Notes from AGM, page-26

You can't actually measure expanding drainage area. What you actually measure is the pressure drop vs volume of water produced.

You back out drainage area from this, but it requires a lot of assumptions. It may be that drainage area is changing but it also could be something else changing.

So when they started, they would have produced, say, 10,000 barrels of water and then when they shut the well in and measured the buildup pressure, it might have dropped 100 psi.

Then after the workovers and all the time it spent shut in, they might have produced another 10,000 barrels of water but this time, when they shut the well in, it only dropped 50 psi.

That tells you the well is 'seeing' a larger volume of water. The simplest way to match that in the equation is to make the drainage area higher. But that relies on the assumption that nothing else has changed in the reservoir. That may not be a valid assumption.

Regardless, if you're not dropping the pressure as much as you were before for the same volume of water, that means you have to pump more water to get back to desorption pressure, which is what they are saying in the presentation.

I don't know what to make of it and I'm not sure STX really do either. I understand why they are claiming larger drainage area (it's the simplest explanation) but you still need to explain how a well you flowed for several months suddenly sees a larger drainage area after you shut it in.

I actually think the answer is more likely to be mathematical than physical. Well modelling involves a lot of simplifying assumptions and one of these usually is the assumption of what's called pseudo-steady state flow (PSS). If the well isn't in proper PSS flow then well models based on that assumption may give strange results. It's a bit hard to explain my reasoning in layman's terms but I suspect these wells aren't in proper PSS flow because of the frac.