On the shortage I can say with certainty there have been some near misses in recent times, most notably 2022, and it did indeed end up with a particular large gas user directed to cease taking gas.
I'll avoid names as I'm not sure if that bit's confidential or not but the location was Victoria and a direction means just that - you will not use gas. Bearing in mind the user in question is large enough that real time monitoring of their consumption is available to AEMO and others so any breach would be immediately identified.
Due to physical network constraints in the energy industry (gas and electricity) any discussion will commonly refer to the south-eastern states (NSW, ACT, Vic, Tas, SA collectively) as a separate place to Qld or NT despite the existence of a pipeline linking Moomba (SA) with Qld and also Qld with NT via Mt Isa (a major load). Noting that Moomba is linked directly to SA, NSW and ACT, and indirectly to Vic and Tas.
Reason being simply due to capacity constraints on pipelines - a bottleneck between Qld and the SE states is a few orders of magnitude more plausible and significant than any constraint within the SE states, although the latter isn't zero.
Ignore the numbers which are current data and will change but the map here shows the basics:
Noting that's only showing major pipelines, there's a lot of detail of lesser pipelines left out.
Present storage is as follows. Data in the table shows current gas in storage, the numbers on the map show forecast injection or withdrawal for today, 25 April. All figures are in TJ (terajoules):
In terms of supply, the key issues are the serious decline of production processed via the Longford gas plant in SE Victoria (where the Longford - Melbourne pipeline meets with the pipeline to Tasmania on the above map) noting that's by far the largest gas source in the SE states, indeed it's larger than all others combined. That's in very steep decline, capacity for this coming winter being limited to 700 TJ/d versus historic maximum capacity of 1168 TJ/d. Gas plant No.1 is now closed due to that, plants 2 & 3 are still running for the time being but that won't be for too much longer, the gas feeding them is running out.
For the others Moomba (SA), Lang Lang (between Longford and Melbourne) and Athena (SW Vic near the Iona storage) are also substantially down from their historic peak (noting that Lang Lang and Athena have always been relatively minor sources but Moomba is major - at it's peak it supplied the whole of SA, NSW and ACT in full). That leaves the Orbost plant, east of Longford, going strong although it's about the same size as Athena and Lang Lang, it's not major (and doesn't have the greatest track record for reliability, but that's another story).
Hence the plans to ship LNG in via a terminal at Port Kembla (NSW south of Sydney) being developed by one of Andrew Forest's companies. Also fairly advanced is a proposal to do likewise at Outer Harbour (Adelaide) whilst less advanced are two separate proposals near Geelong Vic.
Regarding that, Geelong isn't ideal due to capacity limits on existing pipelines. AGL did try to build an import terminal at Westernport, very close to the former BP oil refinery, but it turns out there's a wetland nearby.....
In terms of consumption, it's not as you might expect. On a cold winter day Victoria uses more than all other SE states combined, it's by far the largest user indeed it's around 60% of the combined SE states maximum demand. Victoria's demand is highly variable seasonally however and overall it uses just under 50% of gas between the SE states. NSW + ACT about 31%, SA 17%, Tas 1.7%
That's only looking at the south-east. I'll post some details for other states another time. Physically though Qld is connected to Moomba (SA) and Qld also connected to NT, but those interconnections are capacity constrained in practice.
Key concept to understand there is timeframe. Gas in the ground is one thing and determines future production. Gas produced over 12 months has a lot of relevance to company finances, tax revenue and so on.
When it comes to the ability to meet customer demand for gas however, very much shorter timeframes are relevant. Exactly how short depends on the detail, but it tends to be shorter in Victoria than elsewhere and comes down to around 4 hours during winter. So it's entirely possible to have a shortage of gas, an inability to meet consumer demand, despite annual production being adequate if the shorter term production is inadequate. There's a lot more to it than just looking at annual figures or even seasonal - a shortage and surplus on the same day aren't impossible.
Next level of complexity is with storage operation. Not only do they have limited injection and withdrawal rates but the two don't match and due to the need for gas compression, and in the case of Newcastle (NSW) and Dandenong (Melbourne) liquefaction, putting gas in is far slower than taking gas out. They're a lot slower to fill than to empty if operated to their limit of capacity.
With a further complexity that for compressed storage, most notably Iona, there's a threshold below which the discharge rate tapers off. Gas needs to be above that level to achieve nameplate MDQ (Maximum Daily Quantity). Below that and gas still flows but does so at an ever diminishing rate. Let the air out of a tyre, without any load on it, if you want to understand that concept better - as pressure drops, so does the flow rate.
My point being not to baffle with science but simply to say "it's complex" and that a lot of caution is needed in analysing physical supply data. Just because it's adequate over one time period doesn't automatically mean it works over a different time period.
Exports of LNG, the majority of gas extraction, and the majority of reserves are in WA, NT and Qld. I'll post figures for those later.