Evaluation of displacement effects of different injection media in tight oil sandstone by online nuclear magnetic resonance

Abstract

In order to evaluate the displacement effect of four kinds of injection media in tight oil sandstone, water, active water, CO2, N2 flooding experiments were carried out in laboratory. Online Nuclear Magnetic Resonance (NMR) spectrometers combine the advantages of NMR technology and core displacement experiments. In the displacement experiment, NMR data of different injection volumes were obtained and magnetic resonance imaging (MRI) was carried out. The results showed that micro and sub-micropores provided 62-97% of the produced crude oil. The enhanced oil recovery ratio of active water flooding was higher than that of conventional water flooding up to 10%. The recovery ratio of gas flooding in micro and sub-micropores was 60-70% higher than that of water flooding. The recovery ratio of CO2 flooding was 10% higher than that of N2 flooding. The remaining oil was mainly distributed in pores larger than 0.1 µm. Under the same permeability level, the remaining oil saturation of cores after gas flooding was 10-25% lower than water flooding. From MRI images, the displacement effects from good to bad were as follows: CO2 flooding, N2 flooding, active water flooding, and conventional water flooding.