煤系沉积岩多重分形维数计算及影响因素分析

Calculation of multi-fractal dimension of coal measure sedimentary rock and analysis of influencing factors

  • 摘要: 为表征煤系沉积岩的孔隙结构与分形特征,选取中侏罗统页岩、泥岩和砂岩3种典型沉积岩进行了X射线衍射(XRD)分析、核磁共振(NMR)实验,运用分形理论讨论了NMR分形维数与矿物组成、物性参数之间的相互关系。结果表明:①基于弛豫时间截止值T2C,可将页岩、泥岩NMR分形维数划分为吸附孔隙分形维数DA(T2≤3 ms)和渗流孔隙分形维数DS(T2>3 ms)。②储层物性方面,NMR分形维数Df与孔隙率、渗透率、储层质量指数呈良好的线性负相关关系,说明NMR分形维数能够作为衡量岩石物性的重要指标。③矿物成分方面,石英、长石含量与分形维数Df呈弱负相关关系,黏土矿物由于受到沉积环境、理化性质和矿物本身含量等多因素作用,对分形维数的影响差异较为显著。

     

    Abstract: In order to characterize the pore structure and fractal characteristics of coal-measure sedimentary rocks, three types of typical sedimentary rocks of the Middle Jurassic shale, mudstone and sandstone were selected as the research objects. Through X-ray diffraction(XRD)analysis and nuclear magnetic resonance(NMR)experiment, the correlation between NMR fractal dimension, mineral composition and physical property parameters was discussed by using fractal theory. The results are as follows: ① Based on the relaxation time cut-off value T2C, the NMR fractal dimension of shale and mudstone can be divided into the fractal dimension of adsorption pore DA(T2 ≤3 ms)and the fractal dimension of seepage pore DS (T2 >3 ms). ② In terms of reservoir physical properties, NMR fractal dimension Df has a good linear negative correlation with porosity, permeability, and reservoir quality index, indicating that NMR fractal dimension can be used as an important indicator of rock physical properties. ③ In terms of mineral composition, the content of quartz and feldspar has a weak negative correlation with the fractal dimension Df, and clay minerals have different influences on the fractal dimension due to multiple factors such as sedimentary environment, physical and chemical properties and mineral content.

     

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