Effect of flue gas and n-hexane on heavy oil properties in steam flooding process

Heavy-oil reservoirs with thin-pay and bottomwater can be exploited effectively by thermal recovery process assisted by flue gas and n-hexane. The interface properties between flue gas/n-hexane and heavy oil and viscosity reduction of the heavy oil were investigated by laboratory experiments. Steam flooding, flue gas assisted steam flooding, n-hexane assisted flooding and flue gas and n-hexane assisted steam flooding were conducted to research the displacement pressure difference, oil displacement efficiency and component variation of produced and residual oils. The results show that the flue gas dissolving in heavy oil can effectively reduce oil viscosity, increase the flow capability, and make the heavy oil swell. Higher pressure reduces surface tension of heavy oil and gas, and higher temperature increases surface tension. Compared with flue gas, n-hexane can reduce heavy oil viscosity and surface tension more obviously. The flue gas and n-hexane can effectively improve the development effect of the steam flooding. The pressure difference of steam flooding assisted by flue gas and n-hexane is the lowest, the oil production rate is greatest, and the oil recovery efficiency can reach 80%. Flue gas and n-hexane can effectively change crude oil properties. The heavy components, molecular weight of asphaltene and oil viscosity for the produced oil all reduced. The heavy components and molecular weight of asphaltene for the residual oil in sandpacks all increased. The effect of flue gas and n-hexane together on heavy oil is the greatest. The asphaltenes component in the residual oil is not as stable as that in produced oil. The experimental results not only show that flue gas and n-hexane can successfully improve the performance of steam flooding process, but also provide a deep understanding of properties changes of produced and residual oils for the flooding.