Reservoir Diagenesis Characteristic Of The Ahe Formation Of Jurassic In Yiqikelike Structural Belt

The paper has studied on the reservoir petrography diagenesis features of the Ahe Formation of Jurassic in Yiqikelike Structural belt,using core,thin section,logging,wellogging,and combined with basin numerical sumulaton model and fluid inclusions data.In the end,we summarized the diagenetic evolution model of four type sandstone,and analyzed the distribution characteristics of different types of sandstone.The reservoir densification and accumulation process is complicated,and its heterogeneity is strong,so that,the exploration is difficult.The result shows the tight sandstone of lower jurassic Ahe formarion experienced two oil and gas filling,and petrological characteristics of tight sandstone reservoir have significantly influence on diagenesis,becoming reservoir,migration and accumulation.On the basis of the Dickinson's triangle,combined with the content of calcium cement,ductile debris and rigid particles,the author divides the sandstone of Ahe formation into four types,type C is calcareous cementitious sandstone(the content of calcium cement is more than 15%),type A is lithic sandstone with high rigid particles(the content of ductile debris is less then 10%),type D is lithic sandstone with medium ductile debris(10%-25%),type B is ductile-rich lithic sandstone which have more than 25% ductile debris.Type A and D are effective reservoirs of tight gas.The permeability of type A is high(10mD-100mD),its porosity ditribution is larger(6%-11%),the blue fluorescence which represent the second oil(gas)fillling is strong,as a result of high emposieu and structural fractures.The content of feldspar and ductile debris is a little high in type D,its porosity is higher(the porosity of oil layer is between 10%-11%),but its permeability is low(1mD-10mD),as a result of late dissolution.About 76% sample of type D in oil layer have yellow and blue fluorescence.When the early oil filling,the average porosity of type D is higher(about 15%),but when the second oil and gas filling happens,its average porosity slight decline(about 9%).The compaction and cementation of type A and B is stronger,their physical property is poor,a few sample have yellow fluorescence(13%),there is no blue fluorescence,and they are all effective reservoir.There are difference in diagenesis and accumulation between type B1 and B2.The early oil filling of type D slowed the occurrence of structural compaction and carbonate cementation,and change its wettability,and it's conducive to the late acid dissolution and oil(gas)filling.The structural fractures affect the performance of type A,the second oil(gas)filling affect by structural fractures,rather than the early oil filling.Type A often occur on medium sandstone,or conglomeratic santstone,in the low or middle of the cycle,where have high permeablity and porosity.This sandstone possible come from braid channel which is under water,and lateral continuity is better.Type B often have much ductile debris,and it's fine sandstone,which is occuring in bank and the upper of the under water braid channel,it's on the upper of the cycle.Type C appear in the top or bottom of the braid channel,and it mabye influnce the type A sandstone.Type D more appear in the mouth bar,distalba,and it's continuity is poor then type A.