Experimental investigation on remaining oil distribution and recovery performances after different flooding methods

Abstract

Nowadays most of the oilfield in China have entered the middle-late development stages with the problem of high water cut and low permeability. Many studies have been conducted on the mechanism of chemical flooding to enhance oil recovery. However, there has been less previous evidence for accurate identification and distribution of remaining oil. Therefore, we proposed a new nuclear magnetic resonance (NMR) interpretation method as well as a new residual oil fluorescence analysis method. In this study, we conducted core displacement experiments with different methods. The nuclear magnetic resonance (NMR) tests and fluorescence analysis of frozen slides were performed in each stage after flooding to study the effect of different displacement methods on the recovery degree and the remaining oil distribution. The results showed that alkali can only slightly improve the recovery of macropores and free-state oil due to its poor sweep volume and oil washing efficiency. Surfactants can increase oil recovery in mesopores and the type of bound-state remaining oil by reducing interfacial tension (IFT). Although the injection of polymer can enlarge the sweep volume, the effect of displacement efficiency is poor in narrow space. Therefore, it can only improve the recovery factor in smallpores and mesopores as well as the type of free-state remaining oil. The synergistic effect of ASP system not only can form ultra-low interfacial tension to enhance the recovery of bound-state and half-bound state, but also can help surfactants and alkali enter smallpores according to the injection of polymer. Thus, the oil recovery is significantly improved. Moreover, our study provided a micro-level understanding as the occurrence state and distribution of remaining oil. The result also lays the foundation for further enhance oil recovery in oilfield.