Co-evolution of paleo-environment and bio-precursors in a Permian alkaline lake, Mahu mega-oil province, Junggar Basin: Implications for oil sources

Xia, Liuwen; Cao, Jian; Bian, Lizeng; Hu, Wenxuan; Wang, Tingting; Zhi, Dongming; Tang, Yong; Li, Erting

doi:10.1007/s11430-021-9861-4

Cited by 24 publications

(10 citation statements)

References 45 publications

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“…Zhang et al (2019) identified organic‐rich shales of Shahejie Formation in Dongpu Sag of Bohai Bay Basin by optical microscopy and scanning electron microscopy, and found many dinoflagellates, cyanobacteria, green algae and charophytes. Xia et al (2022) confirmed the presence of Dunaliella in the shale of Fengcheng Formation in the Mahu Sag, Junggar Basin using organic geochemical indicators such as the C 28 /C 29 sterane ratio and β‐carotene index.…”

Section: Biological Activity Of the Saline Lacustrine Basinmentioning

confidence: 99%

Organic matter enrichment mechanism in saline lacustrine basins: A review

Wang

Bai³

et al. 2023

Geological Journal

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Organic‐rich shale in saline lacustrine basins holds significant importance as a source rock for conventional hydrocarbon exploration and has emerged as a prominent target for unconventional hydrocarbon exploration and development in recent years. Based on saline lacustrine basins, this paper provides a summary of the organic matter enrichment mechanisms in saline lacustrine basins, considering sedimentary characteristics, biological activities, factors for the organic matter enrichment and consumption, and hydrocarbon generation. The implications for these factors are discussed in relation to the distribution prediction of high‐quality lacustrine shale district settings and the exploration and development of shale oil. Saline lacustrine basins undergo distinct evolutionary stages, each corresponding to different sedimentary stages involving carbonate minerals, sulphate minerals, and alkaline minerals. Moreover, these basins exhibit diverse biological types and experience extensive biological activities. The prosperity of organisms and the accumulation of sedimentary organic matter are ensured by halophilic organisms. Organic matter enrichment in saline lacustrine basins is influenced by two main aspects: the primary productivity of organic matter, which is promoted by the proliferation of halophilic organisms, and the efficient preservation of organic matter facilitated by the strong reducing environment resulting from promoted water salinity stratification. The organic matter consumption in saline lacustrine basins involves bacterial sulphate reduction (BSR) in the early stages, thermochemical sulphate reduction (TSR) in the late stages, and dilution of salt minerals with higher depositional rates. of the presence of salt beds and saline minerals positively influences hydrocarbon generation and expulsion in organic‐rich shale within saline lacustrine deposition. Consequently, continental saline lacustrine basins in China offer favourable conditions for the formation of organic‐rich shale and present broad prospects for the exploration of shale oil and gas resources.

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Section: Biological Activity Of the Saline Lacustrine Basinmentioning

confidence: 99%

Organic matter enrichment mechanism in saline lacustrine basins: A review

Wang

Bai³

et al. 2023

Geological Journal

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“…Three mature to highly mature source rocks exist in the Shawan Sag-the Lower Wuerhe (P 2 w), Fengcheng (P 1 f), and Jiamuhe (P 1 j) formations-leading to large-scale hydrocarbon production in the P 3 w Formation (Zhang et al, 2015;Du et al, 2019;Xia et al, 2022). Two periods of oil and gas emplacement occurred (during the Middle Jurassic and Early Cretaceous) as the faults became active allowing migration (Wang, 2016;Pan et al, 2021).…”

Section: Geologic Settingmentioning

confidence: 99%

Authigenic calcite as a record of geologic fluids in siliciclastic rocks: Evidences from the Upper Permian Wuerhe Formation, Junggar basin, NW China

Qu²,

Huang³

et al. 2023

Front. Earth Sci.

