Depositional Characteristics And Reservoir Prediction Of The Dengying Period In The Dangyang Synclinorium And Its Surrounding Areas

With successful exploration of natural gas of Weiyuan and Gaoshiti areas of Sichuan Basin,the Dengying Formation in Dangyang synclinorium and its surrounding areas has become one of the most important targets for hydrocarbon exploration.The early geological data and special study of the Dengying Formation are limited in the Dangyang synclinorium and its surrounding area,which leading to the weakness of study on the stratigraphic division,sedimentary facies and their evolution.In that case,the deployments of petroleum exploration in the study area are restricted.In this thesis,sequence stratigraphy,sedimentary facies and reservoir characteristics have been studied using data of outcrop,drilling,well logging,thin sections based on synthesis application of geological theories and technologies.First,the comprehensive analysis of outcrop,drilling and logging data suggests that the main sedimentary environment of study area is carbonate platform in shallow water.And the Dengying Formation can be divided into 5 third-order sequences,only consisting of high stand system tract and transgressive system tract,without low stand system tract.Then,based on the analysis of petrological composition and sequence stratigraphic evolution,the Dengying Formation is characterized by restricted platform facies,4sedimentary subfacies(shoal,algal mound,lagoon,and tidal flat)and 14 microfacies in the study area.This paper also researched their distribution characteristics through planimentric and sectional maps of the sedimentary facies.Tidal flat is the main subfacies in the carbonate restricted platform.Shoal and algal mound mainly developed in the surrounding area of lagoon area of the Changlinggang outcrop in Yuan'an county,distributed in belt,decreasing from W-S to E-N and bottom to top.At last,based on rock types,reservoir space,diagenesis and evolution,this paper has cleared the dolomite reservoir characteristics and development rules of Dengying Formation in the study area.The main types of reservoir are composed of silt-fine dolomite,algal dolomite and sandy dolomite.Intergranular dissolved pore,intercrystalline solution pore,solution cave and microfissure are the main reservoir space.The reservoir is characteristic by low porosity and low permeability.According to the comprehensive analysis,the matching of sedimentary facies and dissolution is the key to control the reservoir quality in this area.With good property,strong dissolution and developed fractures,the dolomite of shoal subfacies of SQ5 of the Dengying stage in the Dangyang synclinorium is the most favorable exploration belt in the study area.