Study On The Formation Mechanism Of The Dolostone Reservoir In Sinian Dengying Formation,Sichuan Basin

The Sinian Dengying Formation in Sichuan Basin is a hot target of exploration in recent years.Study on the formation mechanism of the reservoir in Sinian Dengying Formation has important realistic meaning and theoretical significance.Based on core and outcrop section observation,the study summarizes the main types of rock and special structure and common diagenesis and reservoir characteristics in Dengying Formation by the thin section oberservation and X-ray diffraction(XRD)etc.The results showed that the main types of rock include laminite,stromatolite,spongiostromata-type dolostone,thrombolite,cyanobacteria bound frame dolostone,cyanobacteria related dolarenite,cyanobacteria related carbonate breccia,etc.and the frame-like structure is an important sedimentary structure in the microbial mound.The Dengying Formation in Sichuan Basin is carbonate platform facies.The microbial mound-shoal complex is the widespread facies.Microbial mound-shoal complex can divide into five parts as mound base,mound core,mound flat,mound cap,mound flank.Dolomitization and dissolution are important diagenesis of the reservoir.The framework residual pores is the principal reservoir space.The reservoir has low porosity and low permeability.The study shows that the mound-shoal complex is the principal oil and gas reservoir facies of the Dengying Formation in the Sichuan Basin.Based on the change of sea level,three vertical depositional models has been concluded as mound base-core-cap and mound base-core-flat and mound base-core-flank.The types of reservoirs in the mound-shoal complex are divided into three types: the platform margin mound-shoal complex,the platform interior mound-shoal complex and the platform interior flat.The platform margin mound-shoal complex is the highest reservoir of the Sinian Dengying Formation.