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Recently, as the demand for fossil and renewable energy continuously increases, enhancing oil recovery has become one of the key methods to meet the increased requirement. However, most of the oilfields are facing serious problems, including formation heterogeneity and low recovery factor. Therefore, further analysis is required to study the distribution of remaining oil and how to enhance oil recovery effectively. In this study, the core samples of different reservoir types were employed and characteristics of pore structure were measured by a high‐pressure mercury porosimeter. The recovery factor and distribution of remaining oil with different reservoir types were determined by core flooding experiments and nuclear magnetic resonance tests. According to the results, the heterogeneity of pore structure becomes weaker as the permeability of the reservoir increases. The recovery during different periods improved as the core permeability increased. The distribution of remaining oil in different pore sizes has an obvious difference. The contribution of the recovery factor is highest in smallpores and mesopores for type II reservoir while is greatest in mesopores and macropores for type III reservoir. These results can provide theoretical and technical support for further enhancing oil recovery. [ABSTRACT FROM AUTHOR]

An oilfield has been developed with waterflooding for a long time, and the water cut has reached a high level. Surfactant-polymer (SP) flooding is considered as the following enhanced oil recovery (EOR) technique. To determine the feasibility of SP flooding in this oilfield, the microscopic oil displacement experiments are performed, and the distribution of remaining oil after waterflooding and SP flooding is observed. The recovery rates are measured by the producing liquid amount and nuclear magnetic resonance (NMR) technique. The two methods show similar measurement results, with deviations of about 10%. The contributions of different pore and throat diameters are analyzed with the NMR technique. The results show that SP flooding has a much lower contribution limit of pore and throat diameter than waterflooding, indicating that SP flooding can effectively improve sweep efficiency. The SP flooding can improve by about 30% EOR rate. The frozen slicing technique and ultraviolet fluorescence excitation are applied to observe the status and distribution of remaining oil. The results show that both waterflooding and SP flooding can effectively reduce all types of remaining oil. Comparing the remaining oil proportions in the high and low permeability cores, we can conclude that the high permeability contributes to the performance of waterflooding and SP flooding. This work proves the efficiency of SP flooding in this oilfield development and provides a microscopic explanation of remaining oil distribution after waterflooding and SP flooding. • SP flooding is an effective approach for EOR compared with waterflooding. • Both waterflooding and SP flooding can effectively reduce all types of remaining oil. • High permeability contributes to the performance of waterflooding and SP flooding. • Recovery after waterflooding and SP flooding can reach 43.58% and 8.21% respectively. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the migration and blocking mechanism of self-aggregated divinylbenzene-co-acrylamide (DCA) microspheres as a novel profile control. Scanning electron microscopy (SEM) and laser diffracting measurement experiments were conducted to examine the shape and size of the microspheres. The optimal matching factor between microsphere diameter and the pore throat was from 0.15 to 0.19. The migration position of DCA microspheres in porous media was studied via SEM. The images revealed that DCA microspheres can exhibit long-distance migration. Moreover, the effects of different matching factors on oil recovery rate have been investigated by the core displacement experiments. The enhanced oil recovery was the highest when the DCA microspheres with the optimum matching factor was injected. Additionally, the oil saturation distribution demonstrates that DCA microspheres with optimal matching factors can enhance sweep efficiency by plugging high-permeability water channels. Image 1 • Self-aggregating microspheres with particle sizes ranging from 50 nm to 102 μm were synthesized. • Self-aggregating microspheres have shell-core structures and can be aggregated by high-valence metal ions. • The optimum matching factor of self-aggregating microspheres is from 0.15 to 0.19. • Self-aggregating microspheres gathered in the pore throat and formed a partial seal inside the core. • Self-aggregating microspheres can block the high-permeability zones and increased sweep efficiency. [ABSTRACT FROM AUTHOR]