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Splice the logs from different runs
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Author:  listmember [ Tue Aug 07, 2012 9:22 am ]
Post subject:  Splice the logs from different runs
Hello!

I need help of experienced petrophysicist. I am in a process of splicing and merging the GR log from different runs. Is it any typical workflow for this job? I am thinking of keeping as a referenced curve the GR log from RUN1 (because is less affected by the hole conditions) and then lateral shifting the GR - RUN2, and then splice the log in an overlapping point.
In this manner I have merged the GR log from 4 different runs. I have observed that there is a general baseline shift of the entire log to the right with the increasing of depth.
My questions are: am I applying the curves splicing correct? What about the baseline shift of GR log, can be adjusted to the shale line (like SP log)?

Any advice would be appreciated.
Author:  javacob [ Wed Aug 08, 2012 10:11 am ]
Post subject:  Re: Splice the logs from different runs
dear
before splicing pl correct ur GR curves for mud and borehole size and standoff(if any used).

thereafter splice.
u may still find some shift on a/c of various companies tools being used.

by looking at resistivity log u can shift the baseline.

i have done this small shift in welledit mode on geoframe.

u may try other software.

S K JHA
Author:  kokokyi [ Wed Aug 08, 2012 3:33 pm ]
Post subject:  Re: Splice the logs from different runs
Dear listmember,

Yes, Javacob is right. Before you splice your different runs of GR logs, you should correct them for respective hole size (using a caliper log) and mud weight used for that hole section. This way all your GR logs will be normalized back to 8 inch hole filled with water. Most petrophysical software will have an environmental correction module for GR log to do that.
After making the environmental corrections, you can then splice you GR logs from different runs.
Even then, you may find that there are still some small shifts between the GR log from each successive run. In this case you can probably shift the GR as required and splice them together.
Watch out for the sections just below the casing shoe for each run. This is where the GR will be most affected by the washout section below the casing shoe. Usually this is also a shale section, as casing shoes are normally set in shale intervals.

Contrary to what you said, the first GR run in the hole will be most affected by the hole size and mud weight, as the top hole is always the biggest size and the formation also tends to washout more because it is usually unconsolidated.

You also need to watch out for the different types of GR tools, different contractors and different modes of recording the GR log, either on LWD or wireline. The LWD tools come in different sizes for different hole sizes, whereas wireline usually has only one size of GR tool (either 3 3/8" or 3 5/8").

Regards,

Ko Ko Kyi
Author:  listmember [ Fri Aug 10, 2012 7:59 am ]
Post subject:  Re: Splice the logs from different runs
Hello javacob & kokokyi,

My situation is like that:
- GR-RUN1 - 17'' open hole
- GR-RUN2 - 12" open hole (overlapping GR1 interval in casing)
- GR-RUN3 - 8" open hole (overlapping GR1 interval in casing)
Contractor is the same, wireline. GR tool size diameter? - dont know.
From your advices, I should use this workflow:
- apply environmental correction of each log run (hole size and mud weight). Is it possible to find formulas to apply this correction (in MS Excel let's say) without using a dedicated petrophysical software?
- Intervals from GR log which are cased-hole recorded (short overlapping interval) should be corrected as for cased-hole? which correction are applying for GR recorded in cased-holes?
- Should I use the gr log from the smallest diameter hole as a reference curve (in my case GR-RUN3)? and then apply shift, then splice ...
Looking forward for your next advices,
Thank you!
Author:  kokokyi [ Mon Aug 20, 2012 3:30 pm ]
Post subject:  Re: Splice the logs from different runs
Hi listmember,

Sorry for my late reply as I was not monitoring this topic on epgeology.
To answer your questions:

1) Yes, you can use a spreadsheet to do the GR correction for hole size and mud weight. Schlumberger has a formula for this in their Log Interpretation Chart book. I believe that other wireline logging companies have similar equations in their chart books also. Unfortunately, I am on vacation and my chart books are in the office. Therefore, I cannot help you on this until I am back in the office early September.
2) Cased hole GR will be a lot lower than the open hole GR log because of the reduction in GR counts due to casing and cement behind the casing. It will not be straight forward to splice the cased hole GR to an open hole GR log. You will probably have to regenerate a pseudo open hole GR from the cased hole one, by applying a minimum and maximum GR values based on the open hole log. However, this may not be accurate.
3) For the three different GR logs in different hole sizes, first make the environmental corrections on each run, using the appropriate hole size, caliper log and mud weight for each section. Use the corrected GR from the smallest hole size as reference, then shift and splice the other GR logs as required. If your first GR run in the biggest hole size has the highest GR readings, you may want to use it as the reference. It does not matter too much, since what you want to achieve is a continuous GR log for the whole well.

I hope these will answer your questions.

Regards,

Ko Ko Kyi
Author:  listmember [ Thu Aug 23, 2012 2:20 pm ]
Post subject:  Re: Splice the logs from different runs
Very good advices, thank you for your reply ....
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