Diagenesis and porosity evolution of the reservoirs from the upper Triassic in the Yichuan basin

The formation of the upper Triassic sandstone in the Yichuan basin is dense and the heterogeneity is strong.Due to unclear understanding of diagenesis and its pore evolution,the hydrocarbon deployment was restricted to some extent.Through thin section,scanning electron microscopy(SEM) and X-ray analysis of the results of research,combined with the burial history,thermal history and other information,the Triassic reservoirs of Yichuan basin are mainly of fine sandstone and feldspar lithic sandstone,with poor physical properties in general,which belongs to low porosity and low permeability sandstone reservoir.Diagenesis of upper Triassic belongs to stage A of middle diagenesis phase.The early diagenetic compaction and cementation are main factors to decreasing porosity of reservoir.The formation of secondary porosity in feldspar corrosion has obvious effect on sandstone reservoir performance.The early diagenesis reservoir has been densified before oil and gas filling.