Distribution and controlling factors of tight sandstone oil in Fuyu oil layers of Da'an area, Songliao Basin, NE China

Abstract

By using core samples, thin section, scanning electron microscope and rate-controlled mercury penetration data etc, the reservoir characteristics, oil-bearing characteristics and main controlling factors of the tight sandstone oil in Fuyu oil layer of Da'an area, Songliao Basin are studied. The oil-bearing characteristics of Fuyu oil layers in Da'an area are as follows: (1) the extensive and continuous distribution, with “sweet spots” in local areas; (2) low oil abundance, and very complex distribution; (3) oil-bearing grade being oil immersion to oil spot, with very low lower-limit of oil-bearing porosity and permeability; and (4) poor differentiation of oil and water, no uniform oil-water contact. The above oil-bearing characteristics of the tight sandstone in Fuyu oil layers are mainly controlled by the spatial distribution of distributary channel sands, the differences in reservoir physical properties, the structure and size of pores and throats. The boundary of distributary channel sandbody is the boundary of tight sandstone oil distribution. The heterogeneity of tight sandstone oil is controlled by the single distributary channel sandbody and the contact relationship between different stages of distributary channel sandbody. Distribution of “sweet spots” and enrichment of tight sandstone oil are controlled by the differences in physical properties. The differentiation of oil and water in the tight sandstone is controlled by the pore structure and pore size. In-situ oil accumulation is controlled by the nano-pore throat structure system.