Relationship between the fluorescence colour of oil inclusions and thermal maturity in the Dongying Depression, Bohai Bay Basin, China: part 2. fluorescence evolution of oil in the context of petroleum generation, expulsion and cracking under geological conditions

Hongwei Ping, Honghan Chen, Simon C. George, Chunquan Li, Shouzhi Hu

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Abundant measured data from source rocks, crude oils and oil inclusions in the Dongying Depression were used to identify the oil generation, expulsion and cracking stages under geological conditions, so as to build a fluorescence evolutionary model that considers all petroleum generation, expulsion and cracking processes. In the model, oil generation consists of three successive processes: bitumen generation, bitumen decomposition into oil, and oil cracking. These three stages are strongly controlled by thermal stress in the Dongying Depression. Kerogen decomposition into bitumen occurs at around 85 °C (0.42 %R o ), while NSO compounds in the bitumen begin to crack into oil at around 120 °C (0.67 %R o ). Competition between bitumen generation and NSO compound cracking leads to peak bitumen generation occurring at around 130 °C (0.75 %R o ). After that, the main phase of oil generation from intense bitumen decomposition occurs. A transition at approximately 160 °C between bitumen decomposition into oil and the inferred start of oil cracking corresponds to 4000 m (0.98–1.11 %R o ). During the bitumen generation and main oil generation stages, the fluorescence colours of the expelled oils are mainly yellow and orange, and a fluorescence blueshift of the oils only occurs during the main oil generation stage. In the late oil generation stage (∼160 °C), the fluorescence colours of the oils may be close to blue. With increasing burial, once the source rock and reservoir temperatures reach the threshold conditions for oil cracking (160 °C), an intense blueshift of the oil occurs in both source rocks and reservoirs, and even in oil inclusions. This blueshift is shown by a decreased dispersion in the fluorescence colour distribution of oil inclusions with increasing burial, from multiple colours at temperatures <160 °C, to only blue colours at temperatures >160 °C. Therefore, in oil-prone source rocks containing Type I and II kerogen, a blue fluorescence colour of oil appears to be strongly related to the secondary cracking process. Blue fluorescent oil inclusions generally have higher thermal maturities than oil inclusions with green or yellow fluorescence for oil-prone source rocks. This relationship is based on the assumption that the oil was not from a gas-prone source-rock, and that secondary alteration processes can be excluded, including migration fractionation, gas deasphalting, trapping fractionation, and phase separation. Furthermore, blue fluorescent oil inclusions may be a good indicator for oil-prone source rocks, which is significant for evaluation of source rock quality in deepwater and ultra deepwater areas in offshore basins.

LanguageEnglish
Pages306-319
Number of pages14
JournalMarine and Petroleum Geology
Volume103
DOIs
Publication statusPublished - May 2019

Fingerprint

thermal maturity
expulsion
crude oil
China
fluorescence
oils
petroleum
inclusions
color
oil
basin
bitumen
source rock
rocks
cracking (fracture)
kerogen
decomposition
fractionation

Keywords

  • Fluid inclusion
  • Petroleum inclusion
  • Fluorescence spectroscopy
  • Vitrinite reflectance
  • Suppression
  • Phase separation
  • Gas washing
  • Gas displacing oil

