Imbibition Effect Of Surfactants On Shale Oil In Jimusaer

Jimusaer shale oil has the poor fluidity,complex reservoir structure and strong rock matrix heterogeneity.It is a typical low-porosity-low-permeability shale reservoir.Spontaneous imbibition is an important mechanism for the development of Jimusaer shale oil during the fracturing stimulation and well soaking.In view of the complexity of pore and fracture structure of the Jimusaer shale reservoir,how to strengthen the spontaneous imbibition of the shale reservoir and improve the effective production of shale oil has an important guiding significance for the higher yield of the Jimusaer shale oil.Using the evaluation parameters such as interfacial tension,wettability,and adhesion work reduction factor,through single-factor experiments,12 kinds of surfactants were screened.SCS-1[m（AS-2）:m（NS-5）=5:5,total mass concentration is0.3%.]was optimized for low tension,good reversal performance of wettability,and small reduction factor of adhesion work.SCS-1 has both low interfacial tension(7.29×10^-2 m N·m^-1)and strong wettability.By improving the performance,the reduction factor of the adhesion work of the system can be reduced to 0.01422 m N·m^-1,and the adhesion work can be reduced by 98.58%,the oil washing efficiency is 81.41%,and the imbibition recovery of SCS-1 is 30.34%,which is 17.16%higher than the deionized water.The effects of concentration of SCS-1,core wettability,core permeability,temperature and salinity on the imbibition of SCS-1 were analyzed.the core permeability is in the range of 0.2 m D to 11.4 m D,the higher the permeability,the higher the imbibition recovery degree under the action of SCS-1.With the increase of temperature,the interfacial tension between SCS-1 and crude oil and the viscosity of emulsion is decreased,but the fluidity of crude oil is increased.At 80°C,the imbibition recovery of SCS-1 is 45.12%,and the imbibition recovery of SCS-1 prepared with on-site formation water is 32.68%,indicating that under the temperature and salinity of the Jimusaer shale reservoir,the SCS-1 has good imbibition oil displacement effect.With the help of nuclear magnetic resonance T2 spectrum and microscopic visualization imbibition oil displacement experiments,the mechanism of surfactant promoting imbibition oil displacement in Jimusaer shale reservoir was revealed from three aspects:SCS-1’s small pore producing ability,emulsifying performance and its effect on residual oil migration after water flooding.The SCS-1 system can produce residual oil in large,medium and small pores by reducing the starting pressure of interfacial tension and changing the oleophilicity of the core to enhance imbibition.SCS-1 has good emulsifying properties,and has a wide range in the matrix,which can change the residual oil occurrence state in the matrix,and promotes its transformation to filamentous and film-like,and improves the filamentous and film-like residual oil displacement performance.