基于成岩—孔隙耦合的致密储层特征及成因机制OA

The Chang 6 oil reservoirs of the Triassic Yanchang Formation in Block X,central Shaanxi Slope,Ordos Basin,is a typical tight reservoir with low porosity and low permeability.Based on core observation,thin section identification,scanning electron microscopy(SEM),X-ray diffraction(XRD)and mercury intrusion porosimetry,this paper systematically investigates the petrological characteristics,physical properties,pore structure and diagenesis of the Chang 6 reservoir.Research results show that the reservoir lithology is mainly feldspar sandstone,and the mineral composition is dominated by feldspar and quartz.Intergranular dissolved pores are the predominant pore type,and the pore-throat structure is characterized by small pores and fine throats.Quantitative evolution analysis of diagenesis-porosity system indicates that the original porosity(approximately 35%)was reduced by 19.1%due to compaction,with an additional loss of 4.3%caused by cementation.The final measured porosity is only 11.6%,among which the pore-increasing effect of dissolution raised the porosity by about 3.1%.Early compaction and cementation are the main factors for reservoir densification,while dissolution plays a key role in improving reservoir quality.This study reveals the formation mechanism of tight Chang 6 reservoirs,and is of great significance for the effectiveness evaluation of tight sandstone reservoirs and the selection of hydrocarbon exploration targets in the Ordos Basin.