鄂尔多斯盆地北部大牛地气田A区山西组致密砂岩储层质量层间差异成因研究OA

The Shanxi Formation is a key target for tight sandstone gas exploration in the northern Ordos Basin.However,significant heterogeneities in reservoir development among sub-members hinder further exploration.To improve the understanding of the Shanxi Formation reservoir characteristics and clarify the genesis of interlayer reservoir quality differences,this study focuses on Block A of the Daniudi Gas Field in the northern Ordos Basin.Core observation,thin-section identification,scanning electron microscopy(SEM),cathodoluminescence(CL),and high-pressure mercury injection(HPMI)tests were used to investigate sandstone composition,pore types,reservoir properties,and diagenetic processes.The results show:(1)The Shanxi Formation mainly comprises lithic quartz sandstones with high lithic fragment and matrix contents.Intragranular and intergranular dissolution pores constitute the main reservoir space.Intragranular pores develop within the lithic fragments,while intergranular pores are intercrystalline micropores formed through the dissolution and alteration of the tuffaceous matrix.(2)Compaction is the primary destructive diagenetic process in the Shanxi Formation,leading to the disappearance of original pores.Dissolution is the primary constructive diagenetic process,with a marked weakening trend from type-I to type-Ⅲ reservoirs.Cementation also influences reservoir properties.(3)Reservoir quality differences are controlled by the depositional system,sandstone thickness,components,and diagenesis.The S2-2 sub-member exhibits the best reservoir conditions,followed by S2-1,with S1-1 being moderate,and S1-2 and S1-3 being the least favorable.This study clarifies the genesis of reservoir quality differences among sub-members of the Shanxi Formation,enhancing the understanding of tight sandstone reservoirs in the northern basin and providing a theoretical basis for precise development and well placement.