(2) Development characteristics

The Du 66 block was developed in 1985 with a square well pattern. The current well spacing is 100 m after secondary infilling adjustment. The main development mode is in-situ combustion in the upper layer and steam huff and puff in the lower layer. Four development stages can be classified. The first stage is from 1985 to 1989, which can be called the production stage. The annual oil production rises to 45 × 10<sup>4</sup> t; the oil recovery rate rises to above 1.0%; the stage production rate is 4.4%. The second stage is from 1989 to 1999, which can be called the stable production stage. The annual oil production is more than 45 × 10<sup>4</sup> t, the oil recovery rate is more than 1.0%, and the stage recovery degree is 13.1%. The third stage is from 1999 to 2005, which can be called the stage of decline in production. The annual oil production drops rapidly, from 45 × 10<sup>4</sup> t to 16 × 10<sup>4</sup> t, and the oil recovery rate drops below 0.5%. The fourth stage is from June 2005 to the present, which is called the in-situ combustion development stage. With the continuous expansion of the scale of fire-flooding, the well opening rate has increased from 23.5% to 87.5%. The daily oil production of the single well has increased from 0.7 t/d to 3.2 t/d. The formation pressure has increased from 1.3 MPa to 3 MPa, and the annual oil production has rebounded, reaching more than 20 × 10<sup>4</sup> t, which means that the oil production by fire-flooding accounts for 80% of the block production.

However, with the expanding scale of the in-situ combustion pilot test in the Du 66 block and the influence of the reservoir heterogeneity, there are some problems, such as the difference of combustion state between the thin interbedded reservoirs, the serious overlap of fire-flooding line in thick interbedded reservoirs, the uneven spread of fire line and the unclear understanding of the combustion state, which affect the efficiency of fire-flooding and the oil recovery. In order to reveal the development mechanisms of the in-situ combustion and better understanding the characteristics of the multi-layer fire wave and determine the main factors affecting the efficiency of fire-flooding, it is necessary to carry out the simulation study of in-situ combustion in the Du 66 block.
