Characteristics and controlling factors of carbonate shoal reservoirs in the lower Triassic Feixianguan Formation, Kaijiang-Liangping Trough, Northeast Sichuan Basin, China

In recent years, the platform margin of the Kaijiang-Liangping Trough in northeastern Sichuan Basin has become a key exploration target for the Feixianguan Formation oolitic shoal gas reservoirs. Previous studies of carbonate reservoirs predominantly utilized conventional analytical methods (e.g., wireline log interpretation and thin-section petrography), which have demonstrated limited efficacy in characterizing the inherent complexity of carbonate reservoirs. This is especially lacking precise lithological information and detailed knowledge of microscale properties, which are crucial for effective carbonate reservoirs evaluation. To enhance the understanding of the characteristics and controlling factors of carbonate shoal reservoirs in the study area, a new method for characterizing carbonate shoal reservoirs was established using conventional microscopic thin sections observation, physical property analysis of porosity and permeability, combined with advanced carbon and oxygen isotopes and scanning electron microscope. Firstly, the analysis of dolomitization environments through carbon and oxygen isotope geochemistry (δ¹³C/δ¹⁸O) provides fundamental constraints for studying the characteristics and controlling factors of carbonate reservoirs. Secondly, using thin sections and scanning electron microscopy to identify the characteristics of different carbonate reservoir spaces, and then determining the type of carbonate reservoir based on physical properties and diagenetic characteristics. Finally, by combining fluctuations of sea-level, tectonic and diagenetic processes, a comprehensive evaluation of carbonate reservoirs is conducted to clarify the characteristics and controlling factors of carbonate shoal facies reservoirs. Based on these studies, the Lower Triassic Feixianguan Formation oolitic dolomite shoal facies along the platform margin should be prioritized as the primary exploration target in the Kaijiang-Liangping Trough. This innovative methodology, integrating both micro- and macro-scale analyses with qualitative and quantitative approaches, demonstrates significant potential for advancing carbonate reservoir exploration and development practices.