Abstract The evaluation of the pore structure of tight oil and gas reservoirs has great significance for the characterization of the reservoir properties and the prediction of reservoir productivity. Fractal analysis is an effective method commonly used to evaluate reservoir pore structure. In previous studies, the fractal dimension of nuclear magnetic resonance (NMR) transverse relaxation time (T2) distribution was calculated to evaluate reservoir pore structure. However, due to the low signal-to-noise ratio (SNR) of the NMR echo data in tight sandstone reservoirs, the T2 distribution obtained by inversion of the echo data with low SNR has great uncertainty, which affects the evaluation accuracy of reservoir pore structure. In this paper, the fractal dimension of the NMR echo data (D_ECHO) is calculated to evaluate the pore structure of tight sandstone reservoirs for the first time. Fast Fourier transform is performed with the NMR echo data and then the D_ECHO is calculated. We analyze the correlation between the fractal dimension and the physical parameters and pore structure parameters, the results showed that 1) compared with the calculation of the fractal dimension of the T2 distribution, the calculation of the D_ECHO has higher stability, which can avoid the influence of the inversion uncertainty of echo data with a low SNR on the evaluation of the reservoir pore structure; 2) the fractal dimension is closely related to pore structure parameters, D_ECHO are well suited for characterizing the pore structure of tight sandstone reservoirs. As the heterogeneity of reservoirs increases, the D_ECHO increases. Numerical simulations, core experiments and NMR logging data processing results verify the effectiveness of the proposed method.

中文翻译：

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基于核磁共振回波数据分形分析的致密砂岩储层孔隙结构表征

摘要 致密油气藏孔隙结构评价对于储层物性表征和储层产能预测具有重要意义。分形分析是一种常用的储层孔隙结构评价方法。在以往的研究中，通过计算核磁共振 (NMR) 横向弛豫时间 (T2) 分布的分形维数来评估储层孔隙结构。但由于致密砂岩储层核磁共振回波数据信噪比低，低信噪比回波数据反演得到的T2分布具有很大的不确定性，影响储层孔隙评价精度。结构体。在本文中，首次利用核磁共振回波数据（D_ECHO）的分形维数评价致密砂岩储层的孔隙结构。使用 NMR 回波数据执行快速傅立叶变换，然后计算 D_ECHO。我们分析了分形维数与物理参数和孔隙结构参数之间的相关性，结果表明：1）与计算T2分布的分形维数相比，D_ECHO的计算具有更高的稳定性，可以避免影响低信噪比回波数据反演不确定性对储层孔隙结构评价的影响；2）分形维数与孔隙结构参数密切相关，D_ECHO非常适合表征致密砂岩储层的孔隙结构。随着储层非均质性的增加，D_ECHO 增加。数值模拟、岩心实验和核磁共振测井数据处理结果验证了所提方法的有效性。