Study Of A Decompression And Augmented Injection System In Low Permeability Reservoir With High Concentration Of Calcium And Magnesium Ions

Problems such as high injection pressure and no effects after injection are present in the developing of low permeability reservoir.After analyzing the reasons why Xianhe O ilfield have a high injection pressure,we optimized a decompression and augmented injection system with the evaluation index such as IFT,scale inhibiting ratio,clay particle size distribution and specific surface area.The optimization system is 0.15% FC-117 + 4% isopropanol + 12mg/L PBTCA + 1.5% DMDAAC.The system can reduce the IFT to 5.36×10-3 mN·m-1 within a short time.It's scale inhibiting ratio is 94.83%.It's antiswelling rate is 86.96%.It also has the ability of preventing the migration of clay grains.The results of comprehensive evaluating shows that the system has the following functions.Firstly,the decompression and augmented injection system can convert the oil-wet surface to wet surface.Secondly,the system can reducing the scaling tendency of formation water.The Core displacement experiment showed that the formation scaling damage rate observably reduced from 84% to 36%.Thirdly,it has better performance of the interface under the conditions of NaCl concentration of less than 300000mg/L,CaC l2 concentrations of less than 5000mg/L,and it has good adaptability for te mperatures below 50 ?~ 90 ?.Finally,the Core displacement experiment showed that the depressurization rate of the decompression and augmented injection system can reach up to 34.67%,and the system has a good decompression and augmented injection effect for the examined low permeability reservoir.The mechanism of decompression and augmented injection was studied,which is,surfactant and alcohol synergistically reducing oil-water interfacial tension to the magnitudes of 10-3mN·m-1.Lower oil-water interfacial tension can effectively improve the reservoir choke caused by Jamin Effect.However,when interfacial tension between 10-2mN·m-1 to 10-3mN·m-1,the phenomenon of emulsification can be reduced.The second mechanism is well changing the wettability of the rock by the adsorption of surfactant.The third mechanism is the system has the ability of scale inhibition and scale dissolution.To high mineralization formation,scaling has serious impact on water injection.The last mechanism is the clay stabilizing agent DMDAAC can prevent the migration or swelling of clay grains.So the injection pressure can be reduced.