Modelling petroleum expulsion in sedimentary basins: The importance of igneous intrusion timing and basement composition

David Gardiner, Nick Schofield, Alex Finlay, Niall Mark, Liam Holt, Clayton Grove, Chris Forster, Julian Moore

Research output: Contribution to journalArticle

Abstract

The concept of a critical moment in a petroleum system (the time of highest probability of entrapment and preservation of oil and gas) has underlain petroleum exploration for over 25 years. However, one area where understanding the critical moment is challenging is the Faroe-Shetland Basin (FSB; offshore UK). Isotopic dating of oils suggests that petroleum generation began between ca. 68 and 90 Ma; however, most basin models invoke an earlier generation beginning in the mid-Cretaceous at ca. 100 Ma, predating deposition of Paleocene and Eocene reservoirs. This time discrepancy has previously been explained by remigration from intermediary accumulations (“motel” hypothesis) and/or overpressure retardation of kerogen maturation. The FSB is characterized by a thick Cretaceous stratigraphic package (up to 5 km) that includes a large net thickness (up to 2 km) of Paleogene igneous material. In our model, separating sedimentary and igneous material and adding the igneous material at the correct time between ca. 58 and 55 Ma shallows the modeled burial depth of the Upper Jurassic source rocks during the Cretaceous sufficiently to delay maturation by 17 m.y. in comparison to results of previous studies. Additionally, previous studies have invoked crustal radiogenic heat production (RHP) based on the Phanerozoic crust averaging ~2.8 μW/m3 in the North Sea (300 km to the east). However, the FSB basement is composed of significantly older, colder Neoarchean orthogneisses (ca. 2.7–2.9 Ga), reducing RHP by up to 50% to ~1.6 μW/m3 (σ = 0.74). For the first time, our model unifies geological, geochronological, and geochemical observations, delaying the onset of petroleum expulsion by up to 40 m.y. in comparison to previous models.

Original languageEnglish
JournalGeology
Volume47
Early online date12 Aug 2019
DOIs
Publication statusE-pub ahead of print - 12 Aug 2019

Fingerprint

sedimentary basin
petroleum
heat production
Cretaceous
modeling
maturation
oil
overpressure
kerogen
Phanerozoic
basin
Paleogene
Paleocene
source rock
Eocene
Jurassic
crust
gas
material
comparison

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Modelling petroleum expulsion in sedimentary basins : The importance of igneous intrusion timing and basement composition. / Gardiner, David; Schofield, Nick; Finlay, Alex; Mark, Niall; Holt, Liam; Grove, Clayton; Forster, Chris; Moore, Julian .

In: Geology, Vol. 47, 12.08.2019.

Research output: Contribution to journalArticle

Gardiner, David ; Schofield, Nick ; Finlay, Alex ; Mark, Niall ; Holt, Liam ; Grove, Clayton ; Forster, Chris ; Moore, Julian . / Modelling petroleum expulsion in sedimentary basins : The importance of igneous intrusion timing and basement composition. In: Geology. 2019 ; Vol. 47.
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abstract = "The concept of a critical moment in a petroleum system (the time of highest probability of entrapment and preservation of oil and gas) has underlain petroleum exploration for over 25 years. However, one area where understanding the critical moment is challenging is the Faroe-Shetland Basin (FSB; offshore UK). Isotopic dating of oils suggests that petroleum generation began between ca. 68 and 90 Ma; however, most basin models invoke an earlier generation beginning in the mid-Cretaceous at ca. 100 Ma, predating deposition of Paleocene and Eocene reservoirs. This time discrepancy has previously been explained by remigration from intermediary accumulations (“motel” hypothesis) and/or overpressure retardation of kerogen maturation. The FSB is characterized by a thick Cretaceous stratigraphic package (up to 5 km) that includes a large net thickness (up to 2 km) of Paleogene igneous material. In our model, separating sedimentary and igneous material and adding the igneous material at the correct time between ca. 58 and 55 Ma shallows the modeled burial depth of the Upper Jurassic source rocks during the Cretaceous sufficiently to delay maturation by 17 m.y. in comparison to results of previous studies. Additionally, previous studies have invoked crustal radiogenic heat production (RHP) based on the Phanerozoic crust averaging ~2.8 μW/m3 in the North Sea (300 km to the east). However, the FSB basement is composed of significantly older, colder Neoarchean orthogneisses (ca. 2.7–2.9 Ga), reducing RHP by up to 50{\%} to ~1.6 μW/m3 (σ = 0.74). For the first time, our model unifies geological, geochronological, and geochemical observations, delaying the onset of petroleum expulsion by up to 40 m.y. in comparison to previous models.",
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AU - Mark, Niall

AU - Holt, Liam

AU - Grove, Clayton

AU - Forster, Chris

AU - Moore, Julian

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