CONTROL FACTORS OF SANDSTONE RESERVOIR OF UPPER SHAXIMIAO FORMATION IN ZHONGJIANG REGION,SICHUAN BASIN

Upper Shaoximiao Formation is one of the gas stratigraphic horizons with great exploration potentiality in Zhongjiang region of Sichuan basin.This reservoir is investigated by analysis of lithology,thin sections,SEM and core properties.It is showed that the types of pore are mainly secondary pore,minor physical pore,and the reservoir is characterized by low porosity and permeability with average porosity of 6.1%,average permeability of 0.105×10-3 μm2.Sedimentary microfacies and digenesis are the main factors which affect the quality of reservoir.Compaction,siliceous cementation,carbonate cementation are unfavorable to the porosity and permeability of the sandstone,while denudation and chlorite cementation are favorable to the porosity and permeability of the sandstone.Distributary channel sandstone of delta front and delta plain are better microfacies for the reservoir development.According to petrophysical properties of reservoir and pore structure parameters,Upper Shaximiao Formation sandstone reservoir in Zhongjiang region could be classified into four types of reservoirs.The typeⅠ and typeⅡ reservoirs can be taken as the major target zones for exploration.Distributary channel sandstone of meandering delta front and meandering delta plain was typeⅠ,distributary channel sandstone of braided delta front and braided delta plain was typeⅡ.