Sedimentary Facies And Reservoir Characteristics Of The Upper Jurassic Penglaizhen Formation In Chadian Of Longquan,Chengdu

The Upper Jurassic Penglaizhen Formation in Chadian of Longquan,Chengdu,is located inside the Sichuan Basin western Sichuan depression,is a good natural gas exploration and development area.Through the oil gas geological exploration of the Jurassic in the middle part of western Sichuan depression,the commercial gas reservoirs such as Luodai,Xindu,Shifang and Majing have been found,which reflects the great potential of exploration of Jurassic.The related scholars study on the Penglaizhen formation as a conventional natural gas reservoirs is more deeply and comprehensive,but there is a lack of research specifically aimed at the field section outcrop in the Penglaizhen formation.Therefore,on the basis of collecting samples in the field and microscope observation the slice,this paper makes an in-depth study of reservoir mineralogy,sedimentary petrology,reservoir sedimentology and petroleum geology in the Upper Jurassic Penglaizhen Formation in Chadian of Longquan,Chengdu,and analyzes the sedimentary facies and reservoir characteristics of the Penglaizhen Formation.Penglaizhen Formation in Chadian of Longquan from the bottom to the top is divided into Peng one?J₃p¹?,Peng two?J₃p²?,Peng Three?J₃p³?,Peng four?J₃p⁴?four lithologic section,the whole is a set of purplish red clastic rocks,mainly quartzite debris sandstone,intercalated by thin layers of mudstone,silty mudstone.Based on the analysis of the types and characteristics of diagenesis in the study area,it is found that the solution dissolution plays a major role in the reservoir property,while compaction,cementation and recrystallization are very unfavorable to pore development and preservation,most of which clog pores and larynx and destroy the reservoir property of rock.Through the field macroscopic observation,the thin section analysis results and combined with the previous summary results can be found in Penglaizhen Formation in Chadian of Longquan,Chengdu deposition,is fan-delta deposit,both alluvial fan deposition,fluvial deposit,deltaic deposit and lake sediment characteristics.Sedimentary facies are the macroscopic factors that control reservoir development,which directly affect sediment type and the primary porosity and permeability of sandstones.In addition,the sedimentary facies control the material composition and structure of sandstone,which indirectly affects the sediment diagenesis,such as compaction,cementation and dissolution.Through the analysis and identification of the slice,it is concluded that the reservoir space type of the Penglaizhen Formation reservoir in Chadian of Longquan are mainly dissolved pores in grains and dissolved pores between grains.The characteristics of low porosity and low permeability are shown in the whole,and the porosity and permeability are well related,which indicates that J₃p gas reservoir is pore reservoir.The reservoir property of J₃p³ and J₃p⁴ sections are better than that of J₃p¹ and J₃p² reservoirs,and J₃p³ and J₃p⁴ are evaluated as high quality reservoirs in the research area.