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Palaeogeographic Reconstruction and Hydrocarbon Reservoir Prediction Using Sedimentary Architectures of Different Carbonate Platform Margins: A Case Study of Carbonate Platform Margins in Feixianguan Period of the Early Triassic, NE Sichuan Basin, China

Abstract

Through analysis of well data, outcrops and seisimic data etc., we identified a N-S oriented open carbonate platform in the Central Sichuan Basin connecting with Kangdian paleo-land in the western side of Sichuan Basin and a N-S oriented isolated carbonate platform in the NE Sichuan Basin in China. These two Early Triassic Feixianguan Period platforms are separated by a narrow N-S oriented Kaijiang-Liangping intra-shelf. Three nearly parallel platform margin oolite belts were identified and they include Yuanba belt on the eastern side of the open platform margin, Puguang belt on the western side of the isolated platform, and Panlongdong belt on the eastern side of the isolated platform. Our study reveals that progradational and aggradational patterns develop in the platform margins. The progradational platform margin illustrated by Yuanba belt and Panlongdong belt have the characteristics of low-angle and rapid progradation, resulting in the development of wide and thin oolitic shoals. The dolomitization in this progradational margin is generally weak and only develops in the relatively steep margin. Aggradational platform margin illustrated by Puguang belt has the characteristics of vertical aggradation during early stage and limited eastward migration during late stage, resulting in the development of narrow and thick oolitic shoals. Slumps develop widely in the aggradational margin slope. The dolomitization develops widely on this margin and occurs in the whole lower Feixianguan oolite interval. The architectures of the Early Triassic Feixianguan platform margins are influenced by palaeogeography, sea-level change, northeastward palaeowind, and northward palaeo-ocean current, etc., and resulted in the carbonate platform migrating toward the east and amalgamating of the open and isolated carbonate platforms. The internal architectures and evolution patterns of the Triassic Feixianguan carbonate platform margins can be used for the reconstruction of palaeogeography, palaeowind direction and palaeo-ocean current on the Yangtze Plate in the south China after the Permian-Triassic extinction. This study also reveals that the reservoirs are controlled by sedimentary architecture of carbonate platform margins in Feixianguan Formation, and the high quality dolomite reservoir can be predicted using the analysis of the variations of different carbonate platform margin belts.