Abstract: In accordance with the fact that many domestic heavy oil reservoirs or blocks have entered into their late stage ofcyclic steam stimulation and hence the development effects are getting worse, feasibility of CO2 injection for different viscosities ofheavy oil reservoirs following steam stimulation is studied using methods of numerical simulation and reservoir engineering andtaking Lengjiabao heavy oil field in Liaohe etc. as samples. And the results from the simulation and field pilot test are evaluatedeconomically. Study shows that for common heavy oil after cyclic steam stimulation, the higher the oil viscosity, the greater theutilization factor of CO, injection, and the more feasible by CO, stimulation process; for extra and super heavy oil, one to threesteam stimulations at least are performed as necessaryfollowed by converting it into CO, stimulation process so that good benefitcould be gained. These results are of significance for field operation and production of heavy oils.

Key words: heavy oil reservoir, steam stimulation, CO, numerical simulation, pilot test