As a development method to replace steam stimulation of heavy oil, in situ combustion often faces many problems in thick reservoir, such as low vertical sweep efficiency and channeling combustion. According to the characteristics and development history of this kind of reservoir, a method of changing plane fire flooding to gravity fire flooding is proposed by using the existing steam stimulation development well pattern and sidetracking horizontal section of vertical production wells. The influence of different factors on sidetracking gravity fire flooding production effect is analyzed from the aspects of reservoir geology and development engineering. The internal stimulation mechanism of this method is further studied, and the evaluation model between recovery factor and main control factor is established by using multiple linear regression equation. The results show that vertical sidetracking gravity fire flooding can improve the recovery of thick heavy oil reservoir by 42%; the better recovery effect can be obtained when the sidetracking length is about 1/2 of the well spacing; the coincidence degree between the established recovery evaluation model and the results of numerical simulation is more than 85%. The research results of this paper can help the mine fire flooding development to change the mining mode and provide some guidance for the medium- and long-term planning.

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