Microscopic pore throat characteristics of tight sandstone reservoirs in Fuyu layer of the fourth member of Quantou Formation in southern Songliao Basin

Key words:  pore throat structure  pore throat parameters  tight sandstone  fourth member of Quantou Formation  southern Songliao Basin

Abstract:

The Fuyu Oil layer of the fourth member of Quantou Formation in southern Songliao Basin was studied in detail for the reservoir space, physical property, micro pore throat distribution and contribution of different pore throat scales to reservoir physical property of tight sandstone reservoirs. A series of techniques were used, including thin section, SEM, high pressure mercury penetration, rate-controlled mercury penetration and image analysis. The correlation of different pore throat parameters and reservoir physical property was analyzed. The results show that, the physical properties of the tight sandstone reservoirs in the study area are poor with small pore throat radius; the reservoir spaces are mainly intra-particles and inter-particles dissolved pores with some primary pores as well as inter-crystal pores in clay minerals. The pore distribution ranges have no significant difference, but the distribution ranges of throat radius and pore throat ratio had apparent difference. In the reservoirs of good physical properties, distribution ranges of throat radius are wider with larger peak values, and more obvious right-skewness. When reservoirs have higher permeability, the pore throat radius that plays major contributions to permeability are larger. Opposite distribution features exist between pore throat ratio and throat radius. Reservoir permeability is mainly contributed by a small amount of pore throat with micron sizes, although the pore throat with nanoscale sizes accounts for great volume because they hold lower filtration capacity. The lower the reservoir permeability is, the larger proportion is for the pore throat with nanoscale sizes. Micro pore throat parameters have effects mainly on permeability but less on porosity.