Characteristics and significance of microscopic pore structure in tight sandstone reservoir of the 8th member of Lower Shihezi Formation in the Su6 area of Sulige Gasfield

Microscopic pore structure characteristics of tight sandstone reservoir of the 8th member of Lower Shihezi Formation in the Su6 area of Sulige Gasfield was quantitatively analyzed by means of casting thin sections, scanning electron microscope, 3D X-ray computed tomography, high pressure mercury injection, constant-rate mercury penetration. The purpose was to discuss the causes of differences of microscopic pore structures, and further to screen evaluation parameter which could reflect the microscopic pore structure characteristics of tight sandstone reservoir. The results are as follows. Reservoir space types include (grains and cements) dissolved pores, clay-mineral intercrystalline pores and primary remained intergranular pores. Reservoirs with different permeability have less differences in pore radius but obvious differences in throat radius. The reservoir is more tight with smaller range and greater proportion of fine pore-throat. The throat also accounted for higher proportion of effective reservoir space. The medium-to-coarse grained lithic sandstones and medium-to-coarse grained lithic quartz sandstones have higher textural maturity and primary porosity, which have experienced strong dissolution. The dissolved pores are large proportion of total pore content, and the pore-throat radius content increases significantly, which are more than 1 μm in the two types of medium-to-coarse grained sandstones. The small grained (feldspar) lithic sandstones have lower textural maturity and primary porosity, which have experienced weak dissolution. The pore types in the small grained sandstones are mainly clay-mineral inter-crystalline pores, and the pore-throat radius in which is less than 0.1 μm. Mainstream throat radius plays the main controlling effect on reservoir permeability, and can well reflect the microscopic pore structure, such as reservoir pore-throat distribution, effective reservoir space and heterogeneity. In conclusion, mainstream throat radius should be an important reservoir evaluation parameter for the tight sandstone reservoir. © 2015, Science Press. All right reserved.