Lower Paleozoic source rocks and natural gas origins in Ordos Basin, NW China

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

Energy Exploration & Exploitation ◽

10.1177/0144598716679962 ◽

2016 ◽

Vol 35 (1) ◽

pp. 103-121 ◽

Cited By ~ 8

Author(s):

Wenxue Han ◽

Shizhen Tao ◽

Guoyi Hu ◽

Weijiao Ma ◽

Dan Liu ◽

...

Keyword(s):

Natural Gas ◽

Ordos Basin ◽

Light Hydrocarbon ◽

Source Rocks ◽

Higher Plant ◽

Gas Field ◽

Gas Source ◽

Upper Paleozoic ◽

Methyl Cyclohexane ◽

Normal Stage

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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Natural gas accumulation and models in Ordovician carbonates, Ordos Basin, NW China

Petroleum Exploration and Development ◽

10.1016/s1876-3804(14)60050-1 ◽

2014 ◽

Vol 41 (4) ◽

pp. 437-448 ◽

Cited By ~ 14

Author(s):

Yanru GUO ◽

Jinhua FU ◽

Xinshan WEI ◽

Wanglin XU ◽

Liuyi SUN ◽

...

Keyword(s):

Natural Gas ◽

Ordos Basin ◽

Nw China ◽

Gas Accumulation

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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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Pore Structures of the Lower Permian Taiyuan Shale and Limestone in the Ordos Basin and the Significance to Unconventional Natural Gas Generation and Storage

Geofluids ◽

10.1155/2022/3156547 ◽

2022 ◽

Vol 2022 ◽

pp. 1-16

Author(s):

L. Zhang ◽

Q. Zhao ◽

C. Wu ◽

Z. Qiu ◽

Q. Zhang ◽

...

Keyword(s):

Organic Matter ◽

Natural Gas ◽

Shale Gas ◽

Pore Volume ◽

Ordos Basin ◽

Source Rocks ◽

Taiyuan Formation ◽

Oil Generation ◽

Unconventional Natural Gas ◽

The Ordos Basin

In the Ordos Basin, multiple sets of coal seams, organic-rich shale, and limestone are well developed in the Permian Taiyuan Formation, which are favorable targets for collaborative exploration of various types of unconventional natural gas resources, including coalbed methane, shale gas, and tight gas. In this study, core samples from the Permian Taiyuan Formation in the eastern margin of the Ordos Basin were used to carry out a series of testing and analysis, such as the organic matter characteristics, the mineral composition, and the pore development characteristics. In the shale of the Taiyuan Formation, the total organic carbon (TOC) content is relatively high, with an average of 5.38%. A thin layer of black shale is developed on the top of the Taiyuan Formation, which is relatively high in TOC content, with an average of 9.72%. The limestone in the Taiyuan Formation is also relatively high in organic matter abundance, with an average of 1.36%, reaching the lower limit of effective source rocks (>1%), being good source rocks. In the shale of the Taiyuan Formation, various types of pores are well developed, with relatively high overall pore volume and pore-specific surface area, averaging 0.028 ml/g and 13.28 m2/g, respectively. The pore types are mainly mineral intergranular pores and clay mineral interlayer fractures, while organic matter-hosted pores are poorly developed. The limestone of the Taiyuan Formation is relatively tight, with lower pore volume and pore-specific surface area than those of shale, averaging 0.0106 ml/g and 2.72 m2/g, respectively. There are mainly two types of pores, namely, organic matter-hosted pores and carbonate mineral dissolution pores, with a high surface pore rate. The organic matter in the limestone belongs to the oil-generation kerogen. During thermal evolution, the organic matter has gone through the oil-generation window, generating a large number of liquid hydrocarbons, which were cracked into a large number of gaseous hydrocarbons at the higher mature stage. As a result, a large number of organic matter-hosted pores were generated. The study results show that in the Ordos Basin, the shale and limestone of the Permian Taiyuan Formation have great potential in terms of unconventional natural gas resources, providing a good geological basis for the collaborative development of coal-bearing shale gas and tight limestone gas in the Taiyuan Formation.

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Environmental Impact of Exploration from Unconventional Gas Deposits in Poland

Ecological Chemistry and Engineering S ◽

10.1515/eces-2015-0043 ◽

2015 ◽

Vol 22 (4) ◽

pp. 703-717

Author(s):

Jan Macuda ◽

Monika Konieczyńska

Keyword(s):

Natural Gas ◽

Environmental Impact ◽

Hydraulic Fracturing ◽

Qualitative Evaluation ◽

Gas Production ◽

Source Rocks ◽

Fracturing Fluid ◽

Horizontal Section ◽

Lower Paleozoic ◽

Natural Gas Production

Abstract Shale formations have been recently treated only as source rocks and sealing packages mainly of conventional deposits. At present shales, which have a considerable concentration of highly mature organic matter appearing in complexes of over 30 m thick are used as unconventional sources for natural gas production with the use of advanced drilling technologies. Natural gas production in such rock formations necessitates performing a horizontal section in the borehole and a big number of hydraulic fracturing jobs. The unconventional shale gas deposits have been prospected also in Poland for a couple of years. Exploration works mainly concentrate on a vast area passing from Pomerania through Mazowsze to the Lublin region in Poland. The analysis of the geologic analyses reveals that the most perspective are shales in the Lower Paleozoic at a depth of 2500 m in the eastern part to about 4000 m in the western part of the area. The paper is focused on the quantitative and qualitative evaluation of environmental impact of natural gas exploration works from unconventional deposits. Special attention was paid to the hydraulic fracturing jobs in shales, which create particular hazard for water and soil environment. These hazards already appear at the stage of preliminary works, when big quantities of chemicals and water for frac jobs are stored in the rig area, and then, during realization of works, when the spent hydraulic fracturing fluid may penetrate the water-bearing horizons in the caprock. The composition of fracturing fluid used in Gapowo B-1A well are given along with the results of chemical analyses of a few parts of spent fracturing fluid samples pumped out from the borehole. The fluid turned out to be high in salt (high specific electrolyte conductance (SEC) and total dissolved substances (TDS) and a high toxicity for most of the living organisms). For this reason the spent fracturing fluid should not enter the environment without control.

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