Abstract: To solve the difficulties of low recovery and reservoir development in ultra-low permeability reservoirs using conventional methods,reservoir simulations using "huff and puff" enhanced oil recovery method were conducted.The lab experiments which combined thermal carriers were carried out with five thermal fluid contents in a way that simulated the formations.The effect of five thermal fluid contents on the recovery,water cut,gas-oil ratio,injection capacity of the combined thermal carrier huff and puff was analyzed.It is shown that the combined thermal carrier huff and puff has a very good effect on the reservoir exploitation,but the effect is related to the thermal fluid content,as well as the huff and puff cycle.When the thermal fluid content increased in a combined carrier and huff and puff cycle,the recovery first increased and then decreased,the water cut increased,and the gas-oil ratio first decreased and then increased,and the injectivity decreased under the same conditions.Results suggest that there is a best thermal fluid content and huff and puff cycle for each individual reservoir.Therefore,lab experiments suggest that it is important to choose the best thermal fluid content and analyze the huff-puff cycle of combined thermal carrier before designing the huff-puff effect of combined thermal carrier.