Naval
An interesting problem. As you didn't mention anything about perforation intervals or number of zones connected to the well I have to assume that an additional zone suddenly started to produce for some reason. It is apparent that the gas has not hurt/displaced the oil zone so it should be from a different zone. It could be due to a change in an offset well (e.g. shut-in of an offset or start-up of injection) that has changed the formation pressure in a zone that was not producing before.
Or it could be a new perforation interval suddenly cleaning up. It wouldn't take much of a change in one or two perforations to allow gas to pass at this rate. Even if there is only one perforation interval I would look to see if there are several fracture or permeable zones that might be possible of production.
In looking at your plot closely three changes may have occurred; On ~15 May the oil production rate stabilizes and become much more consistent than before. Without THP or Choke data I can't tell what may have happened but the trend shows an apparent change. On ~15 June you have the large gas production increase with no change in oil rate. This suggests a new zone is producing. Gas rate continues to increase from that point and I do not see the decrease you mention. Finally, on ~8 July the oil rate appears to improve slightly. Look at the oil rate at the end of the plot vs the earlier data....there is more 'white space' below the oil rate trend and the rate appears to be slightly higher. That could suggest some oil from the "new" interval is starting to be produced. As gas is more mobile than oil the gas may have arrived 'first' and the oil is now arriving.
Next Steps:
I would look at the well logs and see if there were any productive intervals that might be capable of production. Of course, if you have a PLT of the well you can look at that to see what was actually producing. I would also look at the offset wells and see if the zones producing in those wells could suggest productive intervals. And finally, I would examine the completion operation to see if there were any differences between perforation performance of the different intervals. For example, the first zone might be shot underbalance but subsequent zones are all shot on balance/overbalance.
Second, I would look for changes in offset wells back several months particularly a shut-in of a producer or changes in an injector. The timing is very important but they do not have to coincide with the gas production. I have seen changes in offset production delayed by weeks after a water injector shut-in...and I have seen production changes after only a few hours. I have also seen strong responses from producers that were interfering with each other. I would not be too concerned if the zone in the offset is not a good correlation with this well. With a fractured reservoir and difficulty correlating flow through layers it is sometimes difficult to know how oil flows through the reservoir.
Good luck in your well review,
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Dan Gibson
Completion / Well Integrity Advisor
Gibson Petroleum Consultants
FulshearTX
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Original Message:
Sent: Aug 16,2014 04:44 AM
From: Naval Dubey
Subject: Onshore Oil Well:Gas Rate abnormality indication
The onshore oil well having reservoir pressure above bubble point pressure. The common Oil pool has fractured basalt basement containing five wells.best vertical well is giving constant oil rate,gas rate & THP having 1600 m vertical depth but suddenly one day gas rate had shown 200 m3/d increased but there is no change in Oil rate and THP and now from that day only drop of 50 m3/d of gas rate is observed in that particular well.
see the attached plot.
what is this indication?
can anyone suggest?
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Naval Dubey
RE
GSPC
Gandhinagar
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