Comparison analysis of fractal characteristics for tight sandstones using different calculation methods
Comparison analysis of fractal characteristics for tight sandstones using different calculation methods
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不同计算方法致密砂岩分形特征对比分析
DOI：
10.1088/1742-2140/14/1/120
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发表时间：
2017
影响因子：
1.4
通讯作者：
Li Teng
中科院分区：
文献类型：
--
作者：
Zhang Xiaoyang;Wu Caifang;Li Teng
致密砂岩的微孔结构是决定其储量和渗流特征的决定性因素。在致密砂岩气勘探中，准确地描述孔隙结构和完整地表征气水渗透率是至关重要的。分形维数是定量表征低渗透储层孔隙结构非均质性和复杂性的一种简单有效的方法。采用三种不同的压汞孔隙度法（MIP）数据，分析了塔里木盆地南段砂岩的分形维数和分形曲线。临兴地块下石河子组8层（河8段），年代为中二叠统。讨论了分形曲线的形态特征、分形维数的特征以及三种方法的理论差异。结果表明，方法1得到的分形维数反映了未被汞侵入的剩余孔隙的特征，表明所涉及的孔隙尺度更为全面。方法II和方法III均获得了汞侵入孔隙的分形维数，不同之处在于选择了简化的孔隙形态模型，导致分形维数相差1。无论采用哪种方法，临兴区块致密砂岩储层孔隙结构均呈现分形特征。而方法1得到的分形维数更适合描述临兴区块河8段致密砂岩孔隙的复杂性和岩石物性。不同方法得到的分形曲线在形态变化方面具有一定的一致性。小孔隙（<rmax-point）通常表现出更多的分形特征，而大孔隙（>rmax-point）是影响储层渗流特征的关键因素。
The micropore structure of a tight sandstone is the decisive factor in determining its reserve and seepage characteristics. An accurate description of the pore structures and a complete characterization of the gas–water permeability are critical when exploring for tight sandstone gas. One simple and effective way to quantitatively characterize the heterogeneity and complexity of the pore structures in a low permeability reservoir is the fractal dimension. In this study, three different methods, each utilizing mercury intrusion porosimetry (MIP) data, were adopted to analyze the fractal dimensions and the fractal curves of sandstones from the no. 8 layer of the Xiashihezi Formation (He 8 member) in the Linxing block, dated from the Middle Permian. The morphological features of the fractal curves, the characteristics of the fractal dimensions and the theoretical differences between these three methods were also discussed. The results show that the fractal dimensions obtained by method I reflect the characteristics of the remaining pores that are not intruded by mercury, and they show that the involved pore scales are more comprehensive. While in methods II and III, both obtain the fractal dimensions of the pores intruded by mercury, the difference between them is in the selection of a simplified pore shape model, which results in the fractal dimensions differing by a value of 1 between them. No matter which method is adopted, the pore structures of tight sandstone reservoirs in the Linxing block exhibit fractal characteristics. However, the fractal dimensions obtained by method I are more suitable for describing the complexity and petrophysical properties of the tight sandstone pores in the He 8 member of the Linxing block. The fractal curves obtained by different methods are consistent to a certain extent in terms of morphological changes. Small pores (<rmax-point) usually demonstrate more fractal characteristics, while large pores (>rmax-point) are the critical factor affecting the seepage characteristics of the reservoir.