Abstract: Abstract：SJ oil reservoir’s permeability is low and its natural energy is poor. However，because of the inadequate CO2source
and the poor resistance of the pipelines to CO2-corrosion，the continuous CO2injection is unavailable in the field. In that
case，another improved strategy is the replacement of the continuous CO2 injection by CO2slugs pushed by N2. Based on the
formation hydrocarbon characteristics of the pilot test block，we try to compare the mechanism of CO2slugs drive pushed by
N2with the continuous CO2drive. After we tested the recovery percent and minimum miscibility pressure（MMP）of CO2slugs
drive pushed by N2and CO2drive by slim tube experiments，our research are the multiple contact simulation of CO2drive and
N2drive and the one-dimensional simulation of long slim tube of CO2slugs pushed by N2. We analyse the intermiscibility of
gas slug and the crude oil，the interfacial tension between gas phase and liquid phase，the concentration of C2-C6in the two
phases，density and viscosity of such two phases. The simulation results indicate no serious diffusion and dispersion of CO2
and N2occur when CO2slug pushed by N2displaces the crude oil during the long slim tube test. The CO2concentration of the
multicontect front is in a high level to keep a stable miscible displacement front to drive oil. CO2slugs pushed by N2can gain
the same oil recovery with continuous CO2flooding in the same volume of gas injection. Such gas slug displacementreduce
the amount of CO2，so it can slow the CO2-corrosion to the pipelines caused by the continuous CO2injection. The cognition
provides inspiration function for the development and improvement CO2-EOR.

Key words: Key words：low permeability reservoir, CO2–EOR, multicontact miscibility, pre-CO2-slug pushed by N2