| Foam flooding is one of the effective replacement methods for reservoirs with a high water cut after water flooding.One of the dominant advantages of foam flooding is that foam is able to plug some water flowing channels,which results in the increase of both sweep efficiency and displacement efficiency.Despite the advantages of simple foam flooding,air assisted foam flooding has the unique advantage of low temperature oxidation,which belongs to an improved technology.Huge amounts of studies were conducted on the air assisted foam flooding process,and great achievements have been reached through theoretical and experimental researches,as well as field tests.Under the low oil price condition,effective technologies with low cost are in urgent need.However,the foam liquid is usually comprised of high fractions of foaming agent and foam stabilizer,which obviously increases the cost in development of low permeability reservoirs.Therefore,the concentration of the additives and the injection volume should be optimized to obtain a better oil recovery efficiency.In conclusion,the studies on the stability of the foam,compositions as well as the preparation of foaming solution,formulation of foaming agent and injection strategy have a great importance of theoretical and application value.On the other hand,due to low permeability,low natural production capacity of low permeability reservoirs,oil well generally need hydraulic fracturing.There are a large number of micro cracks in the formation,resulting in sudden flood water channeling in water drive stage.In order to obtain better plugging of high permeable channels,combination of gel with air assisted foam flooding may achieve better effect,reducing the dosage of foaming agent and the stability of foam agent.Therefore,it is of practical significance to study the stategy and development effect of combination of air assisted foam flooding and gel.Focusing on the problems said before,the mechanisms of foam formation,stability and rupture are studied in this paper.Besides,the problem of foam stability in oil reservoirs with different levels of permeability is studied.The effects of pressure gradient and performance of foam stabilizer on the foam stability in oil reservoirs with various porosity and permeability were revealed.Besides,the countermeasures improving the stability of the foam in extra low permeability reservoirs were proposed.We carried out experimental studies on the salt tolerance,compatibility,foaming ability and stability of foam stabilizer and static evaluation of hydrogel and a comprehensive drive system adapted to the air assisted foam flooding process in low permeability reservoirs is proposed.After screening and evaluation of various commonly used foaming agents,a new type of foaming agent suitable for low permeability reservoirs is developed.The oxidation performance and plugging performance of air foam drive are studied by different experimental methods,and the injection scheme suitable for field application is optimized.Air foam comprehensive adjustment system in fractured ultra low-permeability reservoirs is applied to target area and the effect is analyzed which provide a guidance to other fractured ultra low-permeability reservoirs.(1)The surface active agent has little effect on the formation of bubbles in the reservoir,but it has a significant effect on the stability of the bubble.Due to the pressure drop at the interface between the foam and air,the pressure difference has little influence on the bubble stability of the medium high permeability reservoir,but it has a great influence on the ultra low permeability reservoir.The foam stability in ultra-low permeability reservoir can be significantly increased by using the proper concentration of surfactant and foam stabilizer.(2)The stability tests of foaming agent and foam stabilizer and static evaluation of gel showed that the foaming agent BK6A had good salt tolerance and compatibility to the water quality of the experimental area.The foaming agent can effectively reduce the interfacial tension of oil and water,and the foam stabilizer should be HPAM,at the same time the best molecular weight is not more than 1600.Besides,for the fractured reservoir.The main advantages of the new gel and gel compatibility is very good,can use this material into the cracks in the barrier to crack.(3)Due to the low permeability reservoir of foaming agent performance requirements more stringent,in order to effectively control the cost,a new type of anionic surface active synthesis of foaming agent,the foaming performance,not easy to adsorption on oil sand has good foaming effect,stable foam,suitable for alkali acid environment,the foam liquid system can also be used in high temperature and high salinity reservoirs for eor.(4)Through the artificial fractured rocks and sand filling model of stratum environment simulation,single and double chamber oil displacement experiment if surface water flooding high water cut after the gel slug injection into the fissure immediately,and then to the foam.in the equipment permit conditions as far as possible the use of short plugs,multiple rounds of injected foam liquid the crack plugging effect is the best.(5)The indoor optimization simulation was carried out through the low temperature oxidation experiment and blocking experiment of air foam flooding to determine the reasonable injection parameters.It is found that the foam plugging ability is the best when the gas and liquid ratio is in the 1:1-2:1 interval,and the foam slug and the gel slug are optimal with 0.6PV and 0.3PV.(6)Based on indoor experimental results,gel injection volume,foaming liquid volume,injection rate is optimized by numerical simulation.Results show that good performance is obtained with gel injection 50 m3,foaming liquid injection volume of 400 m3.gas liquid ratio 2:1 and foaming liquid injection speed 10 m3/d.Optimization result is applied to 1355-1,1335-4,1335-2 and 1337-2 well group.Performance is excellent with water cut reduction 28%and oil production rate of single well is increased by 6.4 times. |
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