Reef-shoal combinations and reservoir characteristics of the Changxing-Feixianguan Formation in the eastern Kaijiang-Liangping trough, Sichuan Basin, China

Reef-shoal reservoirs are important reservoir types of the Changxing-Feixianguan Formation located in the eastern Kaijiang-Liangping trough, Sichuan Basin, China. Understanding the reef-shoal combinations and the reservoirs characteristics are significant for oil and gas exploration in this area. According to field profiles, drilling and seismic data, the reef-shoal development state of Changxing-Feixianguan Formation was sorted out and counted, two main types of complete reef-shoal combination and incomplete reef-shoal combination had been identified based on whether reef or shoal development in the Changxing Formation and shoal development in the Feixianguan Formation, Ten secondary combination models were identified within these main combinations. To analyze the reservoir characteristics, core observations and descriptions, thin section identifications, and physical property testing were selected to match reef-shoal combinations, results show the favorable combination was mainly represented by the complete combination, of which the reservoir performance was relatively good. The platform margin reef facies and platform margin shoal facies constituted the most favorable reservoir facies zone, wherein reef-shoal reservoirs were mainly developed in the high-stand system tract within the sequence, and strong dolomitization was mostly developed at the top of the reef-shoal reservoirs. The formation of high-quality reservoirs was often controlled by the dual factors of sedimentation and diagenesis.