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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[1] www.eia.gov/neic/experts/heatcalc.xls

[2] http://www.eia.gov/tools/faqs/faq.cfm?id=107&t=3

[3] http://www.climatechange2013.org/images/report/WG1AR5_Chapter08_FINAL.pdf
[4] http://www.eia.gov/dnav/ng/ng_cons_sum_dcu_nus_a.htm
[5] http://www.eia.gov/totalenergy/data/monthly/pdf/sec4_5.pdf
[6] http://www.eia.gov/tools/faqs/faq.cfm?id=667&t=8
[7] http://www.eia.gov/electricity/annual/html/epa_a_03.html
[8] http://www.pnas.org/content/109/17/6435.full#F2
[9] http://download.springer.com/static/pdf/5/art%253A10.1007%252Fs10584-011-0061-5.pdf?auth66=1401495762_5479423aee71642f65bd374b10555269&ext=.pdf
[10] http://link.springer.com/article/10.1007/s10584-011-0333-0/fulltext.html
[11] http://www.pnas.org/content/early/2013/09/10/1304880110.full.pdf
[12] http://www.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2014-Chapter-Executive-Summary.pdf
[13] http://www.eia.gov/dnav/ng/ng_cons_sum_dcu_nus_a.htm

Shale Gas: Water, Water Everywhere, but Not a Drop to Drink (2 of 5)

I'll first start by saying this post is not to serve as a complete justification or vindication of shale gas and hydraulic fracturing; it is to provide context. Context can make the case seem better or worse than we expect, but either way we walk away a little more informed.

That said, I outlined my list of grievances (which I believe most concur with) in my earlier post. I'm going to spike out my major concerns that I think merit a closer inspection first. Let's first start with the 1st grievance, that concerning water.

1) Exorbitant use of fresh water.

As I mentioned before, fracking operations use between 4 and 6 million gallons of fresh water in their initial hydraulic fracturing run to break open the shale and release natural gas for roughly a year. I calculated this to be the equivalent of the annual water consumption of 4 US homes per well. There are 400,000 gas wells in the US [1], and 40% of natural gas now comes from shale source [2]. I'm assuming all wells are equal in capacity (not true, but for our purposes not a bad approximation). This means there are 750,000 homes-worth of water being consumed each year in shale operations. Vikram Rao, author of Shale Gas: The Promise and the Peril, believes that underground salt water can be used for the initial frack and that this should be mandated through regulations. Until best practices reveal the means by which salt water can be used, gas drilling companies will use millions of gallons of fresh water for fracking. I thought this was a lot of fresh water. Turns out it's only part of the story.

All thermal power plants require cool fresh water as a heat rejection mechanism. Power plants prefer fresh water over briny water for the same reason fracking wells do: lower risk of scale formation, less corrosion susceptibility, easier materials compatibility. The thing is, power plants use A LOT of water to keep cool. 49% of all water withdrawals in the US is for power plant cooling. That's 200 billion gallons a day. That's a little less than 2 Mississippi Rivers-worth of water. The next closest is irrigation to grow our crops at 31% [3]. I find this number staggering. Admittedly, this is for withdrawals which is different than consumption, and depending on the type of cooling system used, a lot of that water may be returned to the environment. 

Regardless, it's still a large number that dwarfs the water consumption used in fracking. A report from the Harvard Kennedy School estimates that water used in fracking constitutes less than 10% of the water consumed when shale gas is used in a high efficiency combined cycle gas turbine and low-water consumption recirculating cooling (the typical construction cases these days), and that this is a factor 2 lower water consumption/MWh than coal (which uses 2x as much water/energy content in washing coal than fracking) and factor 4 better than nuclear [4]. The Kennedy report is quick to add that hydraulic fracturing water consumption can stress water resources locally due to the short-duration/high-rate at which water is consumed, even though the gross consumption is relatively small. I'll add that the water consumption for wind and solar PV are essentially zero. 

There's a few things I think are important to point out here. The reason natural gas comes out so far ahead of coal and nuclear is mainly due to power plant thermal efficiency. If your power plant is less efficient, more thermal energy needs to be rejected for a given amount of work, so more water is necessary to keep things cool. Combined cycle gas turbine plants are basically two power plants in one (a gas turbine top cycle and steam turbine bottoming cycle), and as such run somewhere in the vicinity of 45% efficient. You can't run a gas turbine on coal (some people are trying though), so you can't leverage a topping cycle, so you're stuck with just one steam turbine cycle and an efficiency of about 33%. Nuclear is de-rated on efficiency for safety and process considerations, so comes in around 29% [5]. The other element I was surprised about was the water intensity of other energy extraction processes. As I mentioned earlier, coal mining is about 2x more water intensive that natural gas fracking, and uranium mining 10x more intensive. It seems to me that not only are we using too much fresh water with even our lowest demanding energy process, but we completely ignore significantly more demanding processes. I find that concerning. The silver lining about all this water research is the fact that 2 renewable energy generation methods, wind and solar PV, use no water at all. This point I believe should be emphasized. 

I think that water use in energy generation is actually a really big problem. It seems in this regard shale gas and hydraulic fracturing for combined cycle gas turbine plants are actually better than the conventional coal or nuclear power plants. While water is a large problem, it's not the only one. We'll look at other environmental impacts in subsequent posts.

