Study On Solvent-assisted Steam Flooding Enhance Recovery Of Heavy Oil

Heavy oil is characterized by high viscosity and poor mobility.Therefore,how to efficiently exploit the heavy oil and save the cost is a great challenge for the oil workers.As the high viscosity of heavy oil is very sensitive to temperature,thermal recovery is the main method of heavy oil exploitation.Steam flooding is one of the most widely-used thermal recovery methods,but the recovery still needs to be enhanced du to the inferior properties of heavy oil.In this paper,solvent-assisted steam flooding improve the oil recovery efficiency of is discussed basically.A simple,flexible and rapid equipment for evaluating the effect of sovent-assisted steam drive was established.The recovery for Liaohe heavy oil and Venezuela Mery16 atmospheric residue was evaluated.The auxiliary effects of different additives were compared,and the optimal injection ratio were determined.By analyzing the phase change of water and additives in the oil chamber,the different phase state changes and corresponding recovery rate were revealed.Results show that the additives have a significant effect on enhanced oil recovery.Under the same conditions,flooding effect of three kinds of additives decreases in the order of n-hexane> n-heptane > n-pentane.The maximum increase of recovery rate for n-hexane ranges from 13.5% to 17.2%.The optimal injection ratio varies for the three additives in the range of 15% to 25%.The ratio for different heavy oil is also different.For the three additives,when the gas injection pressure is 2.2 MPa and the gas injection temperature is 220?,the maximum value of the oil enhanced recovery is obtained.Compound additives also has the same effect for improving oil recovery.For the combination of nC5+nC6 and nC6+nC7,the oil recovery increased with the increase of theratio of nC6;When the proportion of nC5:nC6 is greater than 2:1,nC6:nC7 is less than 1:1,the synergistic effect is shown.As for the combination of nC5+nC7,enhanced oil recovery with the proportion of nC5:nC7=1:1,1:2 and 1:5 presents the greatest value.A synergistic effect is also shown in the selected compound proportion range(3:1~1:5).The added solvents make the phase state changes of water and solvent so that bubble point and dew point separation,causing the steam lowest constant boiling point and minimum azeotrope during the condensation process.For the same assisted solvent,the gas injection pressure is increased by 0.2 MPa,the lowest constant boiling point rises about 5 ?.This results in the viscosity reduction of heavy oil,and thus the recovery rate increases.For the same gas injection pressure,when the gas injection temperature is close to saturation temperature of water,the recovery is improved most efficiently.Due to the saturation temperature of n-hexane is close to that of water,the assisted effect of n-hexane is better than the other two.