Abstract:

Fractures provide both the gathering space and migration pathways for shale gas. They play a significant role in controlling shale gas reservoir. The occurrence, density and combination characteristics of fractures play a decisive role in determining whether the region has exploitation value for shale gas. More than one thousand fractures from thirteen outcrops in six areas of Eastern Qaidam Basin were observed in this study. Detailed statistical analyses of the fractures from three typical shale outcrops were carried out, and the corresponding discrete fracture networks were built. Three groups of fractures were determined in this area through statistical analyses and field observations (one group did not appear in part of the area). The mean and standard deviation of the orientation, length and density of each fracture group were determined, and the threedimensional fracture network models were constructed. The disk model was used in this study, which assumes that each fracture has a single disk shape in threedimensional space. An inverse modeling method was used in the modeling process. The basic principle was based on fitting the observed data of the outcrops to optimize the size and density of the fractures in the threedimensional parameters of the model in order to accurately reproduce the observed actual field data, including the number, density and length of the fractures. The study presented in this paper quantitatively measured the fractures in the shale of Eastern Qaidam Basin and provides essential data for studying the migration of oil and gas in shale.

Key words: Eastern Qaidam Basin, Carboniferous shale, fracture models