Exploration potential of different lithofacies of deep marine shale gas systems: Insight into organic matter accumulation and pore formation mechanisms

Wang, Enze; Guo, Tonglou; Li, Maowen; Li, Changrong; Dong, Xiaoxia; Zhang, Nanxi; Yuan, Feng

doi:10.1016/j.jngse.2022.104563

Cited by 35 publications

(25 citation statements)

References 49 publications

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“…Ternary diagram exhibiting the mineral composition and classification of P l shale. The range is from refs and and not the figure itself.…”

Section: Resultsmentioning

confidence: 99%

“…Redox conditions are the key factors affecting the preservation of organic matter, , and the contents and ratios of redox-sensitive elements are extensively used proxies to characterize redox conditions. − , The rationale is that some redox-sensitive elements have high solubility in the ocean under oxidizing conditions and low solubility in reducing environments; therefore, these elements are less abundant in sediments in oxidizing environments and tend to be enriched in reducing environments. For example, Mo concentrations less than 25 ppm, from 25 to 100 ppm, and greater than 100 ppm represent oxic, dysoxic, and anoxic environments, respectively …”

Section: Discussionmentioning

confidence: 99%

“…As previously mentioned, the strong heterogeneity of marine–continental transitional shale leads to obvious variations in geological characteristics, even in the same layer; therefore, it is necessary to classify the samples into different categories and further discuss them. Lithofacies have been widely evaluated in shale research, and previous authors have classified shales based on the mineral type, ,, organic matter abundance, , and depositional environment. ,, Different lithofacies indicate various depositional environments, which in turn determine the geological characteristics of shales. Therefore, lithofacies classification provides new perspectives and tools for shale refinement studies.…”

Section: Methodsmentioning

confidence: 99%

“…To quantify chemical weathering conditions, the chemical index of alteration (CIA) has been proposed, several researchers have used this value to describe the paleoclimate conditions for shale deposited in different environments (lacustrine, marine–continental transitional, and marine), ,,, and the calculation method is shown in eq . The principle of this index is that under strong weathering conditions, Al is more likely to accumulate in sediments, while K, Na, and Ca tend to be deficient .…”

Section: Methodsmentioning

confidence: 99%

“…Various lithofacies often show different paleoenvironment and petrophysical characteristics, and no uniform standard of shale lithofacies classification has been proposed. Previous researchers used mineral composition, organic matter abundance, and sedimentary structure as parameters to describe the lithofacies, all these methods can reflect the properties of shale from certain perspectives. Many studies have used lithofacies as a method to study the heterogeneity of marine shale and have achieved good results, ,, and there is no doubt that the lithofacies identification provides an effective tool to describe the inner heterogeneity of shales.…”

Section: Introductionmentioning

confidence: 99%

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Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

Wang

Guo

et al. 2022

ACS Earth Space Chem.

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Marine−continental transitional shale gas exploration is one of the hottest topics in the academic and industrial community. Frequent sedimentary environment changes lead to substantial heterogeneity and complex organic matter enrichment mechanisms, and it is of great practical significance to clarify the paleoenvironment of marine−continental transitional shale and reveal the enrichment mechanism of organic matter for subsequent shale gas exploration. However, strong heterogeneity creates divergence for our understanding of organic matter enrichment mechanisms and resource potential. This paper selected the marine−continental transitional shale of the Permian Longtan Formation in the southeastern Sichuan Basin as an example. Through TOC analysis, XRD measurements, and major and trace element analyses, we identify the depositional cycle and lithofacies, characterize the paleosedimentary environments of different lithofacies, establish depositional models, and clarify the organic matter enrichment mechanism. Four lithofacies can be identified in the Longtan Formation in the study area: organic−lean carbonate shale (LC), organic−lean mixed shale (LM), organic−lean argillaceous shale (LCM), and organic−rich argillaceous shale (RCM). The terrestrial detrital influx of the LCM and RCM shales is obviously strong, while the RCM shale was deposited in a relatively dysoxic and humid environment. For the Longtan shale, the terrestrial detrital influx and redox environment determine the enrichment of organic matter. In the lagoon sediment system, due to the high terrestrial detrital influx, the argillaceous shale in the transitional shale gas system should be given more attention in future exploration. For different kinds of shale gas systems (marine, marine− continental transitional, and lacustrine), the effect of the terrestrial detrital influx is the main difference. In marine−continental and lacustrine shale gas systems, shales with high TOC values can still exist in the context of oxic sedimentary environments. The research results of this paper can provide a theoretical basis for future marine−continental transitional shale gas sweet spot prediction and exploration from geochemical perspectives.

