RESERVOIR CHARACTERISTICS AND CONTROLLING FACTORS OF THE UPPER PALEOZOIC SANDSTONE,EASTERN ORDOS BASIN

The Upper Paleozoic in Ordos includes four gas formations such as Tai2, Shan2, He8 and He7. Studies on them show the reservoirs are defined as the pore-type and fracture-pore type sandstone with low porosity and low permeability, as well as markable heterogeneity. The type of reservoir's pore space is mainly pore, which can be subdivided into four sorts, i.e., intergranular pore, residual intergranular, intragranular dissolved pore as well as Kaolin intercrystal pore. The widespreading micro-fracture has minor effect on changing the reservoir's pore space, but it can increase the reservoir's permeability. The main factors that control reservoirs include deposition, diagenesis and tectogenesis. The reservoir with coarser grain size and higher maturity has better porosity and permeability. It's compaction, silicon cement and Kaolin cement that account for the tight reservoir. Dissolution and tectonic micro-fracture are favorable to improve the reservoir.