Evaluation Of Tight Sandstone Reservoirs In The Second Member Of Xujiahe Formation In Jinhua Area,western Sichuan Basin

The Upper Triassic Xujiahe Formation in the Sichuan Basin is the most typical tight sandstone gas distribution area in the basin and has good exploration and development potential.In this paper,the second member of the Upper Triassic Xujiahe Formation(second member of the Xujiahe Formation)in the Jinhua area of central and western Sichuan is used as the research object.Through drilling core observation,thinfilm microscopic identification,scanning electron microscopy,whole rock X-ray diffraction,inclusion temperature measurement,carbon and oxygen isotope determination,and other analytical methods,combined with previous research results,studied the characteristics of sedimentary facies,petrology,diagenesis,and reservoir characteristics of the second member of the Xu 2 Member,and clarified the pore evolution of high-quality reservoirs Characteristics,main control factors and comprehensive evaluation.The second member of the Xu Xujiahe Formation in the Jinhua area is dominated by braided river delta facies as a whole.Sand bodies are mainly developed in estuary dams,distant sand dams and underwater distributary channels.The rock types of sandstones are mainly feldspar detrital sandstones with low maturity of ingredients and structure.The types of diagenesis include compaction and pressure dissolution,authigenic mineral precipitation,dissolution and rupture,etc.,mainly in the stage A of diagenesis and enters the stage B of the middle diagenesis at the latest;the storage space is dominated by intergranular dissolved pores,the porosity is mainly distributed between 4%-8%,and the permeability is mainly distributed between 0.01 m D-0.1m D;the lower limit of permeability of the high-quality reservoir of the second member of Xujiahe is 0.1m D,and the lower limit of porosity of pore-type and fracture-pore type reservoirs is different,the former is 8% and the latter is 5.5%;the main controlling factors of high-quality reservoirs are sedimentary microfacies,paleostructure and diagenesis.The microfacies of estuary dams and underwater distributary channels are the basis for forming high-quality reservoirs.The paleo-uplift in early hydrocarbon generation,authigenic chlorite pore liner,early hydrocarbon filling,fission and midlate dissolution are the keys to the formation of high-quality reservoirs;based on the above knowledge,combined with the thermal evolution history of the Xujiahe source rocks in this area,the pore evolution characteristics of high-quality reservoirs are elaborated in detail;it is clearly pointed out that favorable areas of high-quality reservoirs are mainly distributed in the areas controlled by Jin 106 E well and Jinhua 1 well-Jin 2 well-Jin 31 well,showing east-west distribution characteristics.