Effects of base-level cycle on mouth bar reservoir micro-heterogeneity: A case study of Es2–9 Formation mouth bar reservoirs in Shengtuo Oilfield

Abstract

To identify the factors and mechanisms affecting reservoir micro-heterogeneity in the same type of microfacies at different stages of cycle, the main controlling factors of the reservoir micro-heterogeneity of the mouth bar in Es2–9 Formation of the Shengtuo Oilfield were analyzed based on the sedimentary dynamic analysis of high resolution stratigraphic sequence and quantitative parameters of reservoir micro-heterogeneity. The base level cycles of different stages have a differential control on the reservoir micro-heterogeneity of the mouth bar. The changes of the base level in different orders lead to variation in accommodation space and sediment supply, and in turn changes in sedimentary environments of mouth bar at different stages, as a result, the reservoir micro-heterogeneity of the single mouth bar in short-term base level cycle is strong at bottom and weak at top, the reservoir micro-heterogeneity of compound mouth bar (formed by different stages of single mouth bar) in middle-term base level cycle gets weaker from bottom-up, and the reservoir micro-heterogeneity of compound mouth bar at different stages of long-term base level cycle has no obvious pattern. Key words: base-level cycle, micro-heterogeneity, Shengtuo Oilfield, mouth bar