叠前地球物理技术预测页岩气保存条件——以四川盆地焦石坝构造页岩气藏为例

近年来,随着四川盆地涪陵页岩气田页岩气勘探开发取得重大突破,川东地区上奥陶统五峰组—下志留统龙马溪组巨大的页岩气勘探开发潜力被进一步证实。但是,如何利用地球物理技术更加准确有效地评价页岩气保存条件,目前仍然是该区页岩气勘探开发中亟待解决的问题。为此,基于叠前地震数据,从裂缝发育程度和地层压力的角度出发,首先利用基于叠前方位各向异性的裂缝预测技术进行高角度裂缝的预测,然后利用基于叠前纵波波阻抗反演的压力预测技术描述地层压力的空间分布特征,最终将两者相结合得到评价页岩气保存条件的新参数——保存系数,进而形成了一套可以有效预测页岩气保存条件的新方法 ;将新方法用于涪陵页岩气田焦石坝区块五峰组—龙马溪组页岩气保存条件的评价,并将气井生产资料与保存系数的预测结果进行对比验证。研究结果表明:页岩气保存系数与其无阻流量的对应性较好,并且弥补了低产井与无阻流量之间的不吻合关系。结论认为,保存系数预测结果与钻井生产资料具有较好的吻合度,证明了新的页岩气保存条件评价方法的有效性和可靠性。

Prediction of shale gas preservation conditions by pre-stack geophysical technology: A case study of the shale gas reservoirs in the Jiaoshiba Block of the Sichuan Basin

In recent years, the immense exploration potential of shale gas in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the eastern Sichuan Basin has been further confirmed especially when great breakthroughs were realized in the Fuling Shale Gas Field of the Sichuan Basin. However, how to apply geophysical technologies to evaluate shale gas preservation conditions more accurately and effectively is a burning problem in shale gas exploration and development in this area. From the perspective of fracture development degree and formation pressure, this paper first applied the fracture prediction technology based on pre-stack azimuthal anisotropy to predict high-angle fractures on the basis of pre-stack seismic data. Then, the pressure prediction technology based on pre-stack P-wave impedance inversion was used to describe the spatial distribution characteristics of formation pressure. Finally, both of them were combined to establish a new parameter for evaluating shale gas preservation conditions, i.e., preservation indicator. In this way, a set of new method that can be used to effectively predict shale gas preservation conditions was developed. This new method was used to evaluate the shale gas preservation conditions in the Wufeng–Longmaxi Fms in the Jiaoshiba Block of Fuling Shale Gas Field, and the prediction results of preservation indicator were compared with the production data of gas wells, which demonstrated that the preservation indicator agreed well with the AOF of a shale gas well, making up the previous mismatch between a low-productivity well and its AOF. In conclusion, the predicted preservation indicator is in line with the production data of gas wells, indicating that this new method is valid and reliable in evaluating shale gas preservation conditions.