志丹西部长81亚段砂岩储层特征及致密化因素OA

To identify the principal controlling factors of densification in the Chang 81 submember sand-stone reservoir of the Yanchang Formation in the western Zhidan area,Ordos Basin,an integrated study was conducted based on mechanisms of clastic reservoir diagenesis and pore evolution by utilizing cast thin sections,scanning electron microscopy and petrological-mineralogical testing method,with the res-ervoir characteristics and diagenetic features examined in details.The results indicate that the lithology of the Chang 81 submember reservoir is predominantly silty to fine-grained feldspathic sandstone,with a high content of plastic components such as mica flakes.The cements are mainly clay minerals and car-bonates,and the pore types are dominated by residual intergranular pores,followed by dissolved pores and intercrystalline pores.The reservoir exhibits porosity of 2.1％～16.9％and permeability of 0.01 × 10-3～3.77 × 10-3 μm2,classifying as a low to extra-low porosity and ultra-low permeability reser-voir,with fine pore throats and poor connectivity.The densification of the reservoir results from the combined effects of provenance,sedimentation,and diagenesis,containing provenance conditions rich in feldspar and plastic debris content,and a long-distance transported fine-grained sedimentary back-ground provides critical material foundations for densification.Diagenesis directly leads to reservoir densification,with intense compaction identified as the predominant factor,which causes a decrease of reservoir properties,pore-throat refinement and reduced connectivity.This study clarifies the prove-nance-sedimentation-diagenesis mechanisms and primary controlling factors influencing densification in the Chang 81 submember sandstone reservoir,providing a theoretical basis for the efficient development of tight oil resources in the western Zhidan area.