Abstract: Gravity drainage can be realized in the process of in-situ combustion by using a horizontal well as producer.The process has the similar mechanism as steam assisted gravity drainage （SAGD），which can be called combustion assisted gravity drainage（CAGD）.3D experiment results show that CAGD has high vertical sweep efficiency and relatively stable oil production rate at the earlier stage.However，at the middle and later stage，it is much more difficult than SAGD to control the relationship of injection and production for maintaining stable drainage.Experimental results also indicate that the combustion front will break through along horizontal wellbore in case of high temperature and high oxygen concentration in the horizontal well because of improper regulation of injection and production.After combustion front breakthrough，a considerable bypassed oil area will be left in the reservoir which results in low recovery efficiency.In the same time，the combustion front breakthrough along horizontal well may also lead to damage of the wellbore because of high temperature oxidation（combustion）which will result in considerable engineering risk.

Key words: In-situ combustion, 3D physical modeling, heavy oil reservoir, horizontal well, gravity drainage