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“…Ternary diagram exhibiting the mineral composition and classification of P l shale. The range is from refs and and not the figure itself.…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

Wang

Guo

et al. 2022

ACS Earth Space Chem.

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Shale gas‐bearing capacity and its controlling factors of Wufeng–Longmaxi formations in northern Guizhou, China

Cao,

Xue,

Pan

et al. 2024

Geological Journal

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Great progress has been made in marine shale gas of Wufeng–Longmaxi formations in the Sichuan Basin. However, shale gas exploration in the complex structural belt around the Sichuan Basin still faces great challenges. In this study, shales of Wufeng–Longmaxi formations collected from the northern Guizhou were taken as the studied target, organic matter (OM) characteristics, mineral composition, pore structure, methane adsorption capacity and in situ desorption gas content were measured, and the controlling factors of shale gas content were further discussed. The results indicated that the sedimentary facies of Wufeng–Longmaxi formations in north Guizhou varies from shallow‐water shelf facies to deep‐water shelf facies from south to north, and organic‐rich shales are primarily distributed in Daozhen‐Xishui areas, with a maximum thickness of about 80–100 m. Organic‐rich shales are characterized by high total organic carbon (TOC) content, high thermal maturation and type I–II1 kerogens, which can be comparable with those in commercially produced shale gas field in Sichuan Basin. High‐quality shale gas reservoirs generally have a high content of brittle minerals, making them easier to be fractured. OM pores are the dominanted pore type in the studied shales, followed by intergranular pores associated with brittle minerals, dissolution pores within carbonate grains and microcracks, while clay mineral‐related pores are poorly developed. The Wufeng–Longmaxi Formation shales generally have strong methane adsorption capacities, but these vary greatly across different areas. Shale gas adsorption capacity is primarily controlled by TOC content and thermal maturation level. Similarly, total gas content, including desorption gas and lost gas, varies greatly in different areas, and it is obviously lower than that in Fuling and Luzhou shale gas field, due to the loss of shale gas and low‐pressure coefficient in the complex structural zone. It is worth explaining that shale gas is not always low in northern Guizhou, which is determined by burial depth and the distance of great fractures. Shale gas content is relatively high in LY1 well and DY1 well in Xishui‐Daozhen area, and it is extremely low in TY1 well and AY1 well in Tongzi‐Zheng'an area. Shale gas content in the same structural unit is primarily influenced by TOC content, OM pore development degree and water saturation. However, different structural units have different shale gas contents, due to the differences in preservation conditions. Shale reservoirs with good preservation conditions, that is, wide and gentle structure, far from a large fault and great burial depth, generally have high shale gas contents.

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Decoding the nanoscale porosity in serpentinites from multidimensional electron microscopy and discrete element modelling

Chogani,

Plümper

2023

Contrib Mineral Petrol

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Serpentinites, widespread in Earth's lithosphere, exhibit inherent nanoporosity that may significantly impact their geochemical behaviour. This study provides a comprehensive investigation into the characteristics, scale dependence, and potential implications of nanoporosity in lizardite-dominated serpentinites. Through a combination of multidimensional imaging techniques and molecular-dynamics-based discrete element modelling, we reveal that serpentinites function as nanoporous media with pore sizes predominantly less than 100 nm. Crystallographic relationships between olivine, serpentine, and nanoporosity are explored, indicating a lack of significant correlations. Instead, stochastic growth and random packing of serpentine grains within mesh cores may result in interconnected porosity. The analysis of pore morphology suggests that the irregular pore shapes align with the crystal form of serpentine minerals. Furthermore, the nanoporosity within brucite-rich layers at the serpentine-olivine interface is attributed to delamination along weak van der Waals planes, while pore formation within larger brucite domains likely results from low-temperature alteration processes. The fractal nature of the pore size distribution and the potential interconnectivity of porosity across different scales further support the presence of a pervasive nanoporous network within serpentinites. Confinement within these nanopores may introduce unique emergent properties, potentially influencing fluid transport, mineral solubility, and chemical reactions. As such, these processes may have profound implications for the geochemical evolution of serpentinites.

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Exploration potential of different lithofacies of deep marine shale gas systems: Insight into organic matter accumulation and pore formation mechanisms

Cited by 35 publications

References 49 publications

Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

Shale gas‐bearing capacity and its controlling factors of Wufeng–Longmaxi formations in northern Guizhou, China

Decoding the nanoscale porosity in serpentinites from multidimensional electron microscopy and discrete element modelling

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