The influence of permeability and heterogeneity on water flooding–chemical flooding efficiency and remaining oil distribution ——Based on nuclear magnetic resonance displacement imaging

Abstract

Abstract To clarify the impact of permeability and heterogeneity on oil displacement efficiency and remaining oil distribution of water flooding-chemical flooding, three groups of high and ultrahigh permeability core samples from an ultrahigh water-cut oilfield in western China were selected as the research objects in this study. High-pressure mercury injection, scanning electron microscopy, wettability test, and other methods were used to characterize the reservoir properties of core samples. Six groups of experiments were performed using the nuclear magnetic resonance (NMR) displacement imaging technology to simulate the oilfield development process considering the economic benefits, and the oil displacement efficiency and remaining oil distribution characteristics of water flooding combined with polymer flooding and polymer-surfactant flooding in reservoirs with varying physical properties were discussed. The research shows that during the simulation process of first water flooding followed by chemical flooding and then water flooding in the oilfield, the T2 spectrum signal amplitude increases the most in the two stages, one is from saturated oil flooding to 50% water cut and the other one is from 95% water cut to the end of 1 PV polymer flooding. The oil displacement efficiency increases the most, and the oil is primarily discharged from pore throats larger than 90 ms (or with pore throat radius of 8.37 µm). Higher permeability and the addition of surfactant based on the polymer are beneficial in improving final oil displacement efficiency, and the displacement efficiency is better when the polymer-surfactant binary flooding acts on the reservoir with higher permeability. The fingering phenomenon and remaining oil distribution are controlled by reservoir heterogeneity and gravity: the lower the heterogeneity, the more uniform the remaining oil distribution, and the closer the oil saturation at the experiment’s inlet and outlet. The more heterogeneous the sample, the more obvious is the fingering phenomenon, and the remaining oil is primarily distributed at the outlet end as well as at the top of the sample. The study results provide theoretical guidance for tapping the remaining oil potential of old oilfields with high to ultrahigh permeabilities.