The western margin of the Ordos Basin as a part of the north-south tectonic belt, is not only an important window for studying the basin formation, evolution and hydrocarbon accumulation, but also the hot spot for discussing evolution of the Mesozoic Tethys Ocean and uplifting of the Qinghai-Tibet Plateau in Cenozoic. In this study, we make a high quality structural interpretation with large amount of 2D and 3D seismic data. Numerous small-scale faults have been found within Tianhuan depression where the Cenozoic strata covered. The seismic interpretation shows that small-scale faults have the characteristics of coexistence of normal and reverse faults separating, obvious differences in cutting layers and co-existed with compression folds．The small-scale faults are distributed mainly in NWW-SEE direction along horizon, and together with the large-scale faults in the western front belt, showing a broom-shaped faults arrangement. The Yanshanian Movement in the Late Jurassic induced the NEE-direction compressional stress propagated from south to north. Due to the block of E-W transverse tectonic zone, the tranpressional motion is produced in this area, inducing formation of small-scale faults. After then, the small-scale faults experienced extension in the Early Cretaceous and modification from Late Cretaceous to present. The evolutionary history of small-scale faults are divided into three stages according to the difference in cutting layers and modification. Well and seismic data show that fault movement during stage Ⅰ mainly improves the physical property of the tight reservoir in the Yanchang Formation, leading to oil accumulation in the Yanchang Formation; fault activity during stage Ⅱ mainly promotes the migration of oil, forming reservoirs both in Yanchang Formation and Yan’an Formation; fault activity during stage Ⅲ has a destructive effect on the reservoir preservation.
Liu Yongtao Liu Chiyang Zhao Junfeng Huang Lei Song Xuyang. Forming mechanism of dmall-cale faults and their control for the reservoir formation in the middle of western margin of the Ordos Basin[J]. Chinese Journal of Geology, 2018, 53(3): 922-940.