张北地区天然氢气藏远景区分析评价——基于重力和大地电磁测深的基底构造解释

    Prospect area analysis and evaluation of natural hydrogen reservoirs in the Zhangbei area: Interpretation of basement structures based on gravity and magnetotelluric sounding

    • 摘要: 在张北盆地的土壤氢气地球化学调查中发现了大面积氢气逸出异常,急需通过地球物理方法了解盆地内具有生氢和导氢作用的基底构造特征。为此,首次在张北盆地开展了针对天然氢的重力和大地电磁调查,在研究区内部署了1∶5万重力和大地电磁测量,基于采集的重力和大地电磁数据,以钻井、地质、物性等资料作为约束,反演了一条横跨研究区的大比例尺重力—大地电磁剖面,确定了盆地“两凹三隆”的构造格局,计算得到中新生代盆地总的沉积厚度为0.62~1.9 km;揭示了4条隐伏断裂,其中F1及F4断裂可作为天然氢运移和存储通道;反演结果显示的两个凹陷内地层界面连续稳定、砂岩—泥岩组合层较厚,可有效减少氢气的泄漏,具有良好的封存能力。本次基底构造研究成果可作为区内天然氢远景区评价以及下一步勘查工作部署的重要基础,同时为建立天然氢勘查技术体系和优选勘探靶区提供了重要依据。

       

      Abstract: Large-area hydrogen escape anomalies were detected during the soil hydrogen geochemical survey in the Zhangbei Basin, making it urgent to apply geophysical methods to understand the basement structures that generate and transport hydrogen. For this purpose, the first gravity and magnetotelluric surveys targeting natural hydrogen were conducted in the Zhangbei Basin, with 1∶50,000 gravity and magnetotelluric surveys performed within the study area. Using the collected gravity and magnetotelluric data, a large-scale gravity-magnetotelluric profile across the study area was inverted, constrained by drilling, geological, and physical property data. The study identified a "two depressions and three uplifts" structural pattern in the basin, with a total Mesozoic-Cenozoic sedimentary thickness ranging from 0.62 to 1.9 km. Four concealed faults were revealed, among which faults F1 and F4 can serve as migration pathways and storage channels for natural hydrogen. The inversion results indicate that the two depressions exhibited continuous and stable stratigraphic interfaces and relatively thick sandstone-mudstone assemblage layers, which provide good sealing capacity to reduce hydrogen leakage effectively. These findings on basement structures offer valuable insights for the prospect area evaluation of natural hydrogen and subsequent exploration plans in the area. They also provide a significant basis for establishing a natural hydrogen exploration technology system and selecting optimal exploration targets.

       

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