Sandstone reservoir evaluation of Member 8 of Middle Permian Xiashihezi Formation in the Gaoqiao area of Ordos Basin,China

The reservoir performance of Member 8 of Middle Permian Xiashihezi Formation(He 8) reservoir in the Gaoqiao area of Ordos Basin is summarized and evaluated by analysing the reservoir petrology,reservoir properties,the type of reservoir porosity and pore structure.The lithology of the Upper Paleozoic sandstone reservoir is complicated.There are the lithic quartz-sandstone,quartz sandstone,and lithic sandstones with high compositional maturity and medium textural maturity.The reservoir has low porosity and low permeability.The average porosity is 8.37% and the average permeability is 0.81×10-3 μm2.The pore space of the reservoir mainly includes the secondary dissolved pores between grains,intercrystalline pores,primary residual intergranular pores,and some micro-cracks.The pore structure is expressed as medium-higher displacement pressure,small pore throat radius,and poor connectivity of pore throat.According to the lithology and petrophysical properties of the reservoir,pore type and pore texture parameters,the reservoir is classified into four types.Type II and Ⅲ are the better-medium reservoirs in the research area,and the main reservoirs to increase production in the future.