Not a geo here V8 so may be way off the mark...but would think...

Not a geo here V8 so may be way off the mark...but would think it's a similar exercise to horizontal fracking just without the juice. Initially you set up the verticals and extract from there and then as you exhaust the vertical you bring in the horizontal drill rig.

From this site seems the verticals can flow for years. Biggest distinction I can see is that the coal seams are much shallower than shale deposits so 100s of metres as opposed to 1000s of metres. So down the track I can see them bringing in a horizontal rig unless of course the one they bought can accomodate that kind of drilling. With all the developments going on in the US re fracking rigs I wouldn't be surprised if they havn't come up with some kind of set up that can convert vertical drill rigs to be able to drill on the horizontal (pure speculation on my part).

https://www.naturalcsg.com.au/industry-operations/drilling-well-construction/