An Experimental Investigation of Feasibility of Gas Huff and Puff for Recovering Crude Oil with Different Viscosities

Investigating multi cyclic gas (N2 and CO2) huff and puff have been conducted by long sandpack simulations with four different crude oils from Jiangsu oilfield. According to the production differential pressure and the production regularity during huff and puff, the production process was divided into three sections; the first one is free gas production section; the second section is low viscous oil production section, and the third one is gas driving exploitation section. According to the results, the production decreases with the increase of cycle times at a certain backpressure, and the effect of multi-cycle huff and puff is improved as the backpressure decreases. In the same cycle, the oil production increases as the backpressure declines. In the first huff and puff cycle, positive synergistic effects are generated while CO2 and N2 are being mixed, and there is an optimum ratio between them. The amount of CO2 in the optimum ratio increases as the backpressure rises. The effect of single gas is better than that of mixed gas in multi-cycle huff and puff, and the effect of CO2 is better than that of N2. The effect of huff and puff is not influenced by the injection mode. At a high backpressure, the huff-and-puff effect becomes better as the oil viscosity increases, but at low backpressure, it becomes worse with an increase in oil viscosity. The huff-and-puff effect also gets worse as the temperature rises. The oil recovery degree is improved as the CO2 injection amount increases, but there is an optimal oil exchange ratio. The depressurization process should be neither too quick nor too slow in the CO2 huff-and-puff process. The cyclic oil production is improved with the increase of injection rate while the average injection rate is lower than 90 L/min. The equilibrium time of CO2 is shorter than that of N2. The economic return of N2 huff and puff is better than that of CO2 at high producing pressure drop, and light oil has higher economic returns than heavy oil.