244 / 2019-06-29 22:57:29

Difference of the mound-shoal complex reservoir under different paleogeographic environment of Sinian Dengying Formation, Sichuan Basin, SW China

Mound-shoal complex,Microbialite,Platform margin,Sinian Dengying Formation,Sichuan Basin

Mound-shoal complex is the important reservoir of the Sinian Dengying Formation in the Sichuan Basin. These mound-shoal complexes are divided into different types by paleogeographic environment. Analyzing different mound-shoal complex helps to determine the ‘Sweet spots’. This study is based on outcrop and core observation to obtain geological data. Thin section observation is used to identify the rock structure. Finally, porosity and permeability of samples are tested to analyze reservoir quality. Both the 2nd and the 4th members of the Dengying Formation are carbonate platform deposits, which can be divided into two sedimentary subfacies, the platform margin and the platform interior. Sedimentary environment of the 2nd member is more restricted than the 4th member of the Dengying Formation. During the Dengying Period, Mianyang-Changning rift was mainly situated in NS direction with a steep eastern boundary and a gentle western boundary. Mound refers to microbialite sediments, and shoal refers to grain-supported carbonate sediments. Mound-shoal complex is divided into high-energy zone, transition zone and low-energy zone in order to reflect sedimentary environment and reservoir quality. Different rock types of mound-shoal complex deposited in different sedimentary environments. Keep-up platform margin mound-shoal complex, which is represented by Gaoshiti-Moxi area and Hujiaba section in the 4th member of the Dengying Formation mainly deposited high-energy zone rock types. Catch-up platform margin mound-shoal complex, which is represented by Weiyuan area and Yangba section in the 2nd member of the Dengying Formation mainly deposited transform zone rock types. Give-up platform interior mound-shoal complex, which is represented by Dingshan 1 well and Fucheng section in the 4th member of the Dengying Formation mainly deposited low-energy zone rock types. By comparing reservoir characteristics of three types of mound-shoal complex, it is found that the keep-up platform margin mound-shoal complex is the ‘Sweet spots’ of the Dengying Formation in the Sichuan Basin.