The paper attempted to propose a new method of improving later stage performance of cold production from heavy oil reservoirs in respect of forming secondary foamy oil through gas injection.A foamy oil unconventional swelling experiment was designed and carried out to verify the feasibility of generating secondary foamy oil by gas injection and reveal its mechanism of enhancing oil recovery.And then based on the experiment

a sandpack experiment was performed to study the formation of foamy oil during natural gas huffs and puffs

and continuous and intermittent gas flooding processes.The possibility of establishing a numerical model with gas injection characteristics of foamy oil reservoirs incorporated was explored so as to serve for simulating the mechanism of foamy oil formation and later evaluation of EOR results of secondary foamy oil with different ways of gas injection in fields.The results showed that gas injection formed secondary foamy oil with better EOR results in that the oil facilitated the volume expansion

viscosity reduction and light component increase in heavy crude.Compared with natural depletion

the natural gas huff and puff process

with a rich foamy oil fluid generated

was 7.24% higher in terms of recovery percent of reserves;but the continuous and intermittent gas injection processes yielded negative result as they weakened or totally destroyed the foamy oil.Numerical modeling also indicated that the natural gas huff and puff performed better with a cumulative oil production increased by 14.7% after 8 rounds of huff and puff processes in 12 wells;while the continuous and intermittent gas injections as well as edge gas injection were unable to generate secondary foamy oil fluids because of massive gas channeling.