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[1] http://www.eia.gov/dnav/ng/ng_prod_wells_s1_a.htm

[2] http://www.eia.gov/forecasts/aeo/MT_naturalgas.cfm#natgas_prices?src=Natural-b1

[3] http://pubs.usgs.gov/fs/2009/3098/pdf/2009-3098.pdf

[4] http://belfercenter.ksg.harvard.edu/files/ETIP-DP-2010-15-final-4.pdf

[5] http://www.eia.gov/electricity/annual/html/epa_08_02.html

Shale Gas: An introduction (1 of 5)

Shale gas and hydraulic fracturing is a lighting rod topic in the clean technology sector...which is why it's so much fun to write about. In analyzing the topic over several months, my personal opinion has changed from that of "shale gas is a tempting distraction from what we really need: energy efficiency, wind/solar deployment, electric vehicles, energy storage" to "shale gas and hydraulic fracturing isn't that bad, and the wealth creation, if invested properly (and it needs to be), can fund deployment of more expensive energy systems while still achieving climate goals." I'm first going to write about what is shale gas and what the risks are. I'll discuss why some of my major concerns are reasonably addressed and how we could best manage this newly available energy source effectively in two separate follow-up posts.

Let's first define a few things. "Shale gas" is natural gas (methane) and natural gas liquids (larger molecules in a liquid state found with methane: ethane, propane, and butanes) found locked up in impermeable shale rock (sedimentary rock made from compacted mud, clay and silt). Because of how common the conditions are for shale gas to be formed (350-500 million years ago, algae died and settled on the bottom of sea and river beds, covered by silt and clay, and cooked under pressure and temperature), there's a lot of it.  Shale gas has been rendered an economically viable source of natural gas by "hydraulic fracturing," which is a process of drilling down into gas-containing shale, injecting high pressure water, sand, and some chemicals to break open the impermeable rock and increase porosity, allowing the gas to flow out and be collected. "Proppants" like sand hold open the fissures, allowing the pressure to be relaxed, the water removed, and gas to flow out. The water that comes back (not all of it does; most stays injected underground) is called "flowback water."

The water, sand, and chemicals are pretty key components to the hydraulic fracturing process. One well will use between 4 and 6 million gallons of water in its productive lifetime, which is about 1-2 years. To put this into context, it's about 10 olympic swimming pools, or the amount of water that 4 average homes will use in a year [2]. That's a lot of water for one well. In terms of what's also injected, water makes up ~92% of the fracking fluid, sand ~5%, and the remaining 3% is chemicals comprised of (mostly) acids and pH buffers to prevent scale build up (more on that), biocides to kill bacteria that would return topside with the flowback water, and detergents and oils to change fluid properties. The blend and chemicals change from location to location and are optimized for a given geological area. [3] As I mentioned, most of the water (and chemicals) stay injected in the well: 65-85% of the injected water stays underground and 90% of the chemicals are either consumed in process (like acids removing scale) or also stay underground.

The stuff that comes out is salty. Super salty. Like 10x saltier than ocean water. Stuff that's literally 25% salt. And there's 1.5 million gallons of it to deal with. That's 100 tanker trucks. Of super salty water. That you can't simply pour into the nearest river. In almost all cases it's trucked to special EPA-controled injection wells that basically bury the salty brine in similar geological structures as it came [4]. The reason the fresh water that goes in comes out super salty is because the water that's already down there has been sitting in minerals and rock formations for hundreds of millions of years; the fresh water mixes with it and flushes some of it up to the surface.

Of course after the water comes out, the natural gas that we went through all this trouble to get finally comes out. A well will produce about 250,000-400,000 thousand cubic feet over its lifetime (enough to heat 6500 homes for a year [5]), and at $4/MMBTU (million BTUs) and 1 thousand cubic feet per MMBTU, is valued at $1-1.5 million. But natural gas isn't the only product that comes out; there's also natural gas liquids (NGLs). These are higher-valued commodities that can replace oil as petrochemical feedstocks, and as such are priced similar (but at a slight discount) to oil: something like $70/barrel (42 gal). In current gas plays, there's about 4-12 gallons of NGLs per thousand cubic feet of natural gas. This means that the value over the course of the well is something north of $3 million for NGLs. Most of the value is in these commodity chemicals. This weight toward NGLs basically means that natural gas is viewed as a byproduct and suggests that low prices will continue for some time.

I've summed up the list of grievances against shale gas and hydraulic fracturing as the following:

1. Exorbitant use of fresh water
2. Current inability to treat or dispose of the produced water from wells
3. Accidental spills and leaks of chemicals and methane into surface and groundwater
4. "Fugitive methane emissions:" methane released accidentally or purposefully into the atmosphere
5. Drudging up of natural radioactive sources in flowback water
6. Discounting of renewable energy technologies

In a second post, I'm going to address 1 and 4 directly with personal analysis, as they were my primary concerns when I started learning about shale gas, and I'll discuss what I've learned about 2, 3, and 5 from research. I'll write about 6 in a final post as I think it merits a greater discussion.

Soooo...yeah. There's a lot going on with shale gas. My 3 little (alright, maybe not so little) posts are certainly not going to be the final say on the matter, but I hope it at least puts things into perspective and adds some understanding. 

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[1] Rao, Vikram, "Shale Gas: The Promise and the Peril." RTI International: 2012
[2] http://www.epa.gov/WaterSense/pubs/indoor.html
[3] http://www.halliburton.com/public/projects/pubsdata/Hydraulic_Fracturing/fluids_disclosure.html
[4] http://water.epa.gov/type/groundwater/uic/class2/
[5] http://www.eia.gov/dnav/ng/ng_cons_sum_dcu_nus_a.htm