Study On Flow Characteristics Of Foam At Pore-Level Based On PDMS Chip

In the next few decades,oil still dominates in global energy composition.However,there is a widespread problem of low oil recovery on a global scale at the same time.Therefore,using the tertiary oil recovery technology to further rationally and effectively develop the remaining oil under the stratum,maximizing oil recovery has become an important trend in the middle and late stages of oilfield development.The foam flooding method in tertiary oil recovery can greatly improve oil recovery,which has attracted the attention of many researchers and has been applied in industry.Nevertheless,the understanding of the seepage characteristics and mechanism of foam at the pore scale is not deep enough and comprehensive.At present,there is little research on direct observation of foam flow in microporous media.This paper takes the flow process of foam fluid in microporous media as the research object.And the dimethylsiloxane?PDMS?pore model was used as the experimental section,which combined with microscopic visualization technology to explore the flow characteristics of the foam in the pores at the microscale.The experimental conditions for directly observing the foam fluid flow process at the pore scale are achieved.By adjusting the flow rate of the liquid phase and the gas phase.At the same time,the effects of foam quality,injection rate,permeability and gas type on foam flow characteristics were analyzed.In this paper,an anionic surfactant,sodium dodecyl benzene sulfonate(C₁₈H₂₉NaO₃S)was used as a foaming agent to obtain a surfactant solution having a concentration of 0.5 wt.%.High purity nitrogen gas as experimental gas.In the range of liquid volume flow rate Q_l of 0.1mL/min and foam mass,f_g,of 50%⁹0%,this paper firstly investigates the effect of foam generator on the flow of foam fluid in the pores,and then analyzes the formation,fracture,coalescence and migration mechanism of bubbles at the pore scale.It has been found through experiments that the foam generator can reduce the size of the retained bubbles,help to form a foam with a good foam structure,and enhance the plugging capacity of the foam to the pores.Thin lamella division and snap-off are two main bubble formation mechanisms.The phenomenon of bubble merging occurs at a lower frequency,and the behavior of liquid membrane between the bubbles in contact with each other is an important cause of bubble merging.The flow of the foam in the porous medium is locally unsteady,mainly manifested by the transition of the retained foam and the flowing foam state and the change of the trapped gas fraction,and the re-generation of bubbles and the perturbation of the surrounding bubbles by the flowing bubbles are important reasons for this change.In addition,under experimental conditions with a foam generator,the impact of foam quality,injection rate,permeability and gas type on foam flow characteristics was also analyzed during the experiment.Through experimental research,it is found that with the increase of foam quality,f_g,the foam has better sealing performance for pores,but at high foam quality,due to the disturbing action of flowing bubbles on the trapped bubbles,the trapped gas saturation and trapped gas fraction in the pores is lowered.As the flow rate of the foam fluid increases,the pore model retains the gas saturation,but the gas breakthrough occurs at high flow rates.Compared with CO₂foam,the N₂ foam has better sealing effect on the pore model under the same foam quality,showing a narrower retention bubble size distribution and better foam stability.In the range of foam quality of 50⁷0%,the trapped gas saturation is higher under high permeability conditions,but the trapped gas saturation is higher under low permeability conditions when the foam mass is greater than 70%.When the foam flows in a heterogeneous porous medium,it has a selective plugging effect,and preferentially passes through a region with a high permeability.