Abstract: It is prone to steam channeling during steam flooding in heavy oil reservoirs, which makes the sweep coefficient small and the recovery low. So, thermochemical flooding technology, chemical agent-assisted steam flooding, has been developed. The diffusion laws of chemicals in thermochemical oil displacement systems are unclear and the field application effects are different. So, a mechanism model was constructed on the basis of physical simulation experiments, the diffusion laws of viscosity reducers and foams in different systems were studied qualitatively and quantitatively, and the diffusion laws of chemicals were clarified considering the pressure effect. The study shows that the viscosity reducer plugs diffuse along the dominant channels to promote steam channeling, but foam plugs block steam channels and modify injection profiles in the diffusion, which promotes the uniform expansion of the steam chambers. There is an interplay between the two, and the viscosity reducer plug should be placed in the foam after the plug. Thus, the steam channeling speed and the molar concentration of foam in mainstream directions are reduced by 8% and 30%, respectively. At the same time, a certain displacement pressure difference should be guaranteed, and the pressure could increase the swept volume of the chemicals and average molar concentration by 2.3 times and 1.0 times, respectively. The study has a reference value for the design of thermochemical flooding programs in heavy oil reservoirs.

Key words: thermochemical oil displacement system, steam channeling, diffusion law, numerical simulation, heavy oil