Abstract Considerable attention has been paid to the development of unconventional reservoir fields due to the availability of such resources worldwide. The heterogeneities throughout the pore space structure in a rock and their effects on the occurrence of gas and oil can be quantitatively analysed using fractal theory. This study focuses on the investigation of the fractal dimension (FD) in shale and tight gas sandstones (TGS) from Brazilian oil and gas fields using 3-D X-ray nano- and micro-computed tomography. Obtaining the broad size distribution of pore space structures in unconventional reservoir rocks using 3-D images is challenging due to the multiscale characteristics of the rocks. Thus, sample images were acquired with two voxel size/resolutions (0.064 μm and from 0.46 to 1.20 μm). Very small pores (ganglia), main pore networks and organic matter grains were observed as segmented structures within sample sets for which the FD was assessed and quantified. Box-counting (BC) and pore size distribution (PSD) approaches were applied. The average FD values ranged from 1.78 to 2.59 in shale and from 2.36 to 2.46 in TGS. Correlations of the FD with the experimentally acquired specific surface area, porosity and permeability related petrophysical properties, relevant to the quantitative modelling of gas transport in unconventional reservoirs, were established. The pore scale morphologies described by the FD from 3-D X-ray CT images help on the foundation for further research in shale/tight gas sandstones.

中文翻译：

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使用 X 射线纳米和显微计算机断层扫描技术研究非常规储层岩石孔隙空间的分形维数

摘要 非常规油藏在全球范围内的可得性已成为非常规油田开发的重点。可以使用分形理论定量分析岩石中整个孔隙空间结构的非均质性及其对油气赋存的影响。本研究的重点是使用 3-D X 射线纳米和微型计算机断层扫描技术研究巴西油气田页岩和致密气砂岩 (TGS) 的分形维数 (FD)。由于岩石的多尺度特征，使用 3-D 图像获得非常规储层岩石中孔隙空间结构的广泛尺寸分布具有挑战性。因此，以两种体素尺寸/分辨率（0.064 μm 和 0.46 至 1.20 μm）获取样本图像。非常小的毛孔（神经节），主要孔隙网络和有机质颗粒被观察为样品组内的分段结构，FD 被评估和量化。应用了盒计数 (BC) 和孔径分布 (PSD) 方法。页岩的平均 FD 值为 1.78 至 2.59，TGS 的平均 FD 值为 2.36 至 2.46。建立了 FD 与实验获得的比表面积、孔隙度和渗透率相关的岩石物理特性的相关性，与非常规储层中气体输运的定量建模相关。FD 从 3-D X 射线 CT 图像描述的孔隙尺度形态有助于为页岩/致密气砂岩的进一步研究奠定基础。应用了盒计数 (BC) 和孔径分布 (PSD) 方法。页岩的平均 FD 值为 1.78 至 2.59，TGS 的平均 FD 值为 2.36 至 2.46。建立了 FD 与实验获得的比表面积、孔隙度和渗透率相关的岩石物理性质的相关性，与非常规储层中气体输运的定量建模相关。FD 从 3-D X 射线 CT 图像描述的孔隙尺度形态有助于为页岩/致密气砂岩的进一步研究奠定基础。应用了盒计数 (BC) 和孔径分布 (PSD) 方法。页岩的平均 FD 值为 1.78 至 2.59，TGS 的平均 FD 值为 2.36 至 2.46。建立了 FD 与实验获得的比表面积、孔隙度和渗透率相关的岩石物理特性的相关性，与非常规储层中气体输运的定量建模相关。FD 从 3-D X 射线 CT 图像描述的孔隙尺度形态有助于为页岩/致密气砂岩的进一步研究奠定基础。建立了与非常规储层中气体输运定量模型相关的研究成果。FD 从 3-D X 射线 CT 图像描述的孔隙尺度形态有助于为页岩/致密气砂岩的进一步研究奠定基础。建立了与非常规储层中气体输运定量模型相关的研究成果。FD 从 3-D X 射线 CT 图像描述的孔隙尺度形态有助于为页岩/致密气砂岩的进一步研究奠定基础。