3.3.4. Formation Thickness

In order to improve the calculation accuracy, the grid was encrypted. The plane grid step size was 1 m × 5 m, and the total number of grids was 220 × 1 × 5 = 1100. Comparison of the production indicators (recovery degree, cumulative oil production, gas-oil ratio, and gas production rate) under different formation thickness are shown in Figure 11.

**Figure 11.** Comparison of production indicators under different oil layer thickness. (**a**) Recovery degree; (**b**) cumulative oil production; (**c**) gas-oil ratio; and (**d**) gas production rate.

The dynamic production indicators under di fferent formation thickness have been listed in Table 18. As can be found from Table 18, the cumulative oil production increased with the formation thickness. This was because when the formation thickness increased, the reserve increased. When the formation thickness was 20 m, the oil recovery degree was the highest. With formation thickness increased, the gas appearance time in production well appeared later. The peaks of the gas-oil ratio showed an opposite trend.


**Table 18.** Dynamic production indicators under di fferent formation thickness.

The characteristic parameters of the oil-wall with di fferent formation thickness have been listed in Table 19. As can be found from Table 19, the oil-wall formation time was the same for the four cases. When the formation thickness was 100 m, the oil-wall had highest oil saturation. The features of the oil-wall were more obvious. The oil-wall migration speed is the highest.


The characteristic parameters of the fire wall under di fferent formation thickness have been listed in Table 20. As can be found from Table 20, the average temperature of the fire wall, the distance between the fire wall and the oil-wall, and the fire wall propulsion speed were negatively related with the formation thickness. For formations with too small thickness, the heat loss during the fire propulsion process will be relatively large, which may cause the combustion temperature to be very low. Under this situation, the fire will be extinguished, and the in-situ combustion will fail. In summary, the formation thickness had a grea<sup>t</sup> influence on the characteristics of the oil-wall and the fire wall. Combining above analysis, it can be concluded that the best option for in-situ combustion in this study was when the formation thickness was 20 m.

**Table 20.** Characteristic parameters of fire wall under di fferent formation thickness.

