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Natural gas:

...is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium.

I saw the graphic below in the BBC News article Trump climate: Challenges loom after Obama policies scrapped. It lists natural gas as the source of about 33% of the US electricity generation in 2015, but also lists "Other gases" as the source of less than 1%. Presumably it is a meaningful fraction of that 1% or else the BBC would not have included it. While the source of the data is listed as the US Energy Information Agency, the graphic itself was prepared by the BBC if I understand correctly.

Are thee other gases available from the Earth that could account for this fraction of 1%? I don't mean gases that are produced during an industrial refinement process, but perhaps gases that were simply separated. Just for example could it be natural propane? The same Wikipedia article mentions heavier hydrocarbons, but I don't understand if these are already present in the Earth and just being separated, or if they are produced primarily as reaction products.

EDIT: Based on comments, a substantially different source of gas that was chemically similar to natural gas would still be of interest. So just for example, methane from a bog should count in this case, since it does not involve many of the geological processes involved in the production of fossil fuels (e.g. the same timescales or temperatures).

enter image description here

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    $\begingroup$ I don't know the data or field well enough to know if it qualifies or makes up the leftover, but seems landfill gas is a bit different from natural gas? $\endgroup$ – JeopardyTempest May 28 '17 at 8:05
  • $\begingroup$ @JeopardyTempest well landfill gas is also mostly methane, so in terms of chemistry it's not going to be any different. $\endgroup$ – Gimelist May 28 '17 at 8:11
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    $\begingroup$ @Michael, that's what I was thinking, though saw natural gas may truly be defined as some sort of mixture, so perhaps it'd have a standard, which might mean they classify them differently despite being basically the same idea? Certainly could be the same, though. $\endgroup$ – JeopardyTempest May 28 '17 at 8:15
  • $\begingroup$ @Michael I guess the way the question is written you are right. Landfill gas is really coming from a large, man-made bioreactor so it wouldn't count at all. But methane from a natural one like a bog, something that doesn't involve geological timescales and conditions, that would be good to know about. So I'm going to alter the wording to include this. $\endgroup$ – uhoh May 28 '17 at 8:45
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    $\begingroup$ @JeopardyTempest thank for that thought! I've modified the question so that naturally occurring methane produced in a substantially different way should be counted. $\endgroup$ – uhoh May 28 '17 at 8:50
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Fred's answer looks correct, but in this case, the source is right there under the chart.

US Energy Information Administration (type "other gases" in the search box)

Explained here in the footnotes

Other Gas includes blast furnace gas and other manufactured and waste gases derived from fossil fuels.

0.3% if anyone is interested. Prior to 2011 the definition of other gases was different.

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The category "other gases" may not solely include other naturally occurring gases extracted from the Earth.

As you state natural gas is predominantly methane, extracted from the Earth.

Another type of gas commonly used is petroleum gas, which is prepared by refining petroleum of wet natural gas. Petroleum gas is propane or butane.

Coal gas, which was manufactured from coal and largely consists of hydrogen, carbon monoxide and methane, is no longer manufactured or used.

Another type of gas that could be included in the category is biogas, which is a manufactured gas made from biological waste products, such as: manure, sewage, food waste and green waste. Biogas is predominantly methane.

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    $\begingroup$ I have a hunch that you are right, that "other gases" does not primarily consist of primary gases from the Earth, and likely does refer to source such as the several you've identified here. While "bog gas" might qualify as a source of methane other than "natural gas", I doubt it was a substantial fraction of the <1%. Thanks! $\endgroup$ – uhoh May 28 '17 at 9:18
  • $\begingroup$ Biogas is more likely to have been included under "other renewables" than under "other gases". You can see eia.gov/energyexplained/?page=renewable_home . $\endgroup$ – Pere May 28 '17 at 15:00
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LPG ( liquid petroleum gas) is primarily produced with "natural" gas. It is separated from the methane by condensation ( in "gas plants" ) because it is more valuable . It does not require pipelines for distribution ; ignoring the fairly recent development of LNG ( methane) facilities. "Earth" gas seems a strange term; There are wells that produce primarily CO2, There are wells that produce 75% H2S - Pincher Creek Canada ,( I believe Shell has a field in LA that produced more than 75%.). And do the sub-sea hydrates count ? Some references say they hold more methane than all traditional sources. The CO2 is used to help flush oil and gas from traditional wells so thereby could ultimately generate electricity. My point is that TV "mockumentories" are not a good source for comprehensive facts.

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  • $\begingroup$ Are sub-sea hydrates basically typical natural gas that escaped once, only to be trapped again on the way to the surface? If that's the case, it may be an issue of semantics if it should be called natural gas or not. I'd guess not, but others may think differently. Your answer gives a lot to think about, thanks! $\endgroup$ – uhoh Jun 22 '17 at 14:25
  • $\begingroup$ I suggest checking Wikipedia ( methane hydrate).. $\endgroup$ – blacksmith37 Jun 22 '17 at 14:55
  • $\begingroup$ I'm not sure there is any Wikipedia article that states authoritatively if the subset of sub-sea methane hydrate which originated as natural gas then later being trapped in ice, is still considered natural gas or not. If you have a link to a specific paragraph that resolves this question please post it! $\endgroup$ – uhoh Jun 22 '17 at 15:07
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    $\begingroup$ I think Wiki states there is no consensus on the methane source , which is what i remember. $\endgroup$ – blacksmith37 Jun 23 '17 at 14:58
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To add on to Fred above - There is something called 'Underground coal gasification' where you basically react coal with steam and oxygen underground to produce a stream of carbon monoxide and hydrogen (plus minor methane). This can then be burnt as fuel or used in Fischer-Tropp manufacture of hydrocarbons.

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  • $\begingroup$ Wow I'd never heard of underground coal gasification, thanks for this! How nice of them to have proposed a “Clean Cavern” concept; I'm not sure what the alternative was. Let's hope there aren't too many leftover pockets full of carbon monoxide out there for future generations to inadvertently discover! $\endgroup$ – uhoh Jun 22 '17 at 14:22
  • $\begingroup$ For that matter, coal gas was widely used prior to extensive natural gas development. Coal would be used to make gas in above ground plants in different neighborhoods and piped to houses for use in their gas lights. Unfortunately, these plants left a legacy of coal tar and semi-volatile organic compound contamination in the soil. $\endgroup$ – haresfur Jun 22 '17 at 23:14
  • $\begingroup$ Yes, in the days of 'coal gas', suicide by putting your head in the oven (unlit, with the gas on) was apparently quite commonplace. And for a while after the introduction of natural gas, people would try the same thing, and end up blowing up their house. $\endgroup$ – Andrew Jon Dodds Jun 23 '17 at 7:21
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If you watch older British ( and some American )films you will see large gas accumulators ; typically 50 M in diameter and in height with external steel framework which permitted them to rise and fall depending on storage volume. This was called "water gas" which sounded better than coal gas. There are some "fire flood " fields to produce regular oil and gas ,And kerogen ; air is blown down some wells to burn oil/gas in situ and oil and gas are produced at other wells. Usually the air is alternated with water to also get a water flood.

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  • $\begingroup$ I've seen them in person when I was young. I'd ride past them every few weeks or months and they'd be at different heights than the previous time, never really knew what they were for until now :) $\endgroup$ – uhoh Jun 23 '17 at 19:21

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