Research

17 pages, 8530 KiB

Open AccessArticle

Carbonate Concretions in Triassic Yanchang Formation (Ordos Basin, China) as Evidence of Hydrothermal Activity

by Mengsi Sun, Congjun Feng and Chiyang Liu

Energies 2023, 16(11), 4523; https://doi.org/10.3390/en16114523 - 05 Jun 2023

Cited by 1 | Viewed by 1094

The discovery of concretions of Chang 7 shale formations in the Ordos basin has increased interest in the exploration of lacustrine carbonate genesis in these basins. In this paper, these concretions were sampled and used in major, trace, and isotopic geochemistry tests. We [...] Read more.

The discovery of concretions of Chang 7 shale formations in the Ordos basin has increased interest in the exploration of lacustrine carbonate genesis in these basins. In this paper, these concretions were sampled and used in major, trace, and isotopic geochemistry tests. We used a microscope to investigate these concretions, and the results showed that the concretions consisted of carbonate rocks, the calcite was hydrothermal calcite, and obvious hydrothermal activity was present in the Yanchang period. We used seismic data to interpret the faults, and we determined that tectonic activity was relatively frequent in the middle–late Triassic period and that the faults were channels for hydrothermal upwelling. During the middle–late Triassic period, tectonic movement of the basin occurred, and synsedimentary faults developed in the Yanchang Formation. As deep hydrothermal gushers rose through faults and fractures, they carried particles upward through the deep limestone strata. When the hydrothermal gushers reached the lake bottom, the particles precipitated and eventually formed concretions via diagenesis. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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21 pages, 12309 KiB

Open AccessArticle

Synergistic Evolution of Palaeoenvironment—Bionts and Hydrocarbon Generation of Permian Saline Lacustrine Source Rocks in Jimusar Sag, Junggar Basin

by Zaibo Xie, Huifei Tao, Yongqiang Qu, Tao Wu, Dongzheng Ma, Tianhai Wang, Zhen Qin, Long Su and Zhongping Li

Energies 2023, 16(9), 3797; https://doi.org/10.3390/en16093797 - 28 Apr 2023

Viewed by 1006

Abstract

This study focused on Middle Permian Lucaogou Formation saline lake source rocks, utilizing a combination of biomarkers and hydrocarbon generation thermal simulation to analyze their biological compositions, depositional environments, and hydrocarbon generation potential. The Pr/Ph ratio, Ph/nC₁₈ ratio, and Pr/ [...] Read more.

This study focused on Middle Permian Lucaogou Formation saline lake source rocks, utilizing a combination of biomarkers and hydrocarbon generation thermal simulation to analyze their biological compositions, depositional environments, and hydrocarbon generation potential. The Pr/Ph ratio, Ph/nC₁₈ ratio, and Pr/nC₁₇ ratio indicate that the Lucaogou Formation was in a reducing environment during the deposition period, and the lower part of the Lucaogou Formation (P₂l₁) is more anoxic than the upper part of the Lucaogou Formation (P₂l₂). The maturity index 20S (%) and ββ (%) reflect that the maturity of organic matter in the P₂l₁ is slightly higher than that in the P₂l₂. The G/H index and the ETR index indicate that the stratification of the water column is better during the sedimentary period of Lucaogou Formation and the salinity of the P₂l₁ is higher than that of the P₂l₂. The biomarker parameters of nC₂₁₋/nC₂₂₊, CPI, S/H, and C₂₂T/C₂₁T reflect that the organic matter of the source rocks have a higher abundance of bacteria and algae than higher plants, and the contents of bacteria are more than that of algae. The (7- + 8-MMAs)/C_max and (C₂₈ + C₂₉ − St)/St parameters indicate that cyanobacteria accounted for a certain proportion of bacteria, and the algae are mainly green algae. The co-evolution of the sedimentary environment and the biological composition reflects the control of the sedimentary paleoenvironment on biological composition. According to the relative content of cyanobacteria, green algae, and Rhodophyta, the source rocks of the upper and lower Lucaogou Formation correspond to the low-salinity type (LS-type) and the high-salinity type (HS-type), respectively. Compared with LS-type source rocks, HS-type source rocks have greater generation potential of oil and weaker gas generation potential. This study is valuable for the accurate assessment of source rocks and holds significant practical implications for the exploration of oil and gas resources. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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15 pages, 6094 KiB

