Abstract:

The formation of black shale in sedimentary basins, both domestically and internationally, is often associated with varying degrees of uranium (U) enrichment. Understanding the enrichment mechanisms of U in black shale and its impact on the formation of organic minerals is critical. This study systematically reviews the processes of U enrichment in organic matter, microorganisms, clay minerals, iron-bearing minerals, sulfur-bearing minerals, and phosphorus-bearing minerals. It focuses on the mechanisms of U occurrence in black shale and the effects of U on the oil-generation properties, gas-generation properties, and kerogen structure of organic matter. Uranium enrichment in black shale occurs through diverse pathways, with various shale components enriching U in the environment via mechanisms such as complexation, adsorption, and reduction. The efficiency of U enrichment is influenced by multiple factors, including pH and the concentration of interfering ions. Additionally, the impact of U on the oil and gas production performance of shale organic matter is complex and remains controversial, as simulation experiments have yielded inconsistent results due to differences in experimental conditions and sample characteristics. Despite significant research efforts, many studies on the influence of U on organic matter remain limited to qualitative analysis, leaving several critical issues unresolved. These include: (1) the lack of a clear microscopic mechanism for U enrichment in black shale, hindering the development of a comprehensive U enrichment model; (2) challenges in analyzing the reservoir residence time of crude oil due to the difficulty of effectively characterizing the radiation dose of oil; and (3) uncertainties regarding the similarities and differences between the effects of artificial and natural radiation on the oil and gas production performance of organic matter, making it difficult to identify the primary factors controlling the evolution of organic matter under radiation. Future research should employ advanced analytical techniques to investigate the microscopic mechanisms of radiation effects, conduct molecular composition and structural analysis, identify effective radiation indices in oil, and expand the application of radiation studies in geology. This work has significant implications for advancing the understanding of oil and gas formation processes, exploring new oil and gas resources, and enriching geological knowledge about U in black shale.

Key words: U element, uranium, black shale, enrichment mechanism, organic matter, oil-gas performance