Study On The Mechanism Of Bubble Breakup And Coalescence In The Pore-throat Micromodel Of Formation

The bubble breakup and coalescence behavior in pore-throat structure determines the size distribution,which influences the foam injection,the effective period and the flooding effect.At present,the research results on the bubble flow behavior in porous media stay in the phenomenological description of the experimental phenomena,which lacks quantitative analysis.Therefore,it is of great significance to establish the bubble size prediction model in the foam system for the application of foam technology.Through the design of high-fidelity visualized pore-throat micromodel and modern optical technology,including high-speed cameras,high-definition microscopes,etc.,to study the mechanism of bubble breakup and coalescence in microchannels.Based on the existing research foundation and considering the influence of bulk or interface viscoelasticity,systems with different characteristics were constructed to study the behavior of bubbles.The influence of pore-throat ratio,throat width,throat length,diameter ratio,bubble size,flow velocity and system properties on the bubble behavior were systematically investigated.Based on the dimensional analysis method,a dimensionless quasi-relationship formula for predicting bubble size was established.The results show that the rheological properties of the bulk and interfacial phases affect the breakup mechanism of bubbles,and the transformation between different mechanisms was affected by the geometry of mircomodel.Through the study on the process of bubble breakup,it was found that the average size of daughter bubbles in the process of breakup decreased with the increase of capillary number?Ca?,pore-throat ratio and throat length.However,the process of bubble breakup was different as the system changed.In the conventional foam system and interfacial viscoelastic foam system,the bubble breakup mode was snap-off,and the bubble size in the interfacial viscoelastic foam system was slightly smaller than the size in conventional foam system.In the bulk viscoelastic foam system,in addition to the snap-off,there also existed multiple-bubble pinch-off,and the average size of daughter bubbles decreased with the increase of the elasticity of continuous phase.In conventional foam system,the average size of daughter bubbles followed the ruleD_daughter/w_throat)82(ACa^-0.397;in bulk viscoelastic system,the breakup mode of single bubble snap-off followed the rule D_daughter/w_throat?28?ACa^-0.6503?10?B,breakup mode of multi-bubble pinch-off followed rule D_daughter/w_throat?28?A₁ D_m⁰.^{4 431}Ca^-0.0448?10?B₁.The distribution of bubble size in cascaded pore-throat model revealed that the bubbles intensely broke up in the first pore-throat structure.In the study of bubble coalescence,it was found that the bubble coalescence was mainly affected by the process of liquid film breakup.The breakup rate of liquid film decreased with the increase of surfactant concentration or viscoelasticity of the bulk phase,and changed little with the interfacial viscoelasticity;however,the increase of interfacial viscoelasticity would reduce the frequency of coalescence.The stability of the bubble in the system of DTAB and SiO₂ was approximately 60 times longer than the bubble in the DTAB system.When the system had no subsequent water flooding,gas-liquid mass transfer occured and the mass transfer rate in DTAB system could reach 25 times of the rate in the DTAB and SiO₂ compounding system.