Open AccessArticle

Maceral Control on the Hydrocarbon Generation Potential of Lacustrine Shales: A Case Study of the Chang 7 Member of the Triassic Yanchang Formation, Ordos Basin, North China

by Bei Liu, Juan Teng and Maria Mastalerz

Energies 2023, 16(2), 636; https://doi.org/10.3390/en16020636 - 05 Jan 2023

Cited by 5 | Viewed by 1126

Abstract

Organic matter (OM) type critically controls the hydrocarbon generation potential and organic pore development in black shales. However, maceral variation in lacustrine shales and its control on hydrocarbon generation potential and organic pore development are not yet well understood. In this study, 15 [...] Read more.

Organic matter (OM) type critically controls the hydrocarbon generation potential and organic pore development in black shales. However, maceral variation in lacustrine shales and its control on hydrocarbon generation potential and organic pore development are not yet well understood. In this study, 15 Chang 7 Member shale samples of the Yanchang Formation, Ordos Basin, were investigated with organic petrography, Rock-Eval pyrolysis, and a scanning electron microscope to study the maceral composition, hydrocarbon generation potential, and organic pores in this black shale succession. The results show that the studied shales are in the oil window (R_o~0.70%). OM belongs to Type I and Type III kerogen, as demonstrated by Rock-Eval pyrolysis. Macerals in the Chang 7 Member shales are composed of amorphous OM, alginite, sporinite, liptodetrinite, vitrinite, inertinite, and solid bitumen. Amorphous OM and alginite are major hydrocarbon-generating macerals, and their content determines the hydrocarbon potential of shales. Secondary organic pores were not observed in the studied Chang 7 Member shales due to either a low thermal maturity or a dominance of terrigenous OM. Maceral variation can affect the reliability of using Rock-Eval Tmax as a thermal maturity indicator. This study provides important insights into maceral control on hydrocarbon generation and organic pore development in black shales, calling for a critical evaluation of OM in black shale successions with organic petrography. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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19 pages, 7221 KiB

Open AccessArticle

Pore Characteristics and Influencing Factors of Marine and Lacustrine Shale in the Eastern Sichuan Basin, China

by Jianglin He, Lixia Zhu, Ankun Zhao, Dong Wang, Zhen Qiu and Ping Yang

Energies 2022, 15(22), 8438; https://doi.org/10.3390/en15228438 - 11 Nov 2022

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Abstract

Although almost all the shale gas in China is exploited from marine shale (Wufeng–Longmaxi Formation) in Sichuan Basin and several prolific wells, it has also been obtained in Jurassic lacustrine shale. However, the reservoir conditions of the lacustrine shale are not well understood, [...] Read more.

Although almost all the shale gas in China is exploited from marine shale (Wufeng–Longmaxi Formation) in Sichuan Basin and several prolific wells, it has also been obtained in Jurassic lacustrine shale. However, the reservoir conditions of the lacustrine shale are not well understood, which has impeded a breakthrough regarding lacustrine shale gas in Sichuan Basin. To probe the reservoir conditions of the lacustrine shale in Sichuan Basin, we take the Wufeng–Longmaxi shale and Dongyuemiao shale sampled from wells and outcrops as examples. A series of experiments were conducted, including TOC, XRD, FE-SEM, N₂ adsorption, Micro-CT, vitrinite reflectance and bitumen reflectance. The results show that the pores in marine shale are mainly composed of organic-matter-hosted pores (OM pores). However, in the lacustrine shale, the pores are mainly composed of dissolution pores and intergranular pores. The marine shale is characterized by small-caliber and large-volume pores in which cluster pores are levitated in the shale as kites and connected by past channels. However, in the lacustrine shale, the cluster pores and the past channels are mainly arranged according to the flow channels in the vertical direction. The arrangement of the pores in the marine shale is obviously deformed by compaction. The lacustrine shale is characterized by under-compaction. It can be deduced that the sweet spots for lacustrine shale gas are likely located at the areas characterized by under-compaction resulting from fluid pressure conducted upward, such as the hinge zone of syncline or the core of anticline overlap on the gas reservoirs. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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20 pages, 5326 KiB

Open AccessArticle

Geochemical Characteristics of the Chang 7 Source Rocks of the Triassic Yanchang Formation in Ordos Basin, China: Implications for Organic Matter Accumulation and Shale Oil Potential

by Lewei Hao, Xiaofeng Ma, Wenqiang Gao, Zhaocai Ren, Huifei Tao and Weikai Huang

Energies 2022, 15(20), 7815; https://doi.org/10.3390/en15207815 - 21 Oct 2022

Cited by 3 | Viewed by 1295

Abstract

The Chang 7 member of the Upper Triassic Yanchang Formation in the Ordos Basin is considered to hold the main source rocks for conventional and unconventional oil and gas. The lamination or lithology alteration in vertical and lateral directions, even over a short [...] Read more.

