In the quest to better understand Earth’s subsurface reservoirs, recent research on the Middle Jurassic Yungang Formation offers groundbreaking insights into the complex processes that shape the diagenesis and reservoir quality of fluvial sandstones. Conducted in the Yungang area of the Datong Basin in North China, this study unfolds a detailed narrative of sedimentary evolution, mineralogical transformations, and porosity dynamics in one of the most prospective sedimentary basins, adding valuable knowledge to hydrocarbon exploration and carbon sequestration efforts.
Fluvial sandstones are known for their heterogeneity and intricate diagenetic histories, which profoundly influence their ability to store and transmit fluids such as oil, gas, and water. The Yungang Formation, deposited during the Middle Jurassic period, represents a fluvial depositional system whose sedimentary characteristics and post-depositional alterations have been meticulously investigated in this study. By integrating field observations with advanced petrographic and geochemical analyses, the research deciphers the subtle interplay between depositional facies and diagenetic overprints.
One pivotal aspect illuminated in this investigation pertains to the influence of diagenetic processes on reservoir quality parameters, predominantly porosity and permeability. The study identifies that early cementation by minerals like calcite and kaolinite significantly reduced primary porosity, while subsequent dissolution events could partially enhance secondary porosity. This duality underscores a delicate balance in diagenesis, where mineral precipitation and dissolution cooperate and compete, ultimately controlling the effectiveness of the sandstone as a reservoir.
Furthermore, the research delves into the spatial variability within the fluvial sandstone bodies, highlighting how channel-fill and overbank deposits exhibit contrasting diagenetic trends. Channel sandstones, characterized by coarser grains and higher initial porosity, tend to preserve better reservoir quality despite intense diagenetic modification, while finer-grained overbank deposits suffer more severe cementation, leading to poorer fluid flow properties. Such heterogeneity stresses the importance of small-scale sedimentological variations in evaluating reservoir potential.
The role of authigenic clay minerals emerges as another crucial parameter affecting reservoir quality. The study demonstrates that the precipitation of clay minerals such as illite and chlorite within the pore spaces diminishes permeability by clogging pore throats, yet in some cases, these clays exert a protective effect by inhibiting extensive quartz cementation. This protective mechanism showcases a paradox where certain diagenetic products simultaneously degrade and preserve reservoir characteristics.
Geochemical signatures preserved within the sandstones reveal the diagenetic fluids’ origin and evolution, offering clues about paleofluid migration pathways and thermal histories. Isotopic analyses of carbonate cements suggest multiple phases of fluid-rock interaction, with groundwater influxes possibly linked to tectonic uplift and climatic variations during the Jurassic. These findings integrate diagenesis into broader geodynamic frameworks, connecting local sedimentary processes to regional tectonics.
One striking outcome of this study is the recognition of dissolution features, including secondary porosity generated by the partial acidification of pore waters. This process, possibly driven by organic acids or CO2-charged fluids, effectively remodels parts of the sandstone framework, reopening storage space and enhancing connectivity between pores. These dissolution pathways are crucial for reservoir engineers aiming to tailor extraction strategies or assess CO2 injection viability for carbon capture and storage projects.
The structural control imposed by faults and fractures within the Datong Basin is also scrutinized for its impact on diagenetic alteration. Fracture networks act as conduits for fluid migration, facilitating mineral precipitation or dissolution at various scales. The coupling of structural geology with diagenetic textures provides a comprehensive picture of how tectonism influences reservoir evolution over geological timeframes.
Sediment provenance analysis assists in unraveling the characteristics of source areas feeding the Yungang Formation. Compositional maturity and grain-size distribution delineate how sediment supply and transport mechanisms governed the initial reservoir framework. The provenance fingerprints, when combined with diagenetic alterations, aid in reconstructing the sedimentological history crucial for predicting reservoir heterogeneities.
Porosity-permeability correlations derived from core samples and thin-section observations lend quantitative weight to the study’s qualitative descriptions. Advanced imaging techniques such as scanning electron microscopy and micro-CT scanning reveal pore architecture at microscale, exposing otherwise invisible pore networks and constrictions. These tools unveil the microcosm of rock fabric that ultimately drives fluid behavior within reservoirs.
In the broader context of petroleum geology, the implications of this research extend beyond academic curiosity. Identifying diagenetic pathways that optimize or degrade reservoir quality is central to exploration risk assessments and production forecasting. The Yungang Formation becomes a case study epitomizing the challenges and opportunities inherent in fluvial sandstone reservoirs globally.
Moreover, the article contributes to emerging discussions on the sustainable utilization of subsurface resources, particularly in light of increasing interest in geological carbon storage. Understanding porosity evolution and fluid pathways is indispensable for predicting the long-term fate of injected CO2 and preventing leakage, thereby aligning geological science with environmental stewardship.
Despite the intricate complexity of fluvial systems, this investigation sheds light on the essential controls dictating reservoir development, merging sedimentology, mineralogy, geochemistry, and structural geology into an integrated model. The narrative constructed vividly captures how ancient river systems preserved in stone interplay with post-burial changes to shape Earth’s subsurface fluid habitats.
The meticulous combination of fieldwork, laboratory analysis, and theoretical extrapolation underscores the sophistication modern geoscience demands to unravel diagenesis and reservoir quality. By unlocking these secrets within the Yungang Formation, scientists edge closer to predicting reservoir behavior, enhancing resource extraction efficiency, and mitigating environmental impacts.
This research thus signifies a milestone in basin analysis, carving pathways for future investigations across similar geological settings. The lessons derived from the Datong Basin’s Jurassic sandstones emerge as paradigms advising exploration in analogous fluvial reservoirs worldwide, stirring renewed scientific and industrial interest.
As the energy landscape evolves, the detailed understanding of diagenesis in fluvial sandstones offered by this study will increasingly inform multidisciplinary approaches to subsurface resource management, emphasizing the enduring importance of integrating geological sciences with practical challenges of our time.
Subject of Research: Diagenesis and reservoir quality of fluvial sandstones in the Middle Jurassic Yungang Formation, Datong Basin, North China.
Article Title: Diagenesis and reservoir quality of fluvial sandstones: a case study of outcropped Middle Jurassic Yungang Formation in Yungang area of Datong Basin, North China.
Article References:
Liu, L., Liao, C., Huang, S. et al. Diagenesis and reservoir quality of fluvial sandstones: a case study of outcropped Middle Jurassic Yungang Formation in Yungang area of Datong Basin, North China. Environ Earth Sci 84, 517 (2025). https://doi.org/10.1007/s12665-025-12484-x
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