Control Effect of Pore Throat Radius on Quality of Extra-Low and Ultra-Low Permeability Reservoir in Member 1 of Qingshankou Formation, Southern Songliao Basin

Among the uncertainties in development of extra-low and ultra-low permeability reservoirs in the Qingshankou Formation, it is clear that the main controlling factors of the porosity, permeability, oil saturation and mobility are important issues to be solved. The characteristic parameters of extra-low and ultra-low permeability reservoirs in the Qingshankou Formation of the southern Songliao basin were quantitatively characterized by mercury intrusion, nuclear magnetic resonance, pore-permeability measurement, grain size analysis and X-ray diffraction test in this study. The results show that the pore throat size of the ultra-low permeability reservoir in southern Songliao basin is mainly distributed between 0.3 μm and 1.7 μm, which is the main controlling factor of reservoir property and fluidity. The pore throat radius of more than 1.5 μm corresponds to the conventional low permeability reservoir, and the rock type of the reservoir is mainly composed of fine feldspar lithic sandstone. 0.5-1.5 μm pore throat corresponds to ultra-low permeability reservoir. The rock type is mainly composed of very fine feldspathic lithic sandstone and coarse siltstone. The moveable fluid saturation is more than 65%; 0.1-0.5 μm pore throat corresponds to ultra-low permeability reservoir, and the rock type is mainly coarse-fine siltstone, moveable fluid saturation between 50%-60%. It is concluded that pore throat radius which has been controlled by the sedimentary facies determines the characteristics of reservoir physical properties and fluid saturation, and it should be used as a significant parameter of reservoir evaluation.