Fabrication Of Microfoam Systems And Their Application In Enhanced Oil Recovery

Aimed at the problems of worse injectivity of common foam,the microfoam with bubble diameter mainly distributed in 10 to 100?m was fabricated by gas/fluid flow through sandpack,the migration-plugging characteristics and oil displacement property of microfoam were investigated,which provided a new way for enhancing oil recovery in high temperature,high salinity and middle-low permeability reservoirs.The foaming effect of three foaming devices such as special foam generator,sand core and sandpack were evaluated,the sandpack was the best foaming device for fabricating microfoam,average bubble diameter of microfoam could be tuned from 12.39 to 99.31?m by changing gas liquid ratio,sandpack permeability,injection rate,pressure and temperature.The empirical equation of microfoam average bubble diameter was established with these five factors by stepwise regression analysis,and sandpack permeability was the main controlling factor that affected average bubble diameter of microfoam.The microfoam stability was increased with lower gas liquid ration and higher foam stabilizer concentration.The microfoam could maintain microfoam pattern under condition of standing within 4 hours at90?,200572mg/L salinity and 6MPa pressure by adding foam stablizer.The migration law and plugging mechanism of microfoam were investigated by core displacement experiments and microscopic visualization experiments.When the ration of microfoam average bubble diameter to core average pore diameter was 1.45~2.16,microfoam showed both better injectivity and deep plugging capacity,which considered that microfoam diameter matched with core pore diametr at the moment.Microfoam could enable heterogeneous formation with permeability ratio less than 5.47 to achive profile reverse when it matched with higher permeability core of parallel cores.Microfoam was easier to block pore after adding foam stablier,profile control ability of microfoam was enhanced,but injectivity and deep plugging capacity of microfoam were weakened.The results of microscopic visualization tests showed that microfoam would create a temporary blocking zone in high permeable region through bubble accumulation,and the subsequent microfoam would flow through the low permeable region directly or by means of elastic deformatioin,a small amount of finely textured microfoam with smaller bubbles could occupied pore to form plugging.As the increase of gas liquid ratio,the bubble quantiy of microfoam increased,the blocking mode of microfoam at pore was shown to shift form intermittent plugging towards continuous plugging,leading to enhancement of plugging capacity and deformability of microfoam,microfoam owned strongest plugging capacity as gas liquid ratio was 1.The microfoam's capacity of enhanced oil recovery was verified and oil displacement mechanism was revealed through core flooding experiments and microscopic flooding experiments.When microfoam diameter matched with core pore diametr,microfoam would possess better oil displacement efficiency in the reservoirs with permeability form 0.02 to10.9?m~2,permeability ratio less than 8.13,90?and 200572mg/L salinity by adjusting the microfoam average bubble diameter,microfoam flooding increased oil recovery by 17%on the foundation of water flooding.The main microscopic mechanisms of microfoam flooding for enhanced oil recovery was that Jamin effect,emulsification,squeezing and entrainment.Among them,relying on the microfoam gathered together to produce jamin effect,as well as squeezing and entrainment the oil drop and oil film in the pore wall and blind ends,which played the major roles in improving oil recovery.Microfoam flooding possessed potential of applying to high temperature and high salinity and middle-low permeability reservoirs to enhance oil recovery.