water production issue in dry gas reservoir

[Chee Koh Peh]

Dear Smriti,

(1) If the reservoir is a channel sand, then there may be large scale heterogeneity and the water break though may be due to high perm streaks that are in communication with the aquifer, rather than a uniform upwards movement of the GWC.

(2) Have you looked at the pressure depletion trend in all the wells of the field? Is the pressure depletion trend similar in all wells? If it is not then you have compartments and this may explain the difference between the wells behaviors you see in the field.

(3) Assuming the flowing material balance P/Z plot is correct, for you to have a GWC contact and not to see any pressure support from an aquifer, would require the aquifer to be very small, and/or compartmentalized.

(4) For noticeable waterdrive the aquifer needs to be at least 20 to 50 > than the size of the reservoir, remember waterdrive is provided by the expansion of the aquifer volume.

(5) Additionally gas reservoirs under waterdrive are rate sensitivity and this can mask the strength of the waterdrive. For example if you are producing the gas reservoir faster than the aquifer can provide pressure support, you may not see any noticeable aquifer support.

Rgrds

Chee Koh Peh

[jsusilo]

I would suggest to first look at all available logs (if available) and see weather or not there's disconnect in the OGWC (if you do then you know right away you may have some type of heterogenity as already mentioned in previous post). If in fact you do have some type of heterogenity, you could confirm it through interference test (depending on quality and characteristics of the reservoir this may take too long to be practical). You may also want to look for structural features, does the well that started producing water happen to be the deepest / nearest to potential aquifer.

The other thing could do is to compare well performance / productivity index (if well test data is available), because the poorer the well the more likely to cone early (requires more drawdown for the same cubic feet of gas). If you see a trend that way perhaps your worst well gives you indication what may come ahead in the rest of (better) well meaning its not localize but rather systemic. You may also want to compare cum gas production, are wells that shows increased WGR happen to be well that have been put on production longer, it is possible that few wells have been produced significantly harder (above the critical cone rate) and hence coning up much earlier then the rest.

[Smriti]

Thank you Chee..
This info is very useful.
Pressure depletion trend is almost similar but in one well water suddendly started coming some 3 months back and now that well started showing somewhat constant pressure (showing compartmentalised water support..)
also in some wells no gas water contact is mentioned but water sands are present.In that case is it possible that water cut can occur?