Abstract: Common existence of steam overlay during thermal recovery process may create incline of the steam front, which is of great effect on well test analysis result for the heavy oil reservoir by causing the initial model in the condition of the same inner zone radius of the steam front will not be applicable. For this reason, this paper presents the multilayer reservoir two-region mathematical model for heavy oil thermal recovery considering the steam overlay effect. By this model, the Laplace space solution for bottom-hole pressure and well testing type curves are obtained, and the effect of each parameter on the type curves is analyzed. The multilayer model as new thought has the advantages of avoiding the complex mathematical derivation, simulating the nonlinear steam front and dealing with the vertical heterogeneity in such a reservoir.

Key words: heavy oil reservoir, well test analysis, overlay, thermal recovery, type curve