Comment by fromthestart | Hacker News Reader

Comment by fromthestart | Hacker News Reader

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A couple issues with the science here:

>Between 2005 and 2015, global rates of fracking went from producing 31 billion cubic meters per year to 435 billion

>In the last half of the 20th, century levels of methane in the atmosphere rose. They then plateaued, and spiking in 2008.

So the shale gas revolution started in 2005, but the spike didn't occur until 2008? Also it isn't clear if this was a transient spike or the author is referring to a sudden and sustained increase.

> While methane released in the late 20th century was enriched with the carbon isotope 13C, Howarth highlights methane released in recent years features lower levels. That's because the methane in shale gas has depleted levels of the isotope when compared with conventional natural gas or fossil fuels such as coal, he explained

First, all conventional gas is "shale gas," except for a tiny minority of highly atypical cases where reservoir sections have experienced prolonged high temperatures and matured further. Thus almost all natural gas ultimately comes from shale - fracking is merely extracting it at the source, where it does not significantly differ in composition from gas which has migrated to reservoir in conventional extraction. So, second, I'm suspcious of the use of c13 to differentiate fracking and non fracking sourced methane, but I'm not a petrophysicist. It should be related to the age of the fluid, and I don't expect shale gas to be substantially younger than reservoir gas in most cases.

On the second point, whether ¹³C can be used as a signal to differentiate fracked vs. non-fracked gas, the paper [1] does discuss this a bit. This seems to be the key paragraph:

Several studies have suggested that the δ¹³C signal of methane from shale gas can often be lighter (more depleted in ¹³C) than that from conventional natural gas (Golding et al., 2013; Hao and Zou, 2013; Turner et al., 2017; Botner et al., 2018). This should not be surprising. In the case of conventional gas, the methane has migrated over geological time frames from the shale and other source rocks through permeable strata until trapped below a seal (Fig. 2a). During this migration, some of the methane can be oxidized both by bacteria, perhaps using iron (III) or sulfate as the source of the oxidizing power, and by thermochemical sulfate reduction (Whelan et al., 1986; Burruss and Laughrey, 2010; Rooze et al., 2016). This partial oxidation fractionates the methane by preferentially consuming the lighter ¹²C isotope and gradually enriching the remaining methane in ¹³C (Hao and Zou, 2013; Baldassare et al., 2014), resulting in a δ¹³C signal that is less negative. The methane in shales, on the other hand, is tightly held in the highly reducing rock formation and therefore very unlikely to have been subject to oxidation and the resulting fractionation. The expectation, therefore, is that methane in conventional natural gas should be heavier and less depleted in ¹³C than the methane in shale gas.

[1] https://www.biogeosciences.net/16/3033/2019/

> So the shale gas revolution started in 2005, but the spike didn't occur until 2008?

That sounds reasonable, doesn’t it? I wouldn’t have expected a spike to occur at the start but rather a few years after when production has ramped up?

Yep, also be sure to read to the end of the article to get other caveats and criticisms.

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