Numerical Investigation on Characteristics and Mechanisms of Steam Assisted In-Situ Combustion in Extra Heavy Oil Reservoir

In-situ combustion has become an important way to increase the recovery of extra heavy oil after steam flooding, but it shows a poor effect and a slow start in developing high-viscosity crude oil. Steam-assisted in-situ combustion, as an improved technology, can effectively solve the problems of in-situ combustion and improve the development effect of extra heavy oil reservoirs. Taking the high-viscosity area of Hongqian 1 block in Xinjiang Oilfield as an example, the combustion characteristics, oil displacement characteristics and synergistic mechanism of steam-assisted in-situ combustion are analyzed by numerical simulation, and the superiority and economic applicability are proved by combining steam quality calculation and economic limit calculation. Finally, the influence of various engineering and geological parameters on the development effect of in-situ combustion is investigated, and the controlling factors are ranked according to the proportion of the weight. The results show that steam-assisted in-situ combustion can effectively improve the in-situ combustion in extra heavy oil reservoirs. The injected wet steam absorbs the heat trapped in the combustion zone through heat exchange and transforms into superheated steam, and mixes with air to prolong the duration of the high quality steam, which improves the heat utilization rate while exerting the synergistic leap effect of combustion and oil displacement. Engineering parameters and geological parameters will significantly affect the development. From the engineering parameters, the recommended steam-air ratio is more than 3.0, which is also the main controlling factor, and the injected steam quality should be maintained at about 0.7. The results of the air-oil ratio economic limit calculations also indicate that it is feasible to implement the steam-assisted in-situ combustion in the Hongqian 1 block. The steam assisted In-situ combustion technology has a higher heat utilization than the steam flooding method, and can further improve the exchange heat efficiency per unit, which will help to promote this technology to green and low-carbon development. In the future, it can be considered to increase the engineering parameters or inject the combustion tail gas into the formation to realize the goal of "low energy consumption, low carbon emission, and high oil production". The results of this study are useful for improving the development effect in similar extra heavy oil reservoirs.