Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH
Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH
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DOI：
10.1021/acs.energyfuels.3c02927
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发表时间：
2023-11
期刊：
影响因子：
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通讯作者：
Bingbin Xie;Jingqiang Tan;Qiao Lyu;Chenger Hu;Yonggang Ding;Jindong Shi;Kaixi Wang;Gan Feng-Gan-F
中科院分区：
文献类型：
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作者：
Bingbin Xie;Jingqiang Tan;Qiao Lyu;Chenger Hu;Yonggang Ding;Jindong Shi;Kaixi Wang;Gan Feng-Gan-F
页岩与压裂液的相互作用会改变页岩内部孔隙结构和吸附能力，对页岩气产能有重要影响。研究不同压裂液pH值下页岩声发射能量变化及多重分形特征对页岩气产能的影响。采用pH值分别为6、7、8的压裂液对页岩进行了一系列浸泡实验。在pH值为6、7、8的压裂液浸泡条件下，对页岩进行单轴压缩试验和声发射试验。基于声发射信号，应用多重分形理论分析了单轴压缩过程中裂缝闭合和扩展的演化过程。该研究还考察了压裂液长期浸泡后页岩的变形和裂缝演化，特别强调了流体-岩石反应。结果表明：浸泡后页岩最大累积声发射能高于完整页岩；重点了解页岩在不同阶段单轴压缩下的裂缝演化过程。流体-岩石反应决定了压裂液长期浸泡后页岩的变形和裂缝演化。浸后页岩谱宽Δα增大，说明浸后声发射信号分布更加不均匀。酸性压裂液浸泡后页岩的Δfvalue变化比中性或碱性压裂液浸泡后页岩的Δfvalue变化更明显。页岩样品的分形谱总体上呈左偏态分布。谱参数的取值受浸泡流体、浸泡时间和压缩阶段的影响，导致多重分形特征的变化。浸没中后期粘土矿物水化膨胀占主导地位。研究结果对理解页岩试样的变形和裂缝演化以及岩石-流体反应对其破坏过程的影响具有一定的指导意义。
The interaction between shale and fracturing fluids will change the internal pore structure and adsorption capacity of shale, which have an important impact on shale gas productivity. This study aims to investigate the variations in acoustic emission (AE) energy and multifractal characteristics of shale under different pH values of fracturing fluids with implications for shale gas productivity. A series of immersion experiments were carried out on shale with fracturing fluids, with pH values of 6, 7, and 8, respectively. The uniaxial compression tests and AE tests were conducted on shale under fracturing fluid immersion with pH values of 6, 7, and 8. The multifractal theory is applied to analyze the evolution of fracture closure and propagation during uniaxial compression based on AE signals. The study also examines the deformation and crack evolution of shale after long-term fracturing fluid immersion, with particular emphasis on fluid–rock reactions. The results show that the maximum cumulative AE energy of shale after immersion is higher than that of intact shale. The focus is on understanding the fracture evolution process of shale during uniaxial compression at different stages. The fluid–rock reactions determine the deformation and crack evolution of shale after long-term fracturing fluid immersion. The increase of shale spectrum width Δα after immersion indicates that the distribution of AE signals is more uneven after immersion. The Δfvalue of shale after acid fracturing fluid soaking changes more significantly than those of neutral or alkaline fracturing fluids. All the fractal spectra of shale samples generally show a left-skewed distribution. The values of spectrum parameters are affected by soaking fluid, soaking time, and compression stages, resulting in the variation of multifractal characteristics. Hydration expansion of clay minerals is dominant in the middle and late period of immersion. The research results have a certain guidance for understanding the deformation and crack evolution and the influence of rock–fluid reactions on the failure process of shale samples.