Abstract
The process of spontaneous imbibition is the basis of oil recovery from tight oil reservoirs. In this study,spontaneous imbibition experiments were conducted based on tight oil weakly hydrophilic sandstone cores from the Honghe oilfield in the Ordos Basin. Four different types of surfactants,such as nonionic Triton X-100,nonionic Tween-80,cationic dodecyl trimethyl ammonium bromide,and anionic sodium dodecyl benzene sulfonate,were separately dissolved in 30 g/L potassium chloride solution as simulated formation water. The effects of surfactant type on spontaneous imbibition were analyzed,and the results indicated that,because the nonions are adsorbed on the surface via Van der Waals force and adsorb H+ through hydrogen bonds,the two nonionic surfactants altered the wettability of the core from weakly hydrophilic to strongly hydrophilic,the recovery rate was relatively high. The Triton X-100 was selected for subsequent spontaneous imbibition experiments by changing the mass concentration to adjust interfacial tension. It was found that the maximum recovery rate was 32% when the Triton X-100 mass concentration was 0.1%,which indicates that the enhanced recovery rate of spontaneous imbibition requires a sufficiently low wettability factor and a suitably high interfacial tension factor. Finally,the surfactants mixed with 0.03% sodium dodecylbenzene sulfonate and 0.1% Triton X-100 were used for spontaneous imbibition,attaining an oil recovery of up to 45%,which was 21.6% higher than that of single-surfactant imbibition. It was established that the synergistic mechanism depends on the wettability alteration of nonionic surfactant facilitating the spontaneous imbibition,while the anion accelerates oil removal from the core by continuously encasing oil droplets in the aqueous phase. This paper provides a theoretical basis for the imbibition development of weakly hydrophilic tight sandstone with high-salinity formation water.
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