Distribution and geochemical significance of phenylphenanthrenes and their isomers in selected oils and rock extracts from the Tarim Basin, NW China

Abstract

Twenty-two oil samples and eight source rock samples collected from the Tarim Basin, NW China were geochemically analyzed to investigate the occurrence and distribution of phenylphenanthrene (PhP), phenylanthracene (PhA), and binaphthyl (BiN) isomers and methylphenanthrene (MP) isomers in oils and rock extracts with different depositional environments. Phenylphenanthrenes are present in significant abundance in Mesozoic lacustrine mudstones and related oils. The relative concentrations of PhPs are quite low or below detection limit by routine gas chromatography-mass spectrometry (GC-MS) in Ordovician oils derived from marine carbonates. The ratio of 3-PhP/3-MP was used in this study to describe the relative abundance of phenylphenanthrenes to their alkylated counterparts-methylphenanthrenes. The Ordovician oils in the Tabei Uplift have quite low 3-PhP/3-MP ratios (\0.10), indicating their marine carbonate origin, associating with low Pr/Ph ratios (pristane/phytane), high ADBT/ ADBF values (relative abundance of alkylated dibenzothiophenes to alkylated dibenzofurans), low C 30 diahopane/C 30 hopane ratios, and low Ts/(Ts ? Tm) (18a-22, 29, 30-trisnorneohopane/(18a-22, 29, 30-trisnorneohopane ? 17a-22, 29, 30-trisnorhopane)) values. In contrast, the oils from Mesozoic and Paleogene sandstone reservoirs and related Mesozoic lacustrine mudstones have relatively higher 3-PhP/ 3-MP ratios ([0.10), associating with high Pr/Ph, low ADBT/ ADBF, high Ts/(Ts ? Tm), and C 30 diahopane/C 30 hopane ratios. Therefore, the occurrence of significant amounts of phenylphenanthrenes in oils typically indicates that the organic matter of the source rocks was deposited in a suboxic environment with mudstone deposition. The phenylphenanthrenes may be effective molecular markers, indicating depositional environment and lithology of source rocks.

Practical Application of Reservoir Geochemistry in Petroleum Exploration: Case Study from a Paleozoic Carbonate Reservoir in the Tarim Basin (Northwestern China)

“…The source and origin of the Ordovician petroleum in the cratonic region of the Tarim Basin has long been controversial, because oils were highly thermally mature and deep wells which penetrate potential source rock intervals are rare. , The Cambrian to Lower Ordovician and Middle–Upper Ordovician strata are potential source beds for petroleum accumulations in the Ordovician reservoir. − Various molecular markers and related geochemical indicators have been applied in oil population classification and oil–source correlation for the Ordovician reservoir in the cratonic region of the Tarim Basin. In this study, a total of 15 geochemical parameters that have been successfully used in previous studies in the Tabei Uplift were employed in oil family classification in the Halahatang Oilfield.…”

Phenyldibenzofurans and Methyldibenzofurans in Source Rocks and Crude Oils, and Their Implications for Maturity and Depositional Environment

“…The majority of oil accumulations mainly occur in the Middle and Upper Ordovician carbonate rocks in the Tabei Uplift. Based on various organic geochemical parameters, two petroleum families can be classified in the Tabei Uplift. ,− Oil samples selected from the Ordovician reservoir in the Halahatang Oilfield are considered to derive from the Middle-Upper Ordovician marine carbonates. ,− …”

“…The Fushan Depression, situated in the south of the Qiongzhou Strait, north of Hainan Island, is a Mesozoic–Cenozoic rifting half-graben. , The majority of the oils were discovered mainly in the sandstone reservoir of the third member of the Eocene Liushagang Formation. , Oil accumulation is dominated by light oils or condensates. , The geological settings for the Fushan Depression have been summarized in numerous references. ,,,,, Crude oils discovered in the sandstone reservoir of the third member of the Eocene Liushagang Formation in the Fushan Depression are considered to be typical terrestrial-sourced high-mature oils. ,,,,, Here, all of the oil samples collected from the Fushan Depression represent oils originated from source rocks deposited in a typical terrestrial fluvial/deltaic/fresh water lacustrine environment.…”

“…36,37 Oil accumulation is dominated by light oils or condensates. 33,34 The geological settings for the Fushan Depression have been summarized in numerous references. 13,17,19,31,36,37 Crude oils discovered in the sandstone reservoir of the third member of the Eocene Liushagang Formation in the Fushan Depression are considered to be typical terrestrial-sourced high-mature oils.…”

Geochemistry and origin of Ordovician oils in the Rewapu Block of the Halahatang Oilfield (NW China)

“…Halahatang Oilfield, located in the Tabei Uplift, is one of the most prolific oilfields of the Paleozoic carbonate reservoirs in the cratonic region of the Tarim Basin, northwestern China (Zhu et al 2012;Chang et al 2013a, b;Zhao et al 2015;Huang et al 2016;Liu et al 2016;Xiao et al 2016;Fang et al 2017a;Li et al 2018). Petroleum with different densities, including ultra-heavy oils, heavy oils, normal oils, light oils and condensates, has been discovered in this region during recent oil exploration (Zhu et al 2012;Chang et al 2013a;Cui et al 2013;Xiao et al 2016;Li et al 2018).…”