Abstract:

In this paper, we clarified the microfacies combination characteristics and main factors controlling the reservoir development of the microbial carbonates in the Dengying Formation (the 4^th member) of Sinian System in Gaoshiti Area, Sichuan Basin by utilizing the core observation, microscopic identification, and well-connected sedimentary comparison.The results indicate that: (1) Sedimentary microfacies of the Dengying Formation (the 4^th member) is compose of microbial mounds and grain shoals.The grain shoals upwardly evolve into microbial mounds, and four types of sedimentary sequences are recognized, including the mound base-mound core-mound wing, mound base-mound core-mound cover, mound base-mound core, and inter beach sea-storm beach. (2) The mound-shoal complex and weathering crust are the predominant factors controlling the reservoir development.The mound-shoal complex provides good material basis for reservoirs, and weathering crust karstification greatly improves the reservoir petrophysical properties.Whereas, the burial hydrothermal process performs dual roles in the contribution of reservoir development. (3) There are two main reservoir genetic types in the Dengying Formation (the 4^th member), i.e., the sedimentary-dominated reservoirs and supergene-karst reservoirs, which are developed in the lower and upper part of Dengying Formation, respectively.This study provides basic materials and research examples for the enrichment and improvement of the microfacies classification and controlling factor analysis for the microbial carbonate reservoirs in the Gaoshiti area, which could guide subsequent exploration and development in this region.

Key words: microbiolite, Dengying Formation (the 4^th member), microphase combination, main control factors of reservoir