.
Diving in:
First, we must consider how much primary energy is consumed in delivering the remainder to the point of use in a form that’s helpful to us as a society.
It’s quite an involved subject, so to keep it bite-sized, we have limited the scope for this post to evaluating oil and will cover gas, coal and renewables in the next exciting instalment.
So, let’s establish how we are going to calculate EROEI from this point forward:
An EROEI of 10 implies consuming 1 unit of energy to produce 10.
i.e., 1/10 of our produced energy, or 10%, is consumed in production, with 90% available for something else.
The implications are that with an EROEI of 1.0, all the energy produced is consumed in producing the next unit of energy, leaving nothing for society and the closer the EROEI gets to 1.0 the less sustainable the energy system becomes.
Example: If we use 5% of the produced energy to transport our energy, which had an initial EROEI of 10, we end up with (100%-5%) = 95% of 90%, which is ~86%, having consumed (100% – 86% )= 14% in total.
Therefore, our EROEI now stands at 100/14 = 7.1 (Small percentages make big differences in EROEI).
OIL
We’ll start our assessment with the black gold that has shrunk the world by enabling rapid and low-cost mobility. The supply chain for oil looks something like this:
Approximately one-third of global oil production is transported by tanker, and the rest by pipeline. Oil pipelines are incredibly efficient, consuming much less than 0.1% of the energy transmitted.
To keep it simple, we will ignore energy consumed in oil pipelines as negligible.
Note: This is not a valid assumption for heavy high-viscosity crudes, which must be heated to make them flow. In this case, energy consumption can be 2-3% of energy transmitted.
Once the crude has been refined and converted into products, many are transported by ship.
The combined volume of oil and products transported transoceanic distances by ship accounts for ~60% of the total volume of oil produced.
Massive crude tankers are highly efficient in transporting energy, consuming 1-2% of the energy they transport on a return trip.
Product tankers are typically smaller and, therefore, less efficient, but also travel shorter distances, so we will take an average of 2% for the combined total of crude and shipped products.
But this is where things get a little complicated:
The 2% of the energy we consume in the form of fuel oil has already been through the process we are following. Therefore, the quantity of primary energy consumed by the ship would need to be scaled up to account for the losses in the end-to-end process.
Losses that we haven’t yet calculated.
For example, If our end-to-end EROEI works out to be 3, this means 1/3 = 33% of the original primary energy produced has been used in getting the energy to the ship in a usable form.
Therefore, we should uplift the percentage of primary energy consumed in shipping by 33% to account for this, which would alter our end-to-end EROEI slightly.
While not a negligible effect, it is relatively small, and we will ignore it for simplicity, but it’s an important point to note.
So, our range of EROEI for the 60% of the oil that is shipped, either as oil or as products, has fallen from 4-50 to ~3.7-25 and a weighted average EROEI for all oil is 3.8-35
But there is a fly in the ointment for crude oil, and that is refining. We need to split crude oil into its constituent parts, e.g. gasoline, jet fuel, diesel and fuel oil. We also need to upgrade the low-value parts and remove sulphur, which requires a lot of energy.
Refineries typically consume ~7% of their throughout as fuel, and if we include this in our EROEI for oil, the weighted average comes down to ~2.9-9.1.
Refining implies that no matter how high the upstream EROEI is for crude, the delivered product EROEI will be < 14 and typically much less.
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