San Ardo Oil Field

Energy costs to keep super-giant oilfields operating rise dramatically as extraction rates drop, study finds

by James Ayre, Clean Technica

The energy costs of operating the world’s largest “super-giant” oil fields can rise dramatically as extraction (“production”) rates begin dropping, according to a new study published in the journal Nature Climate Change.

To put that in a very plain way: as extraction begins ramping down at the world’s largest oil fields (those that have produced more than 1 billion barrels of oil), the net energy resulting from the extraction process often begins falling rapidly. One result of that is each unit of oil becomes more carbon intensive.

The researchers behind the new study note that this reality — failing to account for the changing energy requirements of oilfields as they “mature” — can lead to policymakers and oilfield managers underestimating and understating the “true” climate impacts of oil use.
In other words, the new study has implications relating to climate models and long-term carbon emissions predictions, and thus policies.

“Current climate and energy system models typically don’t explore the impacts of oil reservoir depletion in any detail,” commented study co-author Adam Brandt, an assistant professor of energy resources engineering at Stanford’s School of Earth, Energy and Environmental Sciences. “As oilfields run low, emissions per unit of oil increase. This should be accounted for in future modeling efforts.”

There’s also, of course, an impact on the extraction/production costs, and thus on oil market pricing and the profitability of oil companies.

Typically, greenhouse gas estimates are calculated with a sort of economic reverse engineering — where an economic index is used to convert the monetary value of an oilfield’s final products (oil, gas, other petroleum products, etc.) into greenhouse gas emissions. The system the researchers used is different.

“This top-down approach for converting economic values into environmental and energetic costs misses a lot of underlying information,” stated Stanford postdoctoral researcher Mohammad Masnadi.

The press release provides more: “What’s more, many studies look at data from only a single point in time, and as a result capture only a snapshot of an oilfield’s greenhouse gas emissions. But the Stanford scientists argue that in order to paint the most accurate picture of an oilfield’s true climate impacts — and also have the best chance of reducing those impacts — it’s necessary to assess the energy costs associated with every stage of the petroleum production process, and to do so for the oilfield’s entire lifetime.

“Developed in Brandt’s lab at Stanford, a software tool called the Oil Production Greenhouse gas Emissions Estimator (OPGEE) is designed to do just that. For any given oilfield, OPGEE performs what’s known as a lifecycle assessment, analyzing each phase of the oil production process — extraction, refinement and transportation. It then uses computer models to calculate how much energy is consumed during each step. From this, scientists can calculate precisely how much greenhouse gas each oilfield emits.

“‘This bottom-up type of analysis hasn’t been done before because it’s difficult,’ Masnadi said. ‘For this study, we needed over 50 different pieces of data for each oilfield for each year. When you’re trying to analyze an oilfield across decades, that’s a lot of data.’
“Unfortunately, most oil companies are reluctant to release this type of temporal data about their oilfields. The Stanford researchers developed two workarounds to this problem. First, they gathered data from places where transparency laws require oil production data be made publically available. These included Canada, Norway, and the UK, and the state of California in the US. Secondly, the pair conducted a deep data mine of the scientific literature to seek out clues about oilfield production levels in published studies.

“In the end, the pair ended up with data going back decades for 25 globally important super-giant oilfields. Applying OPGEE to this group, the scientists found that for many of the super-giant oilfields, oil production declined with time as the wells were depleted, but the energy expended to capture the remaining oil went up.”

“The more oil that is extracted, the more difficult it becomes to extract the oil that remains, so companies have to resort to increasingly energy-intensive recovery methods, such as water, steam or gas flooding,” Masnadi stated.

Something else that should be noted here is that oil extracted using such methods is more expensive to process — owing to the need to remove the introduced water and/or gas.
“We can show with these results that a typical large oilfield will have a doubling of emissions per barrel of oil over a 25-year operating period,” Brandt concluded.

So, yet another reason that if the goal to limit anthropogenic climate warming to under 2° Celsius is to actually be achieved, then a very rapid shift away from fossil fuel use would be required.


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