I am investigating the role and effect of OM and its type in the uptake of trace elements in sediment-water interfaces. I would like to know why there are differences in the S4 value (measured in 850 C) of samples with the same kerogen type (I) and homogeneous lithology (marl)? Which factors influence the residual carbon content of samples? Does the S4 or residual carbon content still have potential to generate petroleum (theoretically) or do we consider it as a dead (Type IV) carbon?
To the first part of your question, there is always a negligible difference in values even in SI, S2 and S3 in every repitition of the test. This might be referred as detection efficiency of FID and the temperature supplies + the system settings.
I would suugest it oxidized highly mature carbon that does't have hydrogen at all or a very minor hydrogen amount. In general the data are presented in S1, S2 and S3 and petrophysicists are not interested in S4. With more fueling you may get some more gas out of it but Its not economic off-course.
The type of OM which is derived from aquatic environment is already consist mainly from Algae's ,Bacteria ,these particulate OM have bio polymer and mainly content Carbohydrates , Proteins ,Fats and other pigments and so on ..Already determines S1, S2, and S3, promising to generate oil mainly, other wise Higher plants which the mentioned above biopolymer lacking with it, but rich in Lignin (responsible for keeping the plants standing ,is promising to generate gas only .
Regards
Hi Arash,
interesting topic (trace element uptake).
I think your first question is formulated a little bit too "open", so I´m a little bit unsure what you really mean.
Generally, the S4 peak can be influenced by carbonates, for sure at 850°C. At lower temperatures you might get some interference depending on siderite content. If you can rule out influence of carbonates and you are sure S4 is coming from organic carbon, then the S4 should simply be a function of total organic carbon (TOC) content, and the S4 value can be expected to vary in the same way S2 varies.
The information "Type I kerogen" itself does not say anything about measured values! Type I kerogen (if defined by Rock-Eval parameters) usually yields HI values anywhere between 600 and 900 mg HC/g TOC, and thus (for this specific range) assuming an TOC of 1%, S2 can range from 6 to 9 mg HC/g sample. Assuming a fixed HI of 700 mg HC/g TOC, again S2 can vary depending on TOC content (S2= 7 mg/g sample for 1% TOC; S2 = 14 mg/g sample for 2%TOC). The same is true for S4 as it simply represents the amount of TOC which is not pyrolysable. And thus organic matter amount from S4 is usually considered dead!
There nevertheless is some late gas potential mainly for methane left which is not assessed by RE-temperatures up to 650°C (There might be other ways as well how this "dead" OM can "respawn", e.g. thinkable are reactions with water at high temperatures etc.... not the topic here)
Ok, perhaps this helps!
Regards
S1 = quantity of free hydrocarbons (gas + oil), in mg/g of rock
S2 = quantity of thermally generated (cracked) hydrocarbons, in mg/g of rock
S3 = quantity of CO2 generated during pyrolysis of the sample, in mg/g of rock
S4= quantity of CO2 generated during oxidation of the sample, in mg/g of rock
hi dr vosoughi.
When the sample enters the oxidan oven in rock-Eval6 , it burns completely and S4 is calculated, so the total amount of hydrocarbons(total organic carbon) TOC is effective on S4.
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