基于广域电磁法的页岩气有利区预测——以渝东北巫山地区为例

渝东北巫山地区是重要的页岩气勘探远景区,勘探程度较低.本次研究以岩石物理和测井数据为基础,以广域电磁法为手段,开展该区的页岩气有利区评价.通过对地表样品及井孔电阻率测井资料的分析,揭示研究区目的层富有机质页岩层电阻率表现为明显低阻特征,与上覆下伏地层电性差异明显,表明本区分布的上奥陶统五峰—下志留统龙马溪组富有机质页岩具备开展电法勘探工作的物性条件.在对电磁资料处理解释的基础上,查明了重庆巫山地区“隆凹相间”的构造格局,断裂性质主要为逆断层;目的层上奥陶统五峰组—下志留统龙马溪组富有机质泥页岩连续稳定分布,低阻特征明显,埋深范围在800~4 800m之间.综合考虑目的层页岩电阻率、极化率、埋深等因素,预测出页岩气有利区3个,区内富有机质页岩发育,页岩气勘探前景较好.

The prediction of shale gas favorable area based on wide area electromagnetic method:A case study of Wushan area in northeast Chongqing

Wushan area in northeastern Chongqing is an important prospective area for shale gas exploration;nevertheless,the exploration degree of this area is low.In this study,based on rock physics and well logging data,the authors used the wide area electromagnetic method to evaluate the favorable area of shale gas in this area.Through the analysis of the surface sample and borehole resistivity logging data,the authors detected that the resistivity of the target layer with rich organic shale in the study area exhibits obvious characteristics of low resistivity,and the features of overlying and underlying layers are significantly different,suggesting that the upper Ordovician Wufeng-Lower Silurian Longmaxi Formation with rich organic matter shale has the physical conditions for electrical prospecting.Based on processing and interpretation of electromagnetic data,the authors found out the structural pattern of "uplift and depression" in Wushan area of Chongqing.The main fault is reverse fault.Ordovician Wufeng-Lower Silurian Longmaxi organic rich shale exhibits characteristics of continuously stable distribution and low resistance,with the depth in the range of 800~ 4800 m.Considering the resistivity,polarizability and burial depth of the target layer,the authors predicted three favorable areas of shale gas.The organic shale is well developed in this area,and the prospect of shale gas exploration is good.