Study On The Mechanism And Method Of Oil Displacement Of In-situ Emulsification In Oil Reservoir

In chemical flooding process,in-situ emulsification between oil displacing agents and crude oil has a significant effect on enhanced oil recovery.However,the research of relevant theories and technologies on in-situ emulsification are still little understood,currently.Aiming at this problem,this paper starts with the correlation study of the main functional properties of chemical flooding agents,and then explores the in-situ emulsification effect and its related technical conditions for enhancing oil recovery.Using the high temperature emulsification characterizer THE-II to measure the emulsification amount.It is proved that the emulsification index(EI)based on the dynamic curve of emulsified oil ratio can comprehensively reflect the emulsification speed and emulsification amount.And also,EI can fully characterize the emulsification capability of crude oil-water system.Combined with the positive correlation between emulsification amount and EI during the process of oil displacement simulation experiments,it is proved that it is reasonable to characterize the emulsification capability of crude oil-water system by EI.EI is used as the characterization parameter of emulsification difficulty degree of crude oil-water syatem(namely the emulsification capability).Taking three typical kinds of surfactants as examples,the correlation between interfacial tension(IFT)and emulsification capability of crude oil-water system is studied.Through experiments,it is found that,as two important performance parameters of oil displacing agents,the correlation between EI and IFT is variable.In the range of IFT level 10^-4mN/m to10¹mN/m,there is a critical IFT?_c in which the relationship between EI and IFT will alter significantly.In the range of?>?_c,EI and IFT exhibits strong inverse correlation.In this range,the emulsification capability of crude oil-water system significantly increased with the reduction of IFT.In the range of?<?_c,there is no significant correlation between EI and IFT,and also the emulsification capability and interfacial tension can be regarded as two independent performance parameters.Critical IFT value varies with the composition of crude oil and water,and also it is necessary to determine the corresponding?_c value according the measured results of the given crude oil-water system in research and application.The in-situ emulsification oil ratio is used as the characterization parameter of emulsification degree of crude oil-water in experimental cores,and the correlation between in-situ emulsification in porous media and its main controlling factors is obtained.In-situ emulsified oil ratio is negatively correlated with core permeabiity and positively correlated with crude oil-water migration speed.And also,there is a very obvious positive correlation between in-situ emulsified oil ratio and EI.In the range of?<?_c,there is no obvious correlation between the in-situ emulsified oil ratio and IFT.According to the experimental rules of the in-situ emulsified oil ratio and related parameters,the minimum EI(EI_c)and the maximum IFT(?_c)for in-situ emulsification in the reservoirs can be determined.At the displacement speed of 2.0m/d,EI_c is approximately 0.5-0.7,and?_c is on the magnitude of 10^-2mN/m.The glass rod bundle model was used to carry out simulation experiments of residual oil film formation and displacement after water flooding.The experimental results show that for the two kinds of crude oil used in experiments,regardless of whether the IFT is ultra-low,as long as their EI>0.5,the residual oil film displacement efficiency is higher than 80%.Accordingly,the EI of crude oil-water is the main control factor of residual oil film displacement.Based on experimental results,the correlation of residual oil film displacement efficiency with EI and IFT are obtained.The residual oil film displacement efficiency has an obvious positive correlation with EI,and the residual oil film efficiency has no obvious correlation with IFT in the range of?<?_c(10^-1mN/m).Using two oil displacement agents with obvious differences of EI and IFT,the simulation experiments of residual oil film formation and displacement are carried out in the visual sand filling models and cemented micro heterogeneous models.Through the dynamic distribution alteration of water saturation measured in the micro heterogeneous models,it can be clearly seen that the oil displacement agents with strong emulsification capability can significantly improve the microscopic efficiency displacement of microscopic heterogeneous residual oil in relatively low permeability areas,compared with the oil displacement agents with weak emulsification capability and ultra-low IFT.Therefore,for the displacement of microscopic heterogeneous residual oil in reservoir,the EI of oil displacement agent is a more important functional parameter than IFT.Using artificial columanar homogeneous cores and one-dimensional heterogeneous reservoir models,a series of flooding simulation experiments by in-situ emulsification are carried out,and the correlation rules of additional oil displacement efficiency and recovery efficiency with EI are obtained.From the experimental results,it is found that the oil displacement efficiency measured in the artificial columnar homogeneous cores and the recovery efficiency mearsured in the heterogeneous reservoir models have a significant correlation with the EI of oil displacement agents,which have a consistent correlation law.Both the additional oil displacement efficiency-EI and the additional recovery efficiency-EI experimental correlation curves have a critical EI(EI_c).In the range of EI<EI_c,both the additionaloil displacement efficiency and recovery efficiency increase significantly with the increase of EI.In the range of EI>EI_c,the additional oil displacement efficiency and recovery efficiency increase significantly slowly with the increase of EI.Based on the comprehensively analysis of the previous experimental results,there is a critical interfacial tension value?_c in the relationship between IFT and EI,In-situ emulsified oil ratio and IFT,residual oil film displacement efficiency an IFT.In the range of?<?_c,there is no obvious correlation between the three parameters and IFT.According to the experimental results,the main mechanism of residual oil film and micro heterogeneous residual oil in heterogeneous reservoir after water flood is the in-situ emulsification effect of crude oil-water,and also the EI which characterizes the emulsification capability of crude oil-water is the main control functional parameter of oil displacement agents.According to the relevant experimental rules,the technical limits of EI and IFT of the oil displacement agents are determined as EI?0.5 and??10^-1mN/m respectively,within the research conditions of this paper.