| Many companies use gas injection as an EOR technique because of its unique advantages.It has became an indispensable technique in the development of middle and late periods of oilfield.In the simulation of miscible displacement,numerical dispersion is a factor that we can not ignored.The former researches suggest that numerical dispersion is strongly influenced by grid size and degree of heterogeneity,but not affected by any other factors.This academic dissertation divides the factors which influence the gas injection process during production into 3 parts: geological factor,fluid property and development parameters.Based on these former researches,this academic dissertation focuses on the influencing factors of numerical dispersion and field production.In the study of numerical dispersion,we do a lot of simulation with different grid sizes,different well locations,different heterogeneous reservoirs,and different injected gases,trying to find out the differences between physical and numerical dispersion.In the study of field gas injection process,we consider the geology factors such as dip angle,vertical permeability and interlayer,and then do some simulation on production parameters such as oil production rate,well type which may be influenced by the geology factors.The studies shows that:(1)besides grid size and degree of heterogeneity,the location of wells also influences the numerical dispersion.In 2-D simulation,both physical and numerical dispersion have two offsetting impacts on recovery.But we can not equal them because of their different mechanism.(2)the simulation shows that greater inclination angle and vertical permeability are favored reasons for gravity assistant stable drive;meanwhile,it shows that the greater the inclination angle is,the higher oil production rate is.(3)the length of interlayer is a decisive factor in gas injection process.For a wide spread interlayer,it can act to divide a reservoir into two thin reservoirs,which will reduce by nearly 50% of total oil production.3D simulation reveals that the application of horizontal well as production well can perform far better than vertical well;if a vertical well can cover the volume of gas injection,we can use vertical well as injection well.The gas injection rate has two offsetting impacts on miscible displacement:(1)sweeping areas reduce if the injection rate is too low;(2)the oil and gas doesn’t mix well if the injection rate is too high.Therefore,both geology properties and fluid properties during gas injection process should be considered. |
