Fractal and Multifractal Characteristics of Nanopores and their Controlling Factors in Marine–Continental Transitional Shales and their Kerogens from Qinshui Basin, Northern China

Lu, Chengang; Xiao, Xianming; Xue, Zhenqian; Chen, Zhangxin; Li, Gang; Yuan, Feng

doi:10.1007/s11053-023-10222-3

Cited by 11 publications

(7 citation statements)

References 65 publications

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“…Compared to marine shale, lacustrine shale, and marine–continental transitional shale exhibit more frequent interactions and stronger heterogeneity. The kerogen types in the latter two shales are typically types II and III. ,− The development level of OM pores in them is often low, and their pore systems are characterized by strong heterogeneity . Due to differences in shale properties, the gas occurrence space of continental/continental-marine transitional shales may be dominated by inorganic storage spaces.…”

Section: Resultsmentioning

confidence: 99%

Quartz Crystallinity Characteristics and Their Effects on Shale Gas Reservoir Performance: A Case Study of the Deep Longmaxi Formation Shale in the Sichuan Basin, China

Feng,

Xiao,

Wang

et al. 2024

ACS Earth Space Chem.

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Quartz, as a pivotal constituent of shale, has garnered considerable attention in research. Nevertheless, prior studies on quartz in shale have concentrated on its influence on organic matter accumulation, pore development, and physical properties. The crystal morphology of quartz and its implications for shale reservoir performance have been largely overlooked. This study utilizes the Longmaxi (LMX) shale in the Sichuan Basin, China, as an example to conduct this work. We used X-ray powder diffraction, polarizing microscopy, scanning electron microscopy, and cathodoluminescence testing, characterizing the crystallinity and characteristics of quartz, revealing the influence of quartz crystallinity on shale reservoirs. The results indicate that the quartz crystallinity index (QCI) of the LMX shale ranges from 2.81 to 8.09, and a significant correlation between the QCI and the sources of quartz is observed. Shale samples with lower QCI values tend to exhibit a higher content of biogenic quartz, whereas the content of clay-transformed quartz and/or terrigenous detrital quartz increases. Furthermore, the pore structure parameters of shale exhibit synergistic variations with QCI, especially for shale with low crystallinity, despite showcasing differences for pores with different pore sizes. Notably, QCI exhibits the strongest negative correlation with micropores, followed by mesopores, while this correlation is less apparent in macropores. The influence of QCI on pore development is primarily ascribed to its synergistic interaction with organic matter enrichment and the constraints imposed on the development and preservation of organic-matter-hosted pores. Under the well-preserved geological conditions of the LMX shale reservoirs, a definite correlation exists between the QCI value and shale gas content/production. This correlation signifies that QCI could serve as a potential indicator for assessing shale reservoir quality, complementing conventional parameters, such as the contents of total organic carbon and quartz.

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Section: Resultsmentioning

confidence: 99%

Quartz Crystallinity Characteristics and Their Effects on Shale Gas Reservoir Performance: A Case Study of the Deep Longmaxi Formation Shale in the Sichuan Basin, China

Feng,

Xiao,

Wang

et al. 2024

ACS Earth Space Chem.

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“…11,12 While oxygendeficient conditions favor OM enrichment, 13−15 some argue that substantial inputs of terrigenous OM also contribute to OM enrichment. 12,16−18 Given the profound impact of OM abundance on shale gas resources, 19,20 transitional shale deposits is essential for the delineation and prediction of shale gas distributions. Previous studies on paleoenvironmental reconstructions, e.g., paleoclimate, paleosalinity, paleowater depth, paleoredox conditions, paleoproductivity, and terrigenous inputs, are usually employed in various geochemical proxies, 21−23 each critical for understanding OM accumulation and preservation.…”

Section: Introductionmentioning

confidence: 99%

“…Previous studies have demonstrated that the accumulation and preservation of OM in marine shale deposits mainly depended on primary productivity and redox conditions of paleowater. , Marine organic shale deposits typically thrive in surface waters teeming with abundant planktonic organisms, alongside oxygen-deficient bottom waters, which have high primary productivity and good preservation conditions favoring OM enrichment . In contrast, organic shale deposits within marine–continental transitional (MCT) facies are often deposited in shallow-water environments, which are influenced by both sea and river, rendering the mechanisms of OM enrichment in these settings more complex. , While oxygen-deficient conditions favor OM enrichment, − some argue that substantial inputs of terrigenous OM also contribute to OM enrichment. ,− Given the profound impact of OM abundance on shale gas resources, , a further understanding of OM accumulation and its controlling factors within transitional shale deposits is essential for the delineation and prediction of shale gas distributions.…”

Section: Introductionmentioning

confidence: 99%

Geochemical Constraints and Astronomical Forcing on Organic Matter Accumulation of Marine–Continental Transitional Shale Deposits in the Qinshui Basin during the Carboniferous–Permian Transition

Lu,

Gao,

Tiong

et al. 2024

ACS Earth Space Chem.

