whilst we mark time , page-2

Sigh, I'd trade a few thumbs for some discussion here lol.

I have thought some more about seams of 100-200m thickness and some issues/opportunities they might present.

Kingaroy and Wandoan seams are something like 10m and 7m thick I recall ... for a coal density of say 1.4t/m3, the 73 mill tonne JORC resource at Kingaroy would cover an area of about 2.3km by 2.3km ... were the seam to be 100m thick, the area would be just 730m by 730m ... for Wandoan the 340 mill tonne JORC resource would represent an area of about 6km by 6km (or about 1.5km by 1.5km if the seam was 100m thick).

Subsidence associated with burning 7-10m thick seams at depth of 200-400m is likely to be quite manageable imo, and at approaching 400m depth there might even be little surface expression of subsidence.

But, 100-200m thick seams are another story ... I reckon if seams like that could be combusted for their full thickness (and I am not saying they can or would be) the surface expression of subsidence if combusted even at 400m depth would be ... ummmm ... an issue. How would a surface drop of 20-50m or more sound? What an eloquent way to create an inland sea lol.

So, if such seams are to be combusted I can see three ways of thinking about it:

1. Only a manageable 10-20m thickness of coal in the depth range of 200-400m could be combusted irrespective of the total available seam thickness if surface subsidence had to be managed w/o too much visible effect.

2. Given the massive energy stored per m2 of a 100-200m thick seam, much smaller areas need be combusted to secure a commercial quantity of syngas. So if this were the case at Kingaroy an area of 730m by 730m would be developed to supply a 400MW power station for 30 years (not 2300m by 2300m given the actual seam thicknesses). On this basis, rehabilitating the land afterwards may be feasible, as might aiming to leave the area as a potential deep water lake with beaches, golf course and associated prime residential frontages for a premium land development lol.

3. With current open cut mining throughout the Hunter Valley and Central Qld, the pits can be up to 0.5km wide and 6km or more long and generally 100m or more deep. When the operations are finished, the holes are not backfilled and there are mountains of heaped up stripped overburden nearby (often presenting acid leach issues). So would a couple of 0.5km wide 6km long UCG depressions of 20-50m or more really matter in such areas? In fact the UCG area would be much smaller than that for an open cut mine. If UCG could utilise a 100m thick seam the subsidence area would be perhaps no more than 1/5th that area.

So, with a view that UCG is "virtual coal mining", managing the subsidence from combusting certain super thick coal seams in remote/isolated areas may just be a perception thing? Afterall, huge open cut coal mines are dotted around the Hunter Valley in prime rural landscape!.

Like the subject title says ... just marking time 8))

Cheers
Dex