Cite this

@article{aecd38ab50ee46288b954a234d3a322e,
title = "Relationship between the fluorescence colour of oil inclusions and thermal maturity in the Dongying Depression, Bohai Bay Basin, China: part 2. fluorescence evolution of oil in the context of petroleum generation, expulsion and cracking under geological conditions",
abstract = "Abundant measured data from source rocks, crude oils and oil inclusions in the Dongying Depression were used to identify the oil generation, expulsion and cracking stages under geological conditions, so as to build a fluorescence evolutionary model that considers all petroleum generation, expulsion and cracking processes. In the model, oil generation consists of three successive processes: bitumen generation, bitumen decomposition into oil, and oil cracking. These three stages are strongly controlled by thermal stress in the Dongying Depression. Kerogen decomposition into bitumen occurs at around 85 °C (0.42 {\%}R o ), while NSO compounds in the bitumen begin to crack into oil at around 120 °C (0.67 {\%}R o ). Competition between bitumen generation and NSO compound cracking leads to peak bitumen generation occurring at around 130 °C (0.75 {\%}R o ). After that, the main phase of oil generation from intense bitumen decomposition occurs. A transition at approximately 160 °C between bitumen decomposition into oil and the inferred start of oil cracking corresponds to 4000 m (0.98–1.11 {\%}R o ). During the bitumen generation and main oil generation stages, the fluorescence colours of the expelled oils are mainly yellow and orange, and a fluorescence blueshift of the oils only occurs during the main oil generation stage. In the late oil generation stage (∼160 °C), the fluorescence colours of the oils may be close to blue. With increasing burial, once the source rock and reservoir temperatures reach the threshold conditions for oil cracking (160 °C), an intense blueshift of the oil occurs in both source rocks and reservoirs, and even in oil inclusions. This blueshift is shown by a decreased dispersion in the fluorescence colour distribution of oil inclusions with increasing burial, from multiple colours at temperatures <160 °C, to only blue colours at temperatures >160 °C. Therefore, in oil-prone source rocks containing Type I and II kerogen, a blue fluorescence colour of oil appears to be strongly related to the secondary cracking process. Blue fluorescent oil inclusions generally have higher thermal maturities than oil inclusions with green or yellow fluorescence for oil-prone source rocks. This relationship is based on the assumption that the oil was not from a gas-prone source-rock, and that secondary alteration processes can be excluded, including migration fractionation, gas deasphalting, trapping fractionation, and phase separation. Furthermore, blue fluorescent oil inclusions may be a good indicator for oil-prone source rocks, which is significant for evaluation of source rock quality in deepwater and ultra deepwater areas in offshore basins.",
keywords = "Fluid inclusion, Petroleum inclusion, Fluorescence spectroscopy, Vitrinite reflectance, Suppression, Phase separation, Gas washing, Gas displacing oil",
author = "Hongwei Ping and Honghan Chen and George, {Simon C.} and Chunquan Li and Shouzhi Hu",
year = "2019",
month = "5",
doi = "10.1016/j.marpetgeo.2019.02.024",
language = "English",
volume = "103",
pages = "306--319",
journal = "Marine and Petroleum Geology",
issn = "0264-8172",
publisher = "Elsevier",

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TY - JOUR

T1 - Relationship between the fluorescence colour of oil inclusions and thermal maturity in the Dongying Depression, Bohai Bay Basin, China

T2 - Marine and Petroleum Geology

AU - Ping, Hongwei

AU - Chen, Honghan

AU - George, Simon C.

