The Word For The Day: Wobbe Kenobi -- April 5, 2016

A huge shout out to RBN Energy for introducing me to a new word: Wobbe. I guess the word is spelled with an upper case (or as we used to say when I was in second grade with Ms Priebe as my teacher: a capital letter) "W."

Wobbe is a standard measure of the heating value of a volume of natural gas flowing through a hole of a given size over a given length of time. Okay. It seems confusing, but the formula to calculate the Wobbe number is very simple:

Divide the gross caloric value of the gas in Btu/cf by the square root of the gas’s specific gravity with respect to air; overseas, the units of measure are megajoules/cubic meter at a standard temperature of 15 centigrade or MJ/Scm.

Yup, that's all there is to it. LOL. They had me at "Btu/cf."

When talking "international," stick with MJ/Scm."

That's the basic idea. After that it gets, well, dare I saw, more complicated?

Bottom line: the higher the Wobbe, the richer or hotter the gas or LNG.

Japan and South Korea standards call for gas that is rich and hot.

US and UK standards call for "lean" gas with a low Btu/cf.

And, of course, the EU: "a wide range of standards."

Lean, medium, rich:

• Russia: natural gas is "lean"; nearly pure methane (C1); relative low Btu/cf; low Wobbe
• North Sea: gas is "medium"; mostly all methane but some ethane (C2) and a tiny percentage of other natural gas liquids like propane (C3) and butane (C4)
• rich: more ethane and other NGLs); high Wobbe

Reference:

• pure methane: a Wobbe of 1,363 units using the Btu/cf approach / 50.7 using the Mj/Scm approach

Sources/Wobbe (Mj/Smc)

• Alaska: 50.2
• Norway: 52
• Qatar: 52.5
• Australia NWS: 53.5

A significant number of LNG import terminals around the world have Wobbe "correction facilities of one sort or another to either "enrich" or "derich" gas immediately after it is offloaded from LNG vessels and regasified -- and before the gas is fed into the receiving country's pipeline system. == RBN Energy.

So, let's see what googling Bakken gas Wobbe reveals. And here it is, from Midwestern News, not much, but the first hit that includes all three terms:

• For example, the Wobbe Index of the associated from the Three Forks area is on the high side.

Aha! This looks like the mother lode (or at least one mother lode): Gas Enhanced Membrane Fuel Gas Conditioning Solutions for Compressor Stations with Ultra High BTU Gases in Oil-Rich Shale Plays (a PDF, industry journal article):

Let's run through that paper just for the fun of it. It's undated but the more recent reference is from a December, 2010, journal article, so at least we can assume it was written after Bakken boom reached its stride.

From the abstract:

• in condensate-rich shale-gas plays such as Utica, Bakken, Niobrara, Marcellus, Eagle Ford [and I assume the Utica could be added], the raw shale gas is super rich in heavy hydrocarbons
• these raw gases do not meet the methane number, Wobbe index requirements for fuel gas
• problems include pre-detonation, de-rates, emissions issues

Page 12

the ethane content goes up from 12% in Eagle Ford shale to approximately 23% in the Bakken shale along with a considerable increase in the amount of C3+ components as well.

Page  13, this table (the data is dynamic; the comparison between the various plays may be relevant):