Origin of Heavy Oil in Cretaceous Petroleum Reservoirs

Timothy Bata, John Parnell, Stephen Alan Bowden, Adrian Boyce

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Much of the world’s heavy oil is found in Cretaceous reservoir rocks due to a combination of tectonic, climatic, geological, and biological factors. Here we study Cretaceous oil sands from the Neuquén Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Alberta (Canada), Dahomey Basin (Nigeria), Uinta Basin (USA), Western Moray Firth Basin (United Kingdom), and Wessex Basin (United Kingdom) to improve our understanding of the origin of the heavy oils. Our results indicate that the oils were generated as conventional light oil, which later degraded into heavy oils, rather than thermally cracked oils from over matured source rocks. All the studied Cretaceous oil sands are enriched in the polar fraction, and the total ion current (TIC) fragmentogram of the saturate fractions show unresolved complex mixture (UCM) humps indicating that the oils have undergone biodegradation. Sterane data for the Cretaceous oil sands show a selective increase in the C29 regular steranes relative to C27 and C28 regular sterane, which is also consistent with biodegradation. There is also evidence for diasterane degradation in some samples which are related, suggesting severe biodegradation. The trisnorhopane thermal maturity indicator showed that the Cretaceous oil sands have thermal maturity levels equivalent to 0.66–1.32% Ro, consistent with an early to late oil window. 25-norhopanes were not detected in any of the studied Cretaceous oil sands despite sterane degradation. This strongly suggests that biodegradation in the Cretaceous oil sands occurred at shallow depths rather than at greater depths. Pyrite associated with the Cretaceous oil sands was found to be consistently isotopically light. The isotopic fractionation between these pyrites and contemporary seawater sulfate was calculated using the mean δ34S values and the established seawater composition curve. This fractionation exceeded the maximum known kinetic isotope fractionation of ~20‰ that is possible from non-biogenic mechanisms, such as thermochemical sulfate reduction. This strongly suggests that the pyrite precipitated from an open system by means of microbial sulfate reduction as part of the biodegradation process.
Original languageEnglish
Pages (from-to)106-118
Number of pages13
JournalBulletin of Canadian Petroleum Geology
Volume64
Issue number2
DOIs
Publication statusPublished - Jun 2016

Fingerprint

Oil sands
Petroleum reservoirs
heavy oil
oil sand
Crude oil
petroleum
Biodegradation
Cretaceous
Oils
biodegradation
Pyrites
Fractionation
Sulfates
basin
oil
pyrite
thermal maturity
Seawater
sulfate
Rocks

Cite this

Origin of Heavy Oil in Cretaceous Petroleum Reservoirs. / Bata, Timothy; Parnell, John; Bowden, Stephen Alan; Boyce, Adrian.

In: Bulletin of Canadian Petroleum Geology, Vol. 64, No. 2, 06.2016, p. 106-118.

Research output: Contribution to journalArticle

@article{34838cc7986245ee9a0c91e41d5c2bd3,
title = "Origin of Heavy Oil in Cretaceous Petroleum Reservoirs",
abstract = "Much of the world’s heavy oil is found in Cretaceous reservoir rocks due to a combination of tectonic, climatic, geological, and biological factors. Here we study Cretaceous oil sands from the Neuqu{\'e}n Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Alberta (Canada), Dahomey Basin (Nigeria), Uinta Basin (USA), Western Moray Firth Basin (United Kingdom), and Wessex Basin (United Kingdom) to improve our understanding of the origin of the heavy oils. Our results indicate that the oils were generated as conventional light oil, which later degraded into heavy oils, rather than thermally cracked oils from over matured source rocks. All the studied Cretaceous oil sands are enriched in the polar fraction, and the total ion current (TIC) fragmentogram of the saturate fractions show unresolved complex mixture (UCM) humps indicating that the oils have undergone biodegradation. Sterane data for the Cretaceous oil sands show a selective increase in the C29 regular steranes relative to C27 and C28 regular sterane, which is also consistent with biodegradation. There is also evidence for diasterane degradation in some samples which are related, suggesting severe biodegradation. The trisnorhopane thermal maturity indicator showed that the Cretaceous oil sands have thermal maturity levels equivalent to 0.66–1.32{\%} Ro, consistent with an early to late oil window. 25-norhopanes were not detected in any of the studied Cretaceous oil sands despite sterane degradation. This strongly suggests that biodegradation in the Cretaceous oil sands occurred at shallow depths rather than at greater depths. Pyrite associated with the Cretaceous oil sands was found to be consistently isotopically light. The isotopic fractionation between these pyrites and contemporary seawater sulfate was calculated using the mean δ34S values and the established seawater composition curve. This fractionation exceeded the maximum known kinetic isotope fractionation of ~20‰ that is possible from non-biogenic mechanisms, such as thermochemical sulfate reduction. This strongly suggests that the pyrite precipitated from an open system by means of microbial sulfate reduction as part of the biodegradation process.",
author = "Timothy Bata and John Parnell and Bowden, {Stephen Alan} and Adrian Boyce",
note = "Timothy Bata is thankful to the Petroleum Technology Development Fund of Nigeria for sponsoring his PhD research at the University of Aberdeen, and the management of Abubakar Tafawa Balewa University Bauchi, Nigeria, for permitting him to proceed on study leave. We acknowledge the British Geological Survey for providing core samples of the Captain Sand used in this study. We are grateful to Colin Taylor and John Still for their help during laboratory work.",
year = "2016",
month = "6",
doi = "10.2113/gscpgbull.64.2.106",
language = "English",
volume = "64",
pages = "106--118",
journal = "Bulletin of Canadian Petroleum Geology",
issn = "0007-4802",
publisher = "Canadian Society of Petroleum Geologists",
number = "2",

