Characterization of the import of Botryococcus to the source rocks of the upper member of the Lower Ganchaigou Formation in the Yingxi area, Qaidam basin, China

To date, few isotope age constraints on primary oil migration have been reported. Here we present U-Pb dating and characterization of two fracture-filling, oil inclusion-bearing calcite veins hosted in the Paleocene siliciclastic mudstone source rocks in Subei Basin, China. Deposition age of the mudstone formation was estimated to be ca. 60.2−58.0 Ma. The first vein consists of two major phases: a microcrystalline-granular (MG) calcite phase, and a blocky calcite phase, each showing distinctive petrographic features, rare earth element patterns, and carbon and oxygen isotope compositions. The early MG phase resulted from local mobilization of host carbonates, likely associated with disequilibrium compaction over-pressuring or tectonic extension, whereas the late-filling blocky calcite phase was derived from overpressured oil-bearing fluids with enhanced fluid-rock interactions. Vein texture and fluorescence characteristics reveal at least two oil expulsion events, the former represented by multiple bitumen veinlets postdating the MG calcite generation, and the latter marked by blue-fluorescing primary oil inclusions synchronous with the blocky calcite cementation. The MG calcite yields a laser ablation−inductively coupled plasma−mass spectrometry U-Pb age of 55.6 ± 1.4 Ma, constraining the earliest timing of the early oil migration event. The blocky calcite gives a younger U-Pb age of 47.8 ± 2.3 Ma, analytically indistinguishable from the U-Pb age of 46.5 ± 1.7 Ma yielded by the second calcite vein. These two ages define the time of the late oil migration event, agreeing well with the age estimate of 49.7−45.2 Ma inferred from fluid-inclusion homogenization temperature and published burial models. Thermodynamic modeling shows that the oil inclusions were trapped at ∼27.0−40.9 MPa, exceeding corresponding hydrostatic pressures (23.1−26.7 MPa), confirming mild-moderate overpressure created by oil generation-expulsion. This integrated study combining carbonate U-Pb dating and fluid-inclusion characterization provides a new approach for reconstructing pressure-temperature-composition-time points in petroleum systems.

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Mineralogical and isotopic characterization of graphite deposits in the periphery of the Qaidam Basin, northeast Tibetan Plateau, China and its indication to the Great Oxidation Event and Lomagundi-Jatuli Event.

10.7185/gold2021.5021 ◽

2021 ◽

Author(s):

Maoqiang Yan ◽

Wei Junhao ◽

Zhang Daohan ◽

Jan Huizenga

Keyword(s):

Tibetan Plateau ◽

Qaidam Basin ◽

Great Oxidation Event ◽

Isotopic Characterization

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Compositional Characterization of Expelled and Residual Oils in the Source Rocks from Oil Generation–Expulsion Thermal Simulation Experiments

ACS Omega ◽

10.1021/acsomega.9b00260 ◽

2019 ◽

Vol 4 (5) ◽

pp. 8239-8248 ◽

Cited By ~ 2

Author(s):

Yahe Zhang ◽

Yifeng Wang ◽

Wei Ma ◽

Jincheng Lu ◽

Yuhong Liao ◽

...

Keyword(s):

Thermal Simulation ◽

Source Rocks ◽

Simulation Experiments ◽

Oil Generation ◽

Compositional Characterization

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Oil and gas enrichment patterns and major controlling factors for stable and high production of tight lacustrine carbonate rocks, a case study of Yingxi area in Qaidam Basin, West China

Carbonates and Evaporites ◽

10.1007/s13146-019-00529-9 ◽

2019 ◽

Vol 34 (4) ◽

pp. 1815-1831 ◽

Cited By ~ 1

Author(s):

Xinmin Ma ◽

Chenggang Huang ◽

Yajun Shi

Keyword(s):

Carbonate Rocks ◽

Oil And Gas ◽

Qaidam Basin ◽

Controlling Factors ◽

West China ◽

Yingxi Area ◽

Lacustrine Carbonate ◽

High Production

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Geochemical characterization of hydrocarbon source rocks of the Triassic-Jurassic time interval in the Mandawa basin, southern Tanzania: Implications for petroleum generation potential

South African Journal of Geology ◽

10.25131/sajg.123.0037 ◽

2020 ◽

Vol 123 (4) ◽

pp. 587-596

Author(s):

A. Emanuel ◽

C.H. Kasanzu ◽

M. Kagya

Keyword(s):

Source Rocks ◽

Geochemical Data ◽

Time Interval ◽

Type I ◽

Hydrocarbon Generation ◽

Type Ii ◽

Geochemical Characterization ◽

Type Iii ◽

Petroleum Generation

Abstract Triassic to mid-Jurassic core samples of the Mandawa basin, southern Tanzania (western coast of the Indian Ocean), were geochemically analyzed in order to constrain source rock potentials and petroleum generation prospects of different stratigraphic formations within the coastal basin complex. The samples were collected from the Mihambia, Mbuo and Nondwa Formations in the basin. Geochemical characterization of source rocks intersected in exploration wells drilled between 503 to 4042 m below surface yielded highly variable organic matter contents (TOC) rated between fair and very good potential source rocks (0.5 to 8.7 wt%; mean ca. 2.3 wt%). Based on bulk geochemical data obtained in this study, the Mandawa source rocks are mainly Type I, Type II, Type III, mixed Types II/III and Type IV kerogens, with a predominance of Type II, Type III and mixed Type II/III. Based on pyrolysis data (Tmax 417 to 473oC; PI = 0.02 to 0.47; highly variable HI = 13 to 1 000 mg/gTOC; OI = 16 to 225 mg/g; and VR values of between 0.24 to 0.95% Ro) we suggest that the Triassic Mbuo Formation and possibly the mid-Jurassic Mihambia Formation have a higher potential for hydrocarbon generation than the Nondwa Formation as they are relatively thermally mature.

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Characterization of the reservoir-caprock of the large basement reservoir in the Dongping field, Qaidam Basin, China

Energy Exploration & Exploitation ◽

10.1177/0144598718772317 ◽

2018 ◽

Vol 36 (6) ◽

pp. 1498-1518 ◽

Cited By ~ 3

Author(s):

Feng Ma ◽

Wei Yang ◽

Yongshu Zhang ◽

Hongzhe Li ◽

Mei Xie ◽

...

Keyword(s):

Qaidam Basin ◽

Solution Space ◽

Source Rocks ◽

Dominant Factor ◽

Basement Rock ◽

Gas Reservoirs ◽

Large Reservoir ◽

Heterogeneous Distribution ◽

Gas Accumulation ◽

The World

The basement gas reservoir in the Dongping field in the Qaidam Basin is a large reservoir that is different from other basement reservoirs around the world. The basement reservoir does not contain thick mudstone with abundant organic matter that acts as both a source rock and a caprock. The natural gas came from lateral Jurassic source rocks. The basement lithologies in wellblocks Dp3, Dp1, and Dp17 are granite, granitic gneiss, and limestone with slate, respectively, but they all provide effective reservoir space for gas accumulation. The average porosities are 3.3%, 5.2%, and 3.6%, respectively, and the average permeabilities are 0.66 mD, 0.60 mD, and 0.57 mD, respectively. Tectonic fractures are the main factor for improving the physical properties of the reservoir, and secondary solution space is the key factor for the high and stable gas production in the study area. The E1 + 2 Formation, which contains abundant anhydrite, unconformably overlies the basement rock. Some of the anhydrite was deposited as cement and filled the fractures and pores, which led to decreased porosity and to the formation of a tight caprock with a high breaking pressure for hydrocarbon accumulation. The caprock becomes thinner from the lowland to the uplift, and it is missing in wellblock Dp3, which led to the heterogeneous distribution of gas. Anhydrite-bearing caprock is the dominant factor that controls the gas accumulation in the basement rock reservoir in the Dongping field. Studying the spatial distribution of the anhydrite-bearing caprock is important to the exploration and development of basement gas reservoirs in the Qaidam Basin. This unique gas accumulation mechanism in a basement rock reservoir may inspire new ideas for exploring basement oil and gas reservoirs around the world.

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