In recent years，Yanchang Formation of Ordos Basin is one of the key exploration areas of continental shale gas in China. Through the shale outcrop observation，petrology，imaging logging analysis，in-situ stress characteristics and fracturing，etc.，we study the characteristics of shale fracture of Yanchang Formation in the Ordos Basin，and the influence of in-situ stress on the hydraulic fracture. Based on the analysis of petrology，the average content of shale brittle mineral of Chang-7 and Chang-9 Members in Yanchang Formation are higher，57.2% and 44%，respectively. According to the shale outcrop observation and imaging logging analysis，there is a main set of vertical fractures，which strike is the NEE. Meanwhile，there are NNE-trending and N-S-trending vertical fractures. In addition，the predominant orientation of induced fractures and imaging logging analysis show that the orientation of maximum horizontal principal stress is about 70 degrees （i.e. NEE）. Crack opening analysis shows that the NEE-trending to E-W-trending fractures are consistent with the orientation of present maximum horizontal principal stress，and the crack opening condition is better. However，the angle between NNE-trending fracture and present maximum horizontal stress is large，so the condition of crack opening is poor. Because that the horizontal stress ratio （σH/σh = 1.54） of present in-situ stress is low，the induced fractures of shale in Yanchang Formation is more tend to form complex fractures networks during the artificial fracturing stage，this can enable induced fractures and reservoirs to get the maximum contact，and thus more conducive to increase production capacity.
Jiang Lin Qiu Zhen Wang Qingchen Liang Wenquan Xu Fumei. Study on the characteristics of shale fracture and in-situ stress in the Yanchang Formation of the Ordos Basin[J]. Chinese Journal of Geology, 2017, 52(1): 123-140.