The Chang 7 member of the Upper Triassic Yanchang Formation in the Ordos Basin is considered to hold the main source rocks for conventional and unconventional oil and gas. The lamination or lithology alteration in vertical and lateral directions, even over a short distance, is a common feature in lacustrine source rocks. The differences in the geochemical characteristics of black shales, dark mudstones and interbedded sandstones have been scarcely reported, and their influences on the petroleum generation potential and shale oil potential are not clear. To this end, 22 core samples were collected from the Lower and Middle Chang 7 (C7-3 and C7-2) members of the Triassic from well CYX in the Qingcheng area. By conducting a series of geochemical analyses including TOC, Rock-Eval pyrolysis yields, bitumen extraction and quantification, and the separation and quantification of saturates, aromatics, resins and asphaltenes, along with biomarker analyses, several results were found. Firstly, the C7-3 and C7-2 source rocks are thermally mature and have entered into the stage of hydrocarbon generation. The C7-3 and C7-2 source rocks have a good to very good hydrocarbon generation potential especially the C7-3 black shales. Secondly, terrigenous source input is more abundant in C7-2, whereas the source input of phytoplankton, algae or microbial lipids is more abundant in C7-3. Moreover, a high TOC content basically corresponds to low wax indexes, terrigenous/aquatic ratios (TARs), and Pr/nC₁₇ and Ph/nC₁₈ ratios and high C₂₇/C₂₉ regular sterane ratios, which suggests that the source input of phytoplankton, algae or microbial lipids is favorable for OM accumulation. Third, analyses of the molecular composition of saturated fractions in shales and interbedded sandstones and the production index demonstrate the migration of petroleum from organic-rich source rocks to their organic-lean counterparts. The C7-2 dark mudstones could be considered as a potential “sweet spot” since their oil saturation index (OSI) was the highest among all the studied samples and they are more enriched in light aliphatic fractions. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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14 pages, 2359 KiB

Open AccessArticle

Characteristics of Liquid-Hydrocarbon Yield and Biomarkers in Various Thermal-Evolution Stages: A Simulation Experiment with the Middle Jurassic Source Rocks in the Northern Margin of the Qaidam Basin

by Yongxin Chen, Xilong Zhang, Xiang Li, Tao Liu, Yaru Sun, Guotao Zhu and Pengfei Ju

Energies 2022, 15(20), 7793; https://doi.org/10.3390/en15207793 - 21 Oct 2022

Viewed by 1053

Abstract

Although there are many studies on the Jurassic source rocks in the northern margin of the Qaidam Basin, the characteristics of biomarkers and products with the same source rock in different evolutionary stages are still not well understood. Such an understanding is essential [...] Read more.

Although there are many studies on the Jurassic source rocks in the northern margin of the Qaidam Basin, the characteristics of biomarkers and products with the same source rock in different evolutionary stages are still not well understood. Such an understanding is essential for accurately estimating oil and gas resources. In order to explore the hydrocarbon-generation potential of high-quality source rocks of the Middle Jurassic and the evolution of liquid hydrocarbons and biomarkers, we carried out simulation research (under hydrous conditions) at various temperatures (250, 300, 350, 400 and 450 °C) with the mudstone of the Yu 33 well in the Yuka Sag. The results revealed that the “oil window” of the Middle Jurassic source rocks in the Yuka area was 300 °C (simulation temperature, Ro = 0.84%), but this was not the peak of hydrocarbon expulsion, which was gradually reached and stabilized above 350 °C. Overall, the concentration of alkanes and aromatics increased with temperature; although the concentration of alkanes was complex in the low evolutionary stages, temperature (simulated maturity) was still the main factor controlling the change in alkanes and aromatics. Among the maturity parameters of biomarkers, the ratio of ∑tricyclic terpanes/∑hopanes was the most effective parameter for indicating the maturity evolution of the Yuka area, but others were complicated by the increasing temperature. Therefore, when evaluating maturity, the applicability of other parameters needed to be fully considered. The results obtained offer new insights in the research on liquid-hydrocarbon and biomarker evolution of the Middle Jurassic source rocks in the Yuka Sag of the Qaidam Basin. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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15 pages, 4406 KiB

