Effect Evaluation Study Of Air Foam Flooding Effect After Water Flooding In Tight Sandstone Reservoirs

The Chang 6 formation of Qilicun Oilfield has the characteristics of strong heterogeneity and micro-fracture development,where the reservoir belongs to the tight sandstone reservoir.After many years of water flooding,the water breakthrough in the oil well along the fracture direction is fast and the production rate is low,resulting in the gradually reduced effects by water flooding effect.In order to improve the productivity of oil wells and reduce the water cut,the Qilicun Oilfield carried out a two-stage air foam test in June 2016.This paper mainly evaluates the effects of the air foam after water flooding in the tight sandstone reservoir through field tests and laboratory experiments.Laboratory experiments include foaming agent screening and evaluation,air foam plugging evaluation,foam system comparison and optimization,and oil displacement effect evaluation.The results show that 256-type foaming agent with a concentration of 0.3%has the best performance,with good oil resistance,temperature resistance and salt resistance.When the gas-liquid ratio is 2:1,the air foam has the largest resistance,percolating resistance increases with increasing permeability.The temperature rising resistance coefficient decreases,and sealing capacity increases with the increasing pressure.In the foam system comparison experiments,the 256-type foam system has better oil displacement efficiency than the SY-303 type,and the increased oil rate is 28%.In the single-tube core flooding experiment,the oil displacement efficiency increases with the increase of permeability and decreases with the increase of oil saturation.In the double-tube core flooding experiment,the greater the permeability difference,the water flooding and air foam flooding efficiency are both decreasing first and then increasing.Under the same conditions of permeability contrast,as the oil saturation increases,the oil displacement efficiency decreases.By analyzing the on-site dynamic production data,the output of the single well increased significantly after the injection of air foam into the test site,with the highest increase rate of372%and the average decreased water cut by 10%.The foam plugging property is remarkable,and the water absorption rate is lowered significantly in the high permeability layer of the Chang6₁ formation.The economic benefit evaluation results show that the input-output ratio reaches1:2.07.