Cambrian faults and their control on the sedimentation and reservoirs in the Ordos Basin, NW China

Abstract Comprehensively utilizing the seismic, logging, drilling and outcrop data, this research studies the characteristics of the Cambrian faults and their control on the sedimentation and reservoirs in the Ordos Basin. The results show that: (1) Three groups of faults striking North-East (NE), near East-West (EW), and North-West (NW) were developed in the Cambrian. The NE and near EW faults, dominated by the normal faults, are the synsedimentary faults and the main faults of the Cambrian. (2) According to the roles of faults in tectonic units and the development scale of the faults, the Cambrian faults can be divided into three grades. The second-grade faults, large in scale, controlled the boundary of the Cambrian sags of the Ordos Basin. The third-grade faults, smaller in scale than the second-grade fault, controlled the high and low fluctuations of local structures. The fourth-grade faults, very small in scale, were adjusting faults developed inside the local tectonic units. (3) The Cambrian faults had strong control on the sedimentation and reservoir of the Cambrian. Controlled by the second-grade and the third-grade faults, the paleogeographical framework of the Cambrian presents combination characteristics of the bulge-sag macro-structures and the high-low differentiation micro-geomorphology. This paleogeographical pattern not only controlled the development of the oolitic beach facies in the Cambrian but also the distribution of high-quality reservoirs. (4) Under the control of the faults, the micro-paleogeomorphological high parts closely adjacent to the margin of the Cambrian sags are the favorable exploration areas.