川南页岩地层裂缝地震物理模拟及敏感属性分析

四川盆地南部龙马溪组页岩气资源潜力大, 但页岩地层裂缝发育, 对页岩气的保存条件具有较大影响, 在页岩气工程开发过程中容易造成井间压窜, 给页岩气的勘探和开发带来困难。针对LZ区块FJ向斜构造进行地震物理模拟研究, 依据目标工区地质模式、地震解释结果及裂缝发育特征设计地震物理模型, 在目标地层中设计具有不同参数的裂缝带, 进行地震物理模型制作和数据采集, 开展裂缝带的地震波场响应特征分析, 并对物理模型的地震数据进行处理和反演, 开展裂缝预测研究。叠前地震反演结果表明, 经过优选叠前裂缝预测方法, 可利用阻抗因子F和AVO梯度等敏感参数预测裂缝密度, 利用纵波阻抗、λρ和AVO截距等敏感参数预测裂缝倾角。利用地震物理模型技术分析裂缝参数对应的地震响应特征, 可检验不同裂缝预测方法的有效性, 为目标工区的页岩地层裂缝预测和综合解释提供依据。

The Wufeng-Longmaxi shales in the southern Sichuan Basin have substantial potential for industrial production of shale gas.However, the fracture development in the shale formation in this region has a substantial impact on shale gas storage conditions.In addition, the cross-well interaction related to natural fractures occurring during shale gas production can make shale gas exploration and production difficult.Understanding the fracture system can provide evidence for shale evaluation and production.In this study, seismic physical modeling is used to simulate the wave propagation in the shale formation in the target area.The physical model is designed based on the geological pattern, seismic characteristics, and fracture parameters of the target area.To simulate the various fracture developments in the target area in field, fracture zones with varying parameters are distributed in the shale formation layer.Hence, the seismic wavefield responses can be analyzed using the forward modelling data acquired from the physical model.Following the processing and inversion of physical modeling data, the feasibility of fracture prediction methodologies is analyzed and compared and after the evaluation and comparison for the different pre-stack fracture prediction methods, the optimal prediction methods to predict different fracture parameters can be determined.The impedance factor F, AVO gradient could be the preferable sensitive seismic attributes for predicting the fracture density, while the P-wave impendence, λρ and AVO intercept are more relevant for predicting the fracture dip angle.This research could provide the fundamental basis for the fracture system evaluation of shale formation in field.