| Air injection can improve the steam flooding effect of heavy oil.The oxidation of heavy oil to produce coke or asphaltene deposition reduces the permeability of the dominant channels,and the subsequent injection of steam to turn is one of the important mechanisms proposed,but this mechanism still needs to be studied in depth.Based on laboratory experiments,this paper analyzes the nature changes of the remaining heavy oil in the dominant channels of steam flooding,explores the coking amount of heavy oil in the porous medium and its influence on the permeability of the porous medium,and clarifiesthe ability of remaining heavy oil to oxidize coking to block the advantageous channels and turn steam,the research and results carried out are as follows:After obtaining the remaining oil through the steam flooding experiment,the physical properties of the remaining oil and the original oil sample were compared,and the physical properties of the remaining heavy oil after steam flooding were studied.It was found that the residual oil density after steam erosion became larger,the viscosity increased significantly,and the content of heavy components of crude oil increased significantly.Heavy components such as asphaltenes in heavy oils are susceptible to low-temperature oxidation to produce coke products.Therefore,the steam flooding remaining oil has the basis for low-temperature oxidation to produce coke.The static low-temperature oxidation experiment of crude oil under steam mixed air atmosphere was carried out in a high-temperature and high-pressure reactor.The results showed that the reaction temperature and pressure with the best coking effect were 220℃and 2MPa,and the shortest single tube displacement time was determined to be 5h.By adjusting the displacement parameters of the single-tube displacement experiment,the best water-injection speed and gas-steam ratio(mass ratio)of air-assisted steam displacement for coking were selected as 0.2ml/min and 2:30,respectively.The permeability and porosity of the reaction tube before and after coke production by oxidation of heavy oil were measured.The results showed that with the increase of coke deposition in the porous medium,the porous medium permeability maximum decrease is 55%,and the effective porosity also decreased more,the maximum decrease is 7.55%,and the permeability and porosity both decreased linearly.When the steam flooding reaches 40%of the remaining oil saturation,the oil recovery effect is the best.Therefore,the best time for air injection is when the residual oil saturation of the steam flooding reaches about 40%.Air-assisted steam flooding should be implemented after the formation of advantageous seepage channels in the formation,otherwise it will adversely affect the oil recovery effect.Experimental results of air-assisted steam flooding in parallel with reaction tubes of different permeability showed that after air-assisted steam flooding,the permeability of high permeability tube decreased from 6.14μm~2 to 4.57μm~2,and the permeability of low permeability tube decreased from 3.38μm~2 to 3.14μm~2.The difference in permeability decreases from 2.76μm~2 to 1.43μm~2.Combining the liquid production volume and pressure curve,it is clear that the low-temperature oxidation reaction in porous media generates coke with selective plugging of the advantageous channels,improves the heterogeneity of the porous media,and then turns the steam,improves the steam sweep efficiency and enhances the oil recovery potential.This provides a reference for further understanding the mechanism of air-assisted steam flooding. |
PDF Full Text Request