Abstract: Based on the concept of representative elementary volume (REV) proposed by Bear, the heat transfer in oil reservoirs containing multiple fluids was studied. Moreover, the “three box” analysis method was used to simplify the heat transfer model of the reservoir REV. Because the multifield coupling mechanism in porous media of the oil reservoir is complex and difficult to analyze, a new “gray box” analysis model was proposed for estimating thermal conductivity and the corresponding calculation formula was provided. Finally, the model was combined with CMG（computer modelling group) software to simulate the operating conditions of the horizontal well injection with multiple thermal fluids. Furthermore, the physical parameter distribution of the ground was obtained, which verified the usability of the proposed model.

Key words: representative elementary volume, multiple fluid, porous media, thermal transport, numerical simulation