Abstract
Formation pressure-lithofacies type are the most critical factors influencing micro pore structure and porosity in shale reservoir. However, how these two factors jointly affect shale gas accumulation remains unclear. Scanning electron microscopy (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), on-site desorption and low-temperature N2 adsorption (LTNA) are integrated to analyze coupling effects of pressure variation and lithofacies on reservoir quality and gas-bearing characteristics of deep-buried shale. Three lithofacies are identified in Longmaxi deep-buried shale: siliceous lithofacies (S), argillaceous lithofacies (CM) and mixed lithofacies (M). Pores with pore size < 4 nm are the main contributors to the specific surface area (SSA), and pores between 4 nm and 30 nm are the main contributors to the pore volume (PV). Pressure variations directly affect the size and number of organic matter pores but have no impact on intraparticle pores. The variability in interparticle pores indicates that the S lithofacies has a stronger resistance to compaction compared to the M lithofacies. Porosity and micro structure of deep-buried shale reservoir are influenced by lithofacies type, burial depth and pressure variation. Organic-rich S shale and organic-poor S shale demonstrate good reservoir properties under over-pressure and well-preserved conditions, with organic-rich S shale having the strongest resistance to compaction. Organic and inorganic pores are largely lost during compaction of organic-rich M shale. CM lithofacies also has a poor material foundation and the weakest resistance to compaction, making it difficult to preserve original porosity and pore structure during compaction. The decrease in formation pressure results in macropores making almost no contribution to pore volume, while the contribution of mesopores is further enhanced. As the formation pressure decreases, the contribution of micropores to pore volume is gradually increased. As shale porosity decreases, porosity associated with macro pores declines first, followed by that associated with mesopores. Free-gas content in the CM and M lithofacies declines rapidly as porosity decreases. Both adsorbed and free gas decrease sharply as porosity is lost.
Similar content being viewed by others
Data availability
The datasets used and analysed during the current study are available from the corresponding author on reasonable request.
References
Miliken, K. L., Rudnicki, M., Awwiller, D. N. & Zhang, T. Organic matter-hosted pore system, Marcellus formation (Devonian), Pennsylvania. AAPG Bull. 97(2), 177–200 (2013).
Zou, C. et al. Shale gas in China: Characteristics, challenges and prospects (II). Pet. Explor. Dev. 43(2), 182–196 (2016a).
Gu, Y. et al. Evolution of pore structure and fractal characteristics in transitional shale reservoirs: Case study of Shanxi Formation, Eastern Ordos basin. Fractal Fract. 9, 335 (2025).
Mastalerz, M., Schimmelmann, A., Drobniak, A. & Chen, Y. Porosity of devonian and Mississippian new Albany shale across a maturation gradient: Insights from organic petrology, gas adsorption, and mercury intrusion. AAPG Bull. 97(10), 1621–1643 (2013).
Jiang, Z. et al. Characteristic differences and controlling factors of pores in typical South China shale. Oil Gas Geol. 42(1), 41–53 (2021).
Zou, C. et al. Shale gas in China: Characteristics, challenges and prospects (I). Pet. Explor. Dev. 42(6), 689–701 (2016b).
Hunt, J. M. Generation and migration of petroleum from abnormally pressured fluid compartments. AAPG Bull. 74, 1–12 (1990).
Nie, H. et al. Enrichment characteristics and exploration directions of deep shale gas of Ordovician-Silurian in the Sichuan Basin and its surrounding areas, China. Pet. Explor. Dev. 49(4), 648–659 (2022).
Shi, Q. & Chen, P. Rigid-elastic chimera pore model and overpressure porosity measurement method for shale: A case study of the deep overpressure siliceous shale of silurian longmaxi formation in Southern Sichuan Basin, SW China. Pet. Explor. Dev. 50(1), 1–12 (2023).
Wang, E. et al. Geological features and key controlling factors of gas bearing properties of deep marine shale in the Sichuan Basin. J. Cent. South. Univ. Sci. Technol. 53(9), 3615–3627 (2022).
