Light hydrocarbon geochemical characteristics and their application in Upper Paleozoic, Shenmu gas field, Ordos Basin

Light hydrocarbon has abundant geochemical information, but there are few studies on it in Shenmu gas field. Taking Upper Paleozoic in Shenmu gas field as an example, authors use gas chromatography technology to study light hydrocarbon systematically. The results show that (1) The Shenmu gas field is mainly coal-derived gas, which is mixed by partial oil-derived gas due to the experiment data. (2) Based on K1, K2 parameter and Halpern star chart, the Upper Paleozoic gas in Shenmu gas field belongs to the same petroleum system and the depositional environment of natural gas source rocks should be homologous. (3) The source rocks are mainly from terrestrial higher plant origins and belong to swamp facies humic due to methyl cyclohexane index and Mango parameter intersection chart, which excluded the possibility of the Upper Paleozoic limestone as source rocks. (4) The isoheptane ranges from 1.45 to 2.69 with an average of 2.32, and n-heptane ranges from 9.48 to 17.68% with an average of 11.71%, which is below 20%. The maturity of Upper Paleozoic gas in Shenmu gas field is low-normal stage, which is consistent with Ro data. (5) The Upper Paleozoic natural gas in the Shenmu gas field did not experience prolonged migration or secondary changes, thus can be analyzed by light hydrocarbon index precisely.

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Significance and evolution characteristics of the isobutane/n-butane ratio of natural gas

Energy Exploration & Exploitation ◽

10.1177/0144598719880648 ◽

2019 ◽

Vol 38 (2) ◽

pp. 494-518

Author(s):

Nian Liu ◽

Nansheng Qiu ◽

Zhenming Li ◽

Chuan Cai ◽

Xinjie Shan ◽

...

Keyword(s):

Natural Gas ◽

Mathematical Models ◽

Source Rock ◽

Ordos Basin ◽

The United States ◽

Source Rocks ◽

Initial Increase ◽

Gas Field ◽

Gas Source ◽

Carbonium Ion

In previous studies, two conflicting conclusions existed, which were: (a) the isobutane/n-butane ratio of natural gas increases with the increasing maturity (Ro) of source rocks and (b) decreases with the increasing Ro. In this paper, the correlations between the isobutane/n-butane ratios, dryness of natural gases, and the Ro values of source rocks of 77 gas samples from Cretaceous and Tertiary in Kuqa Depression, Tarim Basin, Triassic Xujiahe Formation in central Sichuan Basin, Carboniferous–Permian in Sulige and Yulin gas field, Ordos Basin, China, and 80 shale gas samples from Mississippian Barnett Shale in the Fort Worth Basin, the United States are analyzed to reveal the evolution of the isobutane/n-butane ratios, then mathematical models of the isobutane/n-butane ratios and Ro are attempted to be established. Results show that the isobutane/n-butane ratio initially increases and then decreases with increasing Ro, both coal-derived gas and oil-type gas. Diverse types of kerogens may be responsible for the different corresponding Ro values when the isobutane/n-butane ratios of gases reach their maximum values. The initial increase in the isobutane/n-butane ratios with increasing Ro is the reason that isobutane is mainly generated at a higher rate by carbonium ion reaction of α-olefins with protons during kerogen primary cracking at lower maturity, whereas free radical reactions to form n-butane relatively quickly during oil cracking at higher maturity and isobutane cracked at a higher rate during the wet gas cracking stage may result in the terminal decreases in the isobutane/n-butane ratios. Besides, mathematical models of the isobutane/n-butane ratios of different types of natural gas and maturity are established. Therefore, the maturity of gas source rock can be obtained quickly based on the models using the isobutane/n-butane ratio combined with other component information (such as dryness, wetness, etc.), which is of great significance to the characterization of natural gas maturity and gas source rock correlation.

