| Foam flooding has the feature of “blocking the big but not the small,blocking water but not oil”,which can serve as important means of improving sweep efficiency.Currently,the research on foam drive in macroscopic level has been relatively mature,but the research on foam flooding in microscopic level has not yet formed as a system.Therefore,the research on mechanism of microscopic foam flooding shall have much importance.This paper firstly has designed and produced glass model and slab sand-filling model with different permeability,different pores,different oil saturation and different remaining oil forms,and has established visual and simulative method to evaluate microcosmic mechanism of foam fluid.The paper uses two types of model obtained to carry out visual physical simulation displacement experiment and observe the existing property.Moving form and transfer and drive mechanism of foam fluid in different conditions,and also utilizes sand-filling core model to research the transfer and drive mechanism of foam with different permeability and pore throat,and also evaluates the transfer and drive effect of foam with different oil saturation.Details are as follows: when the pore diameter/ bubble diameter is more than 2:1,the foam are mostly moving in many rows by long and narrow big bubble matching smaller bubble,and when the pore diameter/bubble diameter is around 1:1,the bubble size are relatively even and steady and mainly moves in strand form along the bigger pore,and when the pore diameter/bubble diameter is less than 1:2,the foam is not steady and some of them are cracked,separated and aggregated.The foam has preferable reproducibility,and the smaller the permeability and pore diameter are,the higher possibility of the foam will be.The reproduction by necking down separation and crack mostly occurred in part of hypotonic big pore throat rate(2-3.5),and the reproduction by thin film disjunction mostly occurred in pore branch point(the ligancy of pore is generally more than 3),and reproduction by the hysteresis of liquid film of bubble mostly occurred in large pore path and pore path have not yet involved in foam flooding.There are differences of stability and transfer and drive mechanism of the foam with different oil saturation.If the oil saturation is within 0.02,the stability shall slow down and enhance oil recovery mainly by oil-washing effect of foaming agent solution;between the range of 0.20-0.40,the stability of foam will rapidly declines and the transferring and blocking function and oil-washing function shall be affected synergistically;if exceeding 0.40,the stability will be poor and enhance oil saturation mainly by oil-washing effect of foaming agent solution.In the hypertonic model,stress is put on the mechanism of plugging control,and contribution rate is about 60%.In the hypotonic model,mechanism of scrubbing oil plays an important role,and contribution rate is more than 70%.Among residual oils under different kinds,the mutual transformation may be implemented.Foam might “cut – collect – recut” residual oil.In regard to columnar,island,film-like and corniform residual oil,fuel is scavenged mainly by emulsifying-carrying,dispersing,overriding-cutting,piston action,driving and moving in circles,reverse wetting effect,emulsifying-automatically flowing and perturbation actions.Flake-type residual oil can be cracked easily and is gathered into large bubble to scurry away;gas doping jerking motion will be generated through the extrusion elastic deformation function and cut the flake-type residual oil into different kinds of scattered residual oil;then it will be displaced through the functional mechanism of above scattered residual oil;foam has great displacements effects on residual oil of the top,which is achieved through gas phase-displace-entrainment mechanism. |
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