Hao, F., Zou, H. & Lu, Y. Mechanisms of shale gas storage: Implications for shale gas exploration in China. AAPG Bull. 97, 1325–1346 (2013).
Cao, L. et al. Effects of crosslinking agents and reservoir conditions on the propagation of fractures in coal reservoirs during hydraulic fracturing. Reserv. Sci. 1(1), 36–51 (2025).
Jiang, Z. et al. Controlling factors of marine shale gas differential enrichment in Southern China. Pet. Explor. Dev. 47(3), 617–628 (2020).
Miao, H. et al. Strata uplift controlled deep shale gas accumulation modes: A case study from the Weiyuan block, Sichuan basin. Energy Fuels 37(17), 12889–12904 (2023).
Wang, R. et al. Controlling effect of pressure evolution on shale gas reservoirs: A case study of the Wufeng-Longmaxi formation in the Sichuan basin. Nat. Gas Ind. 40(10), 1–11 (2020).
Tang, L. et al. Overpressure origin and evolution during burial in the shale gas plays of the Wufeng-Longmaxi formations of Southern Sichuan basin. Geoenergy Sci. Eng. 236, 212729 (2024).
Li, J. et al. Geological characteristics and controlling factors of deep shale gas enrichment of the Wufeng-Longmaxi Formation in the southern Sichuan Basin, China. Lithosphere 2022, 4737801 (2022).
Zhou, N. et al. Investigating key pressure loss factors in the Wufeng-Longmaxi formation shale gas reservoirs, Southern Sichuan: A quantitative approach. Mar. Pet. Geol. 182, 107560 (2025).
Zhang, J. et al. Prospect of deep shale gas resources in China. Nat. Gas Ind. 41(1), 15–28 (2021).
Liang, X. et al. Enrichment conditions and exploration and development prospects of shallow marine shale gas in Southern China. Acta Pet. Sin. 43(12), 1730–1749 (2022).
Zhang, K. et al. Formation mechanism of the sealing capacity of the roof and floor strata of marine organic-rich shale and shale itself, and its influence on the characteristics of shale gas and organic matter pore development. Mar. Pet. Geol. 140, 105647 (2022).
Zhang, K. et al. Research on the occurrence state of methane molecules in post-mature marine shales-A case analysis of the lower silurian longmaxi formation shales of the upper Yangtze region in Southern China. Front. Earth Sci. 10, 864279 (2022).
Abouelresh, M. O. An integrated characterization of the porosity in Qusaiba Shale, Saudi Arabia. J. Pet. Sci. Eng. 149, 75–87 (2017).
Wu, J. & Ansari, U. From CO2 sequestration to hydrogen storage: Further utilization of depleted gas reservoirs. Reserv. Sci. 1(1), 19–35 (2025).
Jiang, Y. et al. Evaluation of effective porosity in marine shale reservoir, Western Chongqing. Acta Pet. Sin. 40(10), 1233–1243 (2019).
Zhang, H. et al. Enrichment mechanism and development technology of deep marine shale gas near denudation area, SW China: Insights from petrology, mineralogy and seismic interpretation. Minerals 15, 619 (2025).
Yu, W. et al. The effect of structural preservation conditions on pore structure of marine shale reservoir: A case study of the Wufeng-Longmaxi formation shale Southern Sichuan Basin, China. Front. Earth Sci. 12, 1360202 (2024).
Song, D. et al. New insights into the role of system sealing capacity in shale evolution under conditions analogous to geology: Implications for organic matter evolution and petroleum generation. Mar. Pet. Geol. 140, 105659 (2022).
Wei, F. B. et al. Characteristics of deep and ultra-deep shale reservoirs of the Wufeng–Longmaxi formation in southeastern Sichuan and their implications for shale gas exploration. Petrol. Explor. Exp. Geol. 45(4), 751–760 (2023).
Fan, C. et al. Complicated fault characterization and its influence on shale gas preservation in the southern margin of the Sichuan Basin, China. Lithosphere 12, 8035106 (2022).
