A comparative study of shale gas preservation conditions on both sides of Tianyangping fault in Yichang area

The shale gas content is different in different shale gas survey wells and parameter wells, from both sides of Tianyangping fault in Yichang, Middle Yangtze area. The reasons for the difference of preservation conditions are studied from the aspects of shale tectonic deformation, fracture character and paleo-fluid activity. The following results were obtained: ①Because of the pillar effect of Huangling uplift, the Yichang slope is a simple monoclinic structure with gentle occurrence in the north of Tianyangping fault, and on the other hand, faults and folds are well developed and the occurrence of strata varies greatly of northern part of Yidu-Hefeng anticline in the south of Tianyangping fault. ②Typical wells illustrate that fractures and fracture belts of shale are highly developed in the north of Tianyangping fault, and are the channels for shale gas to escape in the north of Tianyangping fault, while fractures are rare in the south of Tianyangping fault. ③Paleo-fluid reveals that more fractures in the early stage of closed system of shale and fewer in the later stage in the north of Tianyangping fault, while more fractures in the later stage lead to the infiltration depth of ancient meteoric water, over 3 500-4 000 m in the south of Tianyangping fault, and the sealing capacity of the shale get worse. ④The conclusion is that exploration should spread to the Badong-Daye ramp interference fringe, in the east and west of Yichang slope; and there are more exploration risks to spread to the south of Tianyangping fault because of the strong tectonic deformation, and worst protection condition in the north end of Yidu-Hefeng anticlinorium.