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It is preliminary estimated that the proved geological reserves of original low-oil-saturation reservoirs (OLOSRs) of 54 blocks in China are more than 820 million tons. As same as the high water-cut stage of a reservoir after water flooding, the initial water cut of OLOSRS is higher than 80%. The industrial application of EOR technology could efficiently enhance oil recovery rate from 8.4% to 20.1% of reservoirs after water flooding. The suitable measurements of EOR to the OLOSRs probably have a profound impact on achieving higher oilfield reserves and production. In this paper, the main characteristics and reserves potential of OLOSRs have been studied by investigations and laboratory experiments. The relationship between initial oil saturation and displacement efficiency is also analyzed. The feasibility of EOR technologies for different OLOSRs is discussed. The results show that the OLOSRs could be divided into two categories (primary and secondary) by origin of low oil saturation. The two categories contain abundant reserves in China’s major oilfields, but their occurrence states of crude oil are quite different. If the average oil saturation of the OLOSR is defined at 40%, there are 13.1%–54.2% crude oil that could be recovered by using the existing EOR technology, especially in the primary OLOSRs with low permeability and the secondary OLOSRs with high permeability. Keywords: Low oil saturation, Transition zones, Occurrence state, Oil displacement efficiency, Gas flooding, Surfactant flooding

The flow characteristics of dissolved gas driven processes in some heavy oil reservoirs, such as low gas–oil ratio and higher oil recovery rate than expected, are quite different from conventional oil production processes. Foamy oil is considered one of the main reasons behind such a production phenomenon. In this paper, the factors affecting the performance of foamy oil recovery were experimentally investigated in a sandpack medium with the assistance of computed tomography (CT) technology to help further the understanding of the mechanism. Five different experiments were applied and the results showed that (1) the linear pressure drop production model had a similar oil recovery to that of the step-down mode; (2) increasing the depletion rate could be more favorable to the oil recovery rate; (3) under a constant gas–oil ratio, raising the temperature had little impact on oil recovery, but showed obvious impact on the production curve; and (4) with higher permeability, there were more residual oil at the end of the displacement process. Lastly, a dry gas huff and puff experiment was conducted and the decreased oil saturation was observed in the inlet section, while no obvious effect was remarked in the outlet region of the medium. [ABSTRACT FROM AUTHOR]