采用真三轴压裂模拟系统对四川盆地志留系龙马溪组露头页岩开展了压裂模拟实验,将通过岩样剖分和CT扫描获得的水力裂缝扩展形态与声发射监测解释结果进行对比以揭示裂缝扩展过程中的声发射响应特征,并分析水力裂缝连通区域与未连通区域在声发射事件类型上的差异.研究表明,声发射事件点的空间分布能够反映岩样内部水力裂缝扩展形态.水力裂缝起裂的位置声发射事件点较多、分布集中;水力裂缝激活的层理面附近声发射事件点稀疏;裂缝密度越大,声发射事件点的分布越密集.水力裂缝沟通范围与声发射事件点的分布范围存在差别,基于声发射事件的改造体积解释结果偏大.水力裂缝沟通范围内声发射事件以剪切事件和张性事件为主,未被水力裂缝沟通的原始开启层理面附近以剪切事件为主,将二者进行区分可以提高储集层改造体积解释结果的准确性.图7表3参32%A series of laboratory fracturing experiments was performed on samples mined from an outcrop of the Silurian Longmaxi Formation shale in the Sichuan Basin,using a true triaxial fracturing simulation system.To reveal the characteristics of acoustic emission (AE) response in hydraulic fracture (HF) propagation,the HF propagation geometry obtained by specimen splitting and CT scanning technology was compared with the interpretation results of AE monitoring.And the difference of hypoeenter mechanism between hydraulically connected and unconnected regions was further discussed.Experimental results show that the AE events distribution indicates well the internal fractures geometry of the rock samples.Numerous AE events occur and concentrate around the wellbore where the HF initiated.Sparse AE events were presented nearby bedding planes (BP) activated by the HF.AE events tended to be denser where HF geometry was more complex.The hydraulically connected region was obviously distinct with the spatial distribution of AE events,which resulted in the overestimation of stimulated reservoir volume (SRV) based on micro-seismic mapping result.Both tensile and shear events occurred in the zone connected by the hydraulic fractures,while only shear events were observed around BPs those were not hydraulically connected.Thus,the hydraulically connected and unconnected region can be identified in accordance with the hypocenter mechanism,which is beneficial to improve the accuracy of SRV evaluation.
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