Regularity And Mechanism Study Of Surfactant Dynamic Imbibition In Ultra-Low Permeability Reservoir

The offshore low permeability and ultra-low permeability reservoirs are rich in China.The imbibition with surfactant is one of the most effective methods to enhanced oil recovery in ultra-low permeability reservoir.However,most of the previous studies were limited to static imbibition experiments,and there are differences in the process of actual reservoir development.Furthermore,the microscopic mechanism of the imbibition process is not clear yet,and the study of the relevant mechanism of action has important guiding significance for enhanced oil recovery.The betain surfactant static imbibition showed that the 0.1% cocamidopropyl sulfobetaine(ASB)had the highest degree of static imbibition recovery,13.19%.Surfactant could reduce the interfacial tension between oil and water effectively.ASB with a mass concentration of 0.1% could reduce the oil-water interfacial tension to 0.32 mN/m.With the increase of the surfactant concentration,interfacial tension decreased first and then increased.Surfactant could also reduce the adhesion work,calculating its adhesion work reduction factor 0.0024.The surfactant with smaller adhesion reduction factor would have better imbibition effect.Surfactant had the ability to reduce injection rate and enhanced oil recovery.Micro-tube experiments showed that the ASB surfactant's pressure reduction rate reaches about 3%.According to the fluid actual flow rate in matrix-fracture ultra-low permeability reservoir,an experimental double-media matrix-fracture surfactant dynamic imbibition model was prepared for the dynamic imbibition experiments.The indoors dynamic imbibition tests were carried and the experimental results showed that there was a suitable injection rate of 0.1 mL/min at which the maximum oil recovery of ultra-low permeability reservoir,18.02%,could be obtained.The interfacial tension,permeability of matrix in double-media matrix-fracture model,the tortuosity of facture and the temperature would had an influence on the oil recovery.The recovery with 15 mD was higher than that of 0.3 mD.Mercury injection experiments showed that the core with higher permeability is more micro-heterogeneous,which was more suitable for imbibition.The model of triple exponential function was used to calculate the dynamic infiltration results.Compared with the experimental results,the model was different at the beginning stage,but the experimental results could be well fitted in the later stage.Low-field online NMR experiments were carried out to study the distribution and migration of oil and water phase during dynamic imbibition.Ultra-low permeability core dynamic imbibition followed the law of “small pore water absorption,large pore oil discharge”.The results of NMR experiments at different flow rates showed that the recovery rate is the highest at the optimum flow rate,and under this flow rate condition,the oil phase signal amplitude in the small pores decreased by 19.86% Through a microscopic visual experimental device,the regularity of dimensional expansion of the oil droplets on the wall surface of the crack was observed,and it was found that the oil droplets grew faster in height and width in the case of external fluid flow 8.91 and 4.58 times respectively than in the case of no external fluid.The interfacial tension of the surfactant solution,the core thickness,and the core permeability all had an effect on the growth rate of the oil droplets.