Silurian Reef Diagenesis and Reservoir Characterisitics on North & South Margins of Sichuan Basin

Key words: 
• reef /
• diagenesis /
• reservoir /
• Silurian /
• Sichuan basin

Abstract: Having patch reefs,mud mounds and biostromes,the reef types are various in Silurian strata on the north & south margin of Sichuan basin.Owing to the simple regional tectonic movement,the diagenesis, process of the reef carbonate was “progressive diagenesis”which show that the process was from syngenesis,short time fresh water influence get have strongly influence on the reef limestones.Among them,the cementation,corroasion,silicification and dolomitization are the most important.During the burial diagenesis period,the pore spaces in the reefs were filled by calcite cements with multi-generations.The reservoir capacity of the reefs decreased because of the weak epidiagensis influence.The organisms skeletons have the strong influence and reflection to the diagenesis.The original pores and fractures of the reef limestones are mainly skeleton pores and body cavity with some fenestrae in the mudstones and thrombolites.Some intergranular pores and inter-spar crystal pores are in the grainstone.The secondary pores and fractures are epidiagenetically dissoved and corroded cavities and fractures well as structural fractures.According to the clay mineral thermal evolution and inclusions analysis.the period of primary migration of hydrocarbon closed to the burial diagenetic period of the reefs,which was about in the Early Triassic.There were at least two times hydrocarbon migration traces in the reefs,primary migration happened in Early Triassic and secondary migration was about the period of Himalayan orogeny.Because of the strong cementation,the pore spaces in the reef reservoirs derased.