3.3.2. Stratigraphic Layering

Stratigraphic layering (SL) was also an important geological parameter which a ffected reservoir production. The positive SL meant that the permeability of the upper layer was less than the lower layer. The negative SL means that the permeability of upper layer was higher than the lower layer. If the permeability of the upper and lower layer was the same, it could be called "No SL", which also meant that the reservoir was vertically homogenous. In this study, the positive and negative SL models were established, respectively (average permeability is 1000 mD), for the positive SL case, the top layer permeability (600 mD) was lower than the bottom layer permeability (1400 mD). For the negative SL case, the top layer permeability (1400 mD) was higher than the bottom layer permeability (600 mD). Comparison of the production indicators (recovery degree, cumulative oil production, gas-oil ratio, and gas production rate) under di fferent stratigraphic layering are shown in Figure 9.

The dynamic production indicators under di fferent stratigraphic layering (SL) have been listed in Table 14. As can be found from Table 14, the influence of the SL on the recovery degree and cumulative oil production of the reservoir was: no SL > positive SL > negative SL. The positive SL case had the earliest gas appearance in the production well and the no SL case had the latest gas appearance in the production well. It can be seen that the more homogenous of the reservoir, the better the oil recovery for the in-situ combustion scenario.

**Figure 9.** Comparison of production indicators under different stratigraphic layering. (**a**) Recovery degree; (**b**) cumulative oil production; (**c**) gas-oil ratio; and (**d**) gas production rate.


