Later stage gas generation in shale gas systems based on pyrolysis in closed and semi-closed systems

Wu, Liangliang; Wang, Peng; Geng, Ansong

doi:10.1016/j.coal.2019.03.011

Cited by 13 publications

(8 citation statements)

References 60 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Considering the observed linear relationship, at an EE of 0% when the generated crude oil is completely retained in the source rock, the proportion of the cracked gas from retained oil to the total gas is 87.25%. The other minor part is thermally cracked gas from residual solid kerogen. , This finding is consistent with previous pyrolysis experiments, in which cracking gas from retained oil accounts for 80%–85.5% of the total cracking gas. , …”

Section: Discussionsupporting

confidence: 91%

“…With increasing EEs, the gas yields of C 1 –C 5 and C 2–5 /C 1–5 decrease because of less retained oil in the pyrolysis samples (Figure ). The methane yield was nearly consistent and gently increased in the initial maturity range (EasyRo ≤ 1.81%; Figure a), which generally is consistent with previous pyrolysis results from 470 to 500 °C (EasyRo approximately ranges from 1.7% to 2.1%). , The overlap of the methane yield at the different EE values was most likely caused by similar methane generation mechanisms: demethylation reactions and the opening of aromatic rings within this maturity range. , In this stage, the retained oil yielded a large amount of long-chain gaseous hydrocarbons, especially C 3+ alkanes. When the maturity exceeded an EasyRo value of 1.81%, the methane yield from the EE 100% sample was much lower than that of the EE 30% and EE 60% samples (Figure a).…”

Section: Discussionsupporting

confidence: 88%

“…The methane yield was nearly consistent and gently increased in the initial maturity range (EasyRo ≤ 1.81%; Figure 3a), which generally is consistent with previous pyrolysis results from 470 to 500 °C (EasyRo approximately ranges from 1.7% to 2.1%). 11,36 The overlap of the methane yield at the different EE values was most likely caused by similar methane generation mechanisms: demethylation reactions and the opening of aromatic rings within this maturity range. 17,18 In this stage, the retained oil yielded a large amount of long-chain gaseous hydrocarbons, especially C 3+ alkanes.…”

Section: Hydrous Pyrolysis Products and Rock-evalmentioning

confidence: 98%

“…In the oil window, up to 40%–60% of oil could remain in shale. It is the dominant source of gas in the highly to overmature stage. − Numerous geochemical studies about the hydrocarbon composition and the stable carbon and hydrogen isotopes of natural gas have documented that the secondary cracking of oil is the primary origin of highly mature to overmature shale gas. − Exploration results have also verified that shale gas sweet spots of highly mature shale reservoirs are usually related to secondary cracking gas. , Thus, the gas reserves of highly to overmature shale reservoirs depend on the quantity of retained oil which can be substantially influenced by the EEs . Investigations of the gas generation process and potential of organic-rich shales at different EEs could thus be required to predict the resources of highly mature shale reservoirs.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Experimental Gas Generation of Organic-Rich Shales at Different Oil Expulsion Efficiencies: Implications for Shale Gas Evaluation

et al. 2021

View full text Add to dashboard Cite

The assessment of the gas generation potential of highly to overmature shale is key for shale gas evaluation, but it is always fraught with challenges. In this study, immature shale samples with type-I kerogen were investigated for their oil expulsion efficiencies (EEs) by means of pyrolysis in sealed gold tubes to investigate the influence of EEs on the gas generation process. Experimental results were then applied as an analogue to evaluate the gas generation potential of the Lower Cambrian Niutitang shale reservoir in South China. The results demonstrate that the gas yields of C1–C5 alkanes obviously decrease with increasing EEs and are a result of thermal cracking gas caused by a decrease of the oil retention. The change of the gas drying index (i.e., C1/C1–5) indicates that EasyRo of 1.81% calculated from pyrolysis temperature indicates the start of a significant cracking of heavy hydrocarbon gases (C2–5). Before, the generated gas is mainly wet gas, whereas at higher maturities, C2+ alkanes are substantially cracked into methane. The iC4/nC4 and iC5/nC5 ratios exhibit a gently increasing trend, which may result from the catalytic role of clay minerals. Considering the semiquantitative statistical analysis of solid bitumen, the EEs of the Lower Cambrian Niutitang shale in South China were calculated. The gas generation potential of the Niutitang shale of two selected wells is in the range of 4.21–37.62 m3/t and 2.53–11.15 m3/t, respectively, whereas the gas contents of these two wells are low. This mismatch indicates that the gas accumulation in the Niutitang shale reservoir is related to preservation conditions rather than based exclusively on the generation potential of the shale. This study offers a conceptual approach to evaluate the gas generation potential of organic-rich shale after hydrocarbon expulsion and enhances the accuracy of the prediction of highly mature and overmature shale gas resources in South China.

show abstract

Section: Discussionsupporting

confidence: 91%

Section: Discussionsupporting

confidence: 88%

Section: Hydrous Pyrolysis Products and Rock-evalmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Experimental Gas Generation of Organic-Rich Shales at Different Oil Expulsion Efficiencies: Implications for Shale Gas Evaluation

et al. 2021

View full text Add to dashboard Cite

show abstract

“…Previous studies have indicated that the bond cleavage and the formation of free radicals mainly occurred at the early stage of pyrolysis. , The free radicals, namely, the reactive intermediates, can react with each other to form short-chain hydrocarbons . Furthermore, free short-chain hydrocarbons can be incorporated into kerogen or pyrobitumen to replace the bound long-chain hydrocarbons during thermal maturation, ,, resulting in the loss of a part of short-chain hydrocarbon gases in OGW. Therefore, in the early stage of OGW (Calcd R o < 0.7%), compared with the lost amount of C 1 –C 5 indicated by Py-GC, the significantly lower yield of C 1 –C 5 gaseous hydrocarbons from GTCS pyrolysis may be partially due to hydrocarbon gases either participating in the thermal degradation of kerogen (i.e., replacement of the bound long-chain hydrocarbons during the cleavage of long alkyl chains from kerogen) or being adsorbed within kerogen/dissolved in oil.…”

Section: Discussionmentioning

confidence: 99%

Relationship between Hydrocarbon Gas Generation and Kerogen Structural Evolution Revealed by Closed System Pyrolysis and Quantitative Py-GC Analysis of a Type II Kerogen

Zheng

Liao

2020

Energy Fuels

View full text Add to dashboard Cite

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.

show abstract

Differential evolution and the influencing factors of low-maturity terrestrial shale with different types of kerogen: A case study of a Jurassic shale from the northern margin of Qaidam Basin，China

Zhang

Guo

et al. 2020

International Journal of Coal Geology

View full text Add to dashboard Cite

Later stage gas generation in shale gas systems based on pyrolysis in closed and semi-closed systems

Cited by 13 publications

References 60 publications

Experimental Gas Generation of Organic-Rich Shales at Different Oil Expulsion Efficiencies: Implications for Shale Gas Evaluation

Experimental Gas Generation of Organic-Rich Shales at Different Oil Expulsion Efficiencies: Implications for Shale Gas Evaluation

Relationship between Hydrocarbon Gas Generation and Kerogen Structural Evolution Revealed by Closed System Pyrolysis and Quantitative Py-GC Analysis of a Type II Kerogen

Differential evolution and the influencing factors of low-maturity terrestrial shale with different types of kerogen: A case study of a Jurassic shale from the northern margin of Qaidam Basin，China

Contact Info

Product

Resources

About