Study on the Morphological Characteristics of Micro Remaining Oil in Sandstone Reservoirs of Bohai Oilfield

Abstract

Abstract The Bohai Oilfield has entered the stage of high water cut development, with scattered distribution of micro residual oil. Due to different types of micro residual oil production mechanisms, refining the micro residual oil occurrence characteristics at different development stages is beneficial for selecting reasonable methods to improve oil recovery. The oil bearing rock core is subjected to rapid freezing treatment using liquid nitrogen freezing method, and then polished into visualized thin slices no greater than 0.05mm. Based on the length of the corresponding excitation wavelength formed by the electron transition of microscopic residual oil under ultraviolet fluorescence irradiation, the residual oil area in the core thin sections of different water bearing stages is divided into strong water washing zone residual oil and weak water washing zone residual oil using a hierarchical recognition method. Quantitatively characterize the types and abundance of remaining oil based on its morphological characteristics, and classify micro remaining oil of different forms. The results indicate that the remaining oil in the strong water washed area of the sandstone core during the ultra-high water cut stage is mainly in the form of clusters and narrow cracks, while the remaining oil in the weak water washed area is mainly in the form of particle adsorption. Under the same water content condition, lower permeability cores have a more complex pore throat structure, resulting in scattered distribution of remaining oil, with a significant increase in residual oil in particle adsorption, corner shaped, and narrow slit shaped shapes. With the increase of water content, the distribution of remaining oil in various forms tends to be balanced in both strong and weak water washed areas. Refined research on the microscopic characteristics of remaining oil can provide important guidance for the selection of further enhanced oil recovery technologies and ultimately enhanced oil recovery.