| Air injection technique is widely used in the oil field development, whatever in sandstone or carbonate reservoirs, heavy or light oil reservoirs, high or low permeability oil reservoirs or secondary or tertiary oil recovery, air flooding projects in both domestic and international have achieved good development effect and obvious economic benefit without the occurrence of safety accidents. Water injection development for low permeability oil reservoirs is difficult, while air injection development can effectively improve oil recovery through LTO process by gas flooding and thermal effect. Field application based on air injection technology of air foam flooding technology integrates advantages of air flooding and foam flooding, which is suitable for reservoirs with high water cut, serious heterogeneity, cracks or large pore, which has an obvious application effect with low cost, safe and reliable technique to enhance oil recovery.According to the development situation of water flooding development difficulties, and low stratigraphic energy penetration in Zhenjing low permeability reservoirs, through the comprehensive analysis of air injection reservoir characteristics and crude oil property technology application in domestic and foreign oil reservoir, combined with the actual situation of Chang8block in Zhenjing low permeability reservoirs, it was suggested that air foam flooding technology was suitable for the block to enhance development effect and oil recovery. Under the condition of simulated formation, oil displacement effect of seven medium was studied, concluding formation water, nitrogen, carbon dioxide, air, air foam, foam and carbon dioxide foam. It was found that oil displacement effect of carbon dioxide foam flooding was the best, followed by air foam, with the ultimate oil displacement efficiency of70.73%and60.30%, respectively. Simple economic analysis showed that air foam flooding and carbon dioxide foam flooding had an input-output of1.0:11.4and1.0:2.25, respectively. Considering the oil displacement effect, source and cost factors, air foam was selected as the best injection medium for the block for gas injection EOR.In order to make a qualitative description of dynamic oxidation of crude oil in Zhenjing oilfield, static and dynamic oxidation experiment were carried out based on the study of oil displacement mechanisms of low temperature oxidation during air injection in light oil reservoirs, using high voltage static reactor and high pressure oxidation pipe, respectively. Static oxidation test results showed that the oxidation reaction rate was mainly affected by the influence of temperature and pressure under the condition of oil formation. The higher the temperature or pressure was, the better the performance of oil oxidation and the faster of the oxidation rate were. Natural rock mineral composition and water content had little effect on Zhenjing oil oxidation reaction rate, while the catalyst used in the experiment could significantly accelerate the oxidation reaction rate. Dynamic oxidation experiment results showed that in the process of gas injection, air in the high pressure oxidation tube (diameter3.1cm, length47.0cm) took a long time flow until gas channeling. Under the condition of simulated formation, the gas breakthrough time was6.42-25.42h. Oxygen content was1.29%-3.81%in produced gas at the time of gas breakthrough. After the break, oxygen content would stay in11.08%-13.84%and CO2content in2.16%-2.79%. The crude oil composition analysis showed that whether it was static or dynamic oxidation, C14-C36were the main components of crude oil taking part in the reaction of oxidation. In addition, saturated hydrocarbon content of crude oil basically unchanged, aromatic hydrocarbon content decreased, while the non hydrocarbon and asphaltene content increased after the oxidation reaction.Long core displacement experiment results showed that oil displacement efficiency during air foam flooding process increased13.32%,13.09%and11.37%respectively under the water flooding stage at different injection rates. Volume and injection rate of air foam greatly affected oil displacement efficiency of air foam flooding. The experimental study based on the solution and air foam (gas liquid ratio1:1) wag injection way at three injection rate of O.Olml/min,0.02ml/min,0.05ml/min. With the increase of the injection rate, oil displacement efficiency increased, but the growth rate gradually decreased. The higher of injection rate, the earlier of gas breakthrough time. Gas channeling during the process of the experiment did not have significantly effect on oil displacement efficiency. Under the same conditions, air foam injection volum of1.0PV had a better efficiency of oil recovery than that of0.6PV, indicating that the volum increase of air foam injected could enhance the effect of foam flooding, increasing the sweep efficiency and oil displacement efficiency of air foam flooding. Air foam injection rate of0.05ml/min and injection parameters such as volum of1.0PV through the experiment of indoor model can be used for numerical simulation study of future research. |
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