Characterization of lacustrine mixed fine-grained sedimentary rocks using coupled chemostratigraphic-petrographic analysis: A case study from a tight oil reservoir in the Jimusar Sag, Junggar Basin

Zhang, Shaomin; Cao, Yingchang; Liu, Keyu; Jahren, Jens; Xi, Kelai; Zhu, Rixiang; Yang, Tian; Cao, Xu; Wang, Wei

doi:10.1016/j.marpetgeo.2018.10.039

Cited by 45 publications

(31 citation statements)

References 44 publications

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“…(a) Correlation between the Sr/Ba ratio and B/Ga ratio of the Ek 2 3 in the Cangdong sag. (b) Cross plot of (C:P) org versus V/(V + Ni) of the Ek 2 in the Cangdong sag, the boundaries from (Zhang et al, 2019,b) for V/(V + Ni) and (Algeo et al, 2011; Xin et al, 2021) for (C:P) org . (c) Cross plot of La/Th versus Hf of the Ek 2 in the Cangdong sag (modified from Chen et al, 2020)…”

Section: Resultsmentioning

confidence: 99%

“…The redox condition reflects the water column stratification, which affects the sedimentary structures and the amount of organic matter in fine‐grained sedimentary rocks. Some trace elements are sensitive in different oxidation degrees of the water column, such as vanadium (V) and nickel (Ni) (Zhang et al, 2019,b). Therefore, the V/(V + Ni) ratio can be regarded as a redox proxy, which reflects oxic conditions when it is less than 0.46, dysoxic–anoxic conditions when it varies between 0.46 and 0.60, and euxinic conditions when it exceeds 0.84.…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

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 burial depth is about ~2500-4500 m [30,31,34,36]. The Lucaogou Formation consists of variable lithologies, with a large amount of terrigenous sediments and carbonates and a small amount of pyroclastic rocks, which form a mixed sedimentary system with a thickness of about ~90-350 m [44,45] (Figure 1). The two sites with the best oil production are termed the "upper sweet spot" (P 2 l 2 2) and "lower sweet spot" (P 2 l 1 2 ), and there is a thick mudstone section between the two sweet spots [30,34,46].…”

Section: Geological Settingmentioning

confidence: 99%

Revisiting Controls on Shale Oil Accumulation in Saline Lacustrine Basins: The Permian Lucaogou Formation Mixed Rocks, Junggar Basin

Zhang

Cao

et al. 2021

Geofluids

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Fine-grained mixed rocks in saline lacustrine basins are important targets for shale oil exploration. However, the controls on shale oil accumulation are complex due to the multi-source mixed deposition. This is a challenging issue in the study of shale oil. Here, we present a case study in the Middle Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin, northwestern China. Results show that the Lucaogou Formation consists mainly of carbonate rocks, dolomitic or calcareous mudstones, tuffaceous or silty mudstones, and siltstones. The dolomitic/calcareous mudstones ( TO C average = 6.44 wt . % ) and tuffaceous/silty mudstones ( TO C average = 4.83 wt . % ) have the best hydrocarbon generation potential and contain type I–II1 kerogens that are in the peak oil generation stage. However, the shale oil potential is highest for the carbonate rocks and siltstones with average oil saturation index (OSI) values of 315.03 mg HC/g TOC and 343.27 mg HC/g TOC, respectively. This indicates that hydrocarbon generation potential is not the main factor controlling shale oil potential. Micro-nanoscale pores are the main control. Abundant dissolution pores provide excellent reservoir space for near-source migration and accumulation of shale oil. Different mixing processes between lithofacies control the accumulation of shale oil, and shale oil productivity is the best when multi-facies deposition in transitional zones formed the mixed rocks (facies mixing). In addition, local accumulations of calcareous organisms and adjacent carbonate components on terrigenous sediments (in situ mixing) are also conducive to shale oil enrichment. This is an unusual and special feature of saline lacustrine shale oils, which is different from freshwater lacustrine and marine shale oils. Comprehensive assessment of source rock and reservoir is needed to robustly establish a widely applicable method to determine the shale oil potential in such basins.

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“…So far, many breakthroughs have been made on the classification and depositional setting of mixed siliciclastic-carbonate rocks [5,9,10,12]. However, understanding the pore structure and connectivity of mixed siliciclastic-carbonate tight reservoirs, and the associated key controlling factors, is still lacking [14,15].…”

Section: Introductionmentioning

confidence: 99%

Pore Structure and Connectivity of Mixed Siliciclastic-Carbonate Tight Reservoirs in the Palaeogene from Qaidam Basin, NW China

Wang

Zeng

et al. 2021

Geofluids

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The pore structure and connectivity in petroleum reservoirs are controlled in part by their petrological properties. Mixed siliciclastic-carbonate rocks have complex compositions and heterogeneous spatial distributions of the various minerals. As a result, the study of the pore structure and connectivity of mixed siliciclastic-carbonate tight reservoirs has been limited. In this study, methods such as thin section microscopy, X-ray diffraction, X-ray computed tomography, low pressure N2 adsorption, and spontaneous imbibition were adopted to comprehensively analyze the petrological properties, pore structure, and connectivity of the mixed siliciclastic-carbonate tight reservoirs in the upper member of the Xiaganchaigou Formation in the Yingxi Area, Qaidam Basin. The results showed that micrometer-sized pores in mixed siliciclastic-carbonate tight reservoirs are mainly dissolution pores, and that the spatial distribution of the pores is highly heterogeneous. The average pore radius range, average throat radius range, and average coordination number range of micronmeter-sized pores are 2.09~3.42 μm, 1.32~2.19 μm, and 0.48~1.49, respectively. Restricted by the concentrated distribution of local anhydrite, the connectivity of micronmeter-sized pores develops well only in the anhydrite, showing negligible contribution to the overall reservoir connectivity. In contrast, nanometer-sized pores in the mixed siliciclastic-carbonate tight reservoirs are mainly intercrystalline pores in dolomite. The range of nanometer-sized pores diameters is mainly distributed in 1.73-31.47 nm. The pores have a smooth surface, simple structure, and relatively homogeneous spatial distribution. The dissolution of dolomite intercrystalline pores by acidic fluids increases the connectivity of the nanometer-sized pores. This paper presents genetic models for microscopic pore structures and connectivity of mixed siliciclastic-carbonate rocks, making possible the evaluation on the quality of the mixed siliciclastic-carbonate tight reservoirs.

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Characterization of lacustrine mixed fine-grained sedimentary rocks using coupled chemostratigraphic-petrographic analysis: A case study from a tight oil reservoir in the Jimusar Sag, Junggar Basin

Cited by 45 publications

References 44 publications

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

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

Revisiting Controls on Shale Oil Accumulation in Saline Lacustrine Basins: The Permian Lucaogou Formation Mixed Rocks, Junggar Basin

Pore Structure and Connectivity of Mixed Siliciclastic-Carbonate Tight Reservoirs in the Palaeogene from Qaidam Basin, NW China

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