Wednesday, May 28, 2014

Shale Gas: Fugitive Methane Emissions (3 of 5)

An article recently cropped about natural gas methane emissions and it prompted me to pick up where I left off about shale gas. For me, this was more of a question about widespread use of natural gas than shale gas in particular, but research revealed shale has some unique attributes that merit particular attention.

The whole crux of the matter with methane emissions from natural gas wells and associated infrastructure is, "are methane emissions currently high enough to offset the gains in efficiency from burning natural gas?" Natural gas burns more efficiently in boilers [1] and power plants [2], however vented methane from fracking operations and infrastructure leaks has a very high radiative forcing number (86 and 34 at the 20- and 100-yr timeframes respectively) [3]. So, which one wins? Efficiency (less fuel burned means less emissions)? Or leaks (fugitive emissions impact the climate more)? To answer that question, we can take a look at how much more efficient natural gas is over other sources of fuel, the respective greenhouse gas impacts, set a maximum natural gas emission threshold, and then see what the actual leak rate is to determine whether we're over or under.

From the EIA, electric power (33%) and industrial uses (31%) are the largest consumers of natural gas [4], but curiously most of the natural gas in industry isn't in plant and process heating; it's as feedstock (65%) and other non-heat-and-power uses [5]. From that perspective, we'd be fine just looking at the power plant sector. Natural gas is 50% more efficient than coal in power plants [6], and has half as much CO2 per unit energy burned [7], so solving for a maximum leak rate, it ends up being no more than 3.3% for the 20-year outlook and 12.5% over the 100-year outlook. Based on an Environmental Defense Fund/Princeton analysis on similar benefit scenarios, our analysis is looking pretty good [8].

So how are we doing now relative to the actual methane leak rate? Well...depends who you ask. A number of papers have been published to look at exactly this problem. A group of professors (curiously from the evolutionary biology department) pegged fugitive emissions from 3.6-7.9% using a 2010 EPA report [9]. They were panned by another group of Cornell professors, this time from a chemical/biological engineering department and earth/atmospheric sciences department [10], reporting EPA 2011 stating 2.2%. One multi-university team recently measured methane emission directly [11] and calculated 0.42%. I did my own analysis based on EPA's 2014 GHG report and found 1.0% [12] [13].

Basically, this is still early science and a precise number has yet to be nailed down, but by the sounds of it, it doesn't appear to be above the 3.3% threshold for the 20-year timeframe. So that means that we don't seem to be doing any worse for the climate from a greenhouse gas perspective by exploiting natural gas, but that also means we aren't really doing any better, and if you believe anything climate models tell us (and really, you should, because they're correct), we need to be doing better fast. Right now natural gas is 85% of coal greenhouse gas emissions if you take the EPA's 2011 value; it could be 55% if we tightened up our natural gas infrastructure. And it's not like we're doing it just for the sake of the climate (though that's reason enough); that's lost revenue. $2.2 billion/year is leaking out from poorly designed and maintained infrastructure and processes, and that's only set to increase if natural gas development expands. If that isn't a business opportunity, I don't know what is.

Natural gas currently isn't doing us any real favors right now, but it does hold a lot of promise for significantly lowering the carbon footprint of our electrical grid in a very short timeframe. We need to survey the industry for best practices and standardize them, or help bring to market solutions that would capture that lost value. We also need to seriously consider how to best implement natural gas into our energy portfolio to reduce climate risk exposure. It's not a silver bullet (nothing ever is), but at least it's another bullet in the chamber. I'll be discussing my thoughts on economic and environmental strategies in a final post about shale gas soon.


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