This is what I use Kennas to evaluate, although I note that 10 millidarcies or above is okay. I also note that Arrow had a good drill recently with only 1mD I think, which is very surprising! I wrote this in the csm general thread some time back in the earlier days.....
1. Gas content - need to be 3 cubic metres per tonne or higher (I think QGC range from 3 - 9 on their drilling).
2. Permeability - measured in Millidarcies. Average is 50 (now I didn't read that in his document, I seem to think that was average of commercial wells). Richard mentions 10.
3. Gas Saturation - the higher the better obviously. High 90%'s is good.
4. Coal depths - generally 200m to 800m depth for coal seam gas. Gas can be up to 1000m, but must be highly permeable at these depths. eg ESG are deep, up to 1000m, but are higly permeable, and do have seams shallower on the way down.
5. Coal seam thickness - one would think the thicker the better. QGC and PES are finding good thickness, some 25 - 30 metres of seams. However, if it is thick, but not permeable, one can get more gas out of thinner, but more permeable. (QGC and PES drills are highly permeable so far)
6. Type of coal - eg coking coal is high in gas, however, as it has very low permeability, it cannot be extracted in most cases. Brown coals may be better for coal seam gas as more permeable.
7. Just because a company has gas-in-place, does not mean you can extract it. It can be mind boggling when looking at gas-in-place figures, but of no value if you can't get it up out of the ground.