Microscopic Heterogeneity Of Tight Sandstone Reservoirs In The Central Sulige Gas Field

The member 8 of Xiashihezi Formation(He8)in middle region of Sulige gas field is kind of lithological gas reservoir,which is classified as fluvial facies with characteristics of low porosity,low permeability.He8,as the object of the study,corresponding the observation of the hand samples description as the basic data,comprehensive evaluation of single well and reservoir evaluation technology has been studied in four aspects: Petrological Characteristics,sedimentary microfacies,heterogeneity of physical properties and heterogeneity of pore structure.Furthermore,based on these analysis,the controlling factors of reservoir heterogeneity were analyzed.The reservoir rock type of He8 in the study area is most developed by lithic quartz sandstone.The whole diameter and millimeter CT scanning analysis of the rock samples of He8 is carried out.The core samples are divided into four types of reservoirs,of which the permeability of class I and II is relatively high,which is a better reservoir type,and the permeability of class III and type IV is very low and is a poor reservoir.In this paper,5 types of sedimentary facies of Braided River Delta are identified,which are block stratigraphic coarse sand facies,staggered coarse sand facies,sandstone facies in block bedding,staggered bedding sandstone and staggered bedded fine sand facies.The He8 sedimentary facies of coring well box in the study area are determined to be braided River delta sedimentary facies.Sedimentary microfacies are identified as two sedimentary microfacies: underwater braided channel deposits and underwater braided channel deposits.There is no correlation between the reservoir quartz content,clay mineral content,and feldspar content in the reservoir He8 and the depth of the reservoir,showing the heterogeneity of the intergranular content of the detritus particles.The content of clay minerals as interstitials in upper He8 and lower He 8 is different,showing heterogeneity.The relative contents of clay deposits are significantly different at various burial depths,but their correlation with burial depth is weak.There is a positive correlation between the specific surface of the reservoir rock and clay mineral content in He8.The specific surface of the reservoir rock is negatively correlated with the quartz content.The average pore throat radius does not correlate with porosity,but the average pore throat radius has obvious positive correlation with permeability.