mel's riflebird e6 desorb results, geo help?, page-16

Gents,

I guess one thing I didn't mention is that slim cores don't show all the detail you would like. In low rank coals you can get a blocky type cleat that is very large. You would expect to see some of this in core but not very much.

The best coal is black and glossy but I will repost something I did on another forum that might help:

Water content inherent in the coal is not the important factor. That type of water is held within the coals chemical structure and is not given off during dewatering.

Gas and water that affects coal seam gas deliverability is held in the pores of the coal. Saturation is the important factor here as pores that are not occupied by gas are generally occupied by water. This water needs to be pumped to reach a reservoir pressure that is equally to the critical desorption pressure.

The higher rank coals are capable of adsorbing more gas as there are more sites for adsorption as volatiles are driven off during burial or metamorphism. Rank is a double edged sword because higher rank coals are generally less well cleated than lower rank coals. C.f. a typical Bowen Basin coal at a typical rank range of RoMax 0.9 -1.7 with a perm of a few milli-darcies and a Surat coal between 0.4 - 0.8 with perm in the order of 1-3 Darcies. There is a little bit more to it than that but that is the general gist.

So anthracite as the highest rank coal can sorb more gas but you will find these in the deepest areas of the basin.... I havent seen a rank map for the CMB so not sure of their occurrence.... as the Bowen is my expertise. However they do form around intrusions as well but these generally arent good things for gas extraction either. So while having good gas contents Anthracites generally have poor permeability.

Really the make or break in CSG is complex relationships that can be formed between Gas Content, Permeability, Saturation, Seam Thickness, Seam Ash, Gross coal, principal stress orientation and coal rank. It is the combination of these factors (among others) that determine the most suitable drilling and completion methodology that you would use.

So some scenarios are -

Surat - Very high perm, low to moderate gas contents, low - med and high saturations,low rank, good gross coal in seam packages with lots of partings = good vertical production wells reasonably tightly spaced.

Bowen - Very low perm, high gas contents, thick clean high quality seams, reasonably low to moderate gross coal = horizontal completions.