What does the word “signature” mean to you? My signature, usually, is a single paw print on the belly of anyone who will let me jump up on them. (Note: my master does not like it when I do this. Other humans don’t seem to mind too much, tho.) Signatures mark an identity, and just like humans and dogs can have signatures, so too can natural gas.
Now, there’s a lot to learn about what this means. Often called a fingerprint, an isotopic analysis of gas will tell you (in relative terms) what one gas looks like when compared to another. Understanding the details can be rather complicated, even for a dog, but the most simple way to explain it is to say that there will be two numbers, called deltas, that come back from the isotopic analysis. These numbers describe the carbon and the hydrogen of the gas. That is to say, CH4 is methane… and it is made of one carbon for every four hydrogens.
Carbon and hydrogen won’t just be carbon and hydrogen. They’re actually a mixture of regular old carbon and fancy carbon isotopes (called C13); also, a mixture of regular old hydrogen and fancy hydrogen isotopes (called deuterium). The details of this mix–how much of this is mixed with how much of that–is the “delta” number. You get one number for carbon and one number for hydrogen. These wind up as a point plotted onto a graph.
They are almost always a negative number. There are different ranges into which the numbers can fall. The big question in a case of methane migration will be whether the gas that migrated falls into the “thermogenic” (heat-generated) or the “biogenic” (biologically-generated) range. Thermogenic gas is the type for which companies drill. Not only should the migrating gas be in the same range as the gas at the origin, the absolute values should also be quite close.
When the numbers get plotted onto a graph, you would see a dot for, say, a water well, and another dot for, say, a nearby gas well. You look to see if these plot on top of each other. It is important to keep in mind that the isotopic analysis does not tell the entire story.
There are more factors than just the isotopics because gas composition can change as it migrates. Also, you want to know what the prior conditions were regarding any affected water supply. If you do not have a pre-drill test on your water, then I hope you can get one soon…
Well, I don’t know about you, but my mind is dog-tired. Now, it’s time to lay in the sun and take a nap…