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During the Carboniferous–Permian transition, the paleoclimate of Earth transitioned from an icehouse to a greenhouse state, severely impacting the burial patterns of organic matter (OM). Within the Upper Carboniferous–Lower Permian Taiyuan–Shanxi formations (TY–SX) in the Qinshui Basin, North China, lie a series of marine–continental transitional organic-rich shale deposits. However, the mechanism behind the enrichment of OM in these shale deposits, formed during the icehouse–greenhouse transition, remains unclear. To address this issue, a suite of transitional shale deposits was investigated by using geochemical and astronomical cyclostratigraphic analyses. The results show that the depositional age of TY–SX spans from 293.65 to 300.64 ± 0.412 Ma. The depositional environments of these TY–SX shales tended toward oxidation, with the TY shales slightly more reducing than the SX shales. The paleoclimate of the TY–SX shales suggests warm and humid environments with comparatively strong chemical weathering intensity. Primary productivity in these TY–SX shales was estimated to be low, but the influx of terrigenous detritus was robust, driving OM accumulation through terrigenous inputs. The 405-kyr astronomical cycle had a forcing effect on the paleoenvironment variations, and the 173-kyr astronomical cycle showed a covariance with OM enrichment. The TY shales exhibited a stable and moderate sedimentation rate, with enhanced terrigenous OM input leading to OM enrichment, whereas the OM contents of the SX shales, deposited under conditions of low primary productivity and oxidation, experienced dilution of the OM content owing to detrital inputs.

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“…The pores of shale reservoirs are mainly nanosized, and they are important reservoir spaces and migration channels of shale gas. − Therefore, the fine characterization of shale nanopore structure is vital to shale gas reservoir evaluation and development. − …”

Section: Introductionmentioning

confidence: 99%

Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China

Li,

Gao,

et al. 2023

Energy Fuels

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The Lower Cambrian shale is one of the most important marine shale reservoirs in South China, which has huge potential for shale gas resources. However, the Lower Cambrian shale displays strong pore heterogeneity, influencing shale gas exploration. Based on the low-pressure N2 adsorption (LPNA) of the Lower Cambrian shale samples and their isolated kerogens in the western Hubei area, South China, fractal dimensions and their controlling factors of shale nanopores have been investigated. In this study, the pore specific surface area (SSA) and pore volume (PV) of isolated kerogen samples are mainly contributed from micropores and non-micropores, respectively, which are consistent with those of whole-rock samples. The average fractal dimensions of whole-rock samples are higher than those of isolated kerogen samples, suggesting that organic matter (OM) controls the shale pore structure and exerts major influences on fractal characteristics of nanopores and inorganic mineral (IM) enhances the complexity of shale nanopores. The correlations between fractal dimensions and total organic carbon (TOC) and IM contents of whole-rock samples further indicate that the OM simultaneously affects the heterogeneities of the pore surface and structure, while the IM mainly affects the heterogeneity of the pore structure. They both control the fractal characteristics of nanopores in the Lower Cambrian shale. Compared with the Upper Carboniferous–Lower Permian marine-continental transitional (MCT) shale and the Lower Silurian marine shale, the D 1 and D 2 of the studied marine shale display relatively lower and higher values, respectively, revealing that the Lower Cambrian shale has relatively weak adsorption capacity, as well as poor permeability and connectivity.

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Fractal and Multifractal Characteristics of Nanopores and their Controlling Factors in Marine–Continental Transitional Shales and their Kerogens from Qinshui Basin, Northern China

Cited by 11 publications

References 65 publications

Quartz Crystallinity Characteristics and Their Effects on Shale Gas Reservoir Performance: A Case Study of the Deep Longmaxi Formation Shale in the Sichuan Basin, China

Quartz Crystallinity Characteristics and Their Effects on Shale Gas Reservoir Performance: A Case Study of the Deep Longmaxi Formation Shale in the Sichuan Basin, China

Geochemical Constraints and Astronomical Forcing on Organic Matter Accumulation of Marine–Continental Transitional Shale Deposits in the Qinshui Basin during the Carboniferous–Permian Transition

Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China

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