Reservoir characteristics of intra-platform reef-shoal and formation mechanism of the Changxing formation in the eastern Sichuan Basin

In order to reveal the reservoir characteristics of intra-platform reef-shoal as well as to clarify the formation mechanism of the Changxing formation in the eastern Sichuan Basin, through typical field profiles survey, core observation and description. By combining rock thin identification, logging, seismic data and physical property data analysis, it is concluded that reef-shoal reservoirs, have multi-stage cyclicity and show no obvious continuity in the lateral direction, mainly developed in the high-level system domain within the sequence. The results show that the reservoirs are mainly reef-shoal granular dolomite, grain dolomite, reef limestone and reef dolomite. And the average porosity of dissolved pore granular dolomites and granular dolomites is up to 5%. The main storage space types are mainly intergranular dissolved pores, intragranular dissolution pores, intercrystalline pores, and intercrystalline dissolution pores, followed by the intergranular pores, biological cavity pores and fractures. The reservoir development is often controlled by factors such as sedimentary conditions, sea-level fluctuation, and diagenesis. Paleo geomorphic conditions and relatively high-energy facies lay the foundation for reservoir development, and the sea-level fluctuation affects the internal structure of reef-shoal and the circulation distribution of the reservoirs. The dolomite has an obvious promotion effect on the reservoirs. And the distribution of dolomite with large thickness is consistent with that of high porosity area. The mass fraction of dolomite in dominant reservoirs is between 65% and 90%, and the transformation of atmospheric freshwater leaching and burial dissolution further improve and expand the reservoirs. © 2021, Editorial Board of Journal of CUMT. All right reserved.