Wang, D. D. et al. Differential pore structure characteristics and evolution patterns during gas reservoir uplift: A case study of the Wufeng–Longmaxi shale reservoirs in the Sichuan basin and its periphery. Acta Geol. Sin. 99(4), 1381–1397 (2025).
Sun, C. X. et al. Characteristics and differences of deep to ultra-deep shale reservoirs of the Wufeng–Longmaxi Formation in eastern Sichuan. Petrol. Nat. Gas Geol. (in press) (2024).
Song, Y. et al. Preservation mechanism and model of marine shale gas in Southern China. Acta Geol. Sin. 97(9), 2858–2873 (2023).
Miao, H. et al. Dynamic evolution of pressure and gas content of deep shale reservoirs in the longmaxi formation, Sichuan basin. World Petrol. Ind. 31(5), 19–29 (2024).
Borjigen, T. et al. Differential preservation mechanisms of marine shale gas under varying burial conditions in Southern China. Acta Geol. Sin. 98, 3285–3301 (2024).
Cai, G., Gu, Y., Jiang, Y. & Wang, Z. Pore structure and fluid evaluation of deep organic-rich marine shale: A case study from Wufeng-Longmaxi formation of Southern Sichuan basin. Appl. Sci. 13(13), 7827 (2023).
Zhang, K. et al. Mechanism analysis of organic matter enrichment in different sedimentary backgrounds: A case study of the Lower Cambrian and the Upper Ordovician-Lower Silurian, in Yangtze region. Mar. Pet. Geol. 99, 488–497 (2019).
Fu, Y. et al. Microscopic pore-fracture configuration and gas-filled mechanism of shale reservoirs in the Western Chongqing area, Sichuan Basin, China. Pet. Explor. Dev. 48(5), 1063–1076 (2021).
Sun, C. et al. Porosity, permeability and rock mechanics of lower silurian longmaxi formation deep shale under temperature-pressure coupling in the Sichuan Basin, SW China. Pet. Explor. Dev. 50(1), 77–88 (2023).
Loucks, R., Reed, R., Ruppel, S. & Hammes, U. Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related pores. AAPG Bull. 96(6), 1071–1098 (2012).
Rouquerol, J. et al. Recommendations for the characterization of porous solids. Pure Appl. Chem. 66(8), 1739–1758 (1994).
Zhang, J., Liu, S., Wei, X., Tang, X. & Liu, Y. Evaluation of gas content in shale. Oil Gas Geol. 42(1), 28–40 (2021).
Cai, G. et al. Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production. Nat. Gas Ind. B 12, 368–385 (2025).
Zhang, J. C. et al. Advances and trends in field testing techniques for shale gas content. Earth Sci. Front. 31(1), 315–326 (2024).
Han, H. et al. Pore characteristics and factors controlling lacustrine shales from the upper cretaceous Qingshankou formation of the Songliao Basin, Northeast China: A study combining SEM, low-temperature gas adsorption and MICP experiments. Acta Geol. Sin (Engl. Ed.) 95(2), 585–601 (2021).
Gu, Y. et al. Geochemical and geological characterization of upper permian Linghao formation shale in Nanpanjiang Basin, SW China. Front. Earth Sci. 10, 883146 (2022).
McMahon, T., Larson, T., Zhang, T. & Shuster, M. Geologic characteristics, exploration and production progress of shale oil and gas in the united states: An overview. Pet. Explor. Dev. 51(4), 807–828 (2024).
Bertard, C., Bruyet, B. & Gunther, J. Determination of desorbable gas concentration of coal (direct method). In International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts Vol. 7, 43–65 (1970).
Zhao, Q. et al. A new method of calculating the lost gas volume during the shale core desorption test. Nat. Gas Ind. 33(5), 30–34 (2013).
Wei, Q., Yan, B. & Xiao, X. Research progress on the desorption methods of shale gas. Nat. Gas Geosci. 26(9), 1657–1664 (2015).
