Experimental study and cognition on air foam flooding in the typical "three-low" oil reservoirs in Yanchang Oilfield

In order to improve the development results of "three-low" oil reservoirs (low permeability, low temperature and low pressure) in Yanchang Oilfield, it is necessary to explore the feasibility of air foam flooding in this type of oil reservoirs. In this paper, Well blocks Tang 80 and Qi 35 which are the typical well blocks in the east and west of Yanchang Oilfield respectively were selected on the basis of in-house study for field experiment of air foam flooding. It is indicated that the ultimate oil displacement efficiency of air foam flooding can reach over 80%. Compared with the air foam flooding after water flooding, the direct air foam flooding is more efficient and needs less injection for the same higher oil displacement efficiency. The field experiment results of both well blocks show that the maximum monthly oil increment per well is up to 215%, maximum cumulative oil increment per well is nearly 40% and maximum water cut decline per well is over 40%. In Well block Tang 80, the composite water cut drops by 16% and natural decline rate is over 13% lower than that of the water flooding zones, indicating remarkable effect of water cut decreasing and oil production increasing. The safety analysis on oxygen consumption and the monitoring results of field experiment show that the oxygen content of casing head gas is basically below 5% and gets lower and lower as the time goes. It is concluded that air foam flooding is economically and safely feasible for "three-low" oil reservoirs in Yanchang Oilfield. The research and experiment results break the conventional concept that air foam flooding is not suitable for low temperature and low pressure oil reservoirs and they can be used as the reference and guidance for the development of similar oil reservoirs. It is recommended to take some effective measures in the field experiment to slow down gas channeling and strengthen the monitoring and analysis on oil reservoir performance and produced gas so as to realize good oil displacement effect while the safety is guaranteed.