Effects of lacustrine depositional sequences on organic matter enrichment in the Chang 7 Shale, Ordos Basin, China

Hu, Suyun; Bu, Qingyun; Bai, Baojun; Tao, Shizhen; Chen, Yanyan; Pan, Zhejun; Lin, Senhu; Pang, Zhenglian; Xu, Wei; Yuan, Miao; Fan, Jianwei; Sun, Yuanshi; Feng, Xuan

doi:10.1016/j.marpetgeo.2020.104778

Cited by 12 publications

(6 citation statements)

References 88 publications

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“…Moreover, the texture of lacustrine shale was sensitive to sediment environment, in turn leading to complicated laminated development. Hence, the density of laminated reflected vertical changes of lithofacies [32]. Then, we divided Well Y1 into ① ~⑨ units on the basis of core observation (Table 1).…”

Section: Resultsmentioning

confidence: 99%

X-Ray Fluorescence for Laminated Silty Shale Reservoirs in Ordos Basin, China: Implications for Lithology Identification

Cheng

et al. 2022

Geofluids

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Shale lithofacies were an important key for the exploration and development of unconventional oil and gas reservoirs. Previous studies usually use logging data, X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM) to identify shale lithofacies, but these methods cannot accurately and quickly identify geochemical characteristics. Portable X-ray fluorescence (XRF) analysis can identify geochemical characteristics. However, few publications reported the feasibility of XRF identifying lithology. We tested the major elements of this formation systematically by X-ray fluorescence and compared the characteristics of these elements in the silty laminated shales against the calcareous laminated shale and the argillaceous shales. We analyzed the geochemical characteristics of shale using portable XRF and proposed a method to identify argillaceous shale, silty laminated shale, and calcareous laminated shale in the Chang 7 of Well Y1 (in Xiasiwan area). Furthermore, we established a lithoface identification standard. We also found that Ca/Mg of calcareous laminated shale was the highest which indicated a dry depositional environment; in contrast, lowest Ca/Mg of silty laminated shale indicated a humid depositional environment. Argillaceous shale was deposited in a strongly reducing environment because Fe content of argillaceous shale was the highest. Finally, this criterion is tested against the data from the Well Y2, and the results are in good agreement with the thin section analysis and core data.

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Section: Resultsmentioning

confidence: 99%

X-Ray Fluorescence for Laminated Silty Shale Reservoirs in Ordos Basin, China: Implications for Lithology Identification

Cheng

et al. 2022

Geofluids

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“…Jarvie adopted OSI = 100 mg/g as the threshold of shale oil flow based on statistical analysis of marine shale oil data. , However, shale oil primarily occurs in lacustrine deposits in China, − and the geological conditions of shale oil production layers are quite different between China and the United States. Hence, the standard of 100 mg/g may not be suitable for the evaluation of lacustrine shale oil.…”

Section: Results and Discussionmentioning

confidence: 99%

“…The great success of shale oil and gas production in North America has increased the momentum of shale oil and gas exploration worldwide. In 2019, the China National Energy Administration preliminarily estimated that the recoverable resources of shale oil in China range from 7.4 to 37.2 billion tons. , In contrast to shale oil in North America, which is mainly produced from marine strata, , shale oil in China is largely produced from highly heterogeneous lacustrine shale. − Lacustrine shale oil in China faces many problems, such as a complex geological structure, notable heterogeneity, high clay mineral content, low organic matter maturity, and poor crude oil fluidity. − In recent years, much progress has been attained in research on lacustrine shale oil in China, but the output is not high. − For example, the cumulative production of 10 wells, such as Luo 42 and XYS 9, in the Jiyang Depression of the Bohai Bay Basin has exceeded 10 000 tons, but the dedicated exploration wells deployed for shale have not achieved ideal oil production results. , In view of the great difficulty in the exploration and production of lacustrine shale oil in China, shale sections enriched in oil should be the preferred targets for exploration and production. Therefore, accurate and rapid evaluation of shale oil enrichment is highly important.…”

