Cum. production doesn't equal the initially tested production rate.

[HarrisonH]

I've got a special problem. Here's the scenario:
* Many wells were completed in three separate fields. This was some 40 or 50 years ago.
* The three fields are within an area of about four townships
* Geological work shows the fields to be nearly identical. Testing for each field shows large amounts of HC's are present. The HC's in each field are similar in amount, location (same sands), and production rate.
* In two fields, total production was consistent with initial tests.
* The other field missed it's mark by an absurd amount. Cum production revealed about 95% less mcf/d than what was originally expected.
* I believe it's a problem of stratigraphy, not structure.

When given old and often times splotchy well logs/summaries, where would you begin (from an engineering standpoint) to attack this problem? I'm looking for some sort of inconsistency that could explain why cumulative production was so bad in the third field. I realize the possibilities are almost endless, but in a broad sense, what would you advise looking for while in the process of compiling all of this raw data?

 

[DrillerNic]

If it's gas, I'd start with a P/Z plot to see if the third field isn't compartmentalised- it not then start looking at the wells- did they perforate the right place? Could the wells be damaged in some way that sort of thing. Then start looking at the geology ... sands get poorer quality or something?

 

[HarrisonH]

The production data is the problem. It almost looks like they produced about one day out of the month, and missed huge pay zones for no apparent reason. In my opinion, they did not perf the right zones, but I can't for the life of me figure out why. When looking at the logs, the zone they should have perfed is a no-brainer, but this was a respectable company, so I've got to give them some credit. Yea, the wells being damaged is the most likely scenario. They used too heavy of mud for sure. Sand quality is high.

 

[DrillerNic]

That makes me think of Soviet era wells I've worked on where all aspects of data quality were appalling- from the drilling techniques and records, to the log quality, to even the infomation about the logging tool's geometry that are standardised in the west!