Fracture development characteristics and geological significance of tight sandstone of Cretaceous Bashijiqike Formation in Keshen area,Kuqa Depression
Based on the data of core,cast slice and laser confocal scanning electron microscopy,the fracture deve-lopment characteristics and main controlling factors of Cretaceous Bashijiqike Formation in Keshen area of Kuqa Depression are analyzed,and their influence on reservoir physical properties and hydrocarbon accumulation effect is discussed.The results show that:(1)The rock type of Cretaceous Bashijiqike Formation in Keshen area of Kuqa Depression is dominated by lithic feldspar sandstone,which is a typical tight sandstone reservoir.Shear and tension fractures are mainly developed,and high angle and vertical fractures are mainly developed,and unfilled and semi-filled fractures occupy a relatively large proportion.The difference of fracture plane distribu-tion in Keshen A and B gas reservoirs is mainly caused by the difference of structural location and stress evolu-tion,and the fracture effectiveness of A gas reservoir is better than that of B gas reservoir.(2)There are differ-ences for the fracture density and effectiveness in the different structural location.The fracture effectiveness is highest at the high point of the anticline,while the fracture density is high but the effectiveness is low at the saddle and wing near the fracture.The fracture effectiveness in sandstone is higher than that in mudstone.There is a nonlinear relationship between the thickness ratio of sand and mudstone and the fracture density,and the fracture density reaches its maximum value when the thickness ratio of sand and mudstone reaches 6.1,beyond which the fracture density gradually decreases.(3)Fracture development significantly increases the permeability of tight sandstone reservoirs;The fracture network can effectively connect the low permeability reservoir,improve the accumulation efficiency and migration ability of oil and gas,increase the reservoir reserves and enhance the resource development potential of the reservoir.This study has certain guiding significance for the migration and enrichment of oil and gas in the same type reservoir and the productivity of single well.
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