Efficiency of petroleum expulsion from shale source rocks

Leythaeuser, D.; Radke, M.; Schaefer, R. G.

doi:10.1038/319427b0

Cited by 5 publications

(2 citation statements)

References 2 publications

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“…This has also been observed for other source rock types such as shales (e.g. Leythaeuser et al, 1984), but the effects are much more pronounced in coals.…”

Section: Mechanisms Of Expulsionsupporting

confidence: 67%

“…Oil experiences fractionation during expulsion and primary migration, further complicating correlation (e.g. Leythaeuser et al, 1984;Sandvik et al, 1992;Littke and Leythaeuser, 1993;Ritter and Grøver, 2005). In addition to the slightly lower maturity of the extracts, the high percentages of saturated hydrocarbons in the 7128/4-1 oil compared to the strongly polar and more aromatic core-and cutting extracts ( Fig.…”

Section: Oil -Source Rock Correlationmentioning

confidence: 99%

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Oil‐prone Lower Carboniferous Coals in the Norwegian Barents Sea: Implications for a Palaeozoic Petroleum System

Koeverden

Karlsen

Schwark

et al. 2010

Journal of Petroleum Geology

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In this study, we assess the oil generation potential of Lower Carboniferous, liptinite-rich coals in the Tettegras Formation on the Finnmark Platform, southern Norwegian Barents Sea. Oil from these coals has been expelled into intercalated sandstones. The coals may have contributed to petroleum recorded in well 7128/4-1 on the Finnmark Platform and may constitute a new Palaeozoic source rock in the Barents Sea.The Tettegras Formation coals contain up to 80 vol. % liptinite (mineral matter free base) and have low oxygen indices. Hydrogen indices up to 367 mg HC/g TOC indicate liquid hydrocarbon potential. In wells 7128/4-1 and 7128/6-1, the coals have vitrinite reflectance R o = 0.75-0.85 %. Compared to shale and carbonate source rocks, expulsion from coal in general begins at higher maturities (R o = 0.8-0.9% and T max = 444-453°C). Thus, the coals in the wells are mostly immature with regard to oil expulsion. The oil in well 7128/4-1 most likely originates from a more mature part of the Tettegras Formation in the deeper northern part of the Finnmark Platform. Wide variations in biomarker facies parameters and δ 13 C isotope values indicate a heterogeneous paralic depositional setting. The preferential retention by coal strata of naphthenes (e.g. terpanes and steranes) and aromatic compounds, compared to n-alkanes and acyclic isoprenoids, results in a terrigenous and waxy oil. This oil however contains marine biomarkers derived from the intercalated shales and siltstones. It is therefore important to consider the entire coal-bearing sequence, including the intercalated shales, in terms of source rock potential.Coals of similar age occur on Svalbard and Bjørnøya. The results of this study therefore suggest that a Lower Carboniferous coaly source rock may extend over large areas of the Norwegian Barents Sea. This source rock is mature in areas where the otherwise prolific Upper Jurassic marine shales are either immature or missing and may constitute a new Palaeozoic coal-sourced petroleum system in the Barents Sea.

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“…This has also been observed for other source rock types such as shales (e.g. Leythaeuser et al, 1984), but the effects are much more pronounced in coals.…”

Section: Mechanisms Of Expulsionsupporting

confidence: 67%

Section: Oil -Source Rock Correlationmentioning

confidence: 99%

Oil‐prone Lower Carboniferous Coals in the Norwegian Barents Sea: Implications for a Palaeozoic Petroleum System

Koeverden

Karlsen

Schwark

et al. 2010

Journal of Petroleum Geology

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Significant progress of continental petroleum geological theory in basins of Central and Western China

Jia¹,

Zou

Zhi

et al. 2018

Petroleum Exploration and Development

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Oil retention and intrasource migration in the organic-rich lacustrine Chang 7 shale of the Upper Triassic Yanchang Formation, Ordos Basin, central China

Zou

Pan²,

Horsfield

et al. 2019

Bulletin

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The Zhang 22 well was drilled in the Ordos Basin, penetrating the Chang 7 Member of the Yanchang Formation, which has more than 80 m cumulative black organic-rich shale of oil window maturity. Utilizing seventy-six samples collected every 1 meter from the well the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the Chang 7 shale were qualitatively and quantitatively documented. The organic-rich intervals-1,-2 and-5, having an average TOC content of 6.79 wt% and pyrolyzable hydrocarbon potential S2 of 9.40 mg/g rock, are defined as "generative units" in the Chang 7 shale system, compared to the "in-source reservoirs" or "sweet spots"-the third and fourth intervals-which contain lower average TOC content of 4.19 wt% and an average S2 value of 7.17 mg/g rock, but the highest amount of free oil (av. total oil of 7.35 mg/g rock). Geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings. For example, bitumens from the generative units proportionally possess lower saturated hydrocarbons (56% to 66%) than those from the in-source reservoirs (up to 81%). The proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart. The individual molecular weight distribution of sample extracts displays more light-end moieties being enriched in the generative units. By applying the compositional mass balance calculation, the overall and compound-specific expulsion efficiencies in the in-source reservoirs are abnormally negative compared to the positive values in the generative 2 intervals. This finding in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in-source reservoirs together indicate a short-distance intrasource migration of generated petroleum into the sweet spot intervals (intervals-3 and-4) from the overlying units (intervals-1 and-2) and the underlying interval-5. Furthermore, when quantifying the total amount of retained petroleum in the shale system, an amended assessment has been introduced to overcome the systematic misestimations if only unextracted S1 values were considered. Thus, the oil crossover effect, Tmax shift phenomenon and the HI being shifted to higher values after extraction all account for identifying the intervals-3 and-4 as the in-source reservoirs. In this study, we have not only identified a set of promising in-source target for shale oil exploration and production, but we also presented the chemical and molecular composition for these shale oils. We have additionally speculated for the intrasource migration model, and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation, and the stratigraphic fractionation on differentiating the chemical compositions during migration. The improved oil quality by fractionation, the extra storage potential derived from microfos...

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Efficiency of petroleum expulsion from shale source rocks

Cited by 5 publications

References 2 publications

Oil‐prone Lower Carboniferous Coals in the Norwegian Barents Sea: Implications for a Palaeozoic Petroleum System

Oil‐prone Lower Carboniferous Coals in the Norwegian Barents Sea: Implications for a Palaeozoic Petroleum System

Significant progress of continental petroleum geological theory in basins of Central and Western China

Oil retention and intrasource migration in the organic-rich lacustrine Chang 7 shale of the Upper Triassic Yanchang Formation, Ordos Basin, central China

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