Relationship between Hydrocarbon Gas Generation and Kerogen Structural Evolution Revealed by Closed System Pyrolysis and Quantitative Py-GC Analysis of a Type II Kerogen
Bibliographic record
Abstract
Kerogen can release both liquid and gaseous hydrocarbons during thermal maturation. In this study, the maturation and hydrocarbon generation of a low-maturity type II kerogen were simulated via temperature-programmed gold tube closed system (GTCS) pyrolysis at two different heating rates. In addition to the yields of C 1 –C 5 gaseous hydrocarbons, H/C atomic ratios and δ 13 C values were also obtained on the kerogen residues from GTCS pyrolyses. The remaining C 1 –C 5 gaseous hydrocarbon and C 6 + liquid hydrocarbon generation potentials in both the original kerogen and the kerogen residues of various thermal maturities were determined by quantitative flash pyrolysis-gas chromatography (Py-GC) and were used to estimate the loss of aliphatic carbons in artificially matured kerogens compared with that in the original kerogen. The yields of C 1 –C 5 gaseous hydrocarbons from GTCS pyrolysis were compared with the lost amount of C 1 –C 5 gaseous hydrocarbon potentials within the kerogen structure at the same maturities. The results indicate that the H/C atomic ratios of kerogen residues decreased and the δ 13 C values of kerogen residues became progressively heavier (i.e., being enriched in 13 C) with increasing maturity in the oil generation window (OGW) but with δ 13 C becoming slightly lighter above the calculated R o (Calcd R o, namely, Easy R o or equivalent vitrinite reflectance) of 2.5%. It is worth noting that, in the OGW, the yields of C 1 –C 5 gaseous hydrocarbons from GTCS pyrolyses were significantly lower than the amounts of lost C 1 –C 5 potentials indicated by Py-GC. We speculate that hydrocarbon gases generated in OGW may either be partially adsorbed within kerogen and dissolved in oil or participate in the thermal degradation of kerogen during GTCS pyrolyses, resulting in lower yields of C 1 –C 5 gaseous hydrocarbons than the decrease in kerogen C 1 –C 5 potentials. The Py-GC results of kerogen residues also show that the rates of loss for C 1, C 2, and C 3 hydrocarbons are about 92%, 98%, and 99%, respectively, at 1.3% Calcd R o . This indicates that most of the C 2 + alkyl side chains can be cleaved from the kerogen structure within OGW. In comparison, at a Calcd R o of 1.3%, the formation rate of methane (C 1 ) from GTCS pyrolysis of kerogen at a heating rate of 2 °C/h only amounted to about 32%. The results from this study appear to suggest that, in GTCS pyrolysis, most C 1 generated from type II kerogen at the overmature stage cannot be attributed to primary kerogen cracking but to gradual secondary cracking of hydrocarbons with high molecular weights.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".