四川盆地中部地区侏罗系沙溪庙组二段储层特征差异及其形成机理OA

The Jinqiu Block,as one of the core productivity construction areas for the Middle Jurassic Shaximiao Formation gas reservoir in the Sichuan Basin,is currently in the development stage.However,the differences in reservoir characteristics among the sand groups—which serve as fundamental development units—and their underlying formation mechanisms remain poorly understood,which restricts the sweet spot evaluation and well placement.Based on experiments such as casting thin sections,scanning electron microscopy(SEM),X-ray diffraction,physical property testing,and constant-rate mercury injection,this paper characterizes the macroscopic and microscopic reservoir differences among No.6 to 9 sand groups in the 2nd member of Shaximiao Formation(Sha 2 Member)in the central Sichuan Basin,and analyzes the mechanisms driving these reservoir differences.The following results are obtained.First,among these sand groups,No.7 exhibits the best physical properties and the largest average throat radius,followed by No.6,whereas No.8 and No.9 display the poorest physical properties and the smallest average throat radii.Second,these sand groups differ significantly in cement contents,which can be divided into chlorite-zeolite cement facies,chlorite cement facies,and I/S mixed layer-illite cement facies.Third,no significant differences are observed in average pore radius among these sand groups,whereas the throat-radius distribution shifts leftward and becomes narrower as reservoir quality deteriorates.Fourth,the continuous uplift of the Dabashan tectonic belt during the Middle Jurassic is the fundamental reason for the differences in reservoir characteristics among No.6 to 9 sand groups.In conclusion,the macroscopic physical properties of No.6 to No.9 sand groups are directly controlled by the throat size,and the differences in microscopic characteristics are under the control of the chain differentiation among magma material content,diagenetic fluid environment,water-rock reaction types,and comprehensive reservoir-forming effects induced by the provenance migration.