}

TY - JOUR

T1 - Origin of Heavy Oil in Cretaceous Petroleum Reservoirs

AU - Bata, Timothy

AU - Parnell, John

AU - Bowden, Stephen Alan

AU - Boyce, Adrian

N1 - Timothy Bata is thankful to the Petroleum Technology Development Fund of Nigeria for sponsoring his PhD research at the University of Aberdeen, and the management of Abubakar Tafawa Balewa University Bauchi, Nigeria, for permitting him to proceed on study leave. We acknowledge the British Geological Survey for providing core samples of the Captain Sand used in this study. We are grateful to Colin Taylor and John Still for their help during laboratory work.

PY - 2016/6

Y1 - 2016/6

N2 - Much of the world’s heavy oil is found in Cretaceous reservoir rocks due to a combination of tectonic, climatic, geological, and biological factors. Here we study Cretaceous oil sands from the Neuquén Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Alberta (Canada), Dahomey Basin (Nigeria), Uinta Basin (USA), Western Moray Firth Basin (United Kingdom), and Wessex Basin (United Kingdom) to improve our understanding of the origin of the heavy oils. Our results indicate that the oils were generated as conventional light oil, which later degraded into heavy oils, rather than thermally cracked oils from over matured source rocks. All the studied Cretaceous oil sands are enriched in the polar fraction, and the total ion current (TIC) fragmentogram of the saturate fractions show unresolved complex mixture (UCM) humps indicating that the oils have undergone biodegradation. Sterane data for the Cretaceous oil sands show a selective increase in the C29 regular steranes relative to C27 and C28 regular sterane, which is also consistent with biodegradation. There is also evidence for diasterane degradation in some samples which are related, suggesting severe biodegradation. The trisnorhopane thermal maturity indicator showed that the Cretaceous oil sands have thermal maturity levels equivalent to 0.66–1.32% Ro, consistent with an early to late oil window. 25-norhopanes were not detected in any of the studied Cretaceous oil sands despite sterane degradation. This strongly suggests that biodegradation in the Cretaceous oil sands occurred at shallow depths rather than at greater depths. Pyrite associated with the Cretaceous oil sands was found to be consistently isotopically light. The isotopic fractionation between these pyrites and contemporary seawater sulfate was calculated using the mean δ34S values and the established seawater composition curve. This fractionation exceeded the maximum known kinetic isotope fractionation of ~20‰ that is possible from non-biogenic mechanisms, such as thermochemical sulfate reduction. This strongly suggests that the pyrite precipitated from an open system by means of microbial sulfate reduction as part of the biodegradation process.

AB - Much of the world’s heavy oil is found in Cretaceous reservoir rocks due to a combination of tectonic, climatic, geological, and biological factors. Here we study Cretaceous oil sands from the Neuquén Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Alberta (Canada), Dahomey Basin (Nigeria), Uinta Basin (USA), Western Moray Firth Basin (United Kingdom), and Wessex Basin (United Kingdom) to improve our understanding of the origin of the heavy oils. Our results indicate that the oils were generated as conventional light oil, which later degraded into heavy oils, rather than thermally cracked oils from over matured source rocks. All the studied Cretaceous oil sands are enriched in the polar fraction, and the total ion current (TIC) fragmentogram of the saturate fractions show unresolved complex mixture (UCM) humps indicating that the oils have undergone biodegradation. Sterane data for the Cretaceous oil sands show a selective increase in the C29 regular steranes relative to C27 and C28 regular sterane, which is also consistent with biodegradation. There is also evidence for diasterane degradation in some samples which are related, suggesting severe biodegradation. The trisnorhopane thermal maturity indicator showed that the Cretaceous oil sands have thermal maturity levels equivalent to 0.66–1.32% Ro, consistent with an early to late oil window. 25-norhopanes were not detected in any of the studied Cretaceous oil sands despite sterane degradation. This strongly suggests that biodegradation in the Cretaceous oil sands occurred at shallow depths rather than at greater depths. Pyrite associated with the Cretaceous oil sands was found to be consistently isotopically light. The isotopic fractionation between these pyrites and contemporary seawater sulfate was calculated using the mean δ34S values and the established seawater composition curve. This fractionation exceeded the maximum known kinetic isotope fractionation of ~20‰ that is possible from non-biogenic mechanisms, such as thermochemical sulfate reduction. This strongly suggests that the pyrite precipitated from an open system by means of microbial sulfate reduction as part of the biodegradation process.

U2 - 10.2113/gscpgbull.64.2.106

DO - 10.2113/gscpgbull.64.2.106

M3 - Article

VL - 64

SP - 106

EP - 118

JO - Bulletin of Canadian Petroleum Geology

JF - Bulletin of Canadian Petroleum Geology

SN - 0007-4802

IS - 2

ER -