Reservoir Petrology Characteristics Study And Image Method Grain-size Analysis Of Xujiahe Formation In Yuanba Area

To research on the lithology characteristics of reservoir and grain-sizecharacterisics of the upper Triassic xujiahe formation in Yuanba area, knowledge ofsedimentology,petrology and some other discipline has been involved to the castingthin section study.besides,we has observed the core and profile. Some conclutions canbe drawn as below:(1) In the first member of xujiage formation to the five.litharenite is the mainrock type.Little lithic quartz sandstone and feldspar lithic sandstione exist in the Xu1，Xu2and Xu4member.The main type of litharenite in Xu3and Xu5member iscarbonate rock lithic sandstone，which suggested that the source is near close and theburial process is fast.(2) The main lithic fragment type in sandstone is the sedimentary rockdebris,including mudstone debris,siltstone debris and carbonate debris.While themetamorphic rock debris include phyllite debris and metaquartzite debris.The igneousrock debris is mainly acid type.Sedimentary rock debris is difficult to be modified indiagenesis owe to its strong chemical stability and poor mechanical property,which isunfavourable for the reservoir development.(3) The skeleton particles is mainly quartz or debris.Feldspar is few,consideringthe fact that the igneous debris is rare in sandstone, this may result from the lack ofigneous rock in the source.(4) From Xu1member to Xu5member,the matrix content increases,the lowerxujiahe formation has a less content than the upper,considering the poor mechanicalproperty of matrix,on one hand,this may lead to much more remarkable change incompaction，on the other hand,this may indicate that the upper xujiahe formation iscloser to the source.(5) Comparing the mean grain size of five members of xujiahe formation,thegrain size is decrese from Xu1to Xu5.This trend is coincide with the increase of matix content.It is considered that the increase of matrix content is a related changewith the decrease of grain size..(6) According to the standard deviations，it is considered that Xu1member andXu2members have a better sorting characteristics,while Xu2,Xu3and Xu5membershave a moderate one.(7) According to the grainsize probability cumulative curves，the delta isconsidered the major sedimentary facies in xujiahe formation.(8) From Xu1to Xu5,the grain size parameters indicate the environmentchanged from shallow sea-river dominated to delta-river，and the facies change fromthe intial marine to the transitional，at last the continental.