Characteristics and main controlling factors of reservoirs in the fourth member of Sinian Dengying Formation in Yuanba and its peripheral area, northeastern Sichuan Basin, SW China

Abstract

Abstract Based on the abundant outcrops and 3D seismic data in Yuanba and its surrounding areas in northeastern Sichuan Basin, the characteristics, main controlling factors and development regularities of reservoirs in the fourth member of Sinian Dengying Formation (shortened as Deng 4 Member) were analyzed comprehensively. The results show that the reservoirs were mainly developed in microbial dolomite associated with the microbial mound and dolarenite associated with grain beach, and had intergranular dissolution pores, inter-frame dissolution pores and karst caves as main storage space. The reservoirs were large in scale and strong in heterogeneity. The analysis of the reservoir genetic mechanisms shows that the reservoirs in the fourth member of Dengying Formation were the products of karstification on mound-beach facies deposited in the second episode of Tongwan movement. The karstification had the marks of eogenetic karstification such as granophyric karst system and half-dissociation zone. The reservoirs were controlled by the sedimentary facies belt, the mound beach facies was the decisive factor in reservoir development. Further analysis indicates that the Yuanba area had a geological background of well-developed platform margin mound beach facies, so mound beach bodies can be taken as a favorable exploration target.