Simulation of tectonic stress field and prediction of tectonic fractures in shale reservoirs: A case study of the Ansai area in the Ordos Basin, China

The Chang 7 oil-bearing layers from the Ansai area of the Ordos Basin are abundant in oil and gas resources. These layers are chiefly comprised of shales interbedded with tight sandstone. In the regions where the exploration level is relatively low and the structures are gentle in the Ansai area, the distribution of fractures in shale reservoirs and tight sandstone reservoirs is significant for predicting sweet spots and determining the success rate of hydraulic fracturing. In this research, the results acquired from the scanning electron microscope (SEM), cores, thin sections, and image logging determined the developmental characteristics of fractures. Moreover, the Himalayan stress field was modeled using ANSYS, whereas the two-factor method is used to predict the distribution of tectonic fracture by combining stress field and fracture criterion. The results indicate a gradually decreasing trend of the maximum principal stress from east to west. The minimum principal stress in the western part is less than that in the eastern part. The differential stress that can indicate the degree of tectonic deformation ranges from 17 Mpa to 25 MPa. The fracture density ranges from 0 strip/m to 1.5 strip/m. In addition, the areas with more fractures are mainly located in the western and southeastern parts, where shale oil is relatively rich. Similarly, the comparison of different maps illustrates that the distribution of tectonic fracture is related to mechanical parameters and stress fields.