AU - Li, Chunquan

AU - Hu, Shouzhi

PY - 2019/5

Y1 - 2019/5

N2 - Abundant measured data from source rocks, crude oils and oil inclusions in the Dongying Depression were used to identify the oil generation, expulsion and cracking stages under geological conditions, so as to build a fluorescence evolutionary model that considers all petroleum generation, expulsion and cracking processes. In the model, oil generation consists of three successive processes: bitumen generation, bitumen decomposition into oil, and oil cracking. These three stages are strongly controlled by thermal stress in the Dongying Depression. Kerogen decomposition into bitumen occurs at around 85 °C (0.42 %R o ), while NSO compounds in the bitumen begin to crack into oil at around 120 °C (0.67 %R o ). Competition between bitumen generation and NSO compound cracking leads to peak bitumen generation occurring at around 130 °C (0.75 %R o ). After that, the main phase of oil generation from intense bitumen decomposition occurs. A transition at approximately 160 °C between bitumen decomposition into oil and the inferred start of oil cracking corresponds to 4000 m (0.98–1.11 %R o ). During the bitumen generation and main oil generation stages, the fluorescence colours of the expelled oils are mainly yellow and orange, and a fluorescence blueshift of the oils only occurs during the main oil generation stage. In the late oil generation stage (∼160 °C), the fluorescence colours of the oils may be close to blue. With increasing burial, once the source rock and reservoir temperatures reach the threshold conditions for oil cracking (160 °C), an intense blueshift of the oil occurs in both source rocks and reservoirs, and even in oil inclusions. This blueshift is shown by a decreased dispersion in the fluorescence colour distribution of oil inclusions with increasing burial, from multiple colours at temperatures <160 °C, to only blue colours at temperatures >160 °C. Therefore, in oil-prone source rocks containing Type I and II kerogen, a blue fluorescence colour of oil appears to be strongly related to the secondary cracking process. Blue fluorescent oil inclusions generally have higher thermal maturities than oil inclusions with green or yellow fluorescence for oil-prone source rocks. This relationship is based on the assumption that the oil was not from a gas-prone source-rock, and that secondary alteration processes can be excluded, including migration fractionation, gas deasphalting, trapping fractionation, and phase separation. Furthermore, blue fluorescent oil inclusions may be a good indicator for oil-prone source rocks, which is significant for evaluation of source rock quality in deepwater and ultra deepwater areas in offshore basins.

AB - Abundant measured data from source rocks, crude oils and oil inclusions in the Dongying Depression were used to identify the oil generation, expulsion and cracking stages under geological conditions, so as to build a fluorescence evolutionary model that considers all petroleum generation, expulsion and cracking processes. In the model, oil generation consists of three successive processes: bitumen generation, bitumen decomposition into oil, and oil cracking. These three stages are strongly controlled by thermal stress in the Dongying Depression. Kerogen decomposition into bitumen occurs at around 85 °C (0.42 %R o ), while NSO compounds in the bitumen begin to crack into oil at around 120 °C (0.67 %R o ). Competition between bitumen generation and NSO compound cracking leads to peak bitumen generation occurring at around 130 °C (0.75 %R o ). After that, the main phase of oil generation from intense bitumen decomposition occurs. A transition at approximately 160 °C between bitumen decomposition into oil and the inferred start of oil cracking corresponds to 4000 m (0.98–1.11 %R o ). During the bitumen generation and main oil generation stages, the fluorescence colours of the expelled oils are mainly yellow and orange, and a fluorescence blueshift of the oils only occurs during the main oil generation stage. In the late oil generation stage (∼160 °C), the fluorescence colours of the oils may be close to blue. With increasing burial, once the source rock and reservoir temperatures reach the threshold conditions for oil cracking (160 °C), an intense blueshift of the oil occurs in both source rocks and reservoirs, and even in oil inclusions. This blueshift is shown by a decreased dispersion in the fluorescence colour distribution of oil inclusions with increasing burial, from multiple colours at temperatures <160 °C, to only blue colours at temperatures >160 °C. Therefore, in oil-prone source rocks containing Type I and II kerogen, a blue fluorescence colour of oil appears to be strongly related to the secondary cracking process. Blue fluorescent oil inclusions generally have higher thermal maturities than oil inclusions with green or yellow fluorescence for oil-prone source rocks. This relationship is based on the assumption that the oil was not from a gas-prone source-rock, and that secondary alteration processes can be excluded, including migration fractionation, gas deasphalting, trapping fractionation, and phase separation. Furthermore, blue fluorescent oil inclusions may be a good indicator for oil-prone source rocks, which is significant for evaluation of source rock quality in deepwater and ultra deepwater areas in offshore basins.

KW - Fluid inclusion

KW - Petroleum inclusion

KW - Fluorescence spectroscopy

KW - Vitrinite reflectance

KW - Suppression

KW - Phase separation

KW - Gas washing

KW - Gas displacing oil

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U2 - 10.1016/j.marpetgeo.2019.02.024

DO - 10.1016/j.marpetgeo.2019.02.024

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JO - Marine and Petroleum Geology

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SN - 0264-8172

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