As shown in Figure 1, the CNMCC of production well W1 changes nonmonotonically with the C[O.sub.2] injection volume; that is, it increases at the beginning, then decreases later, and increases again.
Since the characteristic of the middle stage is not significant , the CNMCC increases monotonically with C[O.sub.2] injection volume at core scale.
Therefore, the light compositions in produced oil will increase, which results in CNMCC decrease in the late stage.
Based on the above analysis, we propose a conjecture to explain the CNMCC pulse characteristic at reservoir scale: the CNMCC will show back-and-forth pulse characteristic if there is plane heterogeneity in the reservoir, that is, channeling-paths.
The corresponding relative component concentrations are shown in Figure 3 (blue line), illustrating that initial CNMCC is C9.
During C[O.sub.2] flooding process, the CNMCC increases monotonically from C9 to C12 with C[O.sub.2] injection volume.
The CNMCC of produced oil increases from C9 to C30 during C[O.sub.2] injection time 0-210 days.
The CNMCC increases monotonically from C9 to C12 with C[O.sub.2] injection volume in the homogenous model, exhibiting the same change law with the experimental results [10, 11].
The variation of CNMCC shows pulse characteristic in the heterogeneous model (Figure 4), which validates the conjecture in Section 3.
Therefore, the CNMCC increases from C9 to C30 monotonically as well.
Therefore, the CNMCC decreases from C30 to C12 in this period.
The current work proposes a sufficient condition for pulse characteristic of CNMCC at reservoir scale.