Abstract:
The Ordos basin is a crucial comprehensive energy base in China, where coal and sandstone-type uranium resources frequently coexist in an associated form within the same clastic aquifer system, characterized by a typical “coal below, uranium above”configuration. This coal-bearing uranium aquifer possesses a dual nature: it serves as the direct water-filling aquifer for underlying coal seam extraction, impacting coal mine safety, and simultaneously acts as the reservoir and migration pathway for in-situ leaching (ISL) of the overlying uranium deposit, influencing the effective displacement and recovery of lixiviant. Its spatial heterogeneity, manifested in mineral composition, pore structure, sandbody geometry, and spatial distribution, constitutes a significant geological challenge for the safe and efficient coordinated mining of these resources. Therefore, developing a methodological framework capable of systematically revealing and three-dimensionally characterizing the multi-scale heterogeneity of this aquifer is of considerable theoretical and practical value.Focusing on the coal-bearing uranium aquifers of the Jurassic Zhiluo formation and Cretaceous Luohe formation in the Wushen and Hangjin banner areas of the north-central Ordos Basin, a multi-scale, multi-attribute coupled research methodology encompassing micro-, meso-, and macro-scales is proposed. At the microscopic scale, techniques including polarizing microscopy, scanning electron microscopy (SEM), mercury intrusion porosimetry, nuclear magnetic resonance (NMR), and core computed tomography (CT) scanning are employed to quantitatively analyze the compositional and pore-structural heterogeneity at the micrometer level. At the mesoscopic scale, outcrop analysis is integrated with core-logging prediction models to characterize sandstone morphology and vertical heterogeneity at the meter scale. At the macroscopic scale, based on sequence stratigraphic division and sedimentary facies distribution analysis, and combined with geostatistical methods such as sequential Gaussian simulation, a multi-attribute three-dimensional geological model controlled by sedimentary facies is established. This model achieves a three-dimensional spatial characterization of aquifer heterogeneity at the kilometer scale.The results demonstrate that this methodological framework can systematically reveal the heterogeneity characteristics of the coal-bearing uranium aquifer from micro- to macro-scales. The findings provide direct geological basis and a modeling foundation for predicting seepage fields, which is essential for preventing roof water hazards in coal mining and for the in-situ leaching of sandstone-type uranium deposits. This research holds significant importance for ensuring the safe and efficient coordinated mining of coal and uranium resources.