Q.1) Is it really depleting? (Is some of the evidence not clear?)
A.1) Overall the bulk of the evidence does indicate probable depletion.
There are three clues:
i) Declining flow rates
ii) Declining flow pressures (after bulk of water cushion unloaded)
iii) Apparent drop in shut-in pressures from Horner Plot.
However, the apparent drop of 640 psi or 9.7% depletion factor using the Horner plot is invalid. The ISI extrapolation is invalid.
The shut in curve is not sufficiently developed for a reliable Horner plot. This gives an ISI pressure extrapolation that is too high. So is there depletion?
Answer: Probably, because the last measured ISIP of 5978 is higher than the FSI extrapolated pressure of 5935. Depletion of 43 psi is only 0.7% but we know it will be more as the ISIP has not yet stabilized.
Q.2) What would you do if you owned this well?
A.2) If you owned the well, you could:
a. Retest and run a much longer ISI period so that a good Initial pressure can be established, to compare with the FSIP.
b. Use the same gauges as in the first test, placed at the same depths in the DST string, to eliminate problems of miscalibrations between gauges.
c. If the ISI pressure of the second test is the same as the FSI of the first test it is truly depletion.
If the ISI pressure of the second test is higher than the FSI of the first test, the zone has pressured up again in the time between tests and it is probably a dual permeability system.
d. Use someone else's money to pay for this retest, as it does not look economic with such a rapid rate decline in DST 1.