Steam stimulation is widely applied in heavy oil production. The cost of drilling in offshore heavy oil field is high, so that the mode of drilling other wells and injecting heat into the completed wells at the same time can greatly improve the efficiency of drilling and production. However, there is a risk of steam from heat injection well leaking into the drilling well. This paper studies the risk of steam channeling in thermal production wells, and proposes an improved ant colony optimization (IACO) algorithm to solve the drilling sequence that meets the safety distance and has the shortest total drilling period. Firstly, a three-dimensional reservoir was established to simulate the distribution of temperature and pressure fields around the well when injecting heat into the well. The results show that when injecting heat into heterogeneous reservoirs, steam is prone to break through along the high-permeability channels, and the channeling flow can exceed 90 m in 9 days. The results show that, for typical case of Bohai Oilfield, the algorithm can save 15~30 days of total drilling time compared with the manual selection method when the safety distance is set to 400~460 m. The IACO algorithm proposed in this paper can quickly and efficiently output the drilling sequence with the shortest drilling duration, which provides a quantitative method for the optimization of the drilling sequence. It is of great significance for saving drilling costs and enhancing the drilling safety of offshore heavy oil thermal recovery wells.