Liu, G. et al. A critical desorption time method to improve the calculation accuracy of gas loss in shale gas content testing. Nat. Gas Ind. 39(2), 71–75 (2019).
Shtepani, E., Noll, L. A., Elrod, L. W. & Jacobs, P. M. A new regression-based method for accurate measurement of coal and shale gas content. SPE Reserv. Eval. Eng. 13(2), 359–364 (2010).
Guo, X. et al. Study on the micro mechanism of shale self-sealing and shale gas preservation. Petrol. Geol. Exp. 45(5), 821–831 (2023).
Mahmud, H., Hisham, M., Mahmud, W., Leong, V. & Shafiq, M. Petrophysical interpretations of subsurface stratigraphic correlations, Baram Delta, Sarawak, Malaysia. Energy Geosci. 1(3–4), 100–114 (2020).
Xiang, K. M. et al. Characteristics and gas-bearing controlling factors of deep shale gas reservoirs in Southern Sichuan, China. J. Northeast Petrol. Univ 47(3) (2023).
Wu, J. F. et al. Fracture development characteristics of organic-rich shales and their relationship with gas content in the longmaxi Formation, Changning area, Southern Sichuan. Acta Petrol. Sin. 42(4), 428 (2021).
Gao, J. et al. Overpressure generation and evolution in lower paleozoic gas shales of the Jiaoshiba region, China: Implications for shale gas accumulation. Mar. Pet. Geol. 102, 844–859 (2019).
Jia, A. et al. Variations of pore structure in organic-rich shales with different lithofacies from Jiangdong Block, fuling shale gas Field, SW China: Insights into gas storage and pore evolution. Energy Fuels. 34(10), 12457–12475 (2020).
Han, S. et al. Pore types and characteristics of shale gas reservoir: A case study of lower paleozoic shale in Southeast Chongqing. Earth Sci. Front. 20(3), 247–253 (2013).
Li, G. et al. Continuous extensional uplift controls the silurian structural evolution of the Sichuan Basin, Southwest China. Mar. Pet. Geol. 155, 106383 (2023).
Liu, H., Wang, Y., Liu, X., Guo, W. & Pi, S. Shale facies characteristics and bubble pore forming mechanism of longmaxi formation in Sichuan basin. Nat. Gas Ind. 37(S1), 11–16 (2017).
Li, J. et al. Quantitative evaluation of organic and inorganic pore size distribution by NMR: A case from the silurian longmaxi formation gas shale in fuling area, Sichuan basin. Oil Gas Geol. 37(1), 129–134 (2016).
Guan, Q. et al. Fractal characteristics of organic-rich shale pore structure and its geological implications: A case study of the lower silurian longmaxi formation in the Weiyuan block, Sichuan Basin. Nat. Gas Ind. 44(3), 108–118 (2024).
Chen, D. et al. Differences in microporous fractal characteristics of tight sandstones of different diagenetic facies: Chang 6 reservoirs of the triassic Yanchang formation in the Western Ordos Basin, China. Front. Earth Sci. 13, 1583053 (2025).
Rybacki, E., Meier, T. & Dresen, G. What controls the mechanical properties of shale rocks? – Part II: Brittleness. J. Pet. Sci. Eng. 144, 39–58 (2016).
Funding
This study was financially supported by National Natural Science Foundation of China (No. 42302166).
Author information
Authors and Affiliations
Contributions
Y.Z: Writing-Original Draft, Writing –Review & Editing, Data Curation, Formal Analysis, and Validation; H.Z. and L.Z: Formal Analysis, Validation, and Reviewing; J.L., Y.Y., and L.Z.: Data Curation, Validation, and Reviewing.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
About this article
Cite this article
Zhang, Y., Zhang, H., Zhang, L. et al. Pore-micro fracture structure, porosity and gas- bearing property of deep shale under lithofacies-formation pressure coupling. Sci Rep (2026). https://doi.org/10.1038/s41598-026-38352-7
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41598-026-38352-7
