Diagenesis of Chang2 reservoir of Upper Triassic Series in Zichang oilfield and the factors of influencing the physical property of the reservoir

Based on the core observation from over 20 wells and the study of cast thin section and scanning electron microscope analysis results from a great deal of samples, it is held that, (1) Chang2 sandstone reservoir in Zichang oilfield is mainly composed of fine feldspathic sandstone, and there is also a little fine lithic arkose in it, which is characterized by lower composition maturity but higher texture maturity; (2) Chang2 sandstone has reached A period of late diagenesis phase which underwent compaction and clay membrane separating out in early period of early diagenesis phase, pressure solution of quartz and feldspar and secondary adding in late period of early diagenesis phase, authigene cementation and dissolution which results in the forming of secondary pore in early period of late diagenesis phase; (3) in Chang2 sandstone, there are intergranular pore (including relic primary intergranular pore, intergranular dissolution pore), intragranular dissolution pore, micro pore and fracture pore. The main type of pore is intergranular dissolution pore, which amounts to more than 80% of total pore; (4) the physical property of Chang2 reservoir is mainly influenced by sedimentary microfacies and diagenesis, which is shown by the greater effects of the composition (detrical mica, calcite cement) and the texture (grainsize) of Chang2 sandstone on the physical property.