Study On Mechanism Of CO₂ Foam Flooding In Fractured Low-permeability Reservoir

Fractured low-permeability reservoirs are widely distributed throughout the world and are an important component of oil and gas resources.The development of cracks is often complicated,and CO₂ foam injection can effectively improve the problems of turbulence and viscous fingering during conventional mining.It is clear that the mechanism of drainage and recovery of CO₂ foam in fractured low-permeability reservoirs is of great significance for the development and proper application of foam extraction.In this paper,the performance of foaming agent was comprehensively evaluated through laboratory experiments.The effects of mineralization,acidity,oil content,temperature and pressure on foam performance were analyzed.The core injection experiments were carried out to study the injection ability of foam in different permeability cores,and the flow characteristics of foam in different types of fractures were explored.The high temperature and high pressure static infiltration experiments were carried out through a modified new type of osmotic bottle.The influence of CO₂ and surfactant on the seepage and oil recovery under formation conditions was studied.Finally,the effects of surfactant concentration,injection rate and pressure on CO₂foam production in fractured low-permeability reservoirs were analyzed by crack-matrix core experiments.The mechanism of CO₂ foam flooding in fractured low permeability reservoirs was analyzed..The results show that the performance of CQ-05 foam decreases with the increase of salinity and acidity.The higher the crude oil saturation,the stronger the foam stability.The high temperature has a large attenuation of half-life,while the high pressure can greatly improve the foam stability.The foam can significantly increase the flow resistance in the crack,and has a good profile control effect in the multiple cracks,which can effectively enlarge the sweep coefficient of the crack joint network,and the foam is difficult to enter the low permeability matrix.Surfactant concentration and pressure have a significant effect on the osmotic characteristics of the matrix.The addition of surfactant can significantly improve the rate of oil absorption and recovery.The higher the pressure,the lower the interfacial tension of oil and water,the higher the recovery rate.The higher the recovery rate,the combination of crude oil expansion and low interfacial tension.In the fracture-matrix core,with the increase of surfactant concentration,the recovery factor increases;with the increase of displacement velocity,the fracture-matrix core recovery increases first and then decreases.When the displacement speed is too low,the infiltration rate is greater than the displacement rate.There is not enough surfactant solution to participate in the infiltration,resulting in low recovery rate.Excessive displacement speed will inhibit the occurrence of infiltration,which is not conducive to matrix crude oil.The production is reduced,thereby reducing oil recovery.The recovery of CO₂ foam flooding is affected by factors such as pressure and displacement speed.With the increase of pressure,CO₂ can effectively reduce the interfacial tension of the system,improve the foam stability,facilitate the recovery of crude oil in the matrix,and improve the recovery.rate.As the rate of foam displacement increases,the fracture-matrix core recovery increases to a certain extent and remains relatively stable.