They will not be using material balance (pressures as Pet described above) for the reserves cerrtification. Am sure Pet knows this - seems he was showing the possible ranges of in-place on the basis of material balance calculations.
They will use mapping from seismic and well results (logs for porosity, saturations, and fluid contacts), a geostatistical program such as Petrel which ties the two and distributes reservoir properties and does the volumetrics, and combine that with a reservoir/outflow simulator which models reservoir/aquifer and wells/facilities backpressures to model abandonment pressure.
They will likely do the resoures in at least two ways - geostatistically by Petrel or equivalent linked to some type of reservoir/surface facility simulator as mentioned above (the probabilistic approach), and possibly hand mapping of the structure/net pay to develop deterministic results using calculated/estimated recovery factors.
Material balance or p/z plots have far too much uncertainty at this stage, as Pet pointed out: what is the pressure difference due to the production, what is the formation compressibility, is the aquifer providing pressure support, etc? Material balance could provide a negative indicator - compartmentalization or small reserve - if the pressures did not return to their initial pressure. Apparently that has not happened, which is GOOD. Usually material balance methods start being believed after10% or so of reserves are produced and there is a measurable pressure decrease.
Seems to me the question is what have they learned to date? TOT certainly are doing the work mentioned above internally and have a view of reserves/in-place volumes, probably a very good view to boot.
So, why would TOT want to drill an Ant - 7? Not sure, but speculating:
1. they want to delay the cert payment by, say, 90-120 days? Not likely unless they are conserving cash until 2017, which is a possibility (my company is). And maybe they like squeezing IOC to make them drop their asking price for a few % more?
2. so they could pay IOC more (or less) on certification?
a. I don't think they'd want to pay more.
b. Would they want to pay less? Of course. I don't know if there is a mechanism in the SPA for TOT to recover an overpayment on certification, but if not forget recovering those funds.
So if no IOC repayment on a reduced recert size, TOT would definitely want to ensure they were not overpaying and they would draw the fault as close to the current wells as possible.
If that interpretation was wrong, IOC could recover those funds on the recert.
3. right-sizing the LNG plant? doubtful, as most plants in the region are running 3.4-3.8 mtpa/train. Would they want a 5 mtpa/train, or larger - not sure why build big and costly in a soft LNG market
4. they do not think they have enough (7 Ts) for a 6.8 or 7.6 mtpa (2 train) plant and need to verify resources Thats a scary thought! But I don't think its correct - can't believe GLJ would be that wrong with the new well data.
5. Want to eliminate arguments about the reservoir size with IOC and banks for LNG lending? Knowing where the fault is and the reservoir quality over there will help answer a lot of questions
6. Other?
Assuming that the SPA specifies on a reduced recertification size, IOC must repay Total, I'd go for 1 and 5 as the reasons TOT may want to drill. Reduce uncertainty. Unfortunately, 4 may also be an option - prove up more gas.
Any thoughts/comments welcomed. Really thinking out loud and probably missed some (many) things.