Study On The Spontaneous Imbibition Effect Of Fracturing Fluid In Chang 7 Reservoir

The tight pore throat of the tight reservoir is small and the permeability is low.It is difficult to get a good development effect by the conventional water injection,but the capillary of the tight reservoir is strong and the phenomenon of imbibition is very obvious.Therefore,it has an important guiding significance for improving the recovery rate of tight reservoir to strengthenthe mechanism of spontaneous imbibition and influence factors of research in tight reservoirs.This paper takes three blocks of tight sandstone in Chang 7 reservoir as the main research object,based on the laboratory experiment as the main research method and based on repeated washing oil and saturation in the same core as experimental method,the influencing factors of spontaneous imbibition of natural cores in Chang 7 tight sandstone reservoir are analyzed,the following research results and understanding have been obtained:?1?The porosity of the experimental core ranges from 2.00%to 11.05%?average porosity6.40%?,and the permeability ranges from 0.0115×10^-3?m² to 0.3871×10^-3?m²(average permeability 0.172×10^-3?m²),there is a good fitting relationship between the permeability and the porosity,showing a logarithmic positive correlation.Generally speaking,the core is tight and the pore-throat structure is complex.?2?The higher the permeability is,the greater the rate of spontaneous imbibition displacement is,and the relationship between them is logarithmic positive correlation;the greater the viscosity,the slower the speed of spontaneous imbibition,the lower the rate of spontaneous imbibition displacement;the greater the salt concentration difference between the inside and the outside of the core,the higher the replacement rate.When the core is immersed in high salinity brine,the influence of salt ions on the core imbibition is very complicated,which leads to unstable imbibition curve of the core in the brine;the higher the temperature,the rate of spontaneous imbibition displacement,and the influence degree of temperature on the core with low permeability is greater than that of the core with high permeability;the bigger the pressure is,the worse the effect of spontaneous imbibition is.In a certain range,there is a value of interfacial tension makes the rate of spontaneous imbibition displacement is the highest,beyond the scope of the interface tension and the interfacial tension is inversely proportional to the the rate of spontaneous imbibition displacement;No matter what type of reservoir is,the interfacial tension is the dominant factor,so the replacement rate of imbibition can be improved first by changing the interfacial tension in practical application.?3?The stable time of spontaneous imbibition as"V"shaped relationship with permeability,when the permeability is less than 0.18mD,the stable time of spontaneous imbibition decreases with the increase of permeability,more than 0.18mD,the stable time of spontaneous imbibition has not reached a stable state;the higher interfacial tension,the longer the stable time of spontaneous imbibition,and the stable time of distilled water imbibition is1.23 times that of the a concentration of 0.15%ZQ surfactant;the greater the viscosity is,the longer the stable time of spontaneous imbibition is,the stable time of spontaneous imbibition of the viscosity of 5.26 mPa·s is 2-8 times that of the viscosity of 1.87mPa·s;the longer the salinity is,the longer the stable time of spontaneous imbibition is,the stable time of spontaneous imbibition of the salinity of 45000mg/Lis 2-5 times that of the stable time of spontaneous imbibition of the distilled water.