Seismic prediction of fractures with small scale and low dip in shale is difficult.Taking the shale gas reservoir of the Wufeng Fm-1st member of Longmaxi Fm in the Jiaoshiba area of Fuling shale gas field as an example,we explored post-stach seismic fracture prediction method under constraint of stress field.Firstly,the post-stach seismic data were processed to enhance the structure response,so as to improve the ability of identifying faults and fractures,then the high precision seismic curvature volume was trached to describe the level of fracture development.Secondly,the distribu-tion characteristics of present stress field was simulated to reveal the orientation and strain strength of fractures.Finally, the seismic curvature and stress field attributes were normalized to build a fracture prediction model for accurate identifi-cation of orientation and intensity of fracture in the shale reservoirs.The results show that NE-trending fractures with moderate to weah intensity dominate the shale reservoir in the Wufeng Fm-1st member of Longmaxi Fm in the major part of the Jiaoshiba box anticline structure and NE-trending and NW-trending fractures with moderate to strong intensity occur locally on the flanks of structure and fault (fold) belt.The prediction results are in accordance with the geologic understandings.Well-to-seismic calibration reveals that the fracture prediction results correlate well with the fracture leahage zones identified during drilling,further validating the effectiveness and applicability of the method.It can be used to guide the comprehensive evaluation of shale gas reservoirs and drilling engineering.%针对泥页岩整体"小尺度,低角度"裂缝地震预测难度较大的特点,以涪陵页岩气田焦石坝区块五峰组-龙马溪组一段页岩气储层为例,探索了应力场约束的叠后地震裂缝预测技术方法.首先,进行叠后地震数据增强裂缝响应效果的针对性处理,以提高断裂及裂缝识别能力,在此基础上开展表征裂缝发育程度的高精度地震体曲率追踪;其次,模拟现今应力场分布特征,分析裂缝发育方向及应变强度;最后,将体曲率及应力场预测成果归一化,建立归一化应力场与体曲率相乘的裂缝预测模型,从而较有效地预测泥页岩裂缝发育的方向及强度.综合预测结果表明,焦石坝箱状背斜主体五峰组-龙马溪组一段发育北东向为主的中-弱程度裂缝,构造翼部及断裂(褶)带局部发育北东及北西向中-强程度规模裂缝,预测结果符合地质规律.井-震标定结果显示,裂缝综合预测成果与钻井工程裂缝性漏失段具有一一对应关系,进一步验证了该方法的有效性和实用性.该方法对页岩气储层综合评价及钻井工程具有一定的指导意义.
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