It's telling us that the field is declining, like every gas...

It's telling us that the field is declining, like every gas field does. But if you do a decline curve analysis it actually seems to be showing signs of tight gas support, which is not unexpected. That's a good sign for long term EUR.

At any rate I can promise you that NSAI know how to take field decline into account when they calculate 2P reserves! And they currently estimate 2P for Mereenie as 140 PJ. For comparison current production is ~10PJ per year so there's a fair bit of life in the old gal yet. That's without any reserves attributed to the Stairway.