Section: Introductionmentioning

confidence: 99%

Innovative Standard for Graded Evaluation of Oil Enrichment of Lacustrine Shale: A Case Study of the Lower Third Member of the Shahejie Formation, Zhanhua Sag, Eastern China

et al. 2021

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The exploration and production results of lacustrine shale oil are closely related to shale oil enrichment evaluation. However, there exists a lack of rapid and accurate oil enrichment evaluation methods for strongly heterogeneous lacustrine shale. In this study, an innovative standard for graded evaluation of shale oil enrichment is proposed. In the innovative standard, considering the light hydrocarbon loss of shale oil, the free oil (S 1) content is corrected for light hydrocarbons. Moreover, on the basis of the hydrocarbon expulsion threshold theory, and combined with the specific geochemical characteristics of the shale in the study area, the lacustrine shale oil mobility threshold OSI (the oil saturation index) is determined to replace the fixed empirical shale oil mobility threshold (100 mg/g). By combining the absolute oil content (S 1) with the relative oil content (OSI), we are able to divide the shale oil resources into four categories: enriched resources, moderately enriched resources, low-efficient resources, and ineffective resources. This standard is successfully applied to evaluate the oil enrichment degree of the lower third member (Es3 L) of the Shahejie Formation in well Luo 69 of the Zhanhua Sag, Bohai Bay Basin. The oil enrichment degrees of shales with varying kerogen compositions and distinct lithofacies are highly diverse. Shale comprising type I kerogen is the most conducive to shale oil enrichment. However, more than 15% of the tested shales composed of type II1 kerogen include enriched and moderately enriched resources, which should be considered. Organic-fair laminated calcareous shale (OFLCS) is the most favorable lithofacies type for shale oil enrichment. The development of bedding structures and a moderate organic matter content are beneficial for shale oil enrichment. This standard is suitable for graded evaluation of the oil enrichment degree of strongly heterogeneous lacustrine shale worldwide.

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“…The fluctuations of lake level affect the deposition process of sediments (Zhang et al, 2021). Thorium (Th) and uranium (U) are relatively stable radioactive elements in nature, which are less affected by diagenesis and geochemical conditions (Fu, Li, Xu, & Niu, 2018).…”

Section: Palaeowater Depthmentioning

confidence: 99%

Control of sedimentary environment on the lithofacies of lacustrine fine‐grained sedimentary rocks in the second member of the Kongdian Formation in the Cangdong sag, Bohai Bay Basin, China

Fang

Chen

et al. 2022

Geological Journal

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The thick fine‐grained sedimentary rocks in the second member of the Kongdian Formation (Ek2) in the Cangdong sag, Bohai Bay Basin, eastern China, are typical lacustrine source rocks and have recently been regarded as the main target for shale oil exploration. Compared with marine shales, the strong heterogeneity in the mineral composition, structure feature, and vertical association pattern of the Ek2 lacustrine fine‐grained sedimentary rocks in the Cangdong sag is significantly influenced by frequent variations in the sedimentary environment and depositional process. Based on the detailed core and thin‐section description analyses as well as the two‐dimensional X‐ray fluorescence (2D‐XRF) analysis, the Ek2 fine‐grained sedimentary rocks in the Cangdong sag can be classified into six types of lithofacies by employing the content of three main mineral compositions together with structure features, among which five types are mainly deposited, including laminated felsic fine‐grained sedimentary rocks, laminated and massive carbonate fine‐grained sedimentary rocks, and laminated and massive mixed fine‐grained sedimentary rocks. The sedimentary environment during the sedimentary period of the Ek2 in the Cangdong sag was reconstructed by several indexes (including salinity, water depth, redox condition, climate, and detrital input) using the element geochemical parameters. The variations of detrital input and lake physicochemical characteristics driven by climate were vertically divided into four phases, indicating that the lake gradually changed from the transgression to the highstand period. In addition, the water column stratification led to the overall dysoxic–anoxic condition. The depositional process can be interpreted by correlating the lithofacies and the sedimentary environment. The results indicate that the mineral composition is controlled by the detrital input and carbonate production driven by climate and that structural features are mainly affected by the water column stratification. The Ek2 fine‐grained sedimentary rocks in the Cangdong sag present the vertical distribution of lithofacies that matches with the evolution phases of the sedimentary environment. This study's results enhance the understanding of the formation mechanism of lacustrine fine‐grained sedimentary rocks and provide basic geological knowledge for shale oil exploration in the study area.

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Effects of lacustrine depositional sequences on organic matter enrichment in the Chang 7 Shale, Ordos Basin, China

Cited by 12 publications

References 88 publications

X-Ray Fluorescence for Laminated Silty Shale Reservoirs in Ordos Basin, China: Implications for Lithology Identification

X-Ray Fluorescence for Laminated Silty Shale Reservoirs in Ordos Basin, China: Implications for Lithology Identification

Innovative Standard for Graded Evaluation of Oil Enrichment of Lacustrine Shale: A Case Study of the Lower Third Member of the Shahejie Formation, Zhanhua Sag, Eastern China

Control of sedimentary environment on the lithofacies of lacustrine fine‐grained sedimentary rocks in the second member of the Kongdian Formation in the Cangdong sag, Bohai Bay Basin, China

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