Controls on alkylphenol occurrence and distribution in oils from lacustrine rift basins in East China

Abstract

Oils from two lacustrine rift basins in east China are thoroughly investigated using geochemical method to understand controls on alkylphenol occurrence and distribution in oils. Oils in the Lujiapu Depression, Kailu Basin are derived from the Cretaceous source rocks, and those in the Dongying Depression, Bohai Bay Basin, from the Tertiary source rocks. All oils are experienced relatively short distance of migration and have similar maturity in each basin. Differences in homologue distributions from different oilfields are most likely caused by organic facies variation of source rocks. The oils in the Lujiapu Depression are characterized by high proportion of C 3 alkylphenols (prefixes refer to the number of alkylcarbons joined to the aromatic ring of the phenol molecule) and low proportion of cresols and C 2 alkylphenols compared to oils from the Dongying Depression. Alkylphenol isomer distribution is possibly affected by depositional environment especially for C 3 alkylphenols. Dysoxic freshwater environment is favorable for the formation of propyl or isopropyl substituted C 3 alkylphenols, while highly reducing saline water is more suitable for trimethyl substituted C 3 alkylphenols. Variations in alkylphenol concentrations within a petroleum system are controlled mainly by secondary migration processes with alkylphenol concentrations decreasing along migration direction. Interestingly, coupled with geological factors, a subtle change of alkylphenol concentrations can be applied to differentiate carrier systems. When oil migrates through sandy beds, concentrations of total alkylphenols decrease dramatically with migration distance, while such change is less significant when oil migrates vertically along faults. However, most isomer ratios potentially related to migration distance are not as effective as those alkylcarbazoles in migration diagnosis due to complicated affecting factors.

New Insights on Organic Geochemistry Characterization of the Putumayo Basin Using Negative Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Gamacerane, an indicator of low oxygen and/or hypersaline depositional environments, was found in low concentrations reflected in the ratio Gam/H30 between 0.049 and 0.069 for Caballos− Villeta T samples, confirming oxygenated environments. 53 This ratio was higher for Villeta N−Pepinos−Calizas samples (Gam/H30 between 0.059 and 0.077). On the other hand, the ratio 22S/(22S + 22R) H31 for Caballos−Villeta T between 0.600 and 0.615 could be associated with a greater thermal maturity with respect to Villeta N−Pepinos−Calizas, which had a slightly lower ratio between 0.588 and 0.604.…”

“…In the case of Caballos–Villeta T, the DH30/H30 ratio was greater than 0.036, which is an indicator of microbial organic matter in clay-rich environments and suggests siliciclastic environments. Gamacerane, an indicator of low oxygen and/or hypersaline depositional environments, was found in low concentrations reflected in the ratio Gam/H30 between 0.049 and 0.069 for Caballos–Villeta T samples, confirming oxygenated environments . This ratio was higher for Villeta N–Pepinos–Calizas samples (Gam/H30 between 0.059 and 0.077).…”

Environmental threats induced heavy ecological burdens on the coastal zone of the Bohai Sea, China

“…The pollution both from vessels and ports includes not only petroleum-based hydrocarbons, but also water, air, and sound pollution; these have become a very significant threat to the marine environment. Marine oil pollution is regarded as a "marine killer" because of the long duration, large geographic extent, and the severity of negative impacts on the environment (Zhou and Huang, 2008;Fernandez-Tajes et al, 2011;Yim et al, 2017;Chen et al, 2018). Oil pollution can cause problems including large areas of the marine environment becoming oxygen-deficient, abnormal development of marine life (including larvae), and decrease in marine biodiversity (Ladd et al, 2018;Zhang et al, 2018;Neethu et al, 2019).…”