Fracture network complexity of tight sandstone and its influencing factors
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摘要: 致密砂岩裂缝网络复杂性分析对水力压裂优化、裂缝网络预测、裂缝建模等具有重要意义。本文在砂岩复杂裂缝网络动态演化过程及其主控因素实验研究的基础上,通过深入探讨裂缝网络的分形和多重分形谱特征,开展裂缝网络的复杂性分析。结果表明:裂缝的萌生、扩展贯穿于应力-应变的全过程,裂缝网络的复杂性主要受控于自身的微观组构特征,且具有明显的尺度和围压效应。三维裂缝网络的分形维数与多重分形谱的谱宽平均值,两个参数可分别表征裂缝网络空间分布的复杂性和非均质性。砂岩的石英、长石等脆性矿物含量越高、孔隙度越大、粒度越小裂缝网络空间分布越复杂,非均质性越弱;黏土矿物不利于复杂裂缝的形成;抗压强度和弹性模量越大裂缝网络空间分布越复杂,非均质性越弱。Abstract: The fracture network complexity analysis of tight sandstone plays an important role in hydraulic fracturing optimization, fracture network prediction and fracture modeling. Based on the experimental study on the dynamic evolution process and main controlling factors of complex fracture network in sandstone, the complexity analysis of fracture network is carried out by deeply discussing the fractal and multifractal spectrum characteristics of fracture network. The results show that the initiation and propagation of cracks run through the whole process of stress-strain, and the complexity of fracture network is mainly controlled by its own microscopic fabric characteristics, and has obvious scale and confining pressure effects. The fractal dimension of the three-dimensional fracture network and the average spectral width of the multifractal spectrum can represent the complexity and heterogeneity of the spatial distribution of the fracture network, respectively. The higher the content of quartz, feldspar and other brittle minerals in sandstone, the larger the porosity and the smaller the particle size, the more complex the spatial distribution of fracture network and the weaker the heterogeneity. Clay minerals are not conducive to the formation of complex fractures. The larger the compressive strength and elastic modulus, the more complex the spatial distribution of the fracture network and the weaker the heterogeneity.
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Key words:
- Tight sandstone /
- Fracture network /
- Fractal dimension /
- Multifractal spectrum
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