Open AccessArticle

Geochemical Features of Lacustrine Shales in the Upper Cretaceous Qingshankou Formation of Changling Sag, Songliao Basin, Northeast China

by Zhongcheng Li, Zhidong Bao, Zhaosheng Wei, Lei Li and Hailong Wang

Energies 2022, 15(19), 6983; https://doi.org/10.3390/en15196983 - 23 Sep 2022

Cited by 2 | Viewed by 1186

Abstract

The organic-rich shale of the Upper Cretaceous Qingshankou Formation is an important hydrocarbon source rock in Northeast China. In this study, taking the lacustrine shale in the Qingshankou Formation as an example, geochemical analysis, including total organic carbon (TOC), Rock-Eval pyrolysis, maceral compositions, [...] Read more.

The organic-rich shale of the Upper Cretaceous Qingshankou Formation is an important hydrocarbon source rock in Northeast China. In this study, taking the lacustrine shale in the Qingshankou Formation as an example, geochemical analysis, including total organic carbon (TOC), Rock-Eval pyrolysis, maceral compositions, X-ray diffraction (XRD), and biomarker analyses, were carried out on twenty-four shale samples to evaluate the geochemistry and environmental features of this shales. The Qingshankou lacustrine shales contains mainly Type I/II₁ organic matter and is oil prone, with a good to excellent source rock. Vitrinite reflectance and Rock-Eval pyrolysis parameters show that the Qingshankou lacustrine shales is mainly in the mature stage and within the oil window. Biomarker composition of the shales provide evidence that the Qingshankou lacustrine shales was formed in a reductive sedimentary environment with relatively high salinity water. The organic matter came from a mixture of plankton, bacterial and land plants. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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17 pages, 9330 KiB

Open AccessArticle

Lithofacies Characteristics, Depositional Environment and Sequence Stratigraphic Framework in the Saline Lacustrine Basin-A Case Study of the Eocene Low Member of Xingouzui Formation, Jianghan Basin, China

by Xiaojie Fan, Yongchao Lu, Jingyu Zhang, Shiqiang Wu, Liang Zhang, Xiaojuan Du, Qinyu Cui and Hao Wang

Energies 2022, 15(17), 6235; https://doi.org/10.3390/en15176235 - 26 Aug 2022

Cited by 4 | Viewed by 1460

Abstract

The Jianghan Basin is a lacustrine basin in central China developing multiple salt bearing deposits in the Eocene with the success of shale oil exploration in the Qianjiang Formation. The lower member of the Xingouzui Formation in the Chentuokou Depression has become another [...] Read more.

The Jianghan Basin is a lacustrine basin in central China developing multiple salt bearing deposits in the Eocene with the success of shale oil exploration in the Qianjiang Formation. The lower member of the Xingouzui Formation in the Chentuokou Depression has become another exploration target. However, rapid changes in lithofacies and strong sedimentary heterogeneity limit the exploration progress. This study aimed to explore the sequence division, lithofacies characteristics, and sedimentary environment using sedimentological, X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses. The sequence stratigraphic analysis indicates that the low member of the Xingouzui Formation is divided into two third-order sequences, namely SQ₁ and SQ₂, and four system tracts, including highstand systems tract (HST), lake expanding system tract (EST), early highstand system tract (EHST), and late highstand system tract (LHST). Moreover, a total of nine major lithofacies and five lithofacies associations (LA1-5) were identified. The organic geochemical data show that the laminated argillaceous dolomite in EST and EHST developed the best oil content with an average TOC of 1.18% and S₁ of 3.18 mg/g, The laminated argillaceous dolomite deposited in anoxic conditions with a humid climate, moderate salinity, and stratified deep waterbody is a favorable exploration facies for shale oil. Full article

(This article belongs to the Special Issue Sedimentary Organic Matter in Shale Oil/Gas Systems)

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