Technology Of Decreasing Injection Pressure And Increasing Injection Rate By Surfactant In The Low Permeability Oilfield

In recent years, Changqing Oilfield development blocks are blocks of extralow permeability. It features are characterized notably by lowpermeability,low porosity and great effect of microstructure.Flow resistance increases,injectionpressure rises and water injection rate decreases quickly with continuous water advancement.Water injection efficiency depends on whether the injection pressure is high or low in waterinjection wells.High injection pressure will increase the load of formation injection allocationsystem and injection energy consumption,and meanwhile long-term high-pressure water injectioncan result in damage to casing.Analysis of reasons for high water injection pressure:Injecting oxygen in water, the concentration of iron ions, without causing scaling and clay swelling compatibility.Research on surfactant at present is mostly for enhancing oil recovery.Surfactant is a kind of chemical agent which can enhance oil recovery greatly and has wide fitness for purpose and development potential.However,results from production performance of field chemical flooding wells and laboratory core physical simulation experiments show that:surfactant can not only improve oil recovery greatly,but can increase filtration rate of reservoirs and decrease injection pressure also,and thus reduce the water injection difficulty under high pressure for lower permeable reservoirs and save production cost.Firstly on the basis of theories of decreasing starting pressure,combined with laboratory experiments of surfactant solution effect on relative permeability,this paper studies the mechanisms of decreasing pressure and increasing injection rate by surfactantResults show that surfactant solution can reduce oil-water interfacial tension and increase oil flow capacity;changewettabilities of rock surface from oil-wet to water-wet,decrease capillary resistance of water drive;increase water-phase permeability and decrease injection pressure.Then based on analysis of these mechanisms and in accordance with the reservoir characteristics of oilfields in Changqing,a surfactant compound system which is compatible with the reservoir conditions is developed.field surfactant injection test has been done at32wells in the No.4Production Plant for further proving the feasibility of decreasing pressure and increasing injection rate by surfactant,a better pressure decrease is witnessed.Among them, Measures before the average hydraulic16.4MPa, casing pressure15.8MPa; Add ZJ-1DRA100days average oil pressure15.1MPa, casing pressure14.9MPa, the average oil pressure drop1.3MPa, the average casing pressure drop0.9MPa.