The optimization of pre-slug size in CO 2 -N 2 compound flooding

In order to enhance oil recovery in low and ultra-low permeability layer, both of the numerical simulation and physical model experiment have been researched. First, the dynamic distribution of CO 1 and N 1 in the oil and gas phase in the CO 2 -N 2 compound flooding process was numerically simulated by using the long slim-tube model. The results show that the CO 2 slug should have at least 0.3 PV to prevent the impact of N 2 channeling effectively. Second, under the experimental conditions of complete miscibility of CO 2 -crude oil, the two types of natural cores including low and ultra-low permeability, respectively, are used for experimental study on oil displacement. The results confirm that CO 2 -N 2 compound flooding with 0.3 PV CO 2 pre-slug can achieve a good result. Finally, a five-point well pattern element model is established by CMG. The recovery and the gas cost of per ton of oil are calculated respectively for CO 2 -N 2 compound flooding and full CO 2 flooding at 300 m well spacing of low and ultra-low permeability layer. According to the simulation results, the optimal CO 2 pre-slug size in CO 2 -N 2 compound flooding under the condition of low and ultra-low permeability layer five-point well pattern is 0.4 PV.