Research On The Influencing Factors Of Chemical Pressure Reduction And Injection Enhancement Effect In Low-permeability Water-flooding Reservoirs

It is necessary for the water-flooding reservoir with low permeability,narrow pore throat,and complicated seepage to use chemical depressurization and gain injection technology.However,the difference of reservoir proprieties result to varied reasons for high injection pressure,and thus diverse performance of the chemical system.The influence of various properties and the action mode are needed to guide the chemical system screening and optimization.According to the analysis of CH oilfield,mineral composition,reservoir pore throat structure,and fluid properties,the paper gets the main factors resulting to inaccessible injection.The paper respectively investigates the effect and the action mode of the chemical system of anti-swelling property,interfacial tension,emulsifying rate on injection pressure and the impact/contact between the interfacial tension and emulsification rate.At last,the paper made performance requirements of applicable system.The reservoir is low permeability block with wetting reservoir,small pores and small throats,heavy oil,middle water-sensitivity.Reasons for high water injection pressure is expansion and migration of clay minerals,core damage caused by heavy components,the two-phase flow resistance during water flooding.In medium water sensitivity reservoir,the study indicates,when the anti-swelling rate is less than 81%,the permeability damage rate is obvious;while when anti-swelling rate is higher than 81%,improving the rate of anti-swelling,the depressurization effect is obviously.Weakness of the clay swelling,particle migration and heavy oil damage on reservoir are the main reason.Interfacial tension is used to decrease the pressure.When it is less than 5.25mN/m,depressurization can be reached.And the effect is more significant with the reduction of interfacial tension.But when the interfacial tension decreases to 10-1mN/m,impact on the recovery rate is limited.When it arrives to 10-2mN/m,system can't completely reduce the additional resistance of residual oil yet.When it is between 10-1mN/m and 5.25mN/m,the depressurization and recovery rate showed an upward trend.To depressurization and gain injection by emulsifying,when the emulsifying rate is greater than 0.11mL/min,depressurization effect is obvious.The pressure drop increases with the emulsion rate improving.But when it is higher than 0.21mL/min,higher emulsifying rate have small effect on recovery.When it is between 0.11mL/min and 0.21mL/min,the depressurization and recovery rate showed an upward trend.Low interfacial tension mainly lead to high displacement efficiency and flow channel area;while emulsification principally expand the swept volume and increase water channel number.Therefore,the emulsifying rate of suitable surfactant system should be as short as possible and thus let oil emulsified completely to gain rapid expansion.Then the interfacial tension is decreased to augment displacement efficiency for lower pressure and higher recovery.Performance requirements of depressurization and gain injection chemical applicable to the reservoir are as follows.Anti-swelling rate is greater than 81%,interfacial tension between 10-2?10-1mN/m,emulsifying rate between 0.21?0.42mL/min.To form a water-in-oil emulsions and emulsion stability is good.Time forming emulsion is shorter than that used to reach the lowest dynamic interfacial tension value.The above research results contribute to the implementation of chemical depressurization and gain injection technology in low permeability water-flooding reservoir.