Variable Architecture Models of Fluvial Reservoir Controlled by Base-Level Cycle: A Case Study of Jurassic Outcrop in Datong Basin

Most of the fluvial reservoirs have been in the late stage of oilfield development in China, and it is urgent to characterize their complex, internal sedimentary architectures. However, there are few published research documents related to differential architecture models and controlling factors, and there are not enough prediction models for oilfield reservoir architecture characterization. Therefore, taking the outcrop in Datong, Shanxi as the study area, the variable architecture models of fluvial reservoir are established by using the methods of outcrop description and measurement, GR measurement and particle size analysis. The results show that the outcrop area is divided into 9 short-term and 2 medium-term base-level cycles based on sandstone percent and ancient river depth, and the fluvial patterns at different locations of medium-term base-level cycle are obviously different. With the rising of the base level and the transition of fluvial type, architecture distribution changes from narrow and long braided bar to normal braided bar, then transitions to the combination style of narrow band braided bar or point bar, and finally evolves into horseshoe point bar. There is a good positive relationship between the thickness and width of sandy bars (braided bar or point bar), and between the width of sandy bar and the width of channel. The research results can provide guidance for similar outcrop architecture analysis and provide prediction models for the fine architecture characterization of similar oilfields.