What are the main reasons when HI values are more than 100 but Oxygen index values are equal nil ?
Moamen, you should perhaps mention the OM of sampling i.e. locally abundant TOC type. Crudely, I assume that mistake maybe is one of the constituents of the OI equation (was zero) resulting in overall zero outcome. Recheck S3 and %TOC. By the way, low HI value might suggest Type II (as is not close to 500), however only after you restore original value you will know for sure...Cheers, Darko
Dear Dr. Darko Spahić
First of all, many thanks for your help
secondly, the TOC values range from 0.84 to 2.1 (avg. 1.1), but the S3 values are equal null!!
So 0/1.1 *100=0
It probably means that samples mark highly deplted samples, but try to chnage 0 in So calcuations...
Darko Spahić
Is it acceptable to change the analyzed samples? Most of S3 values are equal null, Can I change it to low value like 0.01?
Sure, for the testing purpose why not? But you are aware that low S3 means depleted organic sources, right? :) Try to geologically justify zero value, SR investagations are part of the "game" called "play-to-prospect"! :) Cheers
Dear Moamen
The oxygen index and hydrogen index are calculated-based parameters from the TOC as follow;
OI=(S3/TOC)*100 (mg CO2/g TOC)
HI=(S2/TOC)*100 (mg HC/g TOC)
The S3 is the amount of released CO and CO2 curve/values during combustion/ thermal decomposition of the OM and is measured by an infrared cell with high precision rate. What you should do with your device is to use the lab standards and compare the results of the standard with yours to detect if it still zero, then there is a problem with the infrared cell sensor and needs a maintenance. So, your problem is not with the OI, as we said it is a calculated parameter, but now it, of course, with the S3. As there is a combustion and TOC was measured, absolutely there should be a released CO and CO2.
Also, you should check if your samples were contaminated with oil base mud or migrated hydrocarbons, why?? because contaminated samples will result in high S1, S2, TOC, and lead to a Tmax suppression (find more details in the attached manuscripts). This conditions will results in inconsistency and conflicting the common temperature curves of parameter (i.e. S1, S2, S3..S5), therefore, you should also revise your charts/graphs produced during Rock-Eval pyrolysis, where the common temperature peak of the S3 is recorded between 400 C and the end of measurement. For clarification, look at this figure (aa) as an example, with its caption below;
- Pyrograms of the same sample analyzed by two different analysts. Upper pyrogram is from analyst A, where the FID signal (blue) is shifted to the left when compared to the lower pyrogram from analyst B. The shift (a result of miscalibration and poor maintenance) affected S1 and Tmax values. Notice also how the S3 IR signal (pink) in the problematic pyrogram is larger than in the lower pyrogram. The latter is also an indication of poor maintenance in the pyrolysis oven.
Regards
Ahmed
I guess either instrument failure or peak integration mistake.
It is very unlikely that a samples with HI values between 100 and 280 mg hc/g TOC have OI values of zero - if not impossible.
Check standards, check peak integration.
Dear Dr. Joachim Rinna
Many thanks for your help.
I will check it again.
Hi Moaman, it would be helpful for us to help you if you could show us the complete data table for the 5 samples. Cheers, Andy
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