宽方位叠前振幅各向异性技术预测页岩储层裂缝——以渝西地区足201井区为例

Fracture Prediction in Shale Reservoirs Using Wide-Azimuth Pre-Stack Amplitude Anisotropy Technique—A Case Study of the Zu 201 Well Block, Western Chongqing

摘要: 四川盆地渝西地区足201井区五峰组–龙马溪组页岩储层中天然裂缝较为发育，但裂缝尺度较小且非均质性强，传统叠后地震属性对这类微小裂缝的识别能力有限。针对这一问题，本文利用宽方位三维地震资料，开展了宽方位叠前振幅各向异性(AVAZ)方法研究。根据研究区埋深、构造特征及裂缝发育程度的空间差异性，将工区划分为三个地质子区域，分别优选“炮检距–方位角”叠加参数模板，并采用椭圆拟合方法逐点提取各向异性强度与裂缝优势方位。预测结果显示，研究区裂缝强度自西向东呈“弱–最强–较强”的阶梯状分布特征，优势走向以NE-SW向为主。与电成像测井裂缝解释结果对比表明，预测方位与测井裂缝玫瑰图吻合较好，说明AVAZ技术在研究区微小裂缝预测中是可行且有效的。

Abstract: Natural fractures are well developed in the Wufeng-Longmaxi Formation shale reservoirs in the Zu 201 well block, western Chongqing, Sichuan Basin. However, these fractures are characterized by small scale and strong heterogeneity, making them difficult to identify effectively using conventional post-stack seismic attributes. The wide-azimuth pre-stack amplitude variation with azimuth (AVAZ) technique utilizes fracture-induced seismic anisotropy responses to quantitatively predict the development intensity and dominant orientation of small-scale fractures. In this study, based on wide-azimuth 3D seismic data from the Zu 201 well block, the study area was divided into three geological sub-regions according to spatial differences in burial depth, structural characteristics, and fracture development degree. Offset-azimuth stacking templates were optimally selected for each sub-region, and the ellipse fitting method was employed to extract anisotropy intensity and fracture azimuth on a point-by-point basis. The prediction results reveal a stepped distribution pattern of fracture intensity from west to east, characterized as “weak - strongest - relatively strong,” with the dominant fracture orientation trending NE-SW. Validation against electrical imaging logging fracture interpretation results shows that the predicted fracture azimuths are highly consistent with the fracture rose diagrams from well logging, confirming the reliability and effectiveness of the AVAZ technique in predicting small-scale fractures in shale reservoirs.