Characteristics of Pore Structure and Fluid Saturation of Ultra-low Permeability Reservoirs in Southern Songliao Basin

The oil field in Songliao Basin has been developed for more than 50 years. The ultra-low permeability reservoir has been paid more and more attention. Pore structure and fluid saturation characteristics are the keys and difficult points of ultra-low permeability reservoir research. Based on the analysis of thin sections, routine physical properties and mercury injection, physical properties, pore structure and fluid saturation of reservoir in different facies belts are systematically studied. The ultra-low permeability reservoirs in the southern part of the Songliao Basin are always found in the delta front. The lithology is mainly composed of extremely fine granulate feldspar sandstone, and the rock composition and structure maturity are always low; reservoir physical properties and pore structure are controlled by sedimentary facies. According to the pore structure Nelson plate, the delta front sedimentary can be further divided into inner delta front and the outer delta front. The ultra-low permeability reservoirs are mainly distributed in the outer delta front; the pore throat radius and the movable fluid saturation gradually decreases from the inner delta front to the outer delta front.