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The identification of geologic fluids and related fluid–rock interactions during diagenesis is the subject of much research in sedimentary petrology. Authigenic calcite potentially provides a record of geologic fluids and it occurs heterogeneously in the Upper Permian Wuerhe Formation (P3w) in the Shawan Sag, Junggar Basin, which has a complex history of geologic fluid activity. This provides an ideal opportunity to study the effectiveness of authigenic calcite in tracing fluids. We conducted optical, cathodoluminescence (CL), and scanning electron microscopic observations, as well as the major and trace element and stable carbon and oxygen isotopes of authigenic calcite. The results show that three generations of calcite were precipitated in the P3w Formation, and the diagenetic fluid was affected to varying degrees by paleo-meteoric water and hydrocarbon-bearing fluids. During early diagenesis, diagenetic fluid with low Mn contents precipitated the amorphous early-stage calcite (dark red in CL images, MnO <1.5%, δ13C = −8.6‰ to 2.1‰, VPDB). Its carbon source was mainly meteoric CO2. During mesodiagenesis, the limited hydrocarbon emplacement during the Middle Jurassic enriched the pore fluids in Mn and 13C-depleted organic derived CO2, subsequently precipitating the late-stage sparry calcite I (orange in CL images with MnO of 2.5%–4% and δ13C of −14.5‰ to −8.1‰). The carbon in this calcite came from the dissolution of early-stage calcite and CO2 generated by decarboxylation of organic acids. During the Early Cretaceous, large-scale hydrocarbon charging occurred and the pore fluids were further enriched in Mn and organic derived CO2, eventually precipitating the late-stage sparry calcite II (bright yellow in CL images with MnO of >4% and δ13C of −25.7‰ to −14.9‰). Its carbon source was mainly CO2 produced by the decarboxylation of organic acids. The precipitation of abundant late-stage sC-depleted calcite suggests that the hydrocarbons were oxidized to organic acids in the reservoir. The two periods of hydrocarbon charging caused the dissolution of laumontite and the early-stage calcite, forming secondary minerals and dissolution pores, which increased the porosity and permeability of the rock. Therefore, authigenic calcite is a useful tracer of fluid properties, fluid–rock interactions, and alteration processes in petroliferous basins.

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“…The Mahu Sag is part of the Central Depression and is one of the most hydrocarbon-rich sags in the basin. Two prolific oil provinces with an area of more than 100 km 2 have been discovered in the interior of the Mahu Sag and its northern fault zone (Lei et al, 2017; Tang et al, 2019; Xia et al, 2022). Our study area is located in the southern part of the Mahu Sag and includes four secondary structural units: (1) the Hongche fault zone, (2) the Ke-Bai fault zone, (3) the Zhongguai uplift, and (4) the southern Mahu Sag (Figure 1(b)).…”

Section: Geological Settingmentioning

confidence: 99%

Source identification and accumulation restoration of complex oil reservoirs in Mahu Sag, Junggar Basin

Zhi

Liu

et al. 2023

Energy Exploration & Exploitation

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Oil sources and accumulations in complex oil reservoirs of superimposed basins are difficult to identify and recover because of multiple kitchens and multistage charging processes. Constraining the oil sources and characterizing their accumulation patterns is a critical challenge. In this study, 46 crude oils from the Upper Wuerhe Formation, a widely distributed oil reservoir in the Mahu Sag of the Junggar Basin, NW China, are geochemically characterized to assess their sources and spatial distribution. These oils are divided into four groups: group I oils (characterized by high β-carotane and gammacerane concentrations, low C21/C23 and (C19 + C20)/C23 tricyclic terpane ratios, and low Pr/Ph ratios); group II oils (characterized by low β-carotane and gammacerane concentrations, high C21/C23 and (C19 + C20)/C23 tricyclic terpane ratios, and moderate Pr/Ph ratios); group III oils (very high Pr/Ph ratio (>3), the lowest β-carotane and gammacerane concentrations, and low tricyclic terpane concentration, but relatively high C19 and C20 tricyclic terpane abundance); and group IV oils (refered to here as geochemically hybrid, and inferred to be sourced from mixed P1f and C/P1j source rocks). The integration of oil-source correlation and geological framework indicates that oils generated from multiple kitchens are more likely to be near-sourced accumulations, providing a plausible example for oil accumulation in a complex oil reservoir of superimposed basin with several sets of kitchens and multistage oil charging history. The results show that multisource and multistage hydrocarbon accumulation is a common characteristic of prolific superimposed basins. The oil accumulation pattern must be established by carefully characterizing sources and charging processes to reduce the risk of exploration activities.

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Co-evolution of paleo-environment and bio-precursors in a Permian alkaline lake, Mahu mega-oil province, Junggar Basin: Implications for oil sources

Cited by 24 publications

References 45 publications

Organic matter enrichment mechanism in saline lacustrine basins: A review

Organic matter enrichment mechanism in saline lacustrine basins: A review

Authigenic calcite as a record of geologic fluids in siliciclastic rocks: Evidences from the Upper Permian Wuerhe Formation, Junggar basin, NW China

Source identification and accumulation restoration of complex oil reservoirs in Mahu Sag, Junggar Basin

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