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Natural gas migration and accumulation model and favorable exploration targets in Ordovician dolomite in Jingxi, Ordos Basin

Energy Exploration & Exploitation ◽

10.1177/0144598717743264 ◽

2017 ◽

Vol 36 (3) ◽

pp. 373-387

Author(s):

Jingdong Liu ◽

Youlu Jiang ◽

Xinshe Liu ◽

Rongwei Zhu

Keyword(s):

Natural Gas ◽

Ordos Basin ◽

Source Rocks ◽

Late Triassic ◽

Gas Migration ◽

Formation Model ◽

Long Distance ◽

Gas Reservoir ◽

Upper Paleozoic ◽

Bottom To Top

The Ordovician dolomite reservoir in Ma55–Ma510 sub-members in Jingxi in Ordos Basin is a newly discovered field with multiple natural gas pools. The gas accumulation patterns of the reservoir are unclear. Considering the geological background, the genesis, migration, and accumulation of natural gas in Jingxi were studied systematically, and favorable exploration targets were predicted. Natural gas in Ma55–Ma510 sub-members is a mixture of Upper Paleozoic and Ordovician products. The Upper Paleozoic coaliferous gas was mainly expulsed downward through the hydrocarbon-providing window where the coal-bearing source rocks made contact with the dolomite reservoirs. The gas then migrated from west to east and accumulated under the condition of lithology variation. The Ordovician petroliferous gas mainly migrated from bottom to top through fractures and mixed with the coaliferous gas in Ma55–Ma510 sub-members. The natural gas reservoir formation model was summarized as the migration of gas over a short distance and partial charging into the dolomite reservoirs from the Late Triassic to Middle Jurassic, and the migration of gas over a long distance and massive charging into the dolomite reservoirs during the Late Cretaceous. Ma55 and Ma56 sub-members are the focus of further exploration, and petroliferous gas in Ma57–Ma510 sub-members deserves attention. The dolomite reservoirs of the hydrocarbon-providing windows and the east of these locations are the favorable exploration targets.

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Genetic types and sources of Lower Paleozoic natural gas in the Daniudi gas field, Ordos Basin, China

Energy Exploration & Exploitation ◽

10.1177/0144598716687932 ◽

2017 ◽

Vol 35 (2) ◽

pp. 218-236 ◽

Cited By ~ 2

Author(s):

Xiaoqi Wu ◽

Jianhui Zhu ◽

Chunhua Ni ◽

Kuang Li ◽

Yanqing Wang ◽

...

Keyword(s):

Natural Gas ◽

Ordos Basin ◽

Source Rocks ◽

Light Hydrocarbons ◽

Upper Ordovician ◽

Gas Field ◽

Lower Paleozoic ◽

Upper Carboniferous ◽

Associated Gas ◽

The Ordos Basin

The molecular composition, stable carbon and hydrogen isotopes, and light hydrocarbons of the Lower Paleozoic natural gas in the Daniudi gas field in the Ordos Basin were investigated to study the geochemical characteristics. The Lower Paleozoic gas in the Daniudi gas field displays methane contents of 87.41–93.34%, dryness coefficients (C1/C1–5) ranging from 0.886 to 0.978, δ13C1 and δ13C2 values ranging from −40.3 to −36.4‰, with an average of −38.3‰, and from −33.6 to −24.2‰, with an average of −28.4‰, respectively, and δD1 values ranging from −197 to −160‰. The alkane gas generally displays positive carbon and hydrogen isotopic series, and the C7 and C5–7 light hydrocarbons of the Lower Paleozoic gas are dominated by methylcyclohexane and iso-alkanes, respectively. The Lower Paleozoic gas in the Daniudi gas field is mixed from coal-derived and oil-associated gases, similar to that observed in the Jingbian gas field. The oil-associated gas in the Lower Paleozoic gas is secondary oil cracking gas and displays a lower cracking extent than that in the Jingbian gas field. The coal-derived gas in the Lower Paleozoic gas in the Daniudi gas field migrated from the Upper Paleozoic gas through the window area where the iron–aluminum mudstone caprocks in the Upper Carboniferous Benxi Formation were missing. The oil-associated gas in the Lower Paleozoic gas in the Daniudi gas field was probably derived from presalt source rocks in the Lower Ordovician Majiagou Formation rather than the limestone in the Upper Carboniferous Taiyuan Formation. It seems unlikely that the marlstone in the Upper Ordovician Beiguoshan Formation and shale in the Middle Ordovician Pingliang Formation on the western and southwestern margins of the Ordos Basin contributed to the oil-associated gas in the Lower Paleozoic gas in the Daniudi gas field.

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Quantitative identification and research of mixed-source natural gas-example of natural gas in Jingbian gas field

World Journal of Engineering ◽

10.1260/1708-5284.11.2.147 ◽

2014 ◽

Vol 11 (2) ◽

pp. 147-156

Author(s):

Yifeng Wang ◽

Jian Li ◽

Jianfa Chen ◽

Chengshan Li

Keyword(s):

Natural Gas ◽

Source Rock ◽

Ordos Basin ◽

Weighted Average ◽

Gas Field ◽

Lower Paleozoic ◽

Upper Paleozoic ◽

Geological Conditions ◽

Weathered Crust ◽

Geochemistry Characteristics

It is shown in natural gas proportion mixing experiments that a mixed-source natural gas is the physical combination of end member gas. Both the carbon and hydrogen isotopes in the mixed-source natural gas can be expressed by the weighted average of corresponding components content and isotopes of end member gas. Under certain geological setting, the selection of end member gas is the key to mixed-source ratio calculation. Then, it's better to estimate the mixed-source ratio with δ13C1 and component data according to the weighted average calculation formula. The analysis on natural gas geochemistry characteristics show that the natural gas extracted from Jingbian Gas Field in the Ordos Basin is mainly an upper Paleozoic coal-derived gas. In the analysis of geological conditions for reservoir forming and characteristics of natural gas, natural gas from Longtan 1 Well and Tao 6 Well were selected as the end member gases of lower Paleozoic oil-type gas and upper Paleozoic coal-type gas respectively to calculate the mixed-source ratio of natural gas in Jingbian Gas Field. The ratio of upper Paleozoic coal-derived gas mostly accounts for over 70% and its average ratio reaches 81%. Therefore, the exploration of natural gas of Ordos Basin should be focused on the upper palaeozoic coal source rock, and attention should be paid to the matching of coal source rock in the exploration of weathered crust gas deposit.

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The Evolution of Diagenetic Fluids and Accumulation Characteristics of Tight Sandstone Reservoir in Upper Paleozoic, Southwestern Ordos Basin

Geofluids ◽

10.1155/2021/5541540 ◽

2021 ◽

Vol 2021 ◽

pp. 1-20

Author(s):

Ruijing Zhu ◽

Rongxi Li ◽

Xiaoli Wu ◽

Xiaoli Qin ◽

Bangsheng Zhao ◽

...

Keyword(s):

Natural Gas ◽

Clay Minerals ◽

Ordos Basin ◽

Source Rocks ◽

Fluid Inclusion Study ◽

Hydrocarbon Accumulation ◽

Tight Sandstone ◽

Upper Paleozoic ◽

Two Stages ◽

Accumulation Characteristics

The Upper Paleozoic in the southwestern Ordos Basin has significant potential for natural gas exploration. This study investigated the diagenetic fluid evolution and hydrocarbon accumulation characteristics of He 8 section from Permian Lower Shihezi formation and Shan 1 section from Shanxi formation tight sandstone reservoirs by petrographic observation, scanning electron microscope imaging, fluid inclusion study, and laser Raman spectrum analysis. The results show that He 8 section and Shan 1 section reservoirs are mainly composed of quartz sandstone, subordinate arkose quartz sandstone, and lithic quartz sandstone, with minor lithic sandstone and lithic arkose sandstone. The major pores are intergranular dissolved pores. The main diagenetic minerals include quartz overgrowth, siliceous cement, carbonate cement, illite, montmorillonite, and mixed-layer clay minerals. The overall diagenetic features show strong compaction, multistage siliceous and calcareous cements, and abundant clay minerals, strong dissolution, and well-developed fractures. Two stages of fluid inclusions developed in the He 8 and Shan 1 sections recorded the migration and accumulation of the early-stage and late-stage natural gas, respectively. The reservoir in the study area experienced early and late diagenetic stages, and its formation was simultaneous with or after its densification. The diagenetic environment changed from alkaline to acidic and again into alkaline. There are two stages of fluid activities in the study area, namely, the early diagenetic stage corresponding to hydrocarbon generation and migration and the late diagenetic stage corresponding to hydrocarbon accumulation. This study suggests that Upper Paleozoic natural gas migrated into the reservoir in Weibei Uplift, Yishan Slope, and Tianhuan Depression tectonic units during 220-197 Ma, and the large-scale migration and accumulation occurred in these tectonic units at different times. No natural gas was generated in the west margin of the basin because the temperatures of the hydrocarbon source rocks in the Upper Paleozoic were below the gas window.

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