CHARACTERISTICS AND FORMING MECHANISM OF THE RESERVOIRS IN THE SECOND MEMBER OF DENGYING FORMATION IN NORTHERN SICHUAN

On the basis of the macroscopic and microscopic characteristics and geochemical data from both outcrops and drilling cores, this study is devoted to the detailed investigation of reservoir characteristics of the 2nd Member of Dengying Formation and main controlling factors in northern Sichuan. As the data shows, the reservoir rocks mainly consist of grain conglutinate dolomites, stromatolitic algal dolomites and dolomitic karst breccia. In terms of reservoir space, the reservoirs are dominated by dissolved pores in the algae-adherent rocks, cave-dissolving cavities, karst-dissolve joints and grape cambiums. Most of the reservoirs belong to the hole type, which are characterized by low porosity and low permeability. High-quality reservoirs of the region are composed of the materials from particle gluten beach and algae mound. Compaction-pressure solution and multi-stage cementation are the main reasons to the disappearance of primary pores. Moreover, the epigenetic karst resulted from the EpisodeⅠof Tongwan movement played important role in reservoir forming. The combination of all the processes mentioned above make the reservoirs mainly distributed in the middle and upper part of the 2nd Member of Dengying Formation.