Diagenesis and micro-and nano-scale reservoir spaces evolution of tight sandstones in Quantou4 member of southern Songliao Basin

Based on data of thin section and SEM as well as the observations of rate-controlled mercury injection, the influence of diagenesis on the micro-and nano-scale reservoir spatial evolution, as well as the occurrence and distribution of tight oil and gas were analyzed in Quantou4 member of southern Songliao Basin. The results show that the diagenetic environment experienced a transition from alkalinity through acidity to alkalinity. During the formation of authigenic minerals in different diagenetic environments, a large number of nano-scale intercrystalline pores were also formed when the minerals cemented and/or filled the micro-scale reservoir spaces. Because of the transformation of reservoir spaces from micro-scale to nano-scale, the storage capacity and percolation ability of tight sandstones are reduced, and the driving force is enhanced in the process of tight oil and gas charging, which led to the mercury saturation of throat and the breakthrough pressure increase gradually with the decrease of porosity and permeability in rate-controlled mercury injection experiments. The migration and accumulation of tight oil and gas is the result of dynamic mechanical equilibrium. Therefore, the exploration and development of tight oil and gas in areas far away from source rocks should be pivoted around the sandstones dominated by the micro-scale spaces, whereas the exploration of near-source tight oil and gas should be expanded to the sandstones dominated by the nano-scale spaces. © 2018, Periodical Office of